[compiler-rt] Mark some performance critical buffers uninitialized

[melver]

Summary

With -ftrivial-auto-var-init, do not emit memset() calls for performance
critical stack variables.

compiler-rt/lib/asan/asan_stack.h

 u32 GetMallocContextSize();
 
 } // namespace __asan
 
 // NOTE: A Rule of thumb is to retrieve stack trace in the interceptors
 // as early as possible (in functions exposed to the user), as we generally
 // don't want stack trace to contain functions from ASan internals.
 
-#define GET_STACK_TRACE(max_size, fast)                          \
-  BufferedStackTrace stack;                                      \
-  if (max_size <= 2) {                                           \
-    stack.size = max_size;                                       \
-    if (max_size > 0) {                                          \
-      stack.top_frame_bp = GET_CURRENT_FRAME();                  \
-      stack.trace_buffer[0] = StackTrace::GetCurrentPc();        \
-      if (max_size > 1) stack.trace_buffer[1] = GET_CALLER_PC(); \
-    }                                                            \
-  } else {                                                       \
-    stack.Unwind(StackTrace::GetCurrentPc(),                     \
-                 GET_CURRENT_FRAME(), nullptr, fast, max_size);  \
+#define GET_STACK_TRACE(max_size, fast)                                    \
+  UNINITIALIZED BufferedStackTrace stack;                                  \
+  if (max_size <= 2) {                                                     \
+    stack.size = max_size;                                                 \
+    if (max_size > 0) {                                                    \
+      stack.top_frame_bp = GET_CURRENT_FRAME();                            \
+      stack.trace_buffer[0] = StackTrace::GetCurrentPc();                  \
+      if (max_size > 1)                                                    \
+        stack.trace_buffer[1] = GET_CALLER_PC();                           \
+    }                                                                      \
+  } else {                                                                 \
+    stack.Unwind(StackTrace::GetCurrentPc(), GET_CURRENT_FRAME(), nullptr, \
+                 fast, max_size);                                          \
   }
 
-#define GET_STACK_TRACE_FATAL(pc, bp)              \
-  BufferedStackTrace stack;                        \
-  stack.Unwind(pc, bp, nullptr,                    \
-               common_flags()->fast_unwind_on_fatal)
+#define GET_STACK_TRACE_FATAL(pc, bp)     \
+  UNINITIALIZED BufferedStackTrace stack; \
+  stack.Unwind(pc, bp, nullptr, common_flags()->fast_unwind_on_fatal)
 
 #define GET_STACK_TRACE_FATAL_HERE                                \
   GET_STACK_TRACE(kStackTraceMax, common_flags()->fast_unwind_on_fatal)
 
 #define GET_STACK_TRACE_THREAD                                    \
   GET_STACK_TRACE(kStackTraceMax, true)
 
 #define GET_STACK_TRACE_MALLOC                                                 \

compiler-rt/lib/msan/msan.h

 // Returns a "chained" origin id, pointing to the given stack trace followed by
 // the previous origin id.
 u32 ChainOrigin(u32 id, StackTrace *stack);
 
 const int STACK_TRACE_TAG_POISON = StackTrace::TAG_CUSTOM + 1;
 const int STACK_TRACE_TAG_FIELDS = STACK_TRACE_TAG_POISON + 1;
 const int STACK_TRACE_TAG_VPTR = STACK_TRACE_TAG_FIELDS + 1;
 
-#define GET_MALLOC_STACK_TRACE                                            \
-  BufferedStackTrace stack;                                               \
-  if (__msan_get_track_origins() && msan_inited)                          \
-    stack.Unwind(StackTrace::GetCurrentPc(), GET_CURRENT_FRAME(),         \
-                 nullptr, common_flags()->fast_unwind_on_malloc,          \
-                 common_flags()->malloc_context_size)
+#define GET_MALLOC_STACK_TRACE                                             \
+  UNINITIALIZED BufferedStackTrace stack;                                  \
+  if (__msan_get_track_origins() && msan_inited) {                         \
+    stack.Unwind(StackTrace::GetCurrentPc(), GET_CURRENT_FRAME(), nullptr, \
+                 common_flags()->fast_unwind_on_malloc,                    \
+                 common_flags()->malloc_context_size);                     \
+  }
 
