[gcc r10-10682] sanitizer: Use glibc _thread_db_sizeof_pthread symbol if present

[Jakub Jelinek <jakub@gcc.gnu.org>]

https://gcc.gnu.org/g:fefb97a53606fad6060e217b9b642dbbd3a1e299

commit r10-10682-gfefb97a53606fad6060e217b9b642dbbd3a1e299
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Feb 15 11:18:56 2022 +0100

    sanitizer: Use glibc _thread_db_sizeof_pthread symbol if present
    
    I've cherry-picked following fix from llvm-project.  Recent glibcs
    have _thread_db_sizeof_pthread symbol variable which contains the
    size of struct pthread, so that sanitizers don't need to guess that
    and risk that it will change again.
    
    2022-02-15  Jakub Jelinek  <jakub@redhat.com>
    
            * sanitizer_common/sanitizer_linux_libcdep.cpp: Cherry-pick
            llvm-project revision ef14b78d9a144ba81ba02083fe21eb286a88732b.
    
    (cherry picked from commit c4c0aa60891daeb4ea5a7c265bd681038f6d8271)

Diff:
---
 .../sanitizer_common/sanitizer_linux_libcdep.cpp    | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/libsanitizer/sanitizer_common/sanitizer_linux_libcdep.cpp b/libsanitizer/sanitizer_common/sanitizer_linux_libcdep.cpp
index e09d568d802..7f7191b9c22 100644
--- a/libsanitizer/sanitizer_common/sanitizer_linux_libcdep.cpp
+++ b/libsanitizer/sanitizer_common/sanitizer_linux_libcdep.cpp
@@ -267,10 +267,8 @@ void InitTlsSize() { }
 // sizeof(struct pthread) from glibc.
 static atomic_uintptr_t thread_descriptor_size;
 
-uptr ThreadDescriptorSize() {
-  uptr val = atomic_load_relaxed(&thread_descriptor_size);
-  if (val)
-    return val;
+static uptr ThreadDescriptorSizeFallback() {
+  uptr val = 0;
 #if defined(__x86_64__) || defined(__i386__) || defined(__arm__)
   int major;
   int minor;
@@ -310,8 +308,21 @@ uptr ThreadDescriptorSize() {
 #elif defined(__s390__)
   val = FIRST_32_SECOND_64(1152, 1776); // valid for glibc 2.22
 #endif
+  return val;
+}
+
+uptr ThreadDescriptorSize() {
+  uptr val = atomic_load_relaxed(&thread_descriptor_size);
   if (val)
-    atomic_store_relaxed(&thread_descriptor_size, val);
+    return val;
+  // _thread_db_sizeof_pthread is a GLIBC_PRIVATE symbol that is exported in
+  // glibc 2.34 and later.
+  if (unsigned *psizeof = static_cast<unsigned *>(
+          dlsym(RTLD_DEFAULT, "_thread_db_sizeof_pthread")))
+    val = *psizeof;
+  if (!val)
+    val = ThreadDescriptorSizeFallback();
+  atomic_store_relaxed(&thread_descriptor_size, val);
   return val;
 }