typedef __SIZE_TYPE__ size_t;
static int mymemcmp1 (unsigned long int, unsigned long int)
__attribute__ ((__nothrow__));
__inline static int
mymemcmp1 (unsigned long int a, unsigned long int b)
{
long int srcp1 = (long int) &a;
long int srcp2 = (long int) &b;
unsigned long int a0, b0;
do
{
a0 = ((unsigned char *) srcp1)[0];
b0 = ((unsigned char *) srcp2)[0];
srcp1 += 1;
srcp2 += 1;
}
while (a0 == b0);
return a0 - b0;
}
static int mymemcmp2 (long, long, size_t) __attribute__ ((__nothrow__));
static int
mymemcmp2 (long int srcp1, long int srcp2, size_t len)
{
unsigned long int a0, a1;
unsigned long int b0, b1;
switch (len % 4)
{
default:
case 2:
a0 = ((unsigned long int *) srcp1)[0];
b0 = ((unsigned long int *) srcp2)[0];
srcp1 -= 2 * (sizeof (unsigned long int));
srcp2 -= 2 * (sizeof (unsigned long int));
len += 2;
goto do1;
case 3:
a1 = ((unsigned long int *) srcp1)[0];
b1 = ((unsigned long int *) srcp2)[0];
srcp1 -= (sizeof (unsigned long int));
srcp2 -= (sizeof (unsigned long int));
len += 1;
goto do2;
case 0:
if (16 <= 3 * (sizeof (unsigned long int)) && len == 0)
return 0;
a0 = ((unsigned long int *) srcp1)[0];
b0 = ((unsigned long int *) srcp2)[0];
goto do3;
case 1:
a1 = ((unsigned long int *) srcp1)[0];
b1 = ((unsigned long int *) srcp2)[0];
srcp1 += (sizeof (unsigned long int));
srcp2 += (sizeof (unsigned long int));
len -= 1;
if (16 <= 3 * (sizeof (unsigned long int)) && len == 0)
goto do0;
}
do
{
a0 = ((unsigned long int *) srcp1)[0];
b0 = ((unsigned long int *) srcp2)[0];
if (a1 != b1)
return mymemcmp1 ((a1), (b1));
do3:
a1 = ((unsigned long int *) srcp1)[1];
b1 = ((unsigned long int *) srcp2)[1];
if (a0 != b0)
return mymemcmp1 ((a0), (b0));
do2:
a0 = ((unsigned long int *) srcp1)[2];
b0 = ((unsigned long int *) srcp2)[2];
if (a1 != b1)
return mymemcmp1 ((a1), (b1));
do1:
a1 = ((unsigned long int *) srcp1)[3];
b1 = ((unsigned long int *) srcp2)[3];
if (a0 != b0)
return mymemcmp1 ((a0), (b0));
srcp1 += 4 * (sizeof (unsigned long int));
srcp2 += 4 * (sizeof (unsigned long int));
len -= 4;
}
while (len != 0);
do0:
if (a1 != b1)
return mymemcmp1 ((a1), (b1));
return 0;
}
static int mymemcmp3 (long, long, size_t) __attribute__ ((__nothrow__));
static int
mymemcmp3 (long int srcp1, long int srcp2, size_t len)
{
unsigned long int a0, a1, a2, a3;
unsigned long int b0, b1, b2, b3;
unsigned long int x;
int shl, shr;
shl = 8 * (srcp1 % (sizeof (unsigned long int)));
shr = 8 * (sizeof (unsigned long int)) - shl;
srcp1 &= -(sizeof (unsigned long int));
switch (len % 4)
{
default:
case 2:
a1 = ((unsigned long int *) srcp1)[0];
a2 = ((unsigned long int *) srcp1)[1];
b2 = ((unsigned long int *) srcp2)[0];
srcp1 -= 1 * (sizeof (unsigned long int));
srcp2 -= 2 * (sizeof (unsigned long int));
len += 2;
goto do1;
case 3:
a0 = ((unsigned long int *) srcp1)[0];
a1 = ((unsigned long int *) srcp1)[1];
b1 = ((unsigned long int *) srcp2)[0];
