From 4f051fddcd7af53e1607b6a4866ffa461a0033ef Mon Sep 17 00:00:00 2001
From: Aliaksey Kandratsenka <alk@tut.by>
Date: Sat, 15 Mar 2014 13:18:28 -0700
Subject: [PATCH] eliminated CheckIfKernelSupportsTLS

We don't care about pre-2.6.0 kernels anymore. So we can assume that
if compile time check worked, then at runtime it'll work.
---
 src/tcmalloc.cc     |  4 ----
 src/thread_cache.cc | 40 ----------------------------------------
 src/thread_cache.h  | 18 +++---------------
 src/windows/port.cc |  6 ------
 4 files changed, 3 insertions(+), 65 deletions(-)

diff --git a/src/tcmalloc.cc b/src/tcmalloc.cc
index a796996..1e53f8f 100644
--- a/src/tcmalloc.cc
+++ b/src/tcmalloc.cc
@@ -913,10 +913,6 @@ class TCMallocImplementation : public MallocExtension {
 static int tcmallocguard_refcount = 0;  // no lock needed: runs before main()
 TCMallocGuard::TCMallocGuard() {
   if (tcmallocguard_refcount++ == 0) {
-#ifdef HAVE_TLS    // this is true if the cc/ld/libc combo support TLS
-    // Check whether the kernel also supports TLS (needs to happen at runtime)
-    tcmalloc::CheckIfKernelSupportsTLS();
-#endif
     ReplaceSystemAlloc();    // defined in libc_override_*.h
     tc_free(tc_malloc(1));
     ThreadCache::InitTSD();
diff --git a/src/thread_cache.cc b/src/thread_cache.cc
index b98fbee..444a09f 100644
--- a/src/thread_cache.cc
+++ b/src/thread_cache.cc
@@ -76,46 +76,6 @@ __thread ThreadCache::ThreadLocalData ThreadCache::threadlocal_data_
 bool ThreadCache::tsd_inited_ = false;
 pthread_key_t ThreadCache::heap_key_;
 
-#if defined(HAVE_TLS)
-bool kernel_supports_tls = false;      // be conservative
-# if defined(_WIN32)    // windows has supported TLS since winnt, I think.
-    void CheckIfKernelSupportsTLS() {
-      kernel_supports_tls = true;
-    }
-# elif !HAVE_DECL_UNAME    // if too old for uname, probably too old for TLS
-    void CheckIfKernelSupportsTLS() {
-      kernel_supports_tls = false;
-    }
-# else
-#   include <sys/utsname.h>    // DECL_UNAME checked for <sys/utsname.h> too
-    void CheckIfKernelSupportsTLS() {
-      struct utsname buf;
-      if (uname(&buf) < 0) {   // should be impossible
-        Log(kLog, __FILE__, __LINE__,
-            "uname failed assuming no TLS support (errno)", errno);
-        kernel_supports_tls = false;
-      } else if (strcasecmp(buf.sysname, "linux") == 0) {
-        // The linux case: the first kernel to support TLS was 2.6.0
-        if (buf.release[0] < '2' && buf.release[1] == '.')    // 0.x or 1.x
-          kernel_supports_tls = false;
-        else if (buf.release[0] == '2' && buf.release[1] == '.' &&
-                 buf.release[2] >= '0' && buf.release[2] < '6' &&
-                 buf.release[3] == '.')                       // 2.0 - 2.5
-          kernel_supports_tls = false;
-        else
-          kernel_supports_tls = true;
-      } else if (strcasecmp(buf.sysname, "CYGWIN_NT-6.1-WOW64") == 0) {
-        // In my testing, this version of cygwin, at least, would hang
-        // when using TLS.
-        kernel_supports_tls = false;
-      } else {        // some other kernel, we'll be optimisitic
-        kernel_supports_tls = true;
-      }
-      // TODO(csilvers): VLOG(1) the tls status once we support RAW_VLOG
-    }
-#  endif  // HAVE_DECL_UNAME
-#endif    // HAVE_TLS
-
 void ThreadCache::Init(pthread_t tid) {
   size_ = 0;
 
diff --git a/src/thread_cache.h b/src/thread_cache.h
index 5f0dc12..5edcdfb 100644
--- a/src/thread_cache.h
+++ b/src/thread_cache.h
@@ -59,17 +59,6 @@
 
 namespace tcmalloc {
 
-// Even if we have support for thread-local storage in the compiler
-// and linker, the OS may not support it.  We need to check that at
-// runtime.  Right now, we have to keep a manual set of "bad" OSes.
-#if defined(HAVE_TLS)
-extern bool kernel_supports_tls;   // defined in thread_cache.cc
-void CheckIfKernelSupportsTLS();
-inline bool KernelSupportsTLS() {
-  return kernel_supports_tls;
-}
-#endif    // HAVE_TLS
-
 //-------------------------------------------------------------------
 // Data kept per thread
 //-------------------------------------------------------------------
@@ -395,12 +384,11 @@ inline void ThreadCache::Deallocate(void* ptr, size_t cl) {
 
 inline ThreadCache* ThreadCache::GetThreadHeap() {
 #ifdef HAVE_TLS
-  // __thread is faster, but only when the kernel supports it
-  if (KernelSupportsTLS())
-    return threadlocal_data_.heap;
-#endif
+  return threadlocal_data_.heap;
+#else
   return reinterpret_cast<ThreadCache *>(
       perftools_pthread_getspecific(heap_key_));
+#endif
 }
 
 inline ThreadCache* ThreadCache::GetCacheWhichMustBePresent() {
diff --git a/src/windows/port.cc b/src/windows/port.cc
index 2e5f857..76224a2 100644
--- a/src/windows/port.cc
+++ b/src/windows/port.cc
@@ -83,12 +83,6 @@ extern "C" PERFTOOLS_DLL_DECL void WriteToStderr(const char* buf, int len) {
 // -----------------------------------------------------------------------
 // Threads code
 
-// Declared (not extern "C") in thread_cache.h
-bool CheckIfKernelSupportsTLS() {
-  // TODO(csilvers): return true (all win's since win95, at least, support this)
-  return false;
-}
-
 // Windows doesn't support pthread_key_create's destr_function, and in
 // fact it's a bit tricky to get code to run when a thread exits.  This
 // is cargo-cult magic from http://www.codeproject.com/threads/tls.asp.