diff --git a/src/coreclr/tools/superpmi/mcs/commandline.cpp b/src/coreclr/tools/superpmi/mcs/commandline.cpp
index 86ce6023375d1f..8a2f10c2696778 100644
--- a/src/coreclr/tools/superpmi/mcs/commandline.cpp
+++ b/src/coreclr/tools/superpmi/mcs/commandline.cpp
@@ -335,7 +335,8 @@ bool CommandLine::Parse(int argc, char* argv[], /* OUT */ Options* o)
                 i++;
             processMCL2:
 
-                bool isValidList = MCList::processArgAsMCL(argv[i], &o->indexCount, &o->indexes);
+                bool isValidList = MCList::processArgAsMCL(argv[i], o->indexes);
+                o->indexCount    = (int)o->indexes.size();
                 if (!isValidList)
                     i--;
             }
diff --git a/src/coreclr/tools/superpmi/mcs/commandline.h b/src/coreclr/tools/superpmi/mcs/commandline.h
index ea78f456f91a96..98e7112dac9e35 100644
--- a/src/coreclr/tools/superpmi/mcs/commandline.h
+++ b/src/coreclr/tools/superpmi/mcs/commandline.h
@@ -39,7 +39,6 @@ class CommandLine
             , nameOfFile2(nullptr)
             , nameOfFile3(nullptr)
             , indexCount(-1)
-            , indexes(nullptr)
         {
         }
 
@@ -68,7 +67,7 @@ class CommandLine
         char* nameOfFile2;
         char* nameOfFile3;
         int   indexCount;
-        int*  indexes;
+        std::vector<int> indexes;
     };
 
     static bool Parse(int argc, char* argv[], /* OUT */ Options* o);
diff --git a/src/coreclr/tools/superpmi/mcs/mcs.cpp b/src/coreclr/tools/superpmi/mcs/mcs.cpp
index 2923a4f9186f31..313c98a43ec74b 100644
--- a/src/coreclr/tools/superpmi/mcs/mcs.cpp
+++ b/src/coreclr/tools/superpmi/mcs/mcs.cpp
@@ -43,7 +43,7 @@ int __cdecl main(int argc, char* argv[])
     int exitCode = 0;
     if (o.actionASMDump)
     {
-        exitCode = verbASMDump::DoWork(o.nameOfFile1, o.nameOfFile2, o.indexCount, o.indexes);
+        exitCode = verbASMDump::DoWork(o.nameOfFile1, o.nameOfFile2, o.indexCount, o.indexes.data());
     }
     if (o.actionConcat)
     {
@@ -55,15 +55,15 @@ int __cdecl main(int argc, char* argv[])
     }
     if (o.actionCopy)
     {
-        exitCode = verbStrip::DoWork(o.nameOfFile1, o.nameOfFile2, o.indexCount, o.indexes, false, o.stripCR);
+        exitCode = verbStrip::DoWork(o.nameOfFile1, o.nameOfFile2, o.indexCount, o.indexes.data(), false, o.stripCR);
     }
     if (o.actionDump)
     {
-        exitCode = verbDump::DoWork(o.nameOfFile1, o.indexCount, o.indexes, o.simple);
+        exitCode = verbDump::DoWork(o.nameOfFile1, o.indexCount, o.indexes.data(), o.simple);
     }
     if (o.actionFracture)
     {
-        exitCode = verbFracture::DoWork(o.nameOfFile1, o.nameOfFile2, o.indexCount, o.indexes, o.stripCR);
+        exitCode = verbFracture::DoWork(o.nameOfFile1, o.nameOfFile2, o.indexCount, o.indexes.data(), o.stripCR);
     }
     if (o.actionDumpMap)
     {
@@ -75,7 +75,7 @@ int __cdecl main(int argc, char* argv[])
     }
     if (o.actionILDump)
     {
-        exitCode = verbILDump::DoWork(o.nameOfFile1, o.indexCount, o.indexes);
+        exitCode = verbILDump::DoWork(o.nameOfFile1, o.indexCount, o.indexes.data());
     }
     if (o.actionInteg)
     {
@@ -87,11 +87,11 @@ int __cdecl main(int argc, char* argv[])
     }
     if (o.actionStat)
     {
-        exitCode = verbStat::DoWork(o.nameOfFile1, o.nameOfFile2, o.indexCount, o.indexes);
+        exitCode = verbStat::DoWork(o.nameOfFile1, o.nameOfFile2, o.indexCount, o.indexes.data());
     }
     if (o.actionStrip)
     {
-        exitCode = verbStrip::DoWork(o.nameOfFile1, o.nameOfFile2, o.indexCount, o.indexes, true, o.stripCR);
+        exitCode = verbStrip::DoWork(o.nameOfFile1, o.nameOfFile2, o.indexCount, o.indexes.data(), true, o.stripCR);
     }
     if (o.actionTOC)
     {
diff --git a/src/coreclr/tools/superpmi/mcs/removedup.cpp b/src/coreclr/tools/superpmi/mcs/removedup.cpp
index b2ba784e633f15..4c4f11ebd19306 100644
--- a/src/coreclr/tools/superpmi/mcs/removedup.cpp
+++ b/src/coreclr/tools/superpmi/mcs/removedup.cpp
@@ -118,7 +118,7 @@ bool RemoveDup::uniqueLegacy(MethodContext* mc)
     return true;
 }
 
-bool RemoveDup::CopyAndRemoveDups(const char* nameOfInput, HANDLE hFileOut)
+bool RemoveDup::CopyAndRemoveDups(const char* nameOfInput, FILE* fpOut)
 {
     MethodContextIterator mci(/* progressReport */ true);
     if (!mci.Initialize(nameOfInput))
@@ -138,7 +138,7 @@ bool RemoveDup::CopyAndRemoveDups(const char* nameOfInput, HANDLE hFileOut)
         {
             if (uniqueLegacy(mc))
             {
-                mc->saveToFile(hFileOut);
+                mc->saveToFile(fpOut);
                 savedCount++;
 
                 // In this case, for the legacy comparer, it has placed the 'mc' in the 'm_inFileLegacy' table, so we
@@ -153,7 +153,7 @@ bool RemoveDup::CopyAndRemoveDups(const char* nameOfInput, HANDLE hFileOut)
         {
             if (unique(mc))
             {
-                mc->saveToFile(hFileOut);
+                mc->saveToFile(fpOut);
                 savedCount++;
             }
             delete mc; // we no longer need this
diff --git a/src/coreclr/tools/superpmi/mcs/removedup.h b/src/coreclr/tools/superpmi/mcs/removedup.h
index ee14e636ef7fff..d52b955a6f1510 100644
--- a/src/coreclr/tools/superpmi/mcs/removedup.h
+++ b/src/coreclr/tools/superpmi/mcs/removedup.h
@@ -35,7 +35,7 @@ class RemoveDup
 
     ~RemoveDup();
 
-    bool CopyAndRemoveDups(const char* nameOfInput, HANDLE hFileOut);
+    bool CopyAndRemoveDups(const char* nameOfInput, FILE* fpOut);
 
 private:
 
diff --git a/src/coreclr/tools/superpmi/mcs/verbasmdump.cpp b/src/coreclr/tools/superpmi/mcs/verbasmdump.cpp
index 6d70077b8c7a4e..8c98c1b438d97d 100644
--- a/src/coreclr/tools/superpmi/mcs/verbasmdump.cpp
+++ b/src/coreclr/tools/superpmi/mcs/verbasmdump.cpp
@@ -28,31 +28,25 @@ int verbASMDump::DoWork(const char* nameOfInput, const char* nameOfOutput, int i
         char buff[500];
         sprintf_s(buff, 500, "%s-%d.asm", nameOfOutput, mci.MethodContextNumber());
 
-        HANDLE hFileOut = CreateFileA(buff, GENERIC_WRITE, 0, NULL, CREATE_ALWAYS,
-                                      FILE_ATTRIBUTE_NORMAL | FILE_FLAG_SEQUENTIAL_SCAN, NULL);
-        if (hFileOut == INVALID_HANDLE_VALUE)
+        FILE* fpOut = fopen(buff, "w");
+        if (fpOut == NULL)
         {
-            LogError("Failed to open output '%s'. GetLastError()=%u", buff, GetLastError());
+            LogError("Failed to open output '%s'. errno=%d", buff, errno);
             return -1;
         }
 
         if (mc->cr->IsEmpty())
         {
-            const size_t bufflen = 4096;
-            DWORD        bytesWritten;
-            char         buff[bufflen];
-            ZeroMemory(buff, bufflen * sizeof(char));
-            int buff_offset = sprintf_s(buff, bufflen, ";;Method context has no compile result");
-            WriteFile(hFileOut, buff, buff_offset * sizeof(char), &bytesWritten, nullptr);
+            fprintf(fpOut, ";;Method context has no compile result");
         }
         else
         {
-            ASMDumper::DumpToFile(hFileOut, mc, mc->cr);
+            ASMDumper::DumpToFile(fpOut, mc, mc->cr);
         }
 
-        if (!CloseHandle(hFileOut))
+        if (fclose(fpOut) != 0)
         {
-            LogError("CloseHandle failed. GetLastError()=%u", GetLastError());
+            LogError("fclose failed. errno=%d", errno);
             return -1;
         }
         savedCount++;
diff --git a/src/coreclr/tools/superpmi/mcs/verbconcat.cpp b/src/coreclr/tools/superpmi/mcs/verbconcat.cpp
index 9d6f7b39c0e291..aacc7c9b1a5860 100644
--- a/src/coreclr/tools/superpmi/mcs/verbconcat.cpp
+++ b/src/coreclr/tools/superpmi/mcs/verbconcat.cpp
@@ -14,61 +14,37 @@ int verbConcat::DoWork(const char* nameOfFile1, const char* nameOfFile2)
 
     LogVerbose("Concatenating '%s'+'%s' into %s", nameOfFile1, nameOfFile2, nameOfFile1);
 
-    LARGE_INTEGER DataTemp1;
-    LARGE_INTEGER DataTemp2;
-
-    HANDLE hFileIn1 = CreateFileA(nameOfFile1, GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_ALWAYS,
-                                  FILE_ATTRIBUTE_NORMAL | FILE_FLAG_SEQUENTIAL_SCAN, NULL);
-    if (hFileIn1 == INVALID_HANDLE_VALUE)
-    {
-        LogError("Failed to open input 1 '%s'. GetLastError()=%u", nameOfFile1, GetLastError());
-        return -1;
-    }
-    if (GetFileSizeEx(hFileIn1, &DataTemp1) == 0)
+    FILE* fp1 = fopen(nameOfFile1, "ab+");
+    if (fp1 == NULL)
     {
-        LogError("GetFileSizeEx failed. GetLastError()=%u", GetLastError());
+        LogError("Failed to open input 1 '%s'. errno=%d", nameOfFile1, errno);
         return -1;
     }
 
-    LONG  highDWORD = 0;
-    DWORD dwPtr     = SetFilePointer(hFileIn1, 0, &highDWORD, FILE_END);
-    if (dwPtr == INVALID_SET_FILE_POINTER)
-    {
-        LogError("Failed to SetFilePointer on input 1 '%s'. GetLastError()=%u", nameOfFile1, GetLastError());
-        return -1;
-    }
-
-    HANDLE hFileIn2 = CreateFileA(nameOfFile2, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING,
-                                  FILE_ATTRIBUTE_NORMAL | FILE_FLAG_SEQUENTIAL_SCAN, NULL);
-    if (hFileIn2 == INVALID_HANDLE_VALUE)
-    {
-        LogError("Failed to open input 2 '%s'. GetLastError()=%u", nameOfFile2, GetLastError());
-        return -1;
-    }
-    if (GetFileSizeEx(hFileIn2, &DataTemp2) == 0)
+    FILE* fp2 = fopen(nameOfFile2, "rb");
+    if (fp2 == NULL)
     {
-        LogError("2nd GetFileSizeEx failed. GetLastError()=%u", GetLastError());
+        LogError("Failed to open input 2 '%s'. errno=%d", nameOfFile2, errno);
         return -1;
     }
 
     unsigned char* buffer = new unsigned char[BUFFER_SIZE];
+    int64_t        offset = 0;
 
     st1.Start();
-    for (LONGLONG offset = 0; offset < DataTemp2.QuadPart; offset += BUFFER_SIZE)
+    while (!feof(fp2))
     {
-        DWORD bytesRead = -1;
-        BOOL  res       = ReadFile(hFileIn2, buffer, BUFFER_SIZE, &bytesRead, nullptr);
-        if (res == 0)
+        size_t bytesRead = fread(buffer, 1, BUFFER_SIZE, fp2);
+        if (bytesRead <= 0)
         {
-            LogError("Failed to read '%s' from offset %lld. GetLastError()=%u", nameOfFile2, offset, GetLastError());
+            LogError("Failed to read '%s' from offset %lld. errno=%d", nameOfFile2, offset, errno);
             delete[] buffer;
             return -1;
         }
-        DWORD bytesWritten = -1;
-        BOOL  res2         = WriteFile(hFileIn1, buffer, bytesRead, &bytesWritten, nullptr);
-        if (res2 == 0)
+        size_t bytesWritten = fwrite(buffer, 1, bytesRead, fp1);
+        if (bytesWritten <= 0)
         {
-            LogError("Failed to write '%s' at offset %lld. GetLastError()=%u", nameOfFile1, offset, GetLastError());
+            LogError("Failed to write '%s' at offset %lld. errno=%d", nameOfFile1, offset, errno);
             delete[] buffer;
             return -1;
         }
@@ -78,24 +54,25 @@ int verbConcat::DoWork(const char* nameOfFile1, const char* nameOfFile2)
             delete[] buffer;
             return -1;
         }
+        offset += bytesRead;
     }
     st1.Stop();
 
     delete[] buffer;
 
-    if (CloseHandle(hFileIn1) == 0)
+    if (fclose(fp1) != 0)
     {
-        LogError("CloseHandle failed. GetLastError()=%u", GetLastError());
+        LogError("CloseHandle failed. errno=%d", errno);
         return -1;
     }
-    if (CloseHandle(hFileIn2) == 0)
+    if (fclose(fp2) != 0)
     {
-        LogError("2nd CloseHandle failed. GetLastError()=%u", GetLastError());
+        LogError("2nd CloseHandle failed. errno=%d", errno);
         return -1;
     }
 
-    LogInfo("Read/Wrote %lld MB @ %4.2f MB/s.\n", DataTemp2.QuadPart / (1000 * 1000),
-            (((double)DataTemp2.QuadPart) / (1000 * 1000)) /
+    LogInfo("Read/Wrote %lld MB @ %4.2f MB/s.\n", offset / (1000 * 1000),
+            (((double)offset) / (1000 * 1000)) /
                 st1.GetSeconds()); // yes yes.. http://en.wikipedia.org/wiki/Megabyte_per_second#Megabyte_per_second
 
     return 0;
diff --git a/src/coreclr/tools/superpmi/mcs/verbfracture.cpp b/src/coreclr/tools/superpmi/mcs/verbfracture.cpp
index 549e4ed9322149..a9295481a4b786 100644
--- a/src/coreclr/tools/superpmi/mcs/verbfracture.cpp
+++ b/src/coreclr/tools/superpmi/mcs/verbfracture.cpp
@@ -24,28 +24,27 @@ int verbFracture::DoWork(
     int  fileCount = 0;
     char fileName[512];
 