srcp2 -= 1 * (sizeof (unsigned long int));
len += 1;
goto do2;
case 0:
if (16 <= 3 * (sizeof (unsigned long int)) && len == 0)
return 0;
a3 = ((unsigned long int *) srcp1)[0];
a0 = ((unsigned long int *) srcp1)[1];
b0 = ((unsigned long int *) srcp2)[0];
srcp1 += 1 * (sizeof (unsigned long int));
goto do3;
case 1:
a2 = ((unsigned long int *) srcp1)[0];
a3 = ((unsigned long int *) srcp1)[1];
b3 = ((unsigned long int *) srcp2)[0];
srcp1 += 2 * (sizeof (unsigned long int));
srcp2 += 1 * (sizeof (unsigned long int));
len -= 1;
if (16 <= 3 * (sizeof (unsigned long int)) && len == 0)
goto do0;
}
do
{
a0 = ((unsigned long int *) srcp1)[0];
b0 = ((unsigned long int *) srcp2)[0];
x = (((a2) >> (shl)) | ((a3) << (shr)));
if (x != b3)
return mymemcmp1 ((x), (b3));
do3:
a1 = ((unsigned long int *) srcp1)[1];
b1 = ((unsigned long int *) srcp2)[1];
x = (((a3) >> (shl)) | ((a0) << (shr)));
if (x != b0)
return mymemcmp1 ((x), (b0));
do2:
a2 = ((unsigned long int *) srcp1)[2];
b2 = ((unsigned long int *) srcp2)[2];
x = (((a0) >> (shl)) | ((a1) << (shr)));
if (x != b1)
return mymemcmp1 ((x), (b1));
do1:
a3 = ((unsigned long int *) srcp1)[3];
b3 = ((unsigned long int *) srcp2)[3];
x = (((a1) >> (shl)) | ((a2) << (shr)));
if (x != b2)
return mymemcmp1 ((x), (b2));
srcp1 += 4 * (sizeof (unsigned long int));
srcp2 += 4 * (sizeof (unsigned long int));
len -= 4;
}
while (len != 0);
do0:
x = (((a2) >> (shl)) | ((a3) << (shr)));
if (x != b3)
return mymemcmp1 ((x), (b3));
return 0;
}
__attribute__ ((noinline))
int mymemcmp (const void *s1, const void *s2, size_t len)
{
unsigned long int a0;
unsigned long int b0;
long int srcp1 = (long int) s1;
long int srcp2 = (long int) s2;
if (srcp1 % (sizeof (unsigned long int)) == 0)
return mymemcmp2 (srcp1, srcp2, len / (sizeof (unsigned long int)));
else
return mymemcmp3 (srcp1, srcp2, len / (sizeof (unsigned long int)));
}
char buf[256] __attribute__((aligned (16)));
char buf2[256] __attribute__((aligned (16)));
int
main (void)
{
__builtin_memcpy (buf + 9,
"\x1\x37\x82\xa7\x55\x49\x9d\xbf\xf8\x44\xb6\x55\x17\x8e\xf9", 15);
__builtin_memcpy (buf2 + 24,
"\x1\x37\x82\xa7\x55\x49\xd0\xf3\xb7\x2a\x6d\x23\x71\x49\x6a", 15);
if (mymemcmp (buf + 9, buf2 + 24, 33) != -51)
__builtin_abort ();
return 0;
}
is miscompiled at -O2 or -O2 -fno-strict-aliasing, doesn't return the expected
-51, but something that depends on the stack content etc. (e.g. prints
different
value when run from gdb's inferior and in the program). Note mymemcmp has
a couple of lines that weren't affecting the result removed.
--
Summary: [4.4 Regression] Miscompilation of glibc's memcmp
Product: gcc
Version: 4.4.0
Status: UNCONFIRMED
Keywords: wrong-code
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: jakub at gcc dot gnu dot org
GCC target triplet: x86_64-linux
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38051
