From 96339090681ae1dd9afe186ea14a460b61794707 Mon Sep 17 00:00:00 2001
From: serge-sans-paille <sguelton@redhat.com>
Date: Tue, 11 May 2021 14:38:21 +0200
Subject: [PATCH][compiler-rt] Prevent introduction of a dependency of
 libasan.a on libstdc++

This an attempt to fix an issue introduced by https://reviews.llvm.org/D70662

Function-scope static initialization are guarded in C++, so we should probably
not use it because it introduces a dependency on __cxa_guard* symbols.
In the context of clang, libasan is linked statically, and it currently needs to
the odd situation where compiling C code with clang and asan requires -lstdc++.

I'm unsure of the portability requirements, providing a potential solution in
this review.

Differential Revision: https://reviews.llvm.org/D102475
---
 compiler-rt/lib/sanitizer_common/sanitizer_posix_libcdep.cpp | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_posix_libcdep.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_posix_libcdep.cpp
index 2b10bdd..818f1af 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_posix_libcdep.cpp
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_posix_libcdep.cpp
@@ -15,6 +15,7 @@
 
 #if SANITIZER_POSIX
 
+#include "sanitizer_atomic.h"
 #include "sanitizer_common.h"
 #include "sanitizer_flags.h"
 #include "sanitizer_platform_limits_netbsd.h"
@@ -166,9 +167,14 @@ bool SupportsColoredOutput(fd_t fd) {
 #if !SANITIZER_GO
 // TODO(glider): different tools may require different altstack size.
 static uptr GetAltStackSize() {
-  // SIGSTKSZ is not enough.
-  static const uptr kAltStackSize = SIGSTKSZ * 4;
-  return kAltStackSize;
+  static atomic_uintptr_t kAltStackSize{0};
+  uptr ret = atomic_load(&kAltStackSize, memory_order_relaxed);
+  if (ret == 0) {
+    // SIGSTKSZ is not enough.
+    ret = SIGSTKSZ * 4;
+    atomic_store(&kAltStackSize, ret, memory_order_relaxed);
+  }
+  return ret;
 }
 
 void SetAlternateSignalStack() {
-- 
1.8.3.1