-    HANDLE hFileOut = INVALID_HANDLE_VALUE;
+    FILE* fpOut = NULL;
     while (mci.MoveNext())
     {
         MethodContext* mc = mci.Current();
 
-        if ((hFileOut == INVALID_HANDLE_VALUE) || (((mci.MethodContextNumber() - 1) % rangeSize) == 0))
+        if ((fpOut == NULL) || (((mci.MethodContextNumber() - 1) % rangeSize) == 0))
         {
-            if (hFileOut != INVALID_HANDLE_VALUE)
+            if (fpOut != NULL)
             {
-                if (!CloseHandle(hFileOut))
+                if (fclose(fpOut) != 0)
                 {
-                    LogError("1st CloseHandle failed. GetLastError()=%u", GetLastError());
+                    LogError("1st CloseHandle failed. errno=%d", errno);
                     return -1;
                 }
-                hFileOut = INVALID_HANDLE_VALUE;
+                fpOut = NULL;
             }
             sprintf_s(fileName, 512, "%s-%0*d.mch", nameOfOutput, 5, fileCount++);
-            hFileOut = CreateFileA(fileName, GENERIC_WRITE, 0, NULL, CREATE_ALWAYS,
-                                   FILE_ATTRIBUTE_NORMAL | FILE_FLAG_SEQUENTIAL_SCAN, NULL);
-            if (hFileOut == INVALID_HANDLE_VALUE)
+            fpOut = fopen(fileName, "wb");
+            if (fpOut == NULL)
             {
-                LogError("Failed to open output file '%s'. GetLastError()=%u", fileName, GetLastError());
+                LogError("Failed to open output file '%s'. errno=%d", fileName, errno);
                 return -1;
             }
         }
@@ -54,14 +53,14 @@ int verbFracture::DoWork(
             delete mc->cr;
             mc->cr = new CompileResult();
         }
-        mc->saveToFile(hFileOut);
+        mc->saveToFile(fpOut);
     }
 
-    if (hFileOut != INVALID_HANDLE_VALUE)
+    if (fpOut != NULL)
     {
-        if (!CloseHandle(hFileOut))
+        if (fclose(fpOut) != 0)
         {
-            LogError("2nd CloseHandle failed. GetLastError()=%u", GetLastError());
+            LogError("2nd CloseHandle failed. errno=%d", errno);
             return -1;
         }
     }
diff --git a/src/coreclr/tools/superpmi/mcs/verbmerge.cpp b/src/coreclr/tools/superpmi/mcs/verbmerge.cpp
index 35b7263d4a68b7..ffefe531586fde 100644
--- a/src/coreclr/tools/superpmi/mcs/verbmerge.cpp
+++ b/src/coreclr/tools/superpmi/mcs/verbmerge.cpp
@@ -69,46 +69,36 @@ WCHAR* verbMerge::ConvertMultiByteToWideChar(LPCSTR str)
 // 'buffer' is memory that can be used to do reading/buffering.
 //
 // static
-int verbMerge::AppendFileRaw(HANDLE hFileOut, LPCWSTR fileFullPath, unsigned char* buffer, size_t bufferSize)
+int verbMerge::AppendFileRaw(FILE* fpOut, LPCWSTR fileFullPath, unsigned char* buffer, size_t bufferSize)
 {
     int result = 0; // default to zero == success
 
     char* fileNameAsChar = ConvertWideCharToMultiByte(fileFullPath);
     LogInfo("Appending file '%s'", fileNameAsChar);
 
-    HANDLE hFileIn = CreateFileW(fileFullPath, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING,
-                                 FILE_ATTRIBUTE_NORMAL | FILE_FLAG_SEQUENTIAL_SCAN, NULL);
-    if (hFileIn == INVALID_HANDLE_VALUE)
+    FILE* fpIn = fopen(fileNameAsChar, "rb");
+    if (fpIn == NULL)
     {
         // If you use a relative path, you can get GetLastError()==3, if the absolute path is longer
         // than MAX_PATH.
-        LogError("Failed to open input file '%s'. GetLastError()=%u", fileNameAsChar, GetLastError());
+        LogError("Failed to open input file '%s'. errno=%d", fileNameAsChar, errno);
         return -1;
     }
 
-    LARGE_INTEGER fileSize;
-    if (GetFileSizeEx(hFileIn, &fileSize) == 0)
+    int64_t offset = 0;
+    while (!feof(fpIn))
     {
-        LogError("GetFileSizeEx on '%s' failed. GetLastError()=%u", fileNameAsChar, GetLastError());
-        result = -1;
-        goto CLEAN_UP;
-    }
-
-    for (LONGLONG offset = 0; offset < fileSize.QuadPart; offset += bufferSize)
-    {
-        DWORD bytesRead = -1;
-        BOOL  res       = ReadFile(hFileIn, buffer, (DWORD)bufferSize, &bytesRead, nullptr);
-        if (!res)
+        size_t bytesRead = fread(buffer, 1, bufferSize, fpIn);
+        if (bytesRead <= 0)
         {
-            LogError("Failed to read '%s' from offset %lld. GetLastError()=%u", fileNameAsChar, offset, GetLastError());
+            LogError("Failed to read '%s' from offset %lld. errno=%d", fileNameAsChar, offset, errno);
             result = -1;
             goto CLEAN_UP;
         }
-        DWORD bytesWritten = -1;
-        BOOL  res2         = WriteFile(hFileOut, buffer, bytesRead, &bytesWritten, nullptr);
-        if (!res2)
+        size_t bytesWritten = fwrite(buffer, 1, bytesRead, fpOut);
+        if (bytesWritten <= 0)
         {
-            LogError("Failed to write output file at offset %lld. GetLastError()=%u", offset, GetLastError());
+            LogError("Failed to write output file at offset %lld. errno=%d", offset, errno);
             result = -1;
             goto CLEAN_UP;
         }
@@ -124,22 +114,22 @@ int verbMerge::AppendFileRaw(HANDLE hFileOut, LPCWSTR fileFullPath, unsigned cha
 
     delete[] fileNameAsChar;
 
-    if (CloseHandle(hFileIn) == 0)
+    if (fclose(fpIn) != 0)
     {
-        LogError("CloseHandle failed. GetLastError()=%u", GetLastError());
+        LogError("CloseHandle failed. errno=%d", errno);
         result = -1;
     }
 
     return result;
 }
 
-// AppendFile: append the file named by 'fileFullPath' to the output file referred to by 'hFileOut'. The 'hFileOut'
+// AppendFile: append the file named by 'fileFullPath' to the output file referred to by 'fpOut'. The 'fpOut'
 // handle is assumed to be open, and the file position is assumed to be at the correct spot for writing, to append.
 //
 // 'buffer' is memory that can be used to do reading/buffering.
 //
 // static
-int verbMerge::AppendFile(HANDLE hFileOut, LPCWSTR fileFullPath, bool dedup, unsigned char* buffer, size_t bufferSize)
+int verbMerge::AppendFile(FILE* fpOut, LPCWSTR fileFullPath, bool dedup, unsigned char* buffer, size_t bufferSize)
 {
     int result = 0; // default to zero == success
 
@@ -148,7 +138,7 @@ int verbMerge::AppendFile(HANDLE hFileOut, LPCWSTR fileFullPath, bool dedup, uns
         // Need to conver the fileFullPath to non-Unicode.
         char* fileFullPathAsChar = ConvertWideCharToMultiByte(fileFullPath);
         LogInfo("Appending file '%s'", fileFullPathAsChar);
-        bool ok = m_removeDups.CopyAndRemoveDups(fileFullPathAsChar, hFileOut);
+        bool ok = m_removeDups.CopyAndRemoveDups(fileFullPathAsChar, fpOut);
         delete[] fileFullPathAsChar;
         if (!ok)
         {
@@ -158,7 +148,7 @@ int verbMerge::AppendFile(HANDLE hFileOut, LPCWSTR fileFullPath, bool dedup, uns
     }
     else
     {
-        result = AppendFileRaw(hFileOut, fileFullPath, buffer, bufferSize);
+        result = AppendFileRaw(fpOut, fileFullPath, buffer, bufferSize);
     }
 
     return result;
@@ -454,7 +444,7 @@ int verbMerge::FilterDirectory(LPCWSTR                      dir,
 // Append all files in the given directory matching the file pattern.
 //
 // static
-int verbMerge::AppendAllInDir(HANDLE              hFileOut,
+int verbMerge::AppendAllInDir(FILE*               fpOut,
                               LPCWSTR             dir,
                               LPCWSTR             file,
                               unsigned char*      buffer,
@@ -536,7 +526,7 @@ int verbMerge::AppendAllInDir(HANDLE              hFileOut,
         }
         else
         {
-            result = AppendFile(hFileOut, fileFullPath, dedup, buffer, bufferSize);
+            result = AppendFile(fpOut, fileFullPath, dedup, buffer, bufferSize);
             if (result != 0)
             {
                 // Error was already logged.
@@ -567,7 +557,7 @@ int verbMerge::AppendAllInDir(HANDLE              hFileOut,
         {
             const FindData& findData = fileArray[i];
             LPWSTR subDir            = MergePathStrings(dir, findData.cFileName);
-            result                   = AppendAllInDir(hFileOut, subDir, file, buffer, bufferSize, recursive, dedup, &dirSize);
+            result                   = AppendAllInDir(fpOut, subDir, file, buffer, bufferSize, recursive, dedup, &dirSize);
             delete [] subDir;
 
             if (result != 0)
@@ -623,19 +613,14 @@ int verbMerge::DoWork(const char* nameOfOutputFile, const char* pattern, bool re
         }
     }
 
-    int    nameLength              = (int)strlen(nameOfOutputFile) + 1;
-    LPWSTR nameOfOutputFileAsWchar = new WCHAR[nameLength];
-    MultiByteToWideChar(CP_ACP, 0, nameOfOutputFile, -1, nameOfOutputFileAsWchar, nameLength);
-
     int    patternLength  = (int)strlen(pattern) + 1;
     LPWSTR patternAsWchar = new WCHAR[patternLength];
     MultiByteToWideChar(CP_ACP, 0, pattern, -1, patternAsWchar, patternLength);
 
-    HANDLE hFileOut = CreateFileW(nameOfOutputFileAsWchar, GENERIC_WRITE, 0, NULL, CREATE_ALWAYS,
-                                  FILE_ATTRIBUTE_NORMAL | FILE_FLAG_SEQUENTIAL_SCAN, NULL);
-    if (hFileOut == INVALID_HANDLE_VALUE)
+    FILE* fpOut = fopen(nameOfOutputFile, "wb");
+    if (fpOut == NULL)
     {
-        LogError("Failed to open output file '%s'. GetLastError()=%u", nameOfOutputFile, GetLastError());
+        LogError("Failed to open output file '%s'. errno=%d", nameOfOutputFile, errno);
         return -1;
     }
 
@@ -690,7 +675,7 @@ int verbMerge::DoWork(const char* nameOfOutputFile, const char* pattern, bool re
 
     st1.Start();
 
-    result = AppendAllInDir(hFileOut, dir, file, buffer, BUFFER_SIZE, recursive, dedup, &dirSize);
+    result = AppendAllInDir(fpOut, dir, file, buffer, BUFFER_SIZE, recursive, dedup, &dirSize);
     if (result != 0)
     {
         goto CLEAN_UP;
@@ -708,9 +693,9 @@ int verbMerge::DoWork(const char* nameOfOutputFile, const char* pattern, bool re
     delete[] patternAsWchar;
     delete[] buffer;
 
-    if (CloseHandle(hFileOut) == 0)
+    if (fclose(fpOut) != 0)
     {
-        LogError("CloseHandle failed. GetLastError()=%u", GetLastError());
+        LogError("fclose failed. errno=%d", errno);
         result = -1;
     }
 
@@ -720,7 +705,7 @@ int verbMerge::DoWork(const char* nameOfOutputFile, const char* pattern, bool re
         int st = remove(nameOfOutputFile);
         if (st != 0)
         {
-            LogError("Failed to delete file after MCS /merge failed. GetLastError()=%u", GetLastError());
+            LogError("Failed to delete file after MCS /merge failed. errno=%d", errno);
         }
     }
     else
@@ -734,7 +719,5 @@ int verbMerge::DoWork(const char* nameOfOutputFile, const char* pattern, bool re
         }
     }
 
-    delete[] nameOfOutputFileAsWchar;
-
     return result;
 }
diff --git a/src/coreclr/tools/superpmi/mcs/verbmerge.h b/src/coreclr/tools/superpmi/mcs/verbmerge.h
index ce1eee96b7c522..7106570d44bf62 100644
--- a/src/coreclr/tools/superpmi/mcs/verbmerge.h
+++ b/src/coreclr/tools/superpmi/mcs/verbmerge.h
@@ -83,9 +83,9 @@ class verbMerge
     static char* ConvertWideCharToMultiByte(LPCWSTR wstr);
     static WCHAR* ConvertMultiByteToWideChar(LPCSTR str);
 
-    static int AppendFileRaw(HANDLE hFileOut, LPCWSTR fileFullPath, unsigned char* buffer, size_t bufferSize);
-    static int AppendFile(HANDLE hFileOut, LPCWSTR fileFullPath, bool dedup, unsigned char* buffer, size_t bufferSize);
-    static int AppendAllInDir(HANDLE              hFileOut,
+    static int AppendFileRaw(FILE* fpOut, LPCWSTR fileFullPath, unsigned char* buffer, size_t bufferSize);
+    static int AppendFile(FILE* fpOut, LPCWSTR fileFullPath, bool dedup, unsigned char* buffer, size_t bufferSize);
+    static int AppendAllInDir(FILE*               fpOut,
                               LPCWSTR             dir,
                               LPCWSTR             file,
                               unsigned char*      buffer,
diff --git a/src/coreclr/tools/superpmi/mcs/verbremovedup.cpp b/src/coreclr/tools/superpmi/mcs/verbremovedup.cpp
index a67f7f8debc400..ef4fde2d59d082 100644
--- a/src/coreclr/tools/superpmi/mcs/verbremovedup.cpp
+++ b/src/coreclr/tools/superpmi/mcs/verbremovedup.cpp
@@ -9,25 +9,24 @@ int verbRemoveDup::DoWork(const char* nameOfInput, const char* nameOfOutput, boo
 {
     LogVerbose("Removing duplicates from '%s', writing to '%s'", nameOfInput, nameOfOutput);
 
-    HANDLE hFileOut = CreateFileA(nameOfOutput, GENERIC_WRITE, 0, NULL, CREATE_ALWAYS,
-                                  FILE_ATTRIBUTE_NORMAL | FILE_FLAG_SEQUENTIAL_SCAN, NULL);
-    if (hFileOut == INVALID_HANDLE_VALUE)
+    FILE* fpOut = fopen(nameOfOutput, "wb");
+    if (fpOut == NULL)
     {
-        LogError("Failed to open output '%s'. GetLastError()=%u", nameOfOutput, GetLastError());
+        LogError("Failed to open output '%s'. errno=%d", nameOfOutput, errno);
         return -1;
     }
 
     RemoveDup removeDups;
     if (!removeDups.Initialize(stripCR, legacyCompare, /* cleanup */ false)
-        || !removeDups.CopyAndRemoveDups(nameOfInput, hFileOut))
+        || !removeDups.CopyAndRemoveDups(nameOfInput, fpOut))
     {
         LogError("Failed to remove dups");
         return -1;
     }
 
