https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80479
Alan Modra <amodra at gmail dot com> changed:
What |Removed |Added
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CC| |amodra at gmail dot com
--- Comment #9 from Alan Modra <amodra at gmail dot com> ---
The following doesn't fail, but the strcmp optimization doesn't trigger
either..
#include <stdio.h>
#include <string.h>
#include <sys/mman.h>
int
main ()
{
#if 0
char str1[15];
char str2[15];
#else
const size_t len = 65536;
char *buf1, *buf2, *str1, *str2;
buf1 = mmap (NULL, 2 * len, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (buf1 == MAP_FAILED)
{
perror ("mmap failed");
return 0;
}
if (munmap (buf1 + len, len) < 0)
{
perror ("munmap failed");
return 0;
}
buf2 = mmap (NULL, 2 * len, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (buf2 == MAP_FAILED)
{
perror ("mmap failed");
return 0;
}
if (munmap (buf2 + len, len) < 0)
{
perror ("munmap failed");
return 0;
}
str1 = buf1 + len - 7;
str2 = buf2 + len - 7;
#endif
strcpy (str1, "abcdef");
strcpy (str2, "ABCDEF");
return strcmp (str1, str2);
}
For the #if 1 case, valgrind is complaining about the compare of two eight byte
words read from the stack, which indeed do have one uninitialized byte past the
string terminating zero. I don't believe it matters. (The generated asm looks
OK to me, but that might be because my brain has shut down for the night.)
