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Fix x86_64 memchr for large input sizes

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Current optimized memchr for x86_64 does for input arguments pointers
module 64 in range of [49,63] if there is no searchr char in the rest
of 64-byte block a pointer addition which might overflow:

* sysdeps/x86_64/memchr.S

    77          .p2align 4
    78  L(unaligned_no_match):
    79          add     %rcx, %rdx

Add (uintptr_t)s % 16 to n in %rdx.

    80          sub     $16, %rdx
    81          jbe     L(return_null)

This patch fixes by adding a saturated math that sets a maximum pointer
value if it overflows (UINTPTR_MAX).

Checked on x86_64-linux-gnu and powerpc64-linux-gnu.

	[BZ# 19387]
	* sysdeps/x86_64/memchr.S (memchr): Avoid overflow in pointer
	addition.
	* string/test-memchr.c (do_test): Remove alignment limitation.
	(test_main): Add test that trigger BZ# 19387.
This commit is contained in:
Adhemerval Zanella 2016-12-15 18:17:09 -02:00
parent cecbc7967f
commit 3daef2c8ee
3 changed files with 18 additions and 5 deletions
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8
ChangeLog
View File

@ -1,3 +1,11 @@
2016-12-27 Adhemerval Zanella <adhemerval.zanella@linaro.org>
[BZ# 19387]
* sysdeps/x86_64/memchr.S (memchr): Avoid overflow in pointer
addition.
* string/test-memchr.c (do_test): Remove alignment limitation.
(test_main): Add test that trigger BZ# 19387.
2016-12-26 Nick Alcock <nick.alcock@oracle.com>
[BZ #7065]

9
string/test-memchr.c
View File

@ -76,7 +76,6 @@ do_test (size_t align, size_t pos, size_t len, size_t n, int seek_char)
size_t i;
CHAR *result;
align &= 7;
if ((align + len) * sizeof (CHAR) >= page_size)
return;
@ -194,12 +193,12 @@ test_main (void)
do_test (i, 64, 256, SIZE_MAX, 0);
}
for (i = 1; i < 16; ++i)
for (i = 1; i < 64; ++i)
{
for (j = 1; j < 16; j++)
for (j = 1; j < 64; j++)
{
do_test (0, 16 - j, 16, SIZE_MAX, 23);
do_test (i, 16 - j, 16, SIZE_MAX, 23);
do_test (0, 64 - j, 64, SIZE_MAX, 23);
do_test (i, 64 - j, 64, SIZE_MAX, 23);
}
}

6
sysdeps/x86_64/memchr.S
View File

@ -76,7 +76,13 @@ L(crosscache):
.p2align 4
L(unaligned_no_match):
/* Calculate the last acceptable address and check for possible
addition overflow by using satured math:
rdx = rcx + rdx
rdx |= -(rdx < rcx) */
add %rcx, %rdx
sbb %rax, %rax
or %rax, %rdx
sub $16, %rdx
jbe L(return_null)
add $16, %rdi