-    if (CloseHandle(hFileOut) == 0)
+    if (fclose(fpOut) != 0)
     {
-        LogError("CloseHandle failed. GetLastError()=%u", GetLastError());
+        LogError("CloseHandle failed. errno=%d", errno);
         return -1;
     }
 
diff --git a/src/coreclr/tools/superpmi/mcs/verbstat.cpp b/src/coreclr/tools/superpmi/mcs/verbstat.cpp
index e3cc44de1a0317..b8c9e28cbdf211 100644
--- a/src/coreclr/tools/superpmi/mcs/verbstat.cpp
+++ b/src/coreclr/tools/superpmi/mcs/verbstat.cpp
@@ -18,24 +18,20 @@ int verbStat::DoWork(const char* nameOfInput, const char* nameOfOutput, int inde
 
     int savedCount = 0;
 
-    HANDLE hFileOut = CreateFileA(nameOfOutput, GENERIC_WRITE, 0, NULL, CREATE_ALWAYS,
-                                  FILE_ATTRIBUTE_NORMAL | FILE_FLAG_SEQUENTIAL_SCAN, NULL);
-    if (hFileOut == INVALID_HANDLE_VALUE)
+    FILE* fpOut = fopen(nameOfOutput, "w");
+    if (fpOut == NULL)
     {
-        LogError("Failed to open input 1 '%s'. GetLastError()=%u", nameOfOutput, GetLastError());
+        LogError("Failed to open input 1 '%s'. errno=%d", nameOfOutput, errno);
         return -1;
     }
 
 #define bufflen 50000
-    DWORD bytesWritten;
     char  buff[bufflen];
     int   offset = 0;
     ZeroMemory(&buff[0], bufflen);
     offset += sprintf_s(buff, bufflen, "Title,MC#,");
     offset += MethodContext::dumpStatTitleToBuffer(&buff[offset], bufflen - offset);
-    buff[offset++] = 0x0d;
-    buff[offset++] = 0x0a;
-    WriteFile(hFileOut, &buff[0], offset, &bytesWritten, nullptr);
+    fprintf(fpOut, "%s\n", buff);
 
     while (mci.MoveNext())
     {
@@ -52,15 +48,13 @@ int verbStat::DoWork(const char* nameOfInput, const char* nameOfOutput, int inde
         buff[offset++] = ',';
         offset += sprintf_s(&buff[offset], bufflen - offset, "%d,", mci.MethodContextNumber());
         offset += mc->dumpStatToBuffer(&buff[offset], bufflen - offset);
-        buff[offset++] = 0x0d;
-        buff[offset++] = 0x0a;
-        WriteFile(hFileOut, &buff[0], offset, &bytesWritten, nullptr);
+        fprintf(fpOut, "%s\n", buff);
         savedCount++;
     }
 
-    if (!CloseHandle(hFileOut))
+    if (fclose(fpOut) != 0)
     {
-        LogError("2nd CloseHandle failed. GetLastError()=%u", GetLastError());
+        LogError("fclose failed. errno=%d", errno);
         return -1;
     }
 
diff --git a/src/coreclr/tools/superpmi/mcs/verbstrip.cpp b/src/coreclr/tools/superpmi/mcs/verbstrip.cpp
index a9fe50114c8e44..ad37165c82a339 100644
--- a/src/coreclr/tools/superpmi/mcs/verbstrip.cpp
+++ b/src/coreclr/tools/superpmi/mcs/verbstrip.cpp
@@ -33,11 +33,10 @@ int verbStrip::DoWork(
         return -1;
     }
 
-    HANDLE hFileOut = CreateFileA(nameOfOutput, GENERIC_WRITE, 0, NULL, CREATE_ALWAYS,
-                                  FILE_ATTRIBUTE_NORMAL | FILE_FLAG_SEQUENTIAL_SCAN, NULL);
-    if (hFileOut == INVALID_HANDLE_VALUE)
+    FILE* fpOut = fopen(nameOfOutput, "wb");
+    if (fpOut == NULL)
     {
-        LogError("Failed to open input 1 '%s'. GetLastError()=%u", nameOfOutput, GetLastError());
+        LogError("Failed to open input 1 '%s'. errno=%d", nameOfOutput, errno);
         return -1;
     }
 
@@ -72,13 +71,13 @@ int verbStrip::DoWork(
             delete mc->cr;
             mc->cr = new CompileResult();
         }
-        mc->saveToFile(hFileOut);
+        mc->saveToFile(fpOut);
         savedCount++;
         delete mc;
     }
-    if (CloseHandle(hFileOut) == 0)
+    if (fclose(fpOut) != 0)
     {
-        LogError("2nd CloseHandle failed. GetLastError()=%u", GetLastError());
+        LogError("fclose failed. errno=%d", errno);
         return -1;
     }
     LogInfo("Loaded %d, Saved %d", loadedCount, savedCount);
@@ -100,11 +99,10 @@ int verbStrip::DoWorkTheOldWay(
     bool write;
     int  index = 0; // Can't use MethodContextIterator indexing, since we want the opposite of that.
 
-    HANDLE hFileOut = CreateFileA(nameOfOutput, GENERIC_WRITE, 0, NULL, CREATE_ALWAYS,
-                                  FILE_ATTRIBUTE_NORMAL | FILE_FLAG_SEQUENTIAL_SCAN, NULL);
-    if (hFileOut == INVALID_HANDLE_VALUE)
+    FILE* fpOut = fopen(nameOfOutput, "wb");
+    if (fpOut == NULL)
     {
-        LogError("Failed to open input 1 '%s'. GetLastError()=%u", nameOfOutput, GetLastError());
+        LogError("Failed to open input 1 '%s'. errno=%d", nameOfOutput, errno);
         return -1;
     }
 
@@ -129,14 +127,14 @@ int verbStrip::DoWorkTheOldWay(
                 delete mc->cr;
                 mc->cr = new CompileResult();
             }
-            mc->saveToFile(hFileOut);
+            mc->saveToFile(fpOut);
             savedCount++;
         }
     }
 
-    if (CloseHandle(hFileOut) == 0)
+    if (fclose(fpOut) != 0)
     {
-        LogError("2nd CloseHandle failed. GetLastError()=%u", GetLastError());
+        LogError("fclose failed. errno=%d", errno);
         return -1;
     }
 
diff --git a/src/coreclr/tools/superpmi/mcs/verbtoc.cpp b/src/coreclr/tools/superpmi/mcs/verbtoc.cpp
index d2a384388c12fd..cb45976b0e7e32 100644
--- a/src/coreclr/tools/superpmi/mcs/verbtoc.cpp
+++ b/src/coreclr/tools/superpmi/mcs/verbtoc.cpp
@@ -14,9 +14,7 @@ class TOCElementNode
     TOCElementNode* Next;
     TOCElement      tocElement;
 
-    TOCElementNode(int number, int64_t offset) : Next(nullptr), tocElement(number, offset)
-    {
-    }
+    TOCElementNode(int number, int64_t offset) : Next(nullptr), tocElement(number, offset) {}
 };
 
 int verbTOC::DoWork(const char* nameOfInput)
@@ -55,48 +53,50 @@ int verbTOC::DoWork(const char* nameOfInput)
     char*  nameOfOutput = (char*)_alloca(maxLen);
     strcpy_s(nameOfOutput, maxLen, nameOfInput);
     strcat_s(nameOfOutput, maxLen, ".mct");
-    HANDLE hFileOut =
-        CreateFileA(nameOfOutput, GENERIC_WRITE, FILE_SHARE_WRITE, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
-    if (hFileOut == INVALID_HANDLE_VALUE)
+    FILE* fpOut = fopen(nameOfOutput, "wb");
+    if (fpOut == NULL)
     {
-        LogError("Failed to open input 1 '%s'. GetLastError()=%u", nameOfOutput, GetLastError());
+        LogError("Failed to open input 1 '%s'. errno=%d", nameOfOutput, errno);
         return -1;
     }
 
-    DWORD written;
+    size_t written;
     // Write out the signature "INDX" and then the element count
-    LARGE_INTEGER token;
-    token.u.LowPart  = *(const int*)"INDX"; // cuz Type Safety is for languages that have good IO facilities
-    token.u.HighPart = savedCount;
-    if (!WriteFile(hFileOut, &token, sizeof(token), &written, nullptr) || written != sizeof(token))
+    struct
+    {
+        uint32_t sig;
+        uint32_t count;
+    } token;
+    token.sig    = *(const int*)"INDX"; // cuz Type Safety is for languages that have good IO facilities
+    token.count = savedCount;
+    if ((written = fwrite(&token, sizeof(token), 1, fpOut)) <= 0 || written != sizeof(token))
     {
-        LogError("Failed to write index header. GetLastError()=%u", GetLastError());
+        LogError("Failed to write index header. errno=%d", errno);
     }
 
     // Now just dump sizeof(TOCElement) byte chunks into the file.
     // I could probably do this more efficiently, but I don't think it matters
-    DWORD chunkSize = sizeof(TOCElement);
     for (curElem = head; curElem != nullptr; curElem = curElem->Next)
     {
-        if (!WriteFile(hFileOut, &curElem->tocElement, chunkSize, &written, nullptr) || written != chunkSize)
+        if ((written = fwrite(&curElem->tocElement, sizeof(TOCElement), 1, fpOut)) <= 0 || written != sizeof(TOCElement))
         {
-            LogError("Failed to write index element '%d'. GetLastError()=%u", curElem->tocElement.Number,
-                     GetLastError());
+            LogError("Failed to write index element '%d'. errno=%d", curElem->tocElement.Number,
+                     errno);
             return -1;
         }
     }
     // Now write out a final "INDX" to flag the end of the file...
-    if (!WriteFile(hFileOut, &token.u.LowPart, sizeof(token.u.LowPart), &written, nullptr) ||
-        (written != sizeof(token.u.LowPart)))
+    if ((written = fwrite(&token.sig, sizeof(token.sig), 1, fpOut)) <= 0 ||
+        (written != sizeof(token.sig)))
     {
-        LogError("Failed to write index terminal. GetLastError()=%u", GetLastError());
+        LogError("Failed to write index terminal. errno=%d", errno);
     }
 
     LogInfo("Loaded %d, added %d to Table of Contents", mci.MethodContextNumber(), savedCount);
 
-    if (CloseHandle(hFileOut) == 0)
+    if (fclose(fpOut) != 0)
     {
-        LogError("CloseHandle failed. GetLastError()=%u", GetLastError());
+        LogError("fclose failed. errno=%d", errno);
         return -1;
     }
 
diff --git a/src/coreclr/tools/superpmi/superpmi-shared/asmdumper.cpp b/src/coreclr/tools/superpmi/superpmi-shared/asmdumper.cpp
index 24f355ac895bd9..afe87709591c7a 100644
--- a/src/coreclr/tools/superpmi/superpmi-shared/asmdumper.cpp
+++ b/src/coreclr/tools/superpmi/superpmi-shared/asmdumper.cpp
@@ -4,25 +4,16 @@
 #include "standardpch.h"
 #include "asmdumper.h"
 
-void ASMDumper::DumpToFile(HANDLE hFile, MethodContext* mc, CompileResult* cr)
+void ASMDumper::DumpToFile(FILE* fp, MethodContext* mc, CompileResult* cr)
 {
     CORINFO_METHOD_INFO info;
     unsigned            flags = 0;
     CORINFO_OS          os    = CORINFO_WINNT;
     mc->repCompileMethod(&info, &flags, &os);
 
-#define bufflen 4096
-    DWORD bytesWritten;
-    char  buff[bufflen];
+    fprintf(fp, ";;Generated from SuperPMI on original input '%s'", cr->repProcessName());
 
-    int buff_offset = 0;
-    ZeroMemory(buff, bufflen * sizeof(char));
-    buff_offset += sprintf_s(&buff[buff_offset], bufflen - buff_offset,
-                             ";;Generated from SuperPMI on original input '%s'", cr->repProcessName());
-
-    buff_offset += sprintf_s(&buff[buff_offset], bufflen - buff_offset, "\r\n Method Name \"%s\"",
-                             getMethodName(mc, info.ftn).c_str());
-    WriteFile(hFile, buff, buff_offset * sizeof(char), &bytesWritten, nullptr);
+    fprintf(fp, "\n Method Name \"%s\"", getMethodName(mc, info.ftn).c_str());
 
     ULONG              hotCodeSize;
     ULONG              coldCodeSize;
@@ -56,53 +47,7 @@ void ASMDumper::DumpToFile(HANDLE hFile, MethodContext* mc, CompileResult* cr)
     cr->applyRelocs(&rc, coldCodeBlock, coldCodeSize, orig_coldCodeBlock);
     cr->applyRelocs(&rc, roDataBlock, roDataSize, orig_roDataBlock);
 
-#ifdef USE_MSVCDIS
-
-#ifdef TARGET_AMD64
-    DIS* disasm = DIS::PdisNew(DIS::distX8664);
-#elif TARGET_X86
-    DIS* disasm = DIS::PdisNew(DIS::distX86);
-#endif
-    size_t offset = 0;
-    while (offset < hotCodeSize)
-    {
-        buff_offset = 0;
-        ZeroMemory(buff, bufflen * sizeof(char));
-
-        DIS::INSTRUCTION instr;
-        DIS::OPERAND     ops[3];
-
-        size_t instrSize = disasm->CbDisassemble(0, (void*)(hotCodeBlock + offset), 15);
-        if (instrSize == 0)
-        {
-            LogWarning("Zero sized instruction");
-            break;
-        }
-        disasm->FDecode(&instr, ops, 3);
-
-        WCHAR instrMnemonic[64]; // I never know how much to allocate...
-        disasm->CchFormatInstr(instrMnemonic, 64);
-        std::string instrMnemonicUtf8 = ConvertToUtf8(instrMnemonic);
-        buff_offset += sprintf_s(&buff[buff_offset], bufflen - buff_offset, "\r\n%p %s",
-                                 (void*)((size_t)orig_hotCodeBlock + offset), instrMnemonicUtf8.c_str());
-        buff_offset += sprintf_s(&buff[buff_offset], bufflen - buff_offset, "   ; ");
-        for (unsigned int i = 0; i < instrSize; i++)
-            buff_offset +=
-                sprintf_s(&buff[buff_offset], bufflen - buff_offset, "%02x ", *((BYTE*)(hotCodeBlock + offset + i)));
-        WriteFile(hFile, buff, buff_offset * sizeof(char), &bytesWritten, nullptr);
-        offset += instrSize;
-    }
-
-    delete disasm;
-
-#else // !USE_MSVCDIS
-
-    buff_offset = 0;
-    ZeroMemory(buff, bufflen * sizeof(char));
-    buff_offset += sprintf_s(&buff[buff_offset], bufflen - buff_offset, ";; No disassembler available");
-    WriteFile(hFile, buff, buff_offset * sizeof(char), &bytesWritten, nullptr);
-
-#endif // !USE_MSVCDIS
+    fprintf(fp, ";; No disassembler available");
 
-    FlushFileBuffers(hFile);
+    fflush(fp);
 }
diff --git a/src/coreclr/tools/superpmi/superpmi-shared/asmdumper.h b/src/coreclr/tools/superpmi/superpmi-shared/asmdumper.h
index 90af3ef16febfc..be4987b547c773 100644
--- a/src/coreclr/tools/superpmi/superpmi-shared/asmdumper.h
+++ b/src/coreclr/tools/superpmi/superpmi-shared/asmdumper.h
@@ -11,7 +11,7 @@
 class ASMDumper
 {
 public:
-    static void DumpToFile(HANDLE hFile, MethodContext* mc, CompileResult* cr);
+    static void DumpToFile(FILE* fp, MethodContext* mc, CompileResult* cr);
 };
 
