tcmalloc: Use the default TLS model on arm-gcc, CrOS only.

third_party/tcmalloc/chromium/src/thread_cache.cc

Index: third_party/tcmalloc/chromium/src/thread_cache.cc
diff --git a/third_party/tcmalloc/chromium/src/thread_cache.cc b/third_party/tcmalloc/chromium/src/thread_cache.cc
index 1ad0f6d66d675011b7ec7db74a6f5b1a0afdf9b7..f0b61c9097ee58ee9d8473572da612b1e89338c6 100644
--- a/third_party/tcmalloc/chromium/src/thread_cache.cc
+++ b/third_party/tcmalloc/chromium/src/thread_cache.cc
@@ -66,7 +66,11 @@ ThreadCache* ThreadCache::next_memory_steal_ = NULL;
 __thread ThreadCache* ThreadCache::threadlocal_heap_
 // See comments in thread_cache.h about this. Bug here:
 // http://code.google.com/p/chromium/issues/detail?id=124489
-#if defined(HAVE___ATTRIBUTE__) && !defined(PGO_GENERATE)
+//
+// gcc has a problem with this tls model on arm.
+// See https://bugs.chromium.org/p/chromium/issues/detail?id=650137
+#if defined(HAVE___ATTRIBUTE__) && !defined(PGO_GENERATE) && \
+    (defined(__clang__) || !defined(OS_CHROMEOS) || !defined(__arm__))

[llozano, 2017/01/19 21:38:42]

not gcc does not necessarily mean clang. Is it?

I prefer to read this condition like 
!(GCC && OS_CHROMEOS && ARM)

[llozano, 2017/01/19 22:11:03]

ah, but on ChromeOS .. not GCC implies clang..

[laszio, 2017/01/19 22:11:46]

Done.

    __attribute__ ((tls_model ("initial-exec")))
 # endif
    ;