From 1b42f6058731ea803cebe9620c1d800d997852b8 Mon Sep 17 00:00:00 2001
From: Cody Tapscott <topolarity@tapscott.me>
Date: Thu, 8 May 2025 10:19:13 -0400
Subject: [PATCH] Delete (very) slow-path in stacktrace pointer lookup

This slow-path is hard to justify, both because it is slow (it scans
1-by-1 through every symbol in a library) and also because its results
are very frequently thrown out and replaced with fast-lookup from the
DWARF info right after.

The latter issue could be resolved with some re-factoring, but the
former is bad enough that I think we should just delete this and take
the policy that stack frame lookup requires unwind or debug info in your
libraries.

(cherry picked from commit f1b424a31c789eb4e789436a7ec374c3aaa9d147)
---
 src/debuginfo.cpp | 62 +++--------------------------------------------
 1 file changed, 4 insertions(+), 58 deletions(-)

diff --git a/src/debuginfo.cpp b/src/debuginfo.cpp
index 8625b82aedff8..0725f1f614d6d 100644
--- a/src/debuginfo.cpp
+++ b/src/debuginfo.cpp
@@ -706,7 +706,7 @@ static inline void ignoreError(T &err) JL_NOTSAFEPOINT
 #endif
 }
 
-static void get_function_name_and_base(llvm::object::SectionRef Section, size_t pointer, int64_t slide, bool inimage,
+static void get_function_name_and_base(size_t pointer, int64_t slide, bool inimage,
                                        void **saddr, char **name, bool untrusted_dladdr) JL_NOTSAFEPOINT
 {
     bool needs_saddr = saddr && (!*saddr || untrusted_dladdr);
@@ -731,62 +731,6 @@ static void get_function_name_and_base(llvm::object::SectionRef Section, size_t
         }
 #endif
     }
-    if (Section.getObject() && (needs_saddr || needs_name)) {
-        size_t distance = (size_t)-1;
-        object::SymbolRef sym_found;
-        for (auto sym : Section.getObject()->symbols()) {
-            if (!Section.containsSymbol(sym))
-                continue;
-            auto addr = sym.getAddress();
-            if (!addr)
-                continue;
-            size_t symptr = addr.get();
-            if (symptr > pointer + slide)
-                continue;
-            size_t new_dist = pointer + slide - symptr;
-            if (new_dist > distance)
-                continue;
-            distance = new_dist;
-            sym_found = sym;
-        }
-        if (distance != (size_t)-1) {
-            if (needs_saddr) {
-                uintptr_t addr = cantFail(sym_found.getAddress());
-                *saddr = (void*)(addr - slide);
-                needs_saddr = false;
-            }
-            if (needs_name) {
-                if (auto name_or_err = sym_found.getName()) {
-                    auto nameref = name_or_err.get();
-                    const char globalPrefix = // == DataLayout::getGlobalPrefix
-#if defined(_OS_WINDOWS_) && !defined(_CPU_X86_64_)
-                        '_';
-#elif defined(_OS_DARWIN_)
-                        '_';
-#else
-                        '\0';
-#endif
-                    if (globalPrefix) {
-                        if (nameref[0] == globalPrefix)
-                          nameref = nameref.drop_front();
-#if defined(_OS_WINDOWS_) && !defined(_CPU_X86_64_)
-                        else if (nameref[0] == '@') // X86_VectorCall
-                          nameref = nameref.drop_front();
-#endif
-                        // else VectorCall, Assembly, Internal, etc.
-                    }
-#if defined(_OS_WINDOWS_) && !defined(_CPU_X86_64_)
-                    nameref = nameref.split('@').first;
-#endif
-                    size_t len = nameref.size();
-                    *name = (char*)realloc_s(*name, len + 1);
-                    memcpy(*name, nameref.data(), len);
-                    (*name)[len] = 0;
-                    needs_name = false;
-                }
-            }
-        }
-    }
 #ifdef _OS_WINDOWS_
     // For ntdll and msvcrt since we are currently only parsing DWARF debug info through LLVM
     if (!inimage && needs_name) {
@@ -805,6 +749,8 @@ static void get_function_name_and_base(llvm::object::SectionRef Section, size_t
         }
         uv_mutex_unlock(&jl_in_stackwalk);
     }
+#else
+    (void)needs_name;
 #endif
 }
 
@@ -1133,7 +1079,7 @@ bool jl_dylib_DI_for_fptr(size_t pointer, object::SectionRef *Section, int64_t *
     // Assume we only need base address for sysimg for now
     if (!inimage || 0 == image_info.fptrs.nptrs)
         saddr = nullptr;
-    get_function_name_and_base(*Section, pointer, entry.slide, inimage, saddr, name, untrusted_dladdr);
+    get_function_name_and_base(pointer, entry.slide, inimage, saddr, name, untrusted_dladdr);
     return true;
 }