[llvm] Fix string copy confusion

[urnathan]

Summary

The microsoft demangler makes copies of the demangled strings, but has some confusion between StringView representation (sans NUL), and C-strings (with NUL). Here we also have a use of strcpy, which happens to work because the incoming string view happens to have a trailing NUL. But a simple memcpy excluding the NUL is sufficient.

This is broken out of D120990 and is a prerequisite of that patch.

[erichkeane]

This looks logical to me. That said, we're deep into files that I don't claim any knowledge/ownership over, so please give this a day or two before committing for others to have a chance to take a look.

[dblaikie]

Yeah, it wouldn't /entirely/ surprise me (knowing little about the code) if something, somewhere, depended on the StringView actually pointing to a null terminated string - but if tests are passing, etc (especially with something like asan), then this sounds OK to me.

[urnathan]

I did look for consumers of the cache of copied names, and AFAICT they handled StringViews, not C-strings. I'll wait a couple of days anyway.

llvm/lib/Demangle/MicrosoftDemangle.cpp

return std::make_pair(Qualifiers(Q_Const | Q_Volatile),
                           PointerAffinity::Pointer);
   }
   // This function is only called if isPointerType() returns true,
   // and it only returns true for the six cases listed above.
   DEMANGLE_UNREACHABLE;
 }
 
 StringView Demangler::copyString(StringView Borrowed) {
-  char *Stable = Arena.allocUnalignedBuffer(Borrowed.size() + 1);
-  std::strcpy(Stable, Borrowed.begin());
+  char *Stable = Arena.allocUnalignedBuffer(Borrowed.size());
+  std::memcpy(Stable, Borrowed.begin(), Borrowed.size());
 
   return {Stable, Borrowed.size()};
 }
 
 SpecialTableSymbolNode *
 Demangler::demangleSpecialTableSymbolNode(StringView &MangledName,
                                           SpecialIntrinsicKind K) {
   NamedIdentifierNode *NI = Arena.alloc<NamedIdentifierNode>();