[NFC][LLVM-MT] Fix buffer-overflow when comparing buffers

[jmmartinez]

I encounter this issue when running the LLVM test suite with the address sanitizer enabled.

[abrachet]

llvm/tools/llvm-mt/llvm-mt.cpp

153–157

That should work too. WDYT?

[jmmartinez]

llvm/tools/llvm-mt/llvm-mt.cpp

153–157

I didn't know about that overload. I'll change it use your version.

[jmmartinez]

Updated to use 4 iterator version of std::equals

[jmmartinez]

In fact, bring back the size comparison to speed up the comparison in the case the sizes do not match

[abrachet]

llvm/tools/llvm-mt/llvm-mt.cpp

153–157

Ah, sorry I didn't mean to keep SameSize in my suggested change. Just this should be sufficient

Same = std::equal(OutputBuffer->getBufferStart(),
                                    OutputBuffer->getBufferEnd(),
                                    FileBuffer->getBufferStart());
                                    FileBuffer->getBufferStart(),
                                    FileBuffer->getBufferEnd());

[jmmartinez]

llvm/tools/llvm-mt/llvm-mt.cpp

153–157

I know, but checking the size first gives a shortcut in case the sizes are different (instead of scanning for a difference). Do you think we can keep it in this case ?

[jmmartinez]

llvm/tools/llvm-mt/llvm-mt.cpp

153–157

I just realized that with the right iterator type, std::equals computes the distance and does the shortcut on its own. I'm removing the size comparison.

[jmmartinez]

Remove size comparison

[jmmartinez]

Duplicated with https://reviews.llvm.org/D139457 (which got merged).

llvm/tools/llvm-mt/llvm-mt.cpp

int llvm_mt_main(int Argc, char **Argv) {
   if (InputArgs.hasArg(OPT_notify_update)) {
     ErrorOr<std::unique_ptr<MemoryBuffer>> OutBuffOrErr =
         MemoryBuffer::getFile(OutputFile);
     // Assume if we couldn't open the output file then it doesn't exist meaning
     // there was a change.
     bool Same = false;
     if (OutBuffOrErr) {
       const std::unique_ptr<MemoryBuffer> &FileBuffer = *OutBuffOrErr;
-      Same = std::equal(OutputBuffer->getBufferStart(),
+      bool SameSize =
+          OutputBuffer->getBufferSize() == FileBuffer->getBufferSize();
+      Same = SameSize && std::equal(OutputBuffer->getBufferStart(),
                                     OutputBuffer->getBufferEnd(),
                                     FileBuffer->getBufferStart());
     }
     if (!Same) {
 #if LLVM_ON_UNIX
       ExitCode = 0xbb;
 #elif defined(_WIN32)
       ExitCode = 0x41020001;
 #endif
     }