 #endif
diff --git a/src/coreclr/tools/superpmi/superpmi-shared/logging.cpp b/src/coreclr/tools/superpmi/superpmi-shared/logging.cpp
index a0de0cda60d122..4236d274771920 100644
--- a/src/coreclr/tools/superpmi/superpmi-shared/logging.cpp
+++ b/src/coreclr/tools/superpmi/superpmi-shared/logging.cpp
@@ -18,7 +18,7 @@
 
 bool             Logger::s_initialized = false;
 UINT32           Logger::s_logLevel    = LOGMASK_DEFAULT;
-HANDLE           Logger::s_logFile     = INVALID_HANDLE_VALUE;
+FILE*            Logger::s_logFile     = NULL;
 char*            Logger::s_logFilePath = nullptr;
 minipal_mutex Logger::s_critSec;
 
@@ -55,12 +55,11 @@ void Logger::Shutdown()
 /* static */
 void Logger::OpenLogFile(const char* logFilePath)
 {
-    if (s_logFile == INVALID_HANDLE_VALUE && logFilePath != nullptr)
+    if (s_logFile == NULL && logFilePath != nullptr)
     {
-        s_logFile = CreateFileA(logFilePath, GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_DELETE, NULL, CREATE_ALWAYS,
-                                FILE_ATTRIBUTE_NORMAL | FILE_FLAG_SEQUENTIAL_SCAN, NULL);
+        s_logFile = fopen(logFilePath, "w");
 
-        if (s_logFile != INVALID_HANDLE_VALUE)
+        if (s_logFile != NULL)
         {
             // We may need the file path later in order to delete the log file
             s_logFilePath = _strdup(logFilePath);
@@ -79,22 +78,22 @@ void Logger::OpenLogFile(const char* logFilePath)
 /* static */
 void Logger::CloseLogFile()
 {
-    if (s_logFile != INVALID_HANDLE_VALUE)
+    if (s_logFile != NULL)
     {
         // Avoid polluting the file system with empty log files
-        if (GetFileSize(s_logFile, nullptr) == 0 && s_logFilePath != nullptr)
+        if (ftell(s_logFile) == 0 && s_logFilePath != nullptr)
         {
             // We can call this before closing the handle because remove just marks the file
             // for deletion, i.e. it does not actually get deleted until its last handle is closed.
             if (remove(s_logFilePath) == -1)
-                fprintf(stderr, "WARNING: [Logger::CloseLogFile] remove failed. GetLastError()=%u\n",
-                        GetLastError());
+                fprintf(stderr, "WARNING: [Logger::CloseLogFile] remove failed. errno=%d\n",
+                        errno);
         }
 
-        if (!CloseHandle(s_logFile))
-            fprintf(stderr, "WARNING: [Logger::CloseLogFile] CloseHandle failed. GetLastError()=%u\n", GetLastError());
+        if (fclose(s_logFile) != 0)
+            fprintf(stderr, "WARNING: [Logger::CloseLogFile] CloseHandle failed. errno=%d\n", errno);
 
-        s_logFile = INVALID_HANDLE_VALUE;
+        s_logFile = NULL;
 
         free(s_logFilePath);
         s_logFilePath = nullptr;
@@ -251,7 +250,7 @@ void Logger::LogVprintf(
 
     fprintf(dest, "%s\n", fullMsg);
 
-    if (s_logFile != INVALID_HANDLE_VALUE)
+    if (s_logFile != NULL)
     {
 #ifndef TARGET_UNIX // TODO: no localtime_s() or strftime() in PAL
         tm      timeInfo;
@@ -276,25 +275,13 @@ void Logger::LogVprintf(
         const char* timeStr = "";
 #endif // TARGET_UNIX
 
-        const char logEntryFmtStr[] = "%s - %s [%s:%d] - %s - %s\r\n";
-        size_t logEntryBuffSize = sizeof(logEntryFmtStr) + strlen(timeStr) + strlen(function) + strlen(file) + /* line number */ 10 +
-                                  strlen(logLevelStr) + strlen(fullMsg);
+        if (fprintf(s_logFile, "%s - %s [%s:%d] - %s - %s\r\n", timeStr, function, file, line, logLevelStr, fullMsg) <= 0)
+            fprintf(stderr, "WARNING: [Logger::LogVprintf] Failed to write to log file. errno=%d\n",
+                    errno);
 
-        char* logEntry = new char[logEntryBuffSize];
-        sprintf_s(logEntry, logEntryBuffSize, logEntryFmtStr, timeStr, function, file, line, logLevelStr, fullMsg);
-        size_t logEntryLen = strlen(logEntry);
-
-        DWORD bytesWritten;
-
-        if (!WriteFile(s_logFile, logEntry, (DWORD)logEntryLen, &bytesWritten, nullptr))
-            fprintf(stderr, "WARNING: [Logger::LogVprintf] Failed to write to log file. GetLastError()=%u\n",
-                    GetLastError());
-
-        if (!FlushFileBuffers(s_logFile))
-            fprintf(stderr, "WARNING: [Logger::LogVprintf] Failed to flush log file. GetLastError()=%u\n",
-                    GetLastError());
-
-        delete[] logEntry;
+        if (fflush(s_logFile) != 0)
+            fprintf(stderr, "WARNING: [Logger::LogVprintf] Failed to flush log file. errno=%d\n",
+                    errno);
 
 #ifndef TARGET_UNIX
         free((void*)timeStr);
diff --git a/src/coreclr/tools/superpmi/superpmi-shared/logging.h b/src/coreclr/tools/superpmi/superpmi-shared/logging.h
index 83559df9befdbf..57685260cee097 100644
--- a/src/coreclr/tools/superpmi/superpmi-shared/logging.h
+++ b/src/coreclr/tools/superpmi/superpmi-shared/logging.h
@@ -65,7 +65,7 @@ class Logger
 private:
     static bool             s_initialized;
     static UINT32           s_logLevel;
-    static HANDLE           s_logFile;
+    static FILE*            s_logFile;
     static char*            s_logFilePath;
     static minipal_mutex s_critSec;
 
diff --git a/src/coreclr/tools/superpmi/superpmi-shared/mclist.cpp b/src/coreclr/tools/superpmi/superpmi-shared/mclist.cpp
index 79dca0cdc766ae..ac19c719474999 100644
--- a/src/coreclr/tools/superpmi/superpmi-shared/mclist.cpp
+++ b/src/coreclr/tools/superpmi/superpmi-shared/mclist.cpp
@@ -9,7 +9,7 @@
 #include "mclist.h"
 #include "logging.h"
 
-bool MCList::processArgAsMCL(char* input, int* count, int** list)
+bool MCList::processArgAsMCL(char* input, std::vector<int>& list)
 {
     // If it contains only '0-9', '-', ',' try to see it as a range list, else try to load as a file
     bool isRangeList = true;
@@ -25,7 +25,6 @@ bool MCList::processArgAsMCL(char* input, int* count, int** list)
     if (isRangeList)
     {
         // Count items
-        *count              = 0;
         unsigned rangeStart = 0;
         bool     inRange    = false;
         unsigned scratch    = 0;
@@ -33,52 +32,9 @@ bool MCList::processArgAsMCL(char* input, int* count, int** list)
 
         char* tail = input + len;
 
-        for (char* head = input; head <= tail; head++)
-        {
-            scratch    = 0;
-            foundDigit = false;
-            while ((head <= tail) && (isdigit((unsigned char)*head)))
-            {
-                scratch    = (scratch * 10) + ((*head) - '0');
-                foundDigit = true;
-                head++;
-            }
-            if (foundDigit)
-            {
-                if (inRange)
-                {
-                    inRange = false;
-                    if (rangeStart >= scratch)
-                    {
-                        LogError("Invalid range in '%s'", input);
-                        return false;
-                    }
-                    (*count) += scratch - rangeStart;
-                }
-                else
-                {
-                    rangeStart = scratch;
-                    (*count)++;
-                }
-            }
-            if (*head == '-')
-                inRange = true;
-        }
-
-        if (*count == 0)
-        {
-            LogError("Didn't find a list!");
-            return false;
-        }
-
         inRange    = false;
         rangeStart = 0;
 
-        int* ll   = new int[*count];
-        *list     = ll;
-        int index = 0;
-        ll[index] = 0;
-
         for (char* head = input; head <= tail; head++)
         {
             scratch    = 0;
@@ -95,12 +51,12 @@ bool MCList::processArgAsMCL(char* input, int* count, int** list)
                 {
                     inRange = false;
                     for (unsigned int i = rangeStart + 1; i <= scratch; i++)
-                        ll[index++]     = i;
+                        list.push_back(i);
                 }
                 else
                 {
-                    rangeStart  = scratch;
-                    ll[index++] = scratch;
+                    rangeStart = scratch;
+                    list.push_back(scratch);
                 }
             }
             if (*head == '-')
@@ -111,6 +67,13 @@ bool MCList::processArgAsMCL(char* input, int* count, int** list)
             LogError("Found invalid external range in '%s'", input);
             return false;
         }
+
+        if (list.empty())
+        {
+            LogError("Didn't find a list!");
+            return false;
+        }
+
         goto checkMCL;
     }
     else
@@ -119,26 +82,25 @@ bool MCList::processArgAsMCL(char* input, int* count, int** list)
         if (lastdot != nullptr && _stricmp(lastdot, ".mcl") == 0)
         {
             // Read MCLFile
-            if (!getLineData(input, count, list))
+            if (!getLineData(input, list))
                 return false;
-            if (*count >= 0)
+            if (list.size() >= 0)
                 goto checkMCL;
         }
         return false;
     }
 
 checkMCL: // check that mcl list is increasing only
-    int* ll = (*list);
-    if (ll[0] == 0)
+    if (list[0] != 1)
     {
         LogError("MCL list needs to start from 1!");
         return false;
     }
-    for (int i = 1; i < *count; i++)
+    for (size_t i = 1; i < list.size(); i++)
     {
-        if (ll[i - 1] >= ll[i])
+        if (list[i - 1] >= list[i])
         {
-            LogError("MCL list must be increasing.. found %d -> %d", ll[i - 1], ll[i]);
+            LogError("MCL list must be increasing.. found %d -> %d", list[i - 1], list[i]);
             return false;
         }
     }
@@ -146,112 +108,60 @@ bool MCList::processArgAsMCL(char* input, int* count, int** list)
 }
 
 // Returns true on success, false on failure.
-// On success, sets *pIndexCount to the number of indices read, and *pIndexes to a new array with all the indices read.
-// The caller must free the memory with delete[].
 /* static */
-bool MCList::getLineData(const char* nameOfInput, /* OUT */ int* pIndexCount, /* OUT */ int** pIndexes)
+bool MCList::getLineData(const char* nameOfInput, std::vector<int>& indexes)
 {
-    HANDLE hFile = CreateFileA(nameOfInput, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING,
-                               FILE_ATTRIBUTE_NORMAL | FILE_FLAG_SEQUENTIAL_SCAN, NULL);
-    if (hFile == INVALID_HANDLE_VALUE)
+    FILE* fp = fopen(nameOfInput, "r");
+    if (fp == NULL)
     {
-        LogError("Unable to open '%s'. GetLastError()=%u", nameOfInput, GetLastError());
-        return false;
-    }
-    LARGE_INTEGER DataTemp;
-    if (!GetFileSizeEx(hFile, &DataTemp))
-    {
-        LogError("GetFileSizeEx failed. GetLastError()=%u", GetLastError());
+        LogError("Unable to open '%s'. errno=%d", nameOfInput, errno);
         return false;
     }
 
-    if (DataTemp.QuadPart > MAXMCLFILESIZE)
+    int value;
+    while (fscanf(fp, "%d", &value) > 0)
     {
-        LogError("Size %d exceeds max size of %d", DataTemp.QuadPart, MAXMCLFILESIZE);
-        return false;
+        indexes.push_back(value);
     }
 
-    int   sz   = DataTemp.u.LowPart;
-    char* buff = new char[sz];
-    DWORD bytesRead;
-    if (ReadFile(hFile, buff, sz, &bytesRead, nullptr) == 0)
+    if (fclose(fp) != 0)
     {
-        LogError("ReadFile failed. GetLastError()=%u", GetLastError());
-        delete[] buff;
+        LogError("fclose failed. errno=%d", errno);
         return false;
     }
-    if (!CloseHandle(hFile))
-    {
-        LogError("CloseHandle failed. GetLastError()=%u", GetLastError());
-        delete[] buff;
-        return false;
-    }
-
-    // Count the lines. Note that the last line better be terminated by a newline.
-    int lineCount = 0;
-    for (int i = 0; i < sz; i++)
-    {
-        if (buff[i] == '\n')
-        {
-            lineCount++;
-        }
-    }
-
-    int* indexes    = new int[lineCount];
-    int  indexCount = 0;
-    int  i          = 0;
-    while (i < sz)
-    {
-        // seek the first number on the line. This will skip empty lines and lines with no digits.
-        while (!isdigit((unsigned char)buff[i]))
-            i++;
-        // read in the number
-        indexes[indexCount++] = atoi(&buff[i]);
-        // seek to the start of next line
-        while ((i < sz) && (buff[i] != '\n'))
-            i++;
-        i++;
-    }
-    delete[] buff;
 
-    *pIndexCount = indexCount;
-    *pIndexes    = indexes;
     return true;
 }
 
 void MCList::InitializeMCL(char* filename)
 {
-    hMCLFile = CreateFileA(filename, GENERIC_WRITE, FILE_SHARE_WRITE, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
-    if (hMCLFile == INVALID_HANDLE_VALUE)
+    fpMCLFile = fopen(filename, "w");
+    if (fpMCLFile == NULL)
     {
-        LogError("Failed to open output file '%s'. GetLastError()=%u", filename, GetLastError());
+        LogError("Failed to open output file '%s'. errno=%d", filename, errno);
     }
 }
 
 void MCList::AddMethodToMCL(int methodIndex)
 {
-    if (hMCLFile != INVALID_HANDLE_VALUE)
+    if (fpMCLFile != NULL)
     {
-        char  strMethodIndex[12];
-        DWORD charCount    = 0;
-        DWORD bytesWritten = 0;
-
-        charCount = sprintf_s(strMethodIndex, sizeof(strMethodIndex), "%d\r\n", methodIndex);
-
-        if (!WriteFile(hMCLFile, strMethodIndex, charCount, &bytesWritten, nullptr) || bytesWritten != charCount)
+        if (fprintf(fpMCLFile, "%d\n", methodIndex) != 0)
         {
-            LogError("Failed to write method index '%d'. GetLastError()=%u", strMethodIndex, GetLastError());
+            LogError("Failed to write method index '%d'. errno=%d", methodIndex, errno);
         }
     }
 }
 
 void MCList::CloseMCL()
 {
-    if (hMCLFile != INVALID_HANDLE_VALUE)
+    if (fpMCLFile != NULL)
     {
-        if (CloseHandle(hMCLFile) == 0)
+        if (fclose(fpMCLFile) == 0)
         {
-            LogError("CloseHandle failed. GetLastError()=%u", GetLastError());
+            LogError("fclose failed. errno=%d", errno);
         }
     }
+
+    fpMCLFile = NULL;
 }
diff --git a/src/coreclr/tools/superpmi/superpmi-shared/mclist.h b/src/coreclr/tools/superpmi/superpmi-shared/mclist.h
index 44291f0600a0e0..9810846e78754a 100644
--- a/src/coreclr/tools/superpmi/superpmi-shared/mclist.h
+++ b/src/coreclr/tools/superpmi/superpmi-shared/mclist.h
@@ -11,12 +11,12 @@
 class MCList
 {
 public:
-    static bool processArgAsMCL(char* input, int* count, int** list);
+    static bool processArgAsMCL(char* input, std::vector<int>& list);
 
