[compiler-rt] r350029 - [xray] Disable alignas() for thread_local objects on NetBSD

[Michal Gorny via llvm-commits]

Author: mgorny
Date: Sun Dec 23 07:09:20 2018
New Revision: 350029

URL: http://llvm.org/viewvc/llvm-project?rev=350029&view=rev
Log:
[xray] Disable alignas() for thread_local objects on NetBSD

Disable enforcing alignas() for structs that are used as thread_local
data on NetBSD.  The NetBSD ld.so implementation is buggy and does
not enforce correct alignment; however, clang seems to take it for
granted and generates instructions that segv on wrongly aligned objects.
Therefore, disable those alignas() statements on NetBSD until we can
establish a better fix.

Apparently, std::aligned_storage<> does not have any real effect
at the moment, so we can leave it as-is.

Differential Revision: https://reviews.llvm.org/D56000

Modified:
    compiler-rt/trunk/lib/xray/xray_basic_logging.cc
    compiler-rt/trunk/lib/xray/xray_defs.h
    compiler-rt/trunk/lib/xray/xray_fdr_logging.cc

Modified: compiler-rt/trunk/lib/xray/xray_basic_logging.cc
URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/xray/xray_basic_logging.cc?rev=350029&r1=350028&r2=350029&view=diff
==============================================================================
--- compiler-rt/trunk/lib/xray/xray_basic_logging.cc (original)
+++ compiler-rt/trunk/lib/xray/xray_basic_logging.cc Sun Dec 23 07:09:20 2018
@@ -55,7 +55,7 @@ struct alignas(16) StackEntry {
 
 static_assert(sizeof(StackEntry) == 16, "Wrong size for StackEntry");
 
-struct alignas(64) ThreadLocalData {
+struct XRAY_TLS_ALIGNAS(64) ThreadLocalData {
   void *InMemoryBuffer = nullptr;
   size_t BufferSize = 0;
   size_t BufferOffset = 0;

Modified: compiler-rt/trunk/lib/xray/xray_defs.h
URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/xray/xray_defs.h?rev=350029&r1=350028&r2=350029&view=diff
==============================================================================
--- compiler-rt/trunk/lib/xray/xray_defs.h (original)
+++ compiler-rt/trunk/lib/xray/xray_defs.h Sun Dec 23 07:09:20 2018
@@ -19,4 +19,14 @@
 #define XRAY_NEVER_INSTRUMENT
 #endif
 
+#if SANITIZER_NETBSD
+// NetBSD: thread_local is not aligned properly, and the code relying
+// on it segfaults
+#define XRAY_TLS_ALIGNAS(x)
+#define XRAY_HAS_TLS_ALIGNAS 0
+#else
+#define XRAY_TLS_ALIGNAS(x) alignas(x)
+#define XRAY_HAS_TLS_ALIGNAS 1
+#endif
+
 #endif  // XRAY_XRAY_DEFS_H

Modified: compiler-rt/trunk/lib/xray/xray_fdr_logging.cc
URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/xray/xray_fdr_logging.cc?rev=350029&r1=350028&r2=350029&view=diff
==============================================================================
--- compiler-rt/trunk/lib/xray/xray_fdr_logging.cc (original)
+++ compiler-rt/trunk/lib/xray/xray_fdr_logging.cc Sun Dec 23 07:09:20 2018
@@ -51,7 +51,7 @@ namespace {
 // call so that it can be initialized on first use instead of as a global. We
 // force the alignment to 64-bytes for x86 cache line alignment, as this
 // structure is used in the hot path of implementation.
-struct alignas(64) ThreadLocalData {
+struct XRAY_TLS_ALIGNAS(64) ThreadLocalData {
   BufferQueue::Buffer Buffer{};
   BufferQueue *BQ = nullptr;
 
@@ -124,8 +124,10 @@ static atomic_sint32_t LogFlushStatus =
 // critical section, calling a function that might be XRay instrumented (and
 // thus in turn calling into malloc by virtue of registration of the
 // thread_local's destructor).
+#if XRAY_HAS_TLS_ALIGNAS
 static_assert(alignof(ThreadLocalData) >= 64,
               "ThreadLocalData must be cache line aligned.");
+#endif
 static ThreadLocalData &getThreadLocalData() {
   thread_local typename std::aligned_storage<
       sizeof(ThreadLocalData), alignof(ThreadLocalData)>::type TLDStorage{};