[lld] r263919 - [COFF] Don't call memcpy with a NULL argument

[David Majnemer via llvm-commits]

Author: majnemer
Date: Sun Mar 20 18:10:12 2016
New Revision: 263919

URL: http://llvm.org/viewvc/llvm-project?rev=263919&view=rev
Log:
[COFF] Don't call memcpy with a NULL argument

Some declarations of memcpy (like glibc's for example) are attributed
with notnull which makes it UB for NULL to get passed in, even if the
memcpy count is zero.

To account for this, guard the memcpy with an appropriate precondition.

This should fix the last UBSan bug, exposed by the test suite, in the
COFF linker.

Modified:
    lld/trunk/COFF/Writer.cpp

Modified: lld/trunk/COFF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/Writer.cpp?rev=263919&r1=263918&r2=263919&view=diff
==============================================================================
--- lld/trunk/COFF/Writer.cpp (original)
+++ lld/trunk/COFF/Writer.cpp Sun Mar 20 18:10:12 2016
@@ -639,7 +639,8 @@ template <typename PEHeaderTy> void Writ
   // The first 4 bytes is length including itself.
   Buf = reinterpret_cast<uint8_t *>(&SymbolTable[NumberOfSymbols]);
   write32le(Buf, Strtab.size() + 4);
-  memcpy(Buf + 4, Strtab.data(), Strtab.size());
+  if (!Strtab.empty())
+    memcpy(Buf + 4, Strtab.data(), Strtab.size());
 }
 
 void Writer::openFile(StringRef Path) {