Set noinline attribute on exported shim layer functions.

base/allocator/allocator_shim_override_glibc_weak_symbols.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifdef BASE_ALLOCATOR_ALLOCATOR_SHIM_OVERRIDE_GLIBC_WEAK_SYMBOLS_H_
 #error This header is meant to be included only once by allocator_shim.cc
 #endif
 #define BASE_ALLOCATOR_ALLOCATOR_SHIM_OVERRIDE_GLIBC_WEAK_SYMBOLS_H_
 
 // Alias the internal Glibc symbols to the shim entry points.
@@ skipping 38 matching lines @@
 void GlibcFreeHook(void* ptr, const void* caller) {
   return ShimFree(ptr, nullptr);
 }
 
 void* GlibcMemalignHook(size_t align, size_t size, const void* caller) {
   return ShimMemalign(align, size, nullptr);
 }
 
 }  // namespace
 
-SHIM_ALWAYS_EXPORT void* (*MALLOC_HOOK_MAYBE_VOLATILE __malloc_hook)(
-    size_t,
-    const void*) = &GlibcMallocHook;
+__attribute__((visibility("default"))) void* (

[Primiano Tucci (use gerrit), 2017/03/15 11:42:59]

Why are you changing this?
If is just about performance I wouldn't bother doing this.
These hooks are really safety belts for very odd code that we should hit
extremely rarely.
The reason of this entire file is an ancient bug about some RedHat6 libraries
that were relying directly on __glibc_malloc (so bypassing the malloc() symbol
redefinition).
i just didn't feel brave enough to take the risk of finding out if the bug was
fixed and just kept these functions when writing the shim.

In other words, I don't think anybody would realize even if you put a
usleep(50000) here :)

+    *MALLOC_HOOK_MAYBE_VOLATILE __malloc_hook)(size_t,
+                                               const void*) = &GlibcMallocHook;
 
-SHIM_ALWAYS_EXPORT void* (*MALLOC_HOOK_MAYBE_VOLATILE __realloc_hook)(
-    void*,
-    size_t,
-    const void*) = &GlibcReallocHook;
+__attribute__((visibility("default"))) void* (
+    *MALLOC_HOOK_MAYBE_VOLATILE __realloc_hook)(void*, size_t, const void*) =
+    &GlibcReallocHook;
 
-SHIM_ALWAYS_EXPORT void (*MALLOC_HOOK_MAYBE_VOLATILE __free_hook)(void*,
-                                                                  const void*) =
-    &GlibcFreeHook;
+__attribute__((visibility("default"))) void (
+    *MALLOC_HOOK_MAYBE_VOLATILE __free_hook)(void*,
+                                             const void*) = &GlibcFreeHook;
 
-SHIM_ALWAYS_EXPORT void* (*MALLOC_HOOK_MAYBE_VOLATILE __memalign_hook)(
-    size_t,
-    size_t,
-    const void*) = &GlibcMemalignHook;
+__attribute__((visibility("default"))) void* (
+    *MALLOC_HOOK_MAYBE_VOLATILE __memalign_hook)(size_t, size_t, const void*) =
+    &GlibcMemalignHook;
 
 // 2) Redefine libc symbols themselves.
 
 SHIM_ALWAYS_EXPORT void* __libc_malloc(size_t size) {
   return ShimMalloc(size, nullptr);
 }
 
 SHIM_ALWAYS_EXPORT void __libc_free(void* ptr) {
   ShimFree(ptr, nullptr);
 }
@@ skipping 26 matching lines @@
   return ShimPosixMemalign(r, a, s);
 }
 
 }  // extern "C"
 
 // Safety check.
 #if !defined(__GLIBC__)
 #error The target platform does not seem to use Glibc. Disable the allocator \
 shim by setting use_experimental_allocator_shim=false in GN args.
 #endif