From 6f9dfc8469a729c161b625350c05f30a75fd9844 Mon Sep 17 00:00:00 2001
From: Bartosz Taudul <wolf@nereid.pl>
Date: Sat, 8 Oct 2022 13:22:56 +0200
Subject: [PATCH] Use dladdr, not libbacktrace in fast callstack decode path.

DecodeCallstackPtrFast() may be called outside the symbol processing thread,
for example in the crash handler. Using the less-capable dladdr functionality
doesn't have a big impact here. Callstack decoding in this context is used to
remove the uninteresting top part of the callstack, so that the callstack ends
at the crashing function, and not in the crash handler. Even if this
functionality would be impacted by this change, the damage done is close to
none.

The other alternative is to use locking each time a libbacktrace is to be
used, which does not seem to be worthy to do, considering that the problem
only occurs in a very rare code path.

NB everything was working when it was first implemented, because back then the
callstack decoding was still performed on the main thread, and not on a
separate, dedicated one.
---
 public/client/TracyCallstack.cpp | 48 ++++++++++----------------------
 1 file changed, 15 insertions(+), 33 deletions(-)

diff --git a/public/client/TracyCallstack.cpp b/public/client/TracyCallstack.cpp
index de38e8f2..75420bff 100644
--- a/public/client/TracyCallstack.cpp
+++ b/public/client/TracyCallstack.cpp
@@ -844,42 +844,24 @@ void EndCallstack()
 #endif
 }
 
-static int FastCallstackDataCb( void* data, uintptr_t pc, uintptr_t lowaddr, const char* fn, int lineno, const char* function )
-{
-    if( function )
-    {
-        strcpy( (char*)data, function );
-    }
-    else
-    {
-        const char* symname = nullptr;
-        auto vptr = (void*)pc;
-        Dl_info dlinfo;
-        if( dladdr( vptr, &dlinfo ) )
-        {
-            symname = dlinfo.dli_sname;
-        }
-        if( symname )
-        {
-            strcpy( (char*)data, symname );
-        }
-        else
-        {
-            *(char*)data = '\0';
-        }
-    }
-    return 1;
-}
-
-static void FastCallstackErrorCb( void* data, const char* /*msg*/, int /*errnum*/ )
-{
-    *(char*)data = '\0';
-}
-
 const char* DecodeCallstackPtrFast( uint64_t ptr )
 {
     static char ret[1024];
-    backtrace_pcinfo( cb_bts, ptr, FastCallstackDataCb, FastCallstackErrorCb, ret );
+    auto vptr = (void*)ptr;
+    const char* symname = nullptr;
+    Dl_info dlinfo;
+    if( dladdr( vptr, &dlinfo ) && dlinfo.dli_sname )
+    {
+        symname = dlinfo.dli_sname;
+    }
+    if( symname )
+    {
+        strcpy( ret, symname );
+    }
+    else
+    {
+        *ret = '\0';
+    }
     return ret;
 }