[asan] Make ScopedInErrorReport::current_error_ linker-initialized

[delcypher]

Based on other code that uses LINKER_INITIALIZED this seems reasonable. However I have no idea how this is supposed to actually work.

lib/asan/asan_report.cc

205

How does LINKER_INITIALIZED guarantee that the linker will actually initialize the struct? It looks like it's just a member of an enum, so it doesn't actually do anything.

My naive reading of this code is that you're trying to avoid the call to internal_memset(this, 0, sizeof(*this)). It looks like this will mean though that the anonymous union won't be initialized.

[kubamracek]

lib/asan/asan_report.cc

205

For global variables, uninitialized = filled with zeroes. Unfortunately, I don't think there is a reasonable way to enforce this. C++14 has constexpr constructors, but I don't think we can use C++14 in compiler-rt (yet).

I have to admit that the way I "tested" the patch was to build compiler-rt, then disassemble the result and look if the static constructor is there or not.

[delcypher]

lib/asan/asan_report.cc

205

For global variables, uninitialized = filled with zeroes.

For simple structs yes. For unions inside structs, I'm not sure what happens.

Regardless of that all that, I think an explanation of why this change is being made is the only thing that is missing to accept this patch.

lib/asan/asan_errors.h

struct ErrorDescription {
   // We can add a wrapper around it to make it "more c++-like", but that would
   // add a lot of code and the benefit wouldn't be that big.
   union {
     ErrorBase Base;
     ASAN_FOR_EACH_ERROR_KIND(ASAN_ERROR_DESCRIPTION_MEMBER)
   };
 
   ErrorDescription() { internal_memset(this, 0, sizeof(*this)); }
+  explicit ErrorDescription(LinkerInitialized) {}
   ASAN_FOR_EACH_ERROR_KIND(ASAN_ERROR_DESCRIPTION_CONSTRUCTOR)
 
   bool IsValid() { return kind != kErrorKindInvalid; }
   void Print() {
     switch (kind) {
       ASAN_FOR_EACH_ERROR_KIND(ASAN_ERROR_DESCRIPTION_PRINT)
       case kErrorKindInvalid:
         CHECK(0);

lib/asan/asan_report.cc

  private:
   ScopedErrorReportLock error_report_lock_;
   // Error currently being reported. This enables the destructor to interact
   // with the debugger and point it to an error description.
   static ErrorDescription current_error_;
   bool halt_on_error_;
 };
 
-ErrorDescription ScopedInErrorReport::current_error_;
+ErrorDescription ScopedInErrorReport::current_error_(LINKER_INITIALIZED);
 
 void ReportDeadlySignal(const SignalContext &sig) {
   ScopedInErrorReport in_report(/*fatal*/ true);
   ErrorDeadlySignal error(GetCurrentTidOrInvalid(), sig);
   in_report.ReportError(error);
 }
 
 void ReportDoubleFree(uptr addr, BufferedStackTrace *free_stack) {