     MCList()
     {
         // Initialize the static file handle
-        hMCLFile = INVALID_HANDLE_VALUE;
+        fpMCLFile = NULL;
     }
 
     // Methods to create an MCL file
@@ -25,9 +25,9 @@ class MCList
     void CloseMCL();
 
 private:
-    static bool getLineData(const char* nameOfInput, /* OUT */ int* pIndexCount, /* OUT */ int** pIndexes);
+    static bool getLineData(const char* nameOfInput, std::vector<int>& indexes);
 
     // File handle for MCL file
-    HANDLE hMCLFile;
+    FILE* fpMCLFile;
 };
 #endif
diff --git a/src/coreclr/tools/superpmi/superpmi-shared/methodcontext.cpp b/src/coreclr/tools/superpmi/superpmi-shared/methodcontext.cpp
index 5202cd73661c44..ecc3ef0f412390 100644
--- a/src/coreclr/tools/superpmi/superpmi-shared/methodcontext.cpp
+++ b/src/coreclr/tools/superpmi/superpmi-shared/methodcontext.cpp
@@ -138,7 +138,7 @@ unsigned int MethodContext::calculateRawFileSize()
            2 /* end canary '4', '2' */;
 }
 
-unsigned int MethodContext::saveToFile(HANDLE hFile)
+unsigned int MethodContext::saveToFile(FILE* fp)
 {
     unsigned int totalLen = calculateFileSize();
     unsigned int totalFileSize =
@@ -165,7 +165,7 @@ unsigned int MethodContext::saveToFile(HANDLE hFile)
 
     Assert(buffIndex == totalFileSize);
 
-    WriteFile(hFile, buff2, totalFileSize, &bytesWritten, NULL);
+    bytesWritten = (DWORD)fwrite(buff2, 1, totalFileSize, fp);
     delete[] buff2;
     return bytesWritten;
 }
@@ -183,12 +183,12 @@ bool MethodContext::Initialize(int mcIndex, unsigned char* buff, DWORD size, /*
 }
 
 // static
-bool MethodContext::Initialize(int mcIndex, HANDLE hFile, /* OUT */ MethodContext** ppmc)
+bool MethodContext::Initialize(int mcIndex, FILE* fp, /* OUT */ MethodContext** ppmc)
 {
     MethodContext* mc = new MethodContext();
     mc->index         = mcIndex;
     *ppmc             = mc;
-    return mc->Initialize(mcIndex, hFile);
+    return mc->Initialize(mcIndex, fp);
 }
 
 bool MethodContext::Initialize(int mcIndex, unsigned char* buff, DWORD size)
@@ -219,21 +219,21 @@ bool MethodContext::Initialize(int mcIndex, unsigned char* buff, DWORD size)
     return result;
 }
 
-bool MethodContext::Initialize(int mcIndex, HANDLE hFile)
+bool MethodContext::Initialize(int mcIndex, FILE* fp)
 {
     bool result = true;
 
     struct Param
     {
-        HANDLE         hFile;
+        FILE*          fp;
         MethodContext* pThis;
     } param;
-    param.hFile = hFile;
+    param.fp = fp;
     param.pThis = this;
 
     PAL_TRY(Param*, pParam, &param)
     {
-        pParam->pThis->MethodInitHelperFile(pParam->hFile);
+        pParam->pThis->MethodInitHelperFile(pParam->fp);
     }
     PAL_EXCEPT_FILTER(FilterSuperPMIExceptions_CatchMC)
     {
@@ -245,18 +245,17 @@ bool MethodContext::Initialize(int mcIndex, HANDLE hFile)
     return result;
 }
 
-void MethodContext::MethodInitHelperFile(HANDLE hFile)
+void MethodContext::MethodInitHelperFile(FILE* fp)
 {
-    DWORD        bytesRead;
     char         buff[512];
     unsigned int totalLen = 0;
 
-    AssertCode(ReadFile(hFile, buff, 2 + sizeof(unsigned int), &bytesRead, NULL) == TRUE,
+    AssertCode(fread(buff, 1, 2 + sizeof(unsigned int), fp) == 2 + sizeof(unsigned int),
                EXCEPTIONCODE_MC); // Read Magic number and totalLen
     AssertCodeMsg((buff[0] == 'm') && (buff[1] == 'c'), EXCEPTIONCODE_MC, "Didn't find magic number");
     memcpy(&totalLen, &buff[2], sizeof(unsigned int));
     unsigned char* buff2 = new unsigned char[totalLen + 2]; // total + End Canary
-    AssertCode(ReadFile(hFile, buff2, totalLen + 2, &bytesRead, NULL) == TRUE, EXCEPTIONCODE_MC);
+    AssertCode(fread(buff2, 1, totalLen + 2, fp) == totalLen + 2, EXCEPTIONCODE_MC);
     AssertCodeMsg((buff2[totalLen] == '4') && (buff2[totalLen + 1] == '2'), EXCEPTIONCODE_MC, "Didn't find end canary");
     MethodInitHelper(buff2, totalLen);
 }
diff --git a/src/coreclr/tools/superpmi/superpmi-shared/methodcontext.h b/src/coreclr/tools/superpmi/superpmi-shared/methodcontext.h
index bf853790fb9d8d..d2ee22207a217e 100644
--- a/src/coreclr/tools/superpmi/superpmi-shared/methodcontext.h
+++ b/src/coreclr/tools/superpmi/superpmi-shared/methodcontext.h
@@ -68,16 +68,16 @@ class MethodContext
 
 private:
     void MethodInitHelper(unsigned char* buff, unsigned int totalLen);
-    void MethodInitHelperFile(HANDLE hFile);
+    void MethodInitHelperFile(FILE* fp);
 
     bool Initialize(int mcIndex, unsigned char* buff, DWORD size);
-    bool Initialize(int mcIndex, HANDLE hFile);
+    bool Initialize(int mcIndex, FILE* fp);
 
     int dumpHashToBuffer(BYTE* pBuffer, int bufLen, char* buff, int len);
 
 public:
     static bool Initialize(int mcIndex, unsigned char* buff, DWORD size, /* OUT */ MethodContext** ppmc);
-    static bool Initialize(int mcIndex, HANDLE hFile, /* OUT */ MethodContext** ppmc);
+    static bool Initialize(int mcIndex, FILE* fp, /* OUT */ MethodContext** ppmc);
     ~MethodContext();
     void Destroy();
 
@@ -87,7 +87,7 @@ class MethodContext
     }
 
     bool Equal(MethodContext* other);
-    unsigned int saveToFile(HANDLE hFile);
+    unsigned int saveToFile(FILE* fp);
     unsigned int calculateFileSize();
     unsigned int calculateRawFileSize();
 
diff --git a/src/coreclr/tools/superpmi/superpmi-shared/methodcontextiterator.cpp b/src/coreclr/tools/superpmi/superpmi-shared/methodcontextiterator.cpp
index 0f9271b142e8ee..e8c460ce316858 100644
--- a/src/coreclr/tools/superpmi/superpmi-shared/methodcontextiterator.cpp
+++ b/src/coreclr/tools/superpmi/superpmi-shared/methodcontextiterator.cpp
@@ -7,24 +7,20 @@
 
 bool MethodContextIterator::Initialize(const char* fileName)
 {
-    m_hFile = CreateFileA(fileName, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING,
-                          FILE_ATTRIBUTE_NORMAL | FILE_FLAG_SEQUENTIAL_SCAN, NULL);
-    if (m_hFile == INVALID_HANDLE_VALUE)
+    m_fp = fopen(fileName, "rb");
+    if (m_fp == NULL)
     {
         LogError("Failed to open file '%s'. GetLastError()=%u", fileName, GetLastError());
         return false;
     }
 
-    LARGE_INTEGER DataTemp;
-    if (GetFileSizeEx(m_hFile, &DataTemp) == 0)
-    {
-        LogError("GetFileSizeEx failed. GetLastError()=%u", GetLastError());
-        CloseHandle(m_hFile);
-        m_hFile = INVALID_HANDLE_VALUE;
-        return false;
-    }
-
-    m_fileSize = DataTemp.QuadPart;
+    fseek(m_fp, 0, SEEK_END);
+#ifdef TARGET_WINDOWS
+    m_fileSize = _ftelli64(m_fp);
+#else
+    m_fileSize = ftell(m_fp);
+#endif
+    fseek(m_fp, 0, SEEK_SET);
 
     if (m_progressReport)
     {
@@ -37,14 +33,14 @@ bool MethodContextIterator::Initialize(const char* fileName)
 bool MethodContextIterator::Destroy()
 {
     bool ret = true; // assume success
-    if (m_hFile != INVALID_HANDLE_VALUE)
+    if (m_fp != NULL)
     {
-        if (!CloseHandle(m_hFile))
+        if (fclose(m_fp) != 0)
         {
-            LogError("CloseHandle failed. GetLastError()=%u", GetLastError());
+            LogError("fclose failed. errno=%d", errno);
             ret = false;
         }
-        m_hFile = INVALID_HANDLE_VALUE;
+        m_fp = NULL;
     }
     delete m_mc;
     m_mc = nullptr;
@@ -72,19 +68,11 @@ bool MethodContextIterator::MoveNext()
     while (true)
     {
         // Figure out where the pointer is currently.
-        LARGE_INTEGER pos;
-        pos.QuadPart = 0;
-        if (SetFilePointerEx(m_hFile, pos, &m_pos, FILE_CURRENT) == 0)
-        {
-            LogError("SetFilePointerEx failed. GetLastError()=%u", GetLastError());
-            return false; // any failure causes us to bail out.
-        }
-
-        if (m_pos.QuadPart >= m_fileSize)
-        {
-            return false;
-        }
-
+#ifdef TARGET_WINDOWS
+        m_pos = _ftelli64(m_fp);
+#else
+        m_pos = ftell(m_fp);
+#endif
         // Load the current method context.
         m_methodContextNumber++;
 
@@ -99,7 +87,7 @@ bool MethodContextIterator::MoveNext()
             }
         }
 
-        if (!MethodContext::Initialize(m_methodContextNumber, m_hFile, &m_mc))
+        if (!MethodContext::Initialize(m_methodContextNumber, m_fp, &m_mc))
             return false;
 
         // If we have an array of indexes, skip the loaded indexes that have not been specified.
diff --git a/src/coreclr/tools/superpmi/superpmi-shared/methodcontextiterator.h b/src/coreclr/tools/superpmi/superpmi-shared/methodcontextiterator.h
index f45e85ea6e3954..ebda6c450efe2c 100644
--- a/src/coreclr/tools/superpmi/superpmi-shared/methodcontextiterator.h
+++ b/src/coreclr/tools/superpmi/superpmi-shared/methodcontextiterator.h
@@ -9,10 +9,11 @@ class MethodContextIterator
 {
 public:
     MethodContextIterator(bool progressReport = false)
-        : m_hFile(INVALID_HANDLE_VALUE)
+        : m_fp(nullptr)
         , m_fileSize(0)
         , m_methodContextNumber(0)
         , m_mc(nullptr)
+        , m_pos(0)
         , m_indexCount(-1)
         , m_index(0)
         , m_indexes(nullptr)
@@ -27,10 +28,11 @@ class MethodContextIterator
     }
 
     MethodContextIterator(const int indexCount, const int* indexes, bool progressReport = false)
-        : m_hFile(INVALID_HANDLE_VALUE)
+        : m_fp(nullptr)
         , m_fileSize(0)
         , m_methodContextNumber(0)
         , m_mc(nullptr)
+        , m_pos(0)
         , m_indexCount(indexCount)
         , m_index(0)
         , m_indexes(indexes)
@@ -73,7 +75,7 @@ class MethodContextIterator
     // Return the file position offset of the current method context.
     int64_t CurrentPos()
     {
-        return m_pos.QuadPart;
+        return m_pos;
     }
 
     int MethodContextNumber()
@@ -82,11 +84,11 @@ class MethodContextIterator
     }
 
 private:
-    HANDLE         m_hFile;
+    FILE*          m_fp;
     int64_t        m_fileSize;
     int            m_methodContextNumber;
     MethodContext* m_mc;
-    LARGE_INTEGER  m_pos;
+    int64_t        m_pos;
 
     // If m_indexCount==-1, use all method contexts. Otherwise, m_indexCount is the number of elements in the
     // m_indexes array, which contains a sorted set of method context indexes to return. In this case, m_index
diff --git a/src/coreclr/tools/superpmi/superpmi-shared/methodcontextreader.cpp b/src/coreclr/tools/superpmi/superpmi-shared/methodcontextreader.cpp
index 3165ac8ab73436..00550f54a92289 100644
--- a/src/coreclr/tools/superpmi/superpmi-shared/methodcontextreader.cpp
+++ b/src/coreclr/tools/superpmi/superpmi-shared/methodcontextreader.cpp
@@ -18,15 +18,14 @@
 #endif // TARGET_UNIX
 
 // Just a helper...
-HANDLE MethodContextReader::OpenFile(const char* inputFile, DWORD flags)
+FILE* MethodContextReader::OpenFile(const char* inputFile)
 {
-    HANDLE fileHandle =
-        CreateFileA(inputFile, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL | flags, NULL);
-    if (fileHandle == INVALID_HANDLE_VALUE)
+    FILE* fp = fopen(inputFile, "rb");
+    if (fp == NULL)
     {
-        LogError("Failed to open file '%s'. GetLastError()=%u", inputFile, GetLastError());
+        LogError("Failed to open file '%s'. errno=%d", inputFile, errno);
     }
-    return fileHandle;
+    return fp;
 }
 
 static std::string to_lower(const std::string& input)
@@ -83,7 +82,7 @@ std::string MethodContextReader::CheckForPairedFile(const std::string& fileName,
 
 MethodContextReader::MethodContextReader(
     const char* inputFileName, const int* indexes, int indexCount, char* hash, int offset, int increment)
-    : fileHandle(INVALID_HANDLE_VALUE)
+    : fp(NULL)
     , fileSize(0)
     , curMCIndex(0)
     , Indexes(indexes)
@@ -123,11 +122,16 @@ MethodContextReader::MethodContextReader(
         this->tocFile.LoadToc(tocFileName.c_str());
 
     // we'll get here even if we don't have a valid index file
-    this->fileHandle = OpenFile(mchFileName.c_str(), (this->hasTOC() && this->hasIndex()) ? FILE_ATTRIBUTE_NORMAL
-                                                                                          : FILE_FLAG_SEQUENTIAL_SCAN);
-    if (this->fileHandle != INVALID_HANDLE_VALUE)
+    this->fp = fopen(mchFileName.c_str(), "rb");
+    if (this->fp != NULL)
     {
-        GetFileSizeEx(this->fileHandle, (PLARGE_INTEGER) & this->fileSize);
+        fseek(this->fp, 0, SEEK_END);
+#ifdef TARGET_WINDOWS
+        this->fileSize = _ftelli64(this->fp);
+#else
+        this->fileSize = ftell(this->fp);
+#endif
+        fseek(this->fp, 0, SEEK_SET);
     }
 
