From ab78d3a7f471fdaa44f6b7bc5feece81cd1d2833 Mon Sep 17 00:00:00 2001
From: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Date: Sat, 22 Aug 2026 17:39:13 -0400
Subject: [PATCH] Give externally-provided symbol declarations default
 visibility

Abseil forward-declares a handful of symbols that are provided by something
outside the object being linked: the compiler-based sanitizer runtime supplies
the Annotate* race annotations and __tsan_read1, and Bionic supplies __mmap2.
None of these have a public header to include, so declaring them locally is the
only option, but the declarations inherit whatever visibility is in effect.

When a translation unit is compiled with -fvisibility=hidden and abseil is
linked into a shared library, those references become hidden undefined symbols
and cannot be resolved from the runtime or from libc, so the link fails:

  ld.lld: error: undefined hidden symbol: AnnotateIgnoreReadsBegin
  ld.lld: error: undefined hidden symbol: AnnotateIgnoreWritesBegin
  ld.lld: error: undefined hidden symbol: __tsan_read1
  ld.lld: error: undefined hidden symbol: __mmap2

Wrap the declarations in a visibility push/pop so they stay resolvable. Every
site is already inside a Bionic or sanitizer guard, so this does not affect
platforms where the attribute is unavailable.
---
 absl/base/dynamic_annotations.h  | 6 ++++++
 absl/base/internal/direct_mmap.h | 2 ++
 absl/synchronization/mutex.cc    | 2 ++
 3 files changed, 10 insertions(+)

diff --git a/absl/base/dynamic_annotations.h b/absl/base/dynamic_annotations.h
index f18b5e0a8fa..1e679a6b139 100644
--- a/absl/base/dynamic_annotations.h
+++ b/absl/base/dynamic_annotations.h
@@ -202,6 +202,7 @@
 
 // Function prototypes of annotations provided by the compiler-based sanitizer
 // implementation.
+#pragma GCC visibility push(default)
 ABSL_INTERNAL_BEGIN_EXTERN_C
 void AnnotateRWLockCreate(const char* file, int line,
                           const volatile void* lock);
@@ -221,6 +222,7 @@ void AnnotateBenignRaceSized(const char* file, int line,
 void AnnotateThreadName(const char* file, int line, const char* name);
 void AnnotateEnableRaceDetection(const char* file, int line, int enable);
 ABSL_INTERNAL_END_EXTERN_C
+#pragma GCC visibility pop
 
 #else  // ABSL_INTERNAL_RACE_ANNOTATIONS_ENABLED == 0
 
@@ -297,12 +299,14 @@ ABSL_INTERNAL_END_EXTERN_C
 
 // Function prototypes of annotations provided by the compiler-based sanitizer
 // implementation.
+#pragma GCC visibility push(default)
 ABSL_INTERNAL_BEGIN_EXTERN_C
 void AnnotateIgnoreReadsBegin(const char* file, int line)
     ABSL_INTERNAL_IGNORE_READS_BEGIN_ATTRIBUTE;
 void AnnotateIgnoreReadsEnd(const char* file,
                             int line) ABSL_INTERNAL_IGNORE_READS_END_ATTRIBUTE;
 ABSL_INTERNAL_END_EXTERN_C
+#pragma GCC visibility pop
 
 #elif defined(ABSL_INTERNAL_ANNOTALYSIS_ENABLED)
 
@@ -353,10 +357,12 @@ ABSL_INTERNAL_STATIC_INLINE void ABSL_INTERNAL_C_SYMBOL(
 
 // Function prototypes of annotations provided by the compiler-based sanitizer
 // implementation.
+#pragma GCC visibility push(default)
 ABSL_INTERNAL_BEGIN_EXTERN_C
 void AnnotateIgnoreWritesBegin(const char* file, int line);
 void AnnotateIgnoreWritesEnd(const char* file, int line);
 ABSL_INTERNAL_END_EXTERN_C
+#pragma GCC visibility pop
 
 #else
 
diff --git a/absl/base/internal/direct_mmap.h b/absl/base/internal/direct_mmap.h
index 1beb2ee4e52..66e35323166 100644
--- a/absl/base/internal/direct_mmap.h
+++ b/absl/base/internal/direct_mmap.h
@@ -52,7 +52,9 @@
 
 // SYS_mmap and SYS_munmap are not defined in Android.
 #ifdef __BIONIC__
+#pragma GCC visibility push(default)
 extern "C" void* __mmap2(void*, size_t, int, int, int, size_t);
+#pragma GCC visibility pop
 #if defined(__NR_mmap) && !defined(SYS_mmap)
 #define SYS_mmap __NR_mmap
 #endif
diff --git a/absl/synchronization/mutex.cc b/absl/synchronization/mutex.cc
index 68782564443..8dcc834ec7e 100644
--- a/absl/synchronization/mutex.cc
+++ b/absl/synchronization/mutex.cc
@@ -2788,7 +2788,9 @@ void ReleasableMutexLock::Release() {
 }
 
 #ifdef ABSL_HAVE_THREAD_SANITIZER
+#pragma GCC visibility push(default)
 extern "C" void __tsan_read1(void* addr);
+#pragma GCC visibility pop
 #else
 #define __tsan_read1(addr)  // do nothing if TSan not enabled
 #endif