[compiler-rt] r337170 - [cfi] Don't pass a uint16_t to memset. Make sure the 16-bit constant is appropriate for us.

[Filipe Cabecinhas via llvm-commits]

Author: filcab
Date: Mon Jul 16 06:41:54 2018
New Revision: 337170

URL: http://llvm.org/viewvc/llvm-project?rev=337170&view=rev
Log:
[cfi] Don't pass a uint16_t to memset. Make sure the 16-bit constant is appropriate for us.

Reviewers: eugenis, pcc, kcc

Subscribers: delcypher, #sanitizers, llvm-commits

Differential Revision: https://reviews.llvm.org/D49252

Modified:
    compiler-rt/trunk/lib/cfi/cfi.cc

Modified: compiler-rt/trunk/lib/cfi/cfi.cc
URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/cfi/cfi.cc?rev=337170&r1=337169&r2=337170&view=diff
==============================================================================
--- compiler-rt/trunk/lib/cfi/cfi.cc (original)
+++ compiler-rt/trunk/lib/cfi/cfi.cc Mon Jul 16 06:41:54 2018
@@ -132,7 +132,10 @@ void ShadowBuilder::Start() {
 void ShadowBuilder::AddUnchecked(uptr begin, uptr end) {
   uint16_t *shadow_begin = MemToShadow(begin, shadow_);
   uint16_t *shadow_end = MemToShadow(end - 1, shadow_) + 1;
-  memset(shadow_begin, kUncheckedShadow,
+  // memset takes a byte, so our unchecked shadow value requires both bytes to
+  // be the same. Make sure we're ok during compilation.
+  static_assert(kUncheckedShadow & 0xff == ((kUncheckedShadow >> 8) & 0xff));
+  memset(shadow_begin, kUncheckedShadow & 0xff,
          (shadow_end - shadow_begin) * sizeof(*shadow_begin));
 }