     ReadExcludedMethods(mchFileName);
@@ -135,9 +139,9 @@ MethodContextReader::MethodContextReader(
 
 MethodContextReader::~MethodContextReader()
 {
-    if (fileHandle != INVALID_HANDLE_VALUE)
+    if (fp != NULL)
     {
-        CloseHandle(this->fileHandle);
+        fclose(fp);
     }
 
     minipal_mutex_destroy(&this->mutex);
@@ -155,32 +159,25 @@ void MethodContextReader::ReleaseLock()
     minipal_mutex_leave(&this->mutex);
 }
 
-bool MethodContextReader::atEof()
-{
-    int64_t pos = 0;
-    SetFilePointerEx(this->fileHandle, *(PLARGE_INTEGER)&pos, (PLARGE_INTEGER)&pos,
-                     FILE_CURRENT); // LARGE_INTEGER is a crime against humanity
-    return pos == this->fileSize;
-}
-
 MethodContextBuffer MethodContextReader::ReadMethodContextNoLock(bool justSkip)
 {
-    DWORD        bytesRead;
     char         buff[512];
     unsigned int totalLen = 0;
-    if (atEof())
+
+    size_t bytesRead = fread(buff, 1, 2 + sizeof(unsigned int), this->fp);
+    if (bytesRead == 0)
     {
         return MethodContextBuffer();
     }
-    Assert(ReadFile(this->fileHandle, buff, 2 + sizeof(unsigned int), &bytesRead, NULL) == TRUE);
+    Assert(bytesRead == 2 + sizeof(unsigned int));
     AssertMsg((buff[0] == 'm') && (buff[1] == 'c'), "Didn't find magic number");
     memcpy(&totalLen, &buff[2], sizeof(unsigned int));
     if (justSkip)
     {
         int64_t pos = totalLen + 2;
         // Just move the file pointer ahead the correct number of bytes
-        AssertMsg(SetFilePointerEx(this->fileHandle, *(PLARGE_INTEGER)&pos, (PLARGE_INTEGER)&pos, FILE_CURRENT) == TRUE,
-                  "SetFilePointerEx failed (Error %X)", GetLastError());
+        AssertMsg(fseek(this->fp, totalLen + 2, SEEK_CUR) == 0,
+                  "fseek failed (Error %d)", errno);
 
         // Increment curMCIndex as we advanced the file pointer by another MC
         ++curMCIndex;
@@ -190,7 +187,7 @@ MethodContextBuffer MethodContextReader::ReadMethodContextNoLock(bool justSkip)
     else
     {
         unsigned char* buff2 = new unsigned char[totalLen + 2]; // total + End Canary
-        Assert(ReadFile(this->fileHandle, buff2, totalLen + 2, &bytesRead, NULL) == TRUE);
+        Assert(fread(buff2, 1, totalLen + 2, this->fp) == totalLen + 2);
 
         // Increment curMCIndex as we read another MC
         ++curMCIndex;
@@ -417,7 +414,7 @@ bool MethodContextReader::hasTOC()
 
 bool MethodContextReader::isValid()
 {
-    return this->fileHandle != INVALID_HANDLE_VALUE;
+    return this->fp != NULL;
 }
 
 // Return a measure of "progress" through the method contexts, as follows:
@@ -438,8 +435,11 @@ double MethodContextReader::Progress()
     else
     {
         this->AcquireLock();
-        int64_t pos = 0;
-        SetFilePointerEx(this->fileHandle, *(PLARGE_INTEGER)&pos, (PLARGE_INTEGER)&pos, FILE_CURRENT);
+#ifdef TARGET_WINDOWS
+        int64_t pos = _ftelli64(this->fp);
+#else
+        int64_t pos = ftell(this->fp);
+#endif
         this->ReleaseLock();
         return (double)pos;
     }
@@ -512,7 +512,7 @@ MethodContextBuffer MethodContextReader::GetSpecificMethodContext(unsigned int m
     {
         return MethodContextBuffer(-2);
     }
-    if (SetFilePointerEx(this->fileHandle, *(PLARGE_INTEGER)&pos, (PLARGE_INTEGER)&pos, FILE_BEGIN))
+    if (fseek(this->fp, (long)pos, SEEK_SET) == 0)
     {
         // ReadMethodContext will release the lock, but we already acquired it
         MethodContextBuffer mcb = this->ReadMethodContext(false);
@@ -534,7 +534,7 @@ MethodContextBuffer MethodContextReader::GetSpecificMethodContext(unsigned int m
 // Read the file with excluded methods hashes and save them.
 void MethodContextReader::ReadExcludedMethods(std::string mchFileName)
 {
-    excludedMethodsList = nullptr;
+    excludedMethodsList.clear();
 
     size_t suffix_offset = mchFileName.find_last_of('.');
     if (suffix_offset == std::string::npos)
@@ -549,83 +549,46 @@ void MethodContextReader::ReadExcludedMethods(std::string mchFileName)
     {
         return;
     }
-    HANDLE excludeFileHandle = OpenFile(excludeFileName.c_str());
-    if (excludeFileHandle != INVALID_HANDLE_VALUE)
+    FILE* fpExclude = OpenFile(excludeFileName.c_str());
+    if (fpExclude != NULL)
     {
-        int64_t excludeFileSizeLong;
-        GetFileSizeEx(excludeFileHandle, (PLARGE_INTEGER)&excludeFileSizeLong);
-        unsigned excludeFileSize = (unsigned)excludeFileSizeLong;
-
-        char* buffer = new char[excludeFileSize + 1];
-        DWORD bytesRead;
-        bool  success = (ReadFile(excludeFileHandle, buffer, excludeFileSize, &bytesRead, NULL) == TRUE);
-        CloseHandle(excludeFileHandle);
-
-        if (!success || excludeFileSize != bytesRead)
-        {
-            LogError("Failed to read the exclude file.");
-            delete[] buffer;
-            return;
-        }
+        char buffer[512];
+        memset(buffer, 0, sizeof(buffer));
 
-        buffer[excludeFileSize] = 0;
-
-        int counter = 0;
-
-        char* curr = buffer;
-        while (*curr != 0)
+        while (fscanf(fpExclude, "%511s", buffer) > 0)
         {
-            while (isspace(*curr))
-            {
-                curr++;
-            }
-
-            std::string hash;
-            while (*curr != 0 && !isspace(*curr))
-            {
-                hash += *curr;
-                curr++;
-            }
+            std::string hash(buffer);
 
             if (hash.length() == MM3_HASH_BUFFER_SIZE - 1)
             {
-                StringList* node    = new StringList();
-                node->hash          = hash;
-                node->next          = excludedMethodsList;
-                excludedMethodsList = node;
-                counter++;
+                excludedMethodsList.push_back(std::move(hash));
             }
             else
             {
                 LogInfo("The exclude file contains wrong values: %s.", hash.c_str());
             }
         }
-        delete[] buffer;
-        LogInfo("Exclude file %s contains %d methods.", excludeFileName.c_str(), counter);
+
+        LogInfo("Exclude file %s contains %d methods.", excludeFileName.c_str(), (int)excludedMethodsList.size());
     }
 }
 
 // Free memory used for excluded methods.
 void MethodContextReader::CleanExcludedMethods()
 {
-    while (excludedMethodsList != nullptr)
-    {
-        StringList* next = excludedMethodsList->next;
-        delete excludedMethodsList;
-        excludedMethodsList = next;
-    }
+    excludedMethodsList.clear();
 }
 
 // Return should this method context be excluded from the replay or not.
 bool MethodContextReader::IsMethodExcluded(MethodContext* mc)
 {
-    if (excludedMethodsList != nullptr)
+    if (!excludedMethodsList.empty())
     {
         char md5HashBuf[MM3_HASH_BUFFER_SIZE] = {0};
         mc->dumpMethodHashToBuffer(md5HashBuf, MM3_HASH_BUFFER_SIZE);
-        for (StringList* node = excludedMethodsList; node != nullptr; node = node->next)
+        for (const std::string& hash : excludedMethodsList)
         {
-            if (strcmp(node->hash.c_str(), md5HashBuf) == 0)
+            if (strcmp(hash.c_str(), md5HashBuf) == 0)
             {
                 return true;
             }
@@ -636,9 +599,7 @@ bool MethodContextReader::IsMethodExcluded(MethodContext* mc)
 
 void MethodContextReader::Reset(const int* newIndexes, int newIndexCount)
 {
-    int64_t pos    = 0;
-    BOOL    result = SetFilePointerEx(fileHandle, *(PLARGE_INTEGER)&pos, NULL, FILE_BEGIN);
-    assert(result);
+    fseek(fp, 0, SEEK_SET);
 
     Indexes     = newIndexes;
     IndexCount  = newIndexCount;
diff --git a/src/coreclr/tools/superpmi/superpmi-shared/methodcontextreader.h b/src/coreclr/tools/superpmi/superpmi-shared/methodcontextreader.h
index f5ef48009b8370..0996ab56a6c3c7 100644
--- a/src/coreclr/tools/superpmi/superpmi-shared/methodcontextreader.h
+++ b/src/coreclr/tools/superpmi/superpmi-shared/methodcontextreader.h
@@ -48,7 +48,7 @@ class MethodContextReader
 {
 private:
     // The MC/MCH file
-    HANDLE fileHandle;
+    FILE* fp;
 
     // The size of the MC/MCH file
     int64_t fileSize;
@@ -82,19 +82,14 @@ class MethodContextReader
     int Offset;
     int Increment;
 
-    struct StringList
-    {
-        StringList* next;
-        std::string hash;
-    };
-    StringList* excludedMethodsList;
+    std::vector<std::string> excludedMethodsList;
 
     // Binary search to get this method number from the index
     // Returns -1 for not found, or -2 for not indexed
     int64_t GetOffset(unsigned int methodNumber);
 
     // Just a helper...
-    static HANDLE OpenFile(const char* inputFile, DWORD flags = FILE_ATTRIBUTE_NORMAL);
+    static FILE* OpenFile(const char* inputFile);
 
     MethodContextBuffer ReadMethodContextNoLock(bool justSkip = false);
     MethodContextBuffer ReadMethodContext(bool acquireLock, bool justSkip = false);
@@ -111,9 +106,6 @@ class MethodContextReader
                                           const std::string& origSuffix,
                                           const std::string& newSuffix);
 
-    // are we're at the end of the file...
-    bool atEof();
-
     // Do we have a valid TOC?
     bool hasTOC();
 
diff --git a/src/coreclr/tools/superpmi/superpmi-shared/tocfile.cpp b/src/coreclr/tools/superpmi/superpmi-shared/tocfile.cpp
index 4898c6d8b9a161..e7e6df7bd12cc9 100644
--- a/src/coreclr/tools/superpmi/superpmi-shared/tocfile.cpp
+++ b/src/coreclr/tools/superpmi/superpmi-shared/tocfile.cpp
@@ -12,48 +12,51 @@
 // Tries to load a Table of Contents
 void TOCFile::LoadToc(const char* inputFileName, bool validate)
 {
-    HANDLE hIndex = CreateFileA(inputFileName, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING,
-                                FILE_ATTRIBUTE_NORMAL | FILE_FLAG_SEQUENTIAL_SCAN, NULL);
-    if (hIndex == INVALID_HANDLE_VALUE)
+    FILE* fpIndex = fopen(inputFileName, "rb");
+    if (fpIndex == NULL)
     {
-        LogError("Failed to open file '%s'. GetLastError()=%u", inputFileName, GetLastError());
+        LogError("Failed to open file '%s'. errno=%d", inputFileName, errno);
         return;
     }
 
     // Now read the index file
-    LARGE_INTEGER val; // I'm abusing LARGE_INTEGER here...
-    DWORD         read;
-    if (!ReadFile(hIndex, &val, sizeof(val), &read, nullptr) || (val.u.LowPart != *(DWORD*)("INDX")))
+    struct
     {
-        CloseHandle(hIndex);
+        uint32_t sig;
+        uint32_t count;
+    } header;
+    if (fread(&header, sizeof(header), 1, fpIndex) != 0 || (header.sig != *(uint32_t*)("INDX")))
+    {
+        fclose(fpIndex);
         LogWarning("The index file %s is invalid: it seems to be missing the starting sentinel/length", inputFileName);
         return;
     }
 
-    this->m_tocCount = val.u.HighPart;
+    this->m_tocCount = header.count;
     this->m_tocArray = new TOCElement[this->m_tocCount];
 
     // Read the whole array
-    if (!ReadFile(hIndex, &this->m_tocArray[0], (DWORD)(this->m_tocCount * sizeof(TOCElement)), &read, nullptr) ||
-        (read != (DWORD)(this->m_tocCount * sizeof(TOCElement))))
+    size_t read = fread(&this->m_tocArray[0], sizeof(TOCElement), this->m_tocCount, fpIndex);
+    if (read != this->m_tocCount * sizeof(TOCElement))
     {
-        CloseHandle(hIndex);
+        fclose(fpIndex);
         this->Clear();
         LogWarning("The index file %s is invalid: it appears to be truncated.", inputFileName);
         return;
     }
 
-    // Get the last 4 byte token (more abuse of LARGE_INTEGER)
-    if (!ReadFile(hIndex, &val.u.HighPart, sizeof(DWORD), &read, nullptr) || (read != sizeof(DWORD)) ||
-        (val.u.LowPart != (DWORD)val.u.HighPart))
+    // Get the last 4 byte token
+    uint32_t sentinal;
+    read = fread(&sentinal, sizeof(sentinal), 1, fpIndex);
+    if ((read != sizeof(sentinal)) || (sentinal != header.sig))
     {
-        CloseHandle(hIndex);
+        fclose(fpIndex);
         this->Clear();
         LogWarning("The index file %s is invalid: it appears to be missing the ending sentinel.", inputFileName);
         return;
     }
 
-    CloseHandle(hIndex);
+    fclose(fpIndex);
 
     if (validate)
     {
diff --git a/src/coreclr/tools/superpmi/superpmi-shim-collector/icorjitcompiler.cpp b/src/coreclr/tools/superpmi/superpmi-shim-collector/icorjitcompiler.cpp
index d7f15ea6cd1fc3..412eaf08ad39a1 100644
--- a/src/coreclr/tools/superpmi/superpmi-shim-collector/icorjitcompiler.cpp
+++ b/src/coreclr/tools/superpmi/superpmi-shim-collector/icorjitcompiler.cpp
@@ -26,7 +26,7 @@ void interceptor_ICJC::finalizeAndCommitCollection(MethodContext* mc, CorJitResu
         mc->cr->recAllocGCInfoCapture();
     }
 
