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Subject: [Bug sanitizer/55309] gcc's address-sanitizer 66% slower than clang's
Date: Fri, 22 Feb 2013 15:06:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55309

--- Comment #53 from Kostya Serebryany <kcc at gcc dot gnu.org> 2013-02-22 15:06:25 UTC ---
The interceptor we have is conservative: 

INTERCEPTOR(int, memcmp, const void *a1, const void *a2, uptr size) {
  if (!asan_inited) return internal_memcmp(a1, a2, size);
  ENSURE_ASAN_INITED();
  unsigned char c1 = 0, c2 = 0;
  const unsigned char *s1 = (const unsigned char*)a1;
  const unsigned char *s2 = (const unsigned char*)a2;
  uptr i;
  for (i = 0; i < size; i++) {
    c1 = s1[i];
    c2 = s2[i];
    if (c1 != c2) break;
  }
  ASAN_READ_RANGE(s1, Min(i + 1, size));
  ASAN_READ_RANGE(s2, Min(i + 1, size));
  return CharCmp(c1, c2);
} 

looks like gcc partially inlines memcmp and 
bypasses out conservative interceptor.

We could make the interceptor more strict (ASAN_READ_RANGE(s2, size);).
I am trying to remember why we didn't do this...