 // For platforms which support slow unwinder only, we restrict the store context
 // size to 1, basically only storing the current pc. We do this because the slow
 // unwinder which is based on libunwind is not async signal safe and causes
 // random freezes in forking applications as well as in signal handlers.
-#define GET_STORE_STACK_TRACE_PC_BP(pc, bp)                                    \
-  BufferedStackTrace stack;                                                    \
-  if (__msan_get_track_origins() > 1 && msan_inited) {                         \
-    int size = flags()->store_context_size;                                    \
-    if (!SANITIZER_CAN_FAST_UNWIND)                                            \
-      size = Min(size, 1);                                                     \
-    stack.Unwind(pc, bp, nullptr, common_flags()->fast_unwind_on_malloc, size);\
+#define GET_STORE_STACK_TRACE_PC_BP(pc, bp)                              \
+  UNINITIALIZED BufferedStackTrace stack;                                \
+  if (__msan_get_track_origins() > 1 && msan_inited) {                   \
+    int size = flags()->store_context_size;                              \
+    if (!SANITIZER_CAN_FAST_UNWIND)                                      \
+      size = Min(size, 1);                                               \
+    stack.Unwind(pc, bp, nullptr, common_flags()->fast_unwind_on_malloc, \
+                 size);                                                  \
   }
 
 #define GET_STORE_STACK_TRACE \
   GET_STORE_STACK_TRACE_PC_BP(StackTrace::GetCurrentPc(), GET_CURRENT_FRAME())
 
 #define GET_FATAL_STACK_TRACE_PC_BP(pc, bp)                              \
-  BufferedStackTrace stack;                                              \
+  UNINITIALIZED BufferedStackTrace stack;                                \
   if (msan_inited) {                                                     \
     stack.Unwind(pc, bp, nullptr, common_flags()->fast_unwind_on_fatal); \
   }
 
 class ScopedThreadLocalStateBackup {
  public:
   ScopedThreadLocalStateBackup() { Backup(); }
   ~ScopedThreadLocalStateBackup() { Restore(); }

compiler-rt/lib/sanitizer_common/sanitizer_allocator_primary32.h

if (kRandomShuffleChunks)
         // The random state is initialized from ASLR (PIE) and time.
         sci->rand_state = reinterpret_cast<uptr>(sci) ^ NanoTime();
     const uptr size = ClassIdToSize(class_id);
     const uptr n_chunks = kRegionSize / (size + kMetadataSize);
     const uptr max_count = TransferBatch::MaxCached(size);
     DCHECK_GT(max_count, 0);
     TransferBatch *b = nullptr;
     constexpr uptr kShuffleArraySize = 48;
-    uptr shuffle_array[kShuffleArraySize];
+    UNINITIALIZED uptr shuffle_array[kShuffleArraySize];
     uptr count = 0;
     for (uptr i = region; i < region + n_chunks * size; i += size) {
       shuffle_array[count++] = i;
       if (count == kShuffleArraySize) {
         if (UNLIKELY(!PopulateBatches(c, sci, class_id, &b, max_count,
                                       shuffle_array, count)))
           return false;
         count = 0;

compiler-rt/lib/sanitizer_common/sanitizer_internal_defs.h

 # define FORMAT(f, a)
 # define NOINLINE __declspec(noinline)
 # define NORETURN __declspec(noreturn)
 # define THREADLOCAL   __declspec(thread)
 # define LIKELY(x) (x)
 # define UNLIKELY(x) (x)
 # define PREFETCH(x) /* _mm_prefetch(x, _MM_HINT_NTA) */ (void)0
 # define WARN_UNUSED_RESULT
+# define UNINITIALIZED
 #else  // _MSC_VER
 # define ALWAYS_INLINE inline __attribute__((always_inline))
 # define ALIAS(x) __attribute__((alias(SANITIZER_STRINGIFY(x))))
 // Please only use the ALIGNED macro before the type.
 // Using ALIGNED after the variable declaration is not portable!
 # define ALIGNED(x) __attribute__((aligned(x)))
 # define FORMAT(f, a)  __attribute__((format(printf, f, a)))
 # define NOINLINE __attribute__((noinline))
 # define NORETURN  __attribute__((noreturn))
 # define THREADLOCAL   __thread
 # define LIKELY(x)     __builtin_expect(!!(x), 1)
 # define UNLIKELY(x)   __builtin_expect(!!(x), 0)
 # if defined(__i386__) || defined(__x86_64__)
 // __builtin_prefetch(x) generates prefetchnt0 on x86
 #  define PREFETCH(x) __asm__("prefetchnta (%0)" : : "r" (x))
 # else
 #  define PREFETCH(x) __builtin_prefetch(x)
 # endif
 # define WARN_UNUSED_RESULT __attribute__((warn_unused_result))
+# if __has_attribute(uninitialized)
+#  define UNINITIALIZED __attribute__((uninitialized))
+# else  // __has_attribute(uninitialized)
+#  define UNINITIALIZED
+# endif  // __has_attribute(uninitialized)
 #endif  // _MSC_VER
 
 #if !defined(_MSC_VER) || defined(__clang__)
 # define UNUSED __attribute__((unused))
 # define USED __attribute__((used))
 #else
 # define UNUSED
 # define USED