-    mc->saveToFile(hFile);
+    mc->saveToFile(fp);
 }
 
 template<typename TPrinter>
diff --git a/src/coreclr/tools/superpmi/superpmi-shim-collector/icorjitcompiler.h b/src/coreclr/tools/superpmi/superpmi-shim-collector/icorjitcompiler.h
index 56e82ca744237c..8c00074cd3faaf 100644
--- a/src/coreclr/tools/superpmi/superpmi-shim-collector/icorjitcompiler.h
+++ b/src/coreclr/tools/superpmi/superpmi-shim-collector/icorjitcompiler.h
@@ -16,7 +16,7 @@ class interceptor_ICJC : public ICorJitCompiler
 public:
     // Added to help us track the original icjc and be able to easily indirect to it.
     ICorJitCompiler* original_ICorJitCompiler;
-    HANDLE           hFile;
+    FILE*            fp;
     CORINFO_OS       currentOs;
 
     void finalizeAndCommitCollection(MethodContext* mc, CorJitResult result, uint8_t* nativeEntry, uint32_t nativeSizeOfCode);
diff --git a/src/coreclr/tools/superpmi/superpmi-shim-collector/superpmi-shim-collector.cpp b/src/coreclr/tools/superpmi/superpmi-shim-collector/superpmi-shim-collector.cpp
index f3ff4af0e6f9db..d185eed6d6de58 100644
--- a/src/coreclr/tools/superpmi/superpmi-shim-collector/superpmi-shim-collector.cpp
+++ b/src/coreclr/tools/superpmi/superpmi-shim-collector/superpmi-shim-collector.cpp
@@ -215,11 +215,10 @@ extern "C" DLLEXPORT ICorJitCompiler* getJit()
 #endif
 
     // create our datafile
-    pJitInstance->hFile = CreateFileA(g_dataFileName.c_str(), GENERIC_READ | GENERIC_WRITE, 0, NULL,
-                                      CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL | FILE_FLAG_SEQUENTIAL_SCAN, NULL);
-    if (pJitInstance->hFile == INVALID_HANDLE_VALUE)
+    pJitInstance->fp = fopen(g_dataFileName.c_str(), "wb+");
+    if (pJitInstance->fp == NULL)
     {
-        LogError("Couldn't open file '%s': error %d", g_dataFileName.c_str(), GetLastError());
+        LogError("Couldn't open file '%s': error %d", g_dataFileName.c_str(), errno);
     }
 
     return pJitInstance;
diff --git a/src/coreclr/tools/superpmi/superpmi/commandline.cpp b/src/coreclr/tools/superpmi/superpmi/commandline.cpp
index 6fd0acfcae6922..4dd70fd155077e 100644
--- a/src/coreclr/tools/superpmi/superpmi/commandline.cpp
+++ b/src/coreclr/tools/superpmi/superpmi/commandline.cpp
@@ -419,7 +419,8 @@ bool CommandLine::Parse(int argc, char* argv[], /* OUT */ Options* o)
                     return false;
                 }
 
-                bool isValidList = MCList::processArgAsMCL(argv[i], &o->indexCount, &o->indexes);
+                bool isValidList = MCList::processArgAsMCL(argv[i], o->indexes);
+                o->indexCount    = (int)o->indexes.size();
                 if (!isValidList)
                 {
                     LogError("Arg '%s' is invalid, needed method context list.", argv[i]);
diff --git a/src/coreclr/tools/superpmi/superpmi/commandline.h b/src/coreclr/tools/superpmi/superpmi/commandline.h
index 02a9ef4ee38466..749fdcb64d1f33 100644
--- a/src/coreclr/tools/superpmi/superpmi/commandline.h
+++ b/src/coreclr/tools/superpmi/superpmi/commandline.h
@@ -36,7 +36,7 @@ class CommandLine
         int   indexCount = -1;  // If indexCount is -1 and hash points to nullptr it means compile all.
         int   failureLimit = -1; // Number of failures after which bail out the replay/asmdiffs.
         int   repeatCount = 1;   // Number of times given methods should be compiled.
-        int*  indexes = nullptr;
+        std::vector<int> indexes;
         char* hash = nullptr;
         char* methodStatsTypes = nullptr;
         char* details = nullptr;
diff --git a/src/coreclr/tools/superpmi/superpmi/fileio.cpp b/src/coreclr/tools/superpmi/superpmi/fileio.cpp
index eaa53fb0c9189e..f538bb479f9ad4 100644
--- a/src/coreclr/tools/superpmi/superpmi/fileio.cpp
+++ b/src/coreclr/tools/superpmi/superpmi/fileio.cpp
@@ -124,17 +124,15 @@ bool FileWriter::Flush()
     if (m_bufferIndex <= 0)
         return true;
 
-    DWORD numWritten;
-    bool result =
-        WriteFile(m_file.Get(), m_buffer.data(), static_cast<DWORD>(m_bufferIndex), &numWritten, nullptr) &&
-        (numWritten == static_cast<DWORD>(m_bufferIndex));
+    size_t numWritten = fwrite(m_buffer.data(), 1, m_bufferIndex, m_file.Get());
+    bool result = (numWritten == m_bufferIndex);
     m_bufferIndex = 0;
     return result;
 }
 
 bool FileWriter::CreateNew(const char* path, FileWriter* fw)
 {
-    FileHandle handle(CreateFile(path, GENERIC_WRITE, 0, nullptr, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, nullptr));
+    FILEHandle handle(fopen(path, "wb"));
     if (!handle.IsValid())
     {
         return false;
@@ -143,64 +141,3 @@ bool FileWriter::CreateNew(const char* path, FileWriter* fw)
     *fw = FileWriter(std::move(handle));
     return true;
 }
-
-bool FileLineReader::Open(const char* path, FileLineReader* fr)
-{
-    FileHandle file(CreateFile(path, GENERIC_READ, FILE_SHARE_READ, nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr));
-    if (!file.IsValid())
-    {
-        return false;
-    }
-
-    LARGE_INTEGER size;
-    if (!GetFileSizeEx(file.Get(), &size))
-    {
-        return false;
-    }
-
-    if (static_cast<ULONGLONG>(size.QuadPart) > SIZE_MAX)
-    {
-        return false;
-    }
-
-    FileMappingHandle mapping(CreateFileMapping(file.Get(), nullptr, PAGE_READONLY, size.u.HighPart, size.u.LowPart, nullptr));
-    if (!mapping.IsValid())
-    {
-        return false;
-    }
-
-    FileViewHandle view(MapViewOfFile(mapping.Get(), FILE_MAP_READ, 0, 0, 0));
-    if (!view.IsValid())
-    {
-        return false;
-    }
-
-    *fr = FileLineReader(std::move(file), std::move(mapping), std::move(view), static_cast<size_t>(size.QuadPart));
-    return true;
-}
-
-bool FileLineReader::AdvanceLine()
-{
-    if (m_cur >= m_end)
-    {
-        return false;
-    }
-
-    char* end = m_cur;
-    while (end < m_end && *end != '\r' && *end != '\n')
-    {
-        end++;
-    }
-
-    m_currentLine.resize(end - m_cur + 1);
-    memcpy(m_currentLine.data(), m_cur, end - m_cur);
-    m_currentLine[end - m_cur] = '\0';
-
-    m_cur = end;
-    if (m_cur < m_end && *m_cur == '\r')
-        m_cur++;
-    if (m_cur < m_end && *m_cur == '\n')
-        m_cur++;
-
-    return true;
-}
diff --git a/src/coreclr/tools/superpmi/superpmi/fileio.h b/src/coreclr/tools/superpmi/superpmi/fileio.h
index 8c721c2545008e..b519ad0cea3587 100644
--- a/src/coreclr/tools/superpmi/superpmi/fileio.h
+++ b/src/coreclr/tools/superpmi/superpmi/fileio.h
@@ -4,6 +4,8 @@
 #ifndef _FileIO
 #define _FileIO
 
+#include <fstream>
+
 template<typename HandleSpec>
 struct HandleWrapper
 {
@@ -54,38 +56,22 @@ struct HandleWrapper
     HandleType m_handle;
 };
 
-struct FileHandleSpec
-{
-    using Type = HANDLE;
-    static HANDLE Invalid() { return INVALID_HANDLE_VALUE; }
-    static void Close(HANDLE h) { CloseHandle(h); }
-};
-
-struct FileMappingHandleSpec
+struct FILEPtrSpec
 {
-    using Type = HANDLE;
-    static HANDLE Invalid() { return nullptr; }
-    static void Close(HANDLE h) { CloseHandle(h); }
+    using Type = FILE*;
+    static FILE* Invalid() { return NULL; }
+    static void Close(FILE* fp) { fclose(fp); }
 };
 
-struct FileViewHandleSpec
-{
-    using Type = LPVOID;
-    static LPVOID Invalid() { return nullptr; }
-    static void Close(LPVOID p) { UnmapViewOfFile(p); }
-};
-
-typedef HandleWrapper<FileHandleSpec> FileHandle;
-typedef HandleWrapper<FileMappingHandleSpec> FileMappingHandle;
-typedef HandleWrapper<FileViewHandleSpec> FileViewHandle;
+typedef HandleWrapper<FILEPtrSpec>    FILEHandle;
 
 class FileWriter
 {
-    FileHandle m_file;
+    FILEHandle        m_file;
     std::vector<char> m_buffer;
     size_t m_bufferIndex = 0;
 
-    explicit FileWriter(FileHandle file)
+    explicit FileWriter(FILEHandle file)
         : m_file(std::move(file))
         , m_buffer(8192)
     {
@@ -130,36 +116,4 @@ class FileWriter
     static bool CreateNew(const char* path, FileWriter* fw);
 };
 
-class FileLineReader
-{
-    FileHandle m_file;
-    FileMappingHandle m_fileMapping;
-    FileViewHandle m_view;
-
-    char* m_cur;
-    char* m_end;
-    std::vector<char> m_currentLine;
-
-    FileLineReader(FileHandle file, FileMappingHandle fileMapping, FileViewHandle view, size_t size)
-        : m_file(std::move(file))
-        , m_fileMapping(std::move(fileMapping))
-        , m_view(std::move(view))
-        , m_cur(static_cast<char*>(m_view.Get()))
-        , m_end(static_cast<char*>(m_view.Get()) + size)
-    {
-    }
-
-public:
-    FileLineReader()
-        : m_cur(nullptr)
-        , m_end(nullptr)
-    {
-    }
-
-    bool AdvanceLine();
-    const char* GetCurrentLine() { return m_currentLine.data(); }
-
-    static bool Open(const char* path, FileLineReader* fr);
-};
-
 #endif
diff --git a/src/coreclr/tools/superpmi/superpmi/methodstatsemitter.cpp b/src/coreclr/tools/superpmi/superpmi/methodstatsemitter.cpp
index 36cee7c6ccdb2d..ed405965e48c94 100644
--- a/src/coreclr/tools/superpmi/superpmi/methodstatsemitter.cpp
+++ b/src/coreclr/tools/superpmi/superpmi/methodstatsemitter.cpp
@@ -14,34 +14,28 @@ MethodStatsEmitter::MethodStatsEmitter(char* nameOfInput)
     char filename[MAX_PATH + 1];
     sprintf_s(filename, MAX_PATH + 1, "%s.stats", nameOfInput);
 
-    hStatsFile =
-        CreateFileA(filename, GENERIC_WRITE, FILE_SHARE_WRITE, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
-    if (hStatsFile == INVALID_HANDLE_VALUE)
+    fpStatsFile = fopen(filename, "w");
+    if (fpStatsFile == NULL)
     {
-        LogError("Failed to open output file '%s'. GetLastError()=%u", filename, GetLastError());
+        LogError("Failed to open output file '%s'. errno=%d", filename, errno);
     }
 }
 
 MethodStatsEmitter::~MethodStatsEmitter()
 {
-    if (hStatsFile != INVALID_HANDLE_VALUE)
+    if (fpStatsFile != NULL)
     {
-        if (CloseHandle(hStatsFile) == 0)
+        if (fclose(fpStatsFile) != 0)
         {
-            LogError("CloseHandle failed. GetLastError()=%u", GetLastError());
+            LogError("fclose failed. errno=%d", errno);
         }
     }
 }
 
 void MethodStatsEmitter::Emit(int methodNumber, MethodContext* mc, ULONGLONG firstTime, ULONGLONG secondTime)
 {
-    if (hStatsFile != INVALID_HANDLE_VALUE)
+    if (fpStatsFile != NULL)
     {
-        // Print the CSV header row
-        char  rowData[2048];
-        DWORD charCount    = 0;
-        DWORD bytesWritten = 0;
-
         if (strchr(statsTypes, '*') != NULL || strchr(statsTypes, 'h') != NULL || strchr(statsTypes, 'H') != NULL)
         {
             // Obtain the method Hash
@@ -49,11 +43,11 @@ void MethodStatsEmitter::Emit(int methodNumber, MethodContext* mc, ULONGLONG fir
             if (mc->dumpMethodHashToBuffer(md5Hash, MM3_HASH_BUFFER_SIZE) != MM3_HASH_BUFFER_SIZE)
                 md5Hash[0] = 0;
 
-            charCount += sprintf_s(rowData + charCount, ARRAY_SIZE(rowData) - charCount, "%s,", md5Hash);
+            fprintf(fpStatsFile, "%s,", md5Hash);
         }
         if (strchr(statsTypes, '*') != NULL || strchr(statsTypes, 'n') != NULL || strchr(statsTypes, 'N') != NULL)
         {
-            charCount += sprintf_s(rowData + charCount, ARRAY_SIZE(rowData) - charCount, "%d,", methodNumber);
+            fprintf(fpStatsFile, "%d,", methodNumber);
         }
         if (strchr(statsTypes, '*') != NULL || strchr(statsTypes, 'i') != NULL || strchr(statsTypes, 'I') != NULL)
         {
@@ -63,7 +57,7 @@ void MethodStatsEmitter::Emit(int methodNumber, MethodContext* mc, ULONGLONG fir
             CORINFO_OS          os    = CORINFO_WINNT;
             mc->repCompileMethod(&info, &flags, &os);
 
-            charCount += sprintf_s(rowData + charCount, ARRAY_SIZE(rowData) - charCount, "%d,", info.ILCodeSize);
+            fprintf(fpStatsFile, "%d,", info.ILCodeSize);
         }
         if (strchr(statsTypes, '*') != NULL || strchr(statsTypes, 'a') != NULL || strchr(statsTypes, 'A') != NULL)
         {
@@ -76,21 +70,14 @@ void MethodStatsEmitter::Emit(int methodNumber, MethodContext* mc, ULONGLONG fir
             else
                 codeSize = 0; // this is likely a thin mc
 
-            charCount += sprintf_s(rowData + charCount, ARRAY_SIZE(rowData) - charCount, "%d,", codeSize);
+            fprintf(fpStatsFile, "%d,", codeSize);
         }
         if (strchr(statsTypes, '*') != NULL || strchr(statsTypes, 't') != NULL || strchr(statsTypes, 'T') != NULL)
         {
-            charCount +=
-                sprintf_s(rowData + charCount, ARRAY_SIZE(rowData) - charCount, "%llu,%llu,", firstTime, secondTime);
+            fprintf(fpStatsFile, "%llu,%llu,", (unsigned long long)firstTime, (unsigned long long)secondTime);
         }
 
-        // get rid of the final ',' and replace it with a '\n'
-        rowData[charCount - 1] = '\n';
-
-        if (!WriteFile(hStatsFile, rowData, charCount, &bytesWritten, nullptr) || bytesWritten != charCount)
-        {
-            LogError("Failed to write row header '%s'. GetLastError()=%u", rowData, GetLastError());
-        }
+        fprintf(fpStatsFile, "\n");
     }
 }
 
@@ -98,30 +85,19 @@ void MethodStatsEmitter::SetStatsTypes(char* types)
 {
     statsTypes = types;
 
