ASAN: keep support for Global::location

[marxin]

Summary

We as GCC still emit __asan_global_source_location for global variables
and we would like to use it in the future. On other hand, we don't
support llvm-symbolizer and the default libbacktraace symbolizer
does not support location info.

Related to: https://reviews.llvm.org/D127552

[hctim]

we don't support llvm-symbolizer and the default libbacktraace symbolizer does not support location info.

is there any chance of fixing this in future?

a longer-term goal is to actually ULEB-stream-compress these __asan_global descriptors to save binary size, which would mean that we'd waste a byte-per-global on this field :(. it would be great to allow that to happen.

compiler-rt/lib/asan/asan_interface_internal.h

56–59

can you please make this gcc_location, and add a comment explaining that clang uses DWARF for asan global symbolization rather than inlining it in the metadata.

[marxin]

In D144424#4142431, @hctim wrote:

we don't support llvm-symbolizer and the default libbacktraace symbolizer does not support location info.

is there any chance of fixing this in future?

Yes, we're discussing learning that to libbacktrace library:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108870

[MaskRay]

In D144424#4147034, @marxin wrote:

In D144424#4142431, @hctim wrote:

we don't support llvm-symbolizer and the default libbacktraace symbolizer does not support location info.

is there any chance of fixing this in future?

Yes, we're discussing learning that to libbacktrace library:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108870

For future patches, it'd be good to include such a feature request link to the summary/commit message :)

compiler-rt/lib/asan/asan_globals.cpp

Report(
       prefix, (void *)&g, (void *)g.beg, g.size, g.size_with_redzone, g.name,
       g.module_name, g.has_dynamic_init, (void *)g.odr_indicator);
 
   DataInfo info;
   Symbolizer::GetOrInit()->SymbolizeData(g.beg, &info);
   if (info.line != 0) {
     Report("  location: name=%s, %d\n", info.file, static_cast<int>(info.line));
   }
+  else if (g.gcc_location != 0) {
+    // Fallback to Global::gcc_location
+    Report("  location: name=%s, %d\n", g.gcc_location->filename, g.gcc_location->line_no);
+  }
 }
 
 static u32 FindRegistrationSite(const Global *g) {
   mu_for_globals.CheckLocked();
   CHECK(global_registration_site_vector);
   for (uptr i = 0, n = global_registration_site_vector->size(); i < n; i++) {
     GlobalRegistrationSite &grs = (*global_registration_site_vector)[i];
     if (g >= grs.g_first && g <= grs.g_last)

 }
 
 void PrintGlobalLocation(InternalScopedString *str, const __asan_global &g) {
   DataInfo info;
   Symbolizer::GetOrInit()->SymbolizeData(g.beg, &info);
 
   if (info.line != 0) {
     str->append("%s:%d", info.file, static_cast<int>(info.line));
+  } else if (g.gcc_location != 0) {
+    // Fallback to Global::gcc_location
+    str->append("%s", g.gcc_location->filename ? g.gcc_location->filename : g.module_name);
+    if (g.gcc_location->line_no) str->append(":%d", g.gcc_location->line_no);
+    if (g.gcc_location->column_no) str->append(":%d", g.gcc_location->column_no);
   } else {
     str->append("%s", g.module_name);
   }
 }
 
 } // namespace __asan
 
 // ---------------------- Interface ---------------- {{{1

compiler-rt/lib/asan/asan_interface_internal.h

extern "C" {
   struct __asan_global {
     uptr beg;                // The address of the global.
     uptr size;               // The original size of the global.
     uptr size_with_redzone;  // The size with the redzone.
     const char *name;        // Name as a C string.
     const char *module_name; // Module name as a C string. This pointer is a
                              // unique identifier of a module.
     uptr has_dynamic_init;   // Non-zero if the global has dynamic initializer.
-    uptr windows_padding;    // TODO: Figure out how to remove this padding
-                             // that's simply here to make the MSVC incremental
-                             // linker happy...
+    __asan_global_source_location *gcc_location;  // Source location of a global,
+                                                  // used by GCC compiler. LLVM uses
+                                                  // llvm-symbolizer that relies
+                                                  // on DWARF debugging info.
     uptr odr_indicator;      // The address of the ODR indicator symbol.
   };
 
   // These functions can be called on some platforms to find globals in the same
   // loaded image as `flag' and apply __asan_(un)register_globals to them,
   // filtering out redundant calls.
   SANITIZER_INTERFACE_ATTRIBUTE
   void __asan_register_image_globals(uptr *flag);