[tsan] Don't demangle names not starting with "_Z"

[kubamracek]

Summary

I noticed that when a symbol is named just "x", it gets demangled to "long long". On POSIX, AFAIK, mangled names always start with "_Z", so lets just require that.

[glider]

lib/sanitizer_common/sanitizer_symbolizer_posix_libcdep.cc

51

Please make sure name[1] is addressable (BTW do we always know name is not NULL?)

[dvyukov]

lib/sanitizer_common/sanitizer_symbolizer_posix_libcdep.cc

51

Assuming that name is NULL, this check is OK. If the string of zero length we will bail out after checking name[0] (which is addressable and contains 0)

[glider]

LGTM

lib/sanitizer_common/sanitizer_symbolizer_posix_libcdep.cc

51

s/NULL/not NULL

agreed

[kubamracek]

Reverted in r253129. There were ARM bot failures: http://lab.llvm.org:8011/builders/clang-cmake-armv7-a15-full/builds/9068

I guess the (de)mangling rules are different there?

[glider]

That's quite strange, I thought name mangling rules depend on the
language/compiler, not the architecture.

By the way, I think we must not demangle names starting with double underscores.

lib/sanitizer_common/sanitizer_symbolizer_posix_libcdep.cc

namespace __cxxabiv1 {
   char *__cxa_demangle(const char *mangled, char *buffer,
                                   size_t *length, int *status);
 }
 
 namespace __sanitizer {
 
 // Attempts to demangle the name via __cxa_demangle from __cxxabiv1.
 const char *DemangleCXXABI(const char *name) {
+  if (name[0] != '_' || name[1] != 'Z')
+    return name;
+
   // FIXME: __cxa_demangle aggressively insists on allocating memory.
   // There's not much we can do about that, short of providing our
   // own demangler (libc++abi's implementation could be adapted so that
   // it does not allocate). For now, we just call it anyway, and we leak
   // the returned value.
   if (__cxxabiv1::__cxa_demangle)
     if (const char *demangled_name =
           __cxxabiv1::__cxa_demangle(name, 0, 0, 0))

test/tsan/Darwin/symbolizer-dladdr.cc

 // RUN: %clangxx_tsan %s -o %t
 // RUN: TSAN_OPTIONS=$TSAN_OPTIONS:verbosity=2:external_symbolizer_path= %deflake %run %t | FileCheck %s
 #include "../test.h"
 
 int GlobalData[10];
+long long x;
 
 void *Thread(void *a) {
   barrier_wait(&barrier);
   GlobalData[2] = 42;
+  x = 7;
   return 0;
 }
 
 int main() {
   barrier_init(&barrier, 2);
   fprintf(stderr, "addr=");
   print_address(GlobalData);
   fprintf(stderr, "\n");
   pthread_t t;
   pthread_create(&t, 0, Thread, 0);
   GlobalData[2] = 43;
+  x = 8;
   barrier_wait(&barrier);
   pthread_join(t, 0);
 }
 
 // CHECK: External symbolizer is explicitly disabled.
 // CHECK: Using dladdr symbolizer.
 // CHECK: addr=[[ADDR:0x[0-9,a-f]+]]
 // CHECK: WARNING: ThreadSanitizer: data race
 // CHECK: Location is global 'GlobalData' at [[ADDR]] ({{.*}}+0x{{[0-9,a-f]+}})
+// CHECK: WARNING: ThreadSanitizer: data race
+// CHECK: Location is global 'x' at {{.*}} ({{.*}}+0x{{[0-9,a-f]+}})