[asan] Block signals when starting threads

[vitalybuka]

Summary

Async signals may crash the process if AsanThread is not fully
initialized. We do the same for other sanitizers already.

Can't have good reproducer for test. We see this in internal test with prob 1e-6.

[vitalybuka]

update

[phosek]

This broke our macOS builders, would it be possible to fix forward or revert?

/opt/s/w/ir/x/w/llvm_build/./bin/clang++ --target=x86_64-apple-darwin20.6.0 --sysroot=/opt/s/w/ir/cache/macos_sdk/XCode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk -DASAN_DYNAMIC=1 -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_LIBCPP_ENABLE_ASSERTIONS -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/opt/s/w/ir/x/w/llvm-llvm-project/compiler-rt/lib/asan/.. -fPIC -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffile-prefix-map=/opt/s/w/ir/x/w/llvm_build/runtimes/runtimes-bins=../llvm_build/runtimes/runtimes-bins -ffile-prefix-map=/opt/s/w/ir/x/w/llvm-llvm-project/= -no-canonical-prefixes -Wall -Wno-unused-parameter -O3 -DNDEBUG -std=c++17 -arch arm64 -arch x86_64 -isysroot /opt/s/w/ir/cache/macos_sdk/XCode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk -stdlib=libc++ -mmacosx-version-min=10.10 -isysroot /opt/s/w/ir/cache/macos_sdk/XCode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk -fPIC -fno-builtin -fno-exceptions -funwind-tables -fno-stack-protector -fno-sanitize=safe-stack -fvisibility=hidden -fno-lto -Wthread-safety -Wthread-safety-reference -Wthread-safety-beta -O3 -g -Wno-gnu -Wno-variadic-macros -Wno-c99-extensions -nostdinc++ -fno-rtti -Wno-format -ftls-model=initial-exec -MD -MT compiler-rt/lib/asan/CMakeFiles/RTAsan_dynamic.osx.dir/asan_interceptors.cpp.o -MF compiler-rt/lib/asan/CMakeFiles/RTAsan_dynamic.osx.dir/asan_interceptors.cpp.o.d -o compiler-rt/lib/asan/CMakeFiles/RTAsan_dynamic.osx.dir/asan_interceptors.cpp.o -c /opt/s/w/ir/x/w/llvm-llvm-project/compiler-rt/lib/asan/asan_interceptors.cpp
/opt/s/w/ir/x/w/llvm-llvm-project/compiler-rt/lib/asan/asan_interceptors.cpp:229:3: error: use of undeclared identifier 'SetSigProcMask'
  229 |   SetSigProcMask(&sigset, nullptr);
      |   ^
/opt/s/w/ir/x/w/llvm-llvm-project/compiler-rt/lib/asan/asan_interceptors.cpp:252:3: error: unknown type name 'ScopedBlockSignals'
  252 |   ScopedBlockSignals block(&sigset);
      |   ^
2 errors generated.

[vitalybuka]

Thanks. Looking.

compiler-rt/lib/asan/asan_interceptors.cpp

 
 #if ASAN_INTERCEPT_PTHREAD_CREATE
 static thread_return_t THREAD_CALLING_CONV asan_thread_start(void *arg) {
   AsanThread *t = (AsanThread *)arg;
   SetCurrentThread(t);
   auto self = GetThreadSelf();
   auto args = asanThreadArgRetval().GetArgs(self);
   t->ThreadStart(GetTid());
+
+  __sanitizer_sigset_t sigset;
+  t->GetStartData(sigset);
+  SetSigProcMask(&sigset, nullptr);
+
   thread_return_t retval = (*args.routine)(args.arg_retval);
   asanThreadArgRetval().Finish(self, retval);
   return retval;
 }
 
 INTERCEPTOR(int, pthread_create, void *thread, void *attr,
             void *(*start_routine)(void *), void *arg) {
   EnsureMainThreadIDIsCorrect();
   // Strict init-order checking is thread-hostile.
   if (flags()->strict_init_order)
     StopInitOrderChecking();
   GET_STACK_TRACE_THREAD;
   bool detached = [attr]() {
     int d = 0;
     return attr && !REAL(pthread_attr_getdetachstate)(attr, &d) &&
            IsStateDetached(d);
   }();
 
   u32 current_tid = GetCurrentTidOrInvalid();
-  AsanThread *t = AsanThread::Create(current_tid, &stack, detached);
+
+  __sanitizer_sigset_t sigset;
+  ScopedBlockSignals block(&sigset);
+
+  AsanThread *t = AsanThread::Create(sigset, current_tid, &stack, detached);
 
   int result;
   {
     // Ignore all allocations made by pthread_create: thread stack/TLS may be
     // stored by pthread for future reuse even after thread destruction, and
     // the linked list it's stored in doesn't even hold valid pointers to the
     // objects, the latter are calculated by obscure pointer arithmetic.
 #    if CAN_SANITIZE_LEAKS