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

[Benjamin Kramer via llvm-commits]

On Mon, Jul 16, 2018 at 3:46 PM Filipe Cabecinhas via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> 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));
>

llvm/projects/compiler-rt/lib/cfi/cfi.cc:137:34: error: & has lower
precedence than ==; == will be evaluated first [-Werror,-Wparentheses]
  static_assert(kUncheckedShadow & 0xff == ((kUncheckedShadow >> 8) &
0xff));
                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
llvm/projects/compiler-rt/lib/cfi/cfi.cc:137:34: note: place parentheses
around the '==' expression to silence this warning
  static_assert(kUncheckedShadow & 0xff == ((kUncheckedShadow >> 8) &
0xff));
                                 ^
                                   (                                       )
llvm/projects/compiler-rt/lib/cfi/cfi.cc:137:34: note: place parentheses
around the & expression to evaluate it first
  static_assert(kUncheckedShadow & 0xff == ((kUncheckedShadow >> 8) &
0xff));
                                 ^
                (                      )
llvm/projects/compiler-rt/lib/cfi/cfi.cc:137:76: error: static_assert with
no message is a C++17 extension [-Werror,-Wc++17-extensions]
  static_assert(kUncheckedShadow & 0xff == ((kUncheckedShadow >> 8) &
0xff));
                                                                           ^

 , ""


> +  memset(shadow_begin, kUncheckedShadow & 0xff,
>           (shadow_end - shadow_begin) * sizeof(*shadow_begin));
>  }
>
>
>
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