-    if (hStatsFile != INVALID_HANDLE_VALUE)
+    if (fpStatsFile != INVALID_HANDLE_VALUE)
     {
-        // Print the CSV header row
-        char  rowHeader[1024];
-        DWORD charCount    = 0;
-        DWORD bytesWritten = 0;
-
         if (strchr(statsTypes, '*') != NULL || strchr(statsTypes, 'h') != NULL || strchr(statsTypes, 'H') != NULL)
-            charCount += sprintf_s(rowHeader + charCount, ARRAY_SIZE(rowHeader) - charCount, "HASH,");
+            fprintf(fpStatsFile, "HASH,");
         if (strchr(statsTypes, '*') != NULL || strchr(statsTypes, 'n') != NULL || strchr(statsTypes, 'N') != NULL)
-            charCount += sprintf_s(rowHeader + charCount, ARRAY_SIZE(rowHeader) - charCount, "METHOD_NUMBER,");
+            fprintf(fpStatsFile, "METHOD_NUMBER,");
         if (strchr(statsTypes, '*') != NULL || strchr(statsTypes, 'i') != NULL || strchr(statsTypes, 'I') != NULL)
-            charCount += sprintf_s(rowHeader + charCount, ARRAY_SIZE(rowHeader) - charCount, "IL_CODE_SIZE,");
+            fprintf(fpStatsFile, "IL_CODE_SIZE,");
         if (strchr(statsTypes, '*') != NULL || strchr(statsTypes, 'a') != NULL || strchr(statsTypes, 'A') != NULL)
-            charCount += sprintf_s(rowHeader + charCount, ARRAY_SIZE(rowHeader) - charCount, "ASM_CODE_SIZE,");
+            fprintf(fpStatsFile, "ASM_CODE_SIZE,");
         if (strchr(statsTypes, '*') != NULL || strchr(statsTypes, 't') != NULL || strchr(statsTypes, 'T') != NULL)
-            charCount += sprintf_s(rowHeader + charCount, ARRAY_SIZE(rowHeader) - charCount, "Time1,Time2,");
-
-        // get rid of the final ',' and replace it with a '\n'
-        rowHeader[charCount - 1] = '\n';
+            fprintf(fpStatsFile, "Time1,Time2,");
 
-        if (!WriteFile(hStatsFile, rowHeader, charCount, &bytesWritten, nullptr) || bytesWritten != charCount)
-        {
-            LogError("Failed to write row header '%s'. GetLastError()=%u", rowHeader, GetLastError());
-        }
+        fprintf(fpStatsFile, "\n");
     }
 }
diff --git a/src/coreclr/tools/superpmi/superpmi/methodstatsemitter.h b/src/coreclr/tools/superpmi/superpmi/methodstatsemitter.h
index 40d38698b3d446..c35d134e346f65 100644
--- a/src/coreclr/tools/superpmi/superpmi/methodstatsemitter.h
+++ b/src/coreclr/tools/superpmi/superpmi/methodstatsemitter.h
@@ -14,8 +14,8 @@ class MethodStatsEmitter
 {
 
 private:
-    char*  statsTypes;
-    HANDLE hStatsFile;
+    char* statsTypes;
+    FILE* fpStatsFile;
 
 public:
     MethodStatsEmitter(char* nameOfInput);
diff --git a/src/coreclr/tools/superpmi/superpmi/parallelsuperpmi.cpp b/src/coreclr/tools/superpmi/superpmi/parallelsuperpmi.cpp
index 07b3cd5805bcb9..b21a6384a9cc9d 100644
--- a/src/coreclr/tools/superpmi/superpmi/parallelsuperpmi.cpp
+++ b/src/coreclr/tools/superpmi/superpmi/parallelsuperpmi.cpp
@@ -72,108 +72,67 @@ bool StartProcess(char* commandLine, HANDLE hStdOutput, HANDLE hStdError, HANDLE
     return true;
 }
 
-void ReadMCLToArray(char* mclFilename, int** arr, int* count)
+void ReadMCLToArray(char* mclFilename, std::vector<int>& MCL)
 {
-    *count     = 0;
-    *arr       = nullptr;
-    char* buff = nullptr;
+    FILE*   fp = fopen(mclFilename, "r");
+    int64_t size;
 
-    HANDLE hFile = CreateFileA(mclFilename, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING,
-                               FILE_ATTRIBUTE_NORMAL | FILE_FLAG_SEQUENTIAL_SCAN, NULL);
-
-    if (hFile == INVALID_HANDLE_VALUE)
-    {
-        LogError("Unable to open '%s'. GetLastError()=%u", mclFilename, GetLastError());
-        goto Cleanup;
-    }
-
-    LARGE_INTEGER DataTemp;
-    if (GetFileSizeEx(hFile, &DataTemp) == 0)
-    {
-        LogError("GetFileSizeEx failed. GetLastError()=%u", GetLastError());
-        goto Cleanup;
-    }
-
-    if (DataTemp.QuadPart > MAXMCLFILESIZE)
+    if (fp == NULL)
     {
-        LogError("Size %d exceeds max size of %d", DataTemp.QuadPart, MAXMCLFILESIZE);
+        LogError("Unable to open '%s'. errno=%d", mclFilename, errno);
         goto Cleanup;
     }
 
-    int sz;
-    sz = (int)(DataTemp.QuadPart);
+    fseek(fp, 0, SEEK_END);
+#ifdef TARGET_WINDOWS
+    size = _ftelli64(fp);
+#else
+    size = ftell(fp);
+#endif
+    fseek(fp, 0, SEEK_SET);
 
-    buff = new char[sz];
-    DWORD bytesRead;
-    if (ReadFile(hFile, buff, sz, &bytesRead, nullptr) == 0)
+    if (size > MAXMCLFILESIZE)
     {
-        LogError("ReadFile failed. GetLastError()=%u", GetLastError());
+        LogError("Size %lld exceeds max size of %d", size, MAXMCLFILESIZE);
         goto Cleanup;
     }
 
-    for (int i = 0; i < sz; i++)
-    {
-        if (buff[i] == 0x0d)
-            (*count)++;
-    }
-
-    if (*count <= 0)
-        return;
-
-    *arr = new int[*count];
-    for (int j = 0, arrIndex = 0; j < sz;)
+    int value;
+    while (fscanf(fp, "%d", &value) > 0)
     {
-        // seek the first number on the line
-        while (!isdigit((unsigned char)buff[j]))
-            j++;
-        // read in the number
-        (*arr)[arrIndex++] = atoi(&buff[j]);
-        // seek to the start of next line
-        while ((j < sz) && (buff[j] != 0x0a))
-            j++;
-        j++;
+        MCL.push_back(value);
     }
 
 Cleanup:
-    if (buff != nullptr)
-        delete[] buff;
-
-    if (hFile != INVALID_HANDLE_VALUE)
-        CloseHandle(hFile);
+    if (fp != NULL)
+        fclose(fp);
 }
 
-bool WriteArrayToMCL(char* mclFilename, int* arr, int count)
+bool WriteArrayToMCL(char* mclFilename, std::vector<int>& MCL)
 {
-    HANDLE hMCLFile =
-        CreateFileA(mclFilename, GENERIC_WRITE, FILE_SHARE_WRITE, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
+    FILE* fpMCLFile = fopen(mclFilename, "w");
     bool result = true;
 
-    if (hMCLFile == INVALID_HANDLE_VALUE)
+    if (fpMCLFile == NULL)
     {
-        LogError("Failed to open output file '%s'. GetLastError()=%u", mclFilename, GetLastError());
+        LogError("Failed to open output file '%s'. errno=%d", mclFilename, errno);
         result = false;
         goto Cleanup;
     }
 
-    for (int i = 0; i < count; i++)
+    for (int val : MCL)
     {
-        char  strMethodIndex[12];
-        DWORD charCount    = 0;
-        DWORD bytesWritten = 0;
-
-        charCount = sprintf_s(strMethodIndex, sizeof(strMethodIndex), "%d\r\n", arr[i]);
-
-        if (!WriteFile(hMCLFile, strMethodIndex, charCount, &bytesWritten, nullptr) || (bytesWritten != charCount))
+        if (fprintf(fpMCLFile, "%d\r\n", val) <= 0)
         {
-            LogError("Failed to write method index '%d'. GetLastError()=%u", strMethodIndex, GetLastError());
+            LogError("Failed to write method index '%d'. errno=%d", val, errno);
             result = false;
             goto Cleanup;
         }
     }
 
 Cleanup:
-    if (hMCLFile != INVALID_HANDLE_VALUE)
-        CloseHandle(hMCLFile);
+    if (fpMCLFile != NULL)
+        fclose(fpMCLFile);
 
     return result;
 }
@@ -295,11 +254,6 @@ BOOL WINAPI CtrlHandler(DWORD fdwCtrlType)
 }
 #endif // !TARGET_UNIX
 
-int __cdecl compareInt(const void* arg1, const void* arg2)
-{
-    return (*(const int*)arg1) - (*(const int*)arg2);
-}
-
 struct PerWorkerData
 {
     HANDLE hStdOutput = INVALID_HANDLE_VALUE;
@@ -314,40 +268,25 @@ struct PerWorkerData
 
 static void MergeWorkerMCLs(char* mclFilename, PerWorkerData* workerData, int workerCount, char* PerWorkerData::*mclPath)
 {
-    int **MCL = new int *[workerCount], *MCLCount = new int[workerCount], totalCount = 0;
+    std::vector<int> MCL;
 
     for (int i = 0; i < workerCount; i++)
     {
         // Read the next partial MCL file
-        ReadMCLToArray(workerData[i].*mclPath, &MCL[i], &MCLCount[i]);
-
-        totalCount += MCLCount[i];
+        ReadMCLToArray(workerData[i].*mclPath, MCL);
     }
 
-    int* mergedMCL = new int[totalCount];
-    int  index     = 0;
-
-    for (int i = 0; i < workerCount; i++)
-    {
-        for (int j             = 0; j < MCLCount[i]; j++)
-            mergedMCL[index++] = MCL[i][j];
-    }
-
-    qsort(mergedMCL, totalCount, sizeof(int), compareInt);
+    std::sort(MCL.begin(), MCL.end());
 
     // Write the merged MCL array back to disk
-    if (!WriteArrayToMCL(mclFilename, mergedMCL, totalCount))
+    if (!WriteArrayToMCL(mclFilename, MCL))
         LogError("Unable to write to MCL file %s.", mclFilename);
-
-    delete[] MCL;
-    delete[] MCLCount;
-    delete[] mergedMCL;
 }
 
 static void MergeWorkerCsvs(char* csvFilename, PerWorkerData* workerData, int workerCount, char* PerWorkerData::* csvPath)
 {
-    FileWriter fw;
-    if (!FileWriter::CreateNew(csvFilename, &fw))
+    FILE* fpWriter = fopen(csvFilename, "w");
+    if (fpWriter == NULL)
     {
         LogError("Could not create file %s", csvFilename);
         return;
@@ -369,24 +308,29 @@ static void MergeWorkerCsvs(char* csvFilename, PerWorkerData* workerData, int wo
                 continue;
         }
 
-        FileLineReader reader;
-        if (!FileLineReader::Open(workerData[i].*csvPath, &reader))
+        FILE* fpReader = fopen(workerData[i].*csvPath, "r");
+
+        if (fpReader == NULL)
         {
             LogError("Could not open child CSV file %s", workerData[i].*csvPath);
             continue;
         }
 
-        if (hasHeader && !reader.AdvanceLine())
+        char buffer[512];
+        if (hasHeader)
         {
-            continue;
+            // Skip the title line
+            fgets(buffer, 511, fpReader);
         }
 
-        while (reader.AdvanceLine())
+        while (!feof(fpReader))
         {
-             fw.Printf("%s\n", reader.GetCurrentLine());
+            fgets(buffer, 511, fpReader);
+            fputs(buffer, fpReader);
         }
 
         hasHeader = true;
+        fclose(fpReader);
     }
 }
 
diff --git a/src/coreclr/tools/superpmi/superpmi/streamingsuperpmi.cpp b/src/coreclr/tools/superpmi/superpmi/streamingsuperpmi.cpp
index 79a08bb4f37ef5..5d6788ed20cca5 100644
--- a/src/coreclr/tools/superpmi/superpmi/streamingsuperpmi.cpp
+++ b/src/coreclr/tools/superpmi/superpmi/streamingsuperpmi.cpp
@@ -154,7 +154,7 @@ int doStreamingSuperPMI(CommandLine::Options& o)
     // Just one worker for now... all method selection done via stream file
     //
     o.workerCount = 1;
-    o.indexes = nullptr;
+    o.indexes.clear();
     o.indexCount = -1;
     o.hash = nullptr;
     o.offset = -1;
@@ -163,7 +163,7 @@ int doStreamingSuperPMI(CommandLine::Options& o)
     // The method context reader handles skipping any unrequested method contexts
     // Used in conjunction with an MCI file, it does a lot less work...
     MethodContextReader* reader =
-        new MethodContextReader(o.nameOfInputMethodContextFile, o.indexes, o.indexCount, o.hash, o.offset, o.increment);
+        new MethodContextReader(o.nameOfInputMethodContextFile, nullptr, o.indexCount, o.hash, o.offset, o.increment);
     if (!reader->isValid())
     {
         return (int)SpmiResult::GeneralFailure;
diff --git a/src/coreclr/tools/superpmi/superpmi/superpmi.cpp b/src/coreclr/tools/superpmi/superpmi/superpmi.cpp
index e7b62be6585330..52f403819634b1 100644
--- a/src/coreclr/tools/superpmi/superpmi/superpmi.cpp
+++ b/src/coreclr/tools/superpmi/superpmi/superpmi.cpp
@@ -335,8 +335,8 @@ int __cdecl main(int argc, char* argv[])
 
     // The method context reader handles skipping any unrequested method contexts
     // Used in conjunction with an MCI file, it does a lot less work...
-    MethodContextReader* reader =
-        new MethodContextReader(o.nameOfInputMethodContextFile, o.indexes, o.indexCount, o.hash, o.offset, o.increment);
+    MethodContextReader* reader = new MethodContextReader(o.nameOfInputMethodContextFile, o.indexes.data(),
+                                                          o.indexCount, o.hash, o.offset, o.increment);
     if (!reader->isValid())
     {
         return (int)SpmiResult::GeneralFailure;
@@ -495,17 +495,16 @@ int __cdecl main(int argc, char* argv[])
                 {
                     char buff[500];
                     sprintf_s(buff, 500, "%s-%d.mc", o.reproName, reader->GetMethodContextIndex());
-                    HANDLE hFileOut = CreateFileA(buff, GENERIC_WRITE, 0, NULL, CREATE_ALWAYS,
-                                                    FILE_ATTRIBUTE_NORMAL | FILE_FLAG_SEQUENTIAL_SCAN, NULL);
-                    if (hFileOut == INVALID_HANDLE_VALUE)
+                    FILE* fpOut = fopen(buff, "wb");
+                    if (fpOut == NULL)
                     {
-                        LogError("Failed to open output '%s'. GetLastError()=%u", buff, GetLastError());
+                        LogError("Failed to open output '%s'. errno=%d", buff, errno);
                         return (int)SpmiResult::GeneralFailure;
                     }
-                    mc->saveToFile(hFileOut);
-                    if (CloseHandle(hFileOut) == 0)
+                    mc->saveToFile(fpOut);
+                    if (fclose(fpOut) != 0)
                     {
-                        LogError("CloseHandle for output file failed. GetLastError()=%u", GetLastError());
+                        LogError("CloseHandle for output file failed. errno=%d", errno);
                         return (int)SpmiResult::GeneralFailure;
                     }
                     LogInfo("Wrote out repro to '%s'", buff);