Merge pull request #82624 from al45tair/eng/PR-154282813

[Backtracing][Linux] Fix crash handler for musl.

Author: al45tair

stdlib/public/RuntimeModule/Elf.swift

@@ -1064,8 +1064,8 @@ struct ElfSymbolTable<SomeElfTraits: ElfTraits>: ElfSymbolTableProtocol {
           continue
         }
 
-        // Ignore anything undefined
-        if symbol.st_shndx == SHN_UNDEF {
+        // Ignore anything undefined or absolute
+        if symbol.st_shndx == SHN_UNDEF || symbol.st_shndx == SHN_ABS {
           continue
         }
 
@@ -1190,6 +1190,8 @@ final class ElfImage<SomeElfTraits: ElfTraits>
   var sectionHeaders: [Traits.Shdr]?
   var shouldByteSwap: Bool { return header.shouldByteSwap }
 
+  var imageBase: ImageSource.Address
+
   @_specialize(kind: full, where SomeElfTraits == Elf32Traits)
   @_specialize(kind: full, where SomeElfTraits == Elf64Traits)
   required init(source: ImageSource,
@@ -1222,11 +1224,21 @@ final class ElfImage<SomeElfTraits: ElfTraits>
 
     var phdrs: [Traits.Phdr] = []
     var phAddr = ImageSource.Address(header.e_phoff)
+    var minAddr: Traits.Address? = nil
     for _ in 0..<header.e_phnum {
       let phdr = maybeSwap(try source.fetch(from: phAddr, as: Traits.Phdr.self))
       phdrs.append(phdr)
       phAddr += ImageSource.Address(header.e_phentsize)
+
+      if phdr.p_type == .PT_LOAD {
+        if let oldMinAddr = minAddr {
+          minAddr = min(oldMinAddr, phdr.p_vaddr)
+        } else {
+          minAddr = phdr.p_vaddr
+        }
+      }
     }
+    imageBase = ImageSource.Address(exactly: minAddr ?? 0)!
     programHeaders = phdrs
 
     if source.isMappedImage {

stdlib/public/RuntimeModule/SymbolicatedBacktrace.swift

@@ -466,9 +466,6 @@ public struct SymbolicatedBacktrace: CustomStringConvertible {
     for frame in backtrace.frames {
       let address = frame.adjustedProgramCounter
       if let imageNdx = theImages.indexOfImage(at: address) {
-        let relativeAddress = ImageSource.Address(
-          address - theImages[imageNdx].baseAddress
-        )
         let name = theImages[imageNdx].name ?? "<unknown>"
         var symbol: Symbol = Symbol(imageIndex: imageNdx,
                                     imageName: name,
@@ -527,13 +524,19 @@ public struct SymbolicatedBacktrace: CustomStringConvertible {
         if let hit = cache.lookup(path: theImages[imageNdx].path) {
           switch hit {
             case let .elf32Image(image):
+              let relativeAddress = ImageSource.Address(
+                address - theImages[imageNdx].baseAddress
+              ) + image.imageBase
               if let theSymbol = lookupSymbol(image: image,
                                               at: imageNdx,
                                               named: name,
                                               address: relativeAddress) {
                 symbol = theSymbol
               }
             case let .elf64Image(image):
+              let relativeAddress = ImageSource.Address(
+                address - theImages[imageNdx].baseAddress
+              ) + image.imageBase
               if let theSymbol = lookupSymbol(image: image,
                                               at: imageNdx,
                                               named: name,

stdlib/public/runtime/CrashHandlerLinux.cpp

@@ -49,6 +49,15 @@
 #include <string.h>
 #include <unistd.h>
 
+#define DEBUG_MEMSERVER 0
+
+#if DEBUG_MEMSERVER
+#include <stdio.h>
+#define memserver_error(x) perror(x)
+#else
+#define memserver_error(x)
+#endif
+
 #include "swift/Runtime/Backtrace.h"
 
 #include <cstring>
@@ -86,8 +95,8 @@ ssize_t safe_read(int fd, void *buf, size_t len) {
     ssize_t ret;
     do {
       ret = read(fd, buf, len);
-    } while (ret < 0 && errno == EINTR);
-    if (ret < 0)
+    } while (ret <= 0 && errno == EINTR);
+    if (ret <= 0)
       return ret;
     total += ret;
     ptr += ret;
@@ -106,8 +115,8 @@ ssize_t safe_write(int fd, const void *buf, size_t len) {
     ssize_t ret;
     do {
       ret = write(fd, buf, len);
-    } while (ret < 0 && errno == EINTR);
-    if (ret < 0)
+    } while (ret <= 0 && errno == EINTR);
+    if (ret <= 0)
       return ret;
     total += ret;
     ptr += ret;
@@ -657,20 +666,28 @@ memserver_start()
   int fds[2];
 
   ret = socketpair(AF_UNIX, SOCK_STREAM, 0, fds);
-  if (ret < 0)
+  if (ret < 0) {
+    memserver_error("memserver_start: socketpair failed");
     return ret;
+  }
 
   memserver_fd = fds[0];
   ret = clone(memserver_entry, memserver_stack + sizeof(memserver_stack),
 #if MEMSERVER_USE_PROCESS
               0,
 #else
-              CLONE_THREAD | CLONE_VM | CLONE_FILES
-              | CLONE_FS | CLONE_IO | CLONE_SIGHAND,
+              #ifndef __musl__
+              // Can't use CLONE_THREAD on musl because the clone() function
+              // there returns EINVAL if we do.
+              CLONE_THREAD | CLONE_SIGHAND |
+              #endif
+              CLONE_VM | CLONE_FILES | CLONE_FS | CLONE_IO,
 #endif
               NULL);
-  if (ret < 0)
+  if (ret < 0) {
+    memserver_error("memserver_start: clone failed");
     return ret;
+  }
 
 #if MEMSERVER_USE_PROCESS
   memserver_pid = ret;
@@ -718,7 +735,7 @@ memserver_entry(void *dummy __attribute__((unused))) {
   int fd = memserver_fd;
   int result = 1;
 
-#if MEMSERVER_USE_PROCESS
+#if MEMSERVER_USE_PROCESS || defined(__musl__)
   prctl(PR_SET_NAME, "[backtrace]");
 #endif
 
@@ -743,8 +760,10 @@ memserver_entry(void *dummy __attribute__((unused))) {
     ssize_t ret;
 
     ret = safe_read(fd, &req, sizeof(req));
-    if (ret != sizeof(req))
+    if (ret != sizeof(req)) {
+      memserver_error("memserver: terminating because safe_read() returned wrong size");
       break;
+    }
 
     uint64_t addr = req.addr;
     uint64_t bytes = req.len;
@@ -761,15 +780,19 @@ memserver_entry(void *dummy __attribute__((unused))) {
       resp.len = ret;
 
       ret = safe_write(fd, &resp, sizeof(resp));
-      if (ret != sizeof(resp))
+      if (ret != sizeof(resp)) {
+        memserver_error("memserver: terminating because safe_write() failed");
         goto fail;
+      }
 
       if (resp.len < 0)
         break;
 
       ret = safe_write(fd, memserver_buffer, resp.len);
-      if (ret != resp.len)
+      if (ret != resp.len) {
+        memserver_error("memserver: terminating because safe_write() failed (2)");
         goto fail;
+      }
 
       addr += resp.len;
       bytes -= resp.len;