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Fix i686 memchr overflow calculation (BZ#21182) 

This patch fixes the regression added by 23d2770 for final address
overflow calculation.  The subtraction of the considered size (16)
at line 120 is at wrong place, for sizes less than 16 subsequent
overflow check will not take in consideration an invalid size (since
the subtraction will be negative).  Also, the lea instruction also
does not raise the carry flag (CF) that is used in subsequent jbe
to check for overflow.

The fix is to follow x86_64 logic from 3daef2c where the overflow
is first check and a sub instruction is issued.  In case of resulting
negative size, CF will be set by the sub instruction and a NULL
result will be returned.  The patch also add similar tests reported
in bug report.

Checked on i686-linux-gnu and x86_64-linux-gnu.

	* string/test-memchr.c (do_test): Add BZ#21182 checks for address
	near end of a page.
	* sysdeps/i386/i686/multiarch/memchr-sse2.S (__memchr): Fix
	overflow calculation.
This commit is contained in:
Adhemerval Zanella 2017-03-14 14:16:13 -03:00
parent 29d92a8eda
commit 3abeeec5f4
3 changed files with 15 additions and 1 deletions
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8
ChangeLog
View File

@ -1,3 +1,11 @@
2017-03-29 Adhemerval Zanella <adhemerval.zanella@linaro.org>
[BZ# 21182]
* string/test-memchr.c (do_test): Add BZ#21182 checks for address
near end of a page.
* sysdeps/i386/i686/multiarch/memchr-sse2.S (__memchr): Fix
overflow calculation.
2017-03-28 Steve Ellcey <sellcey@caviumnetworks.com>
* benchtests/bench-memcpy-random.c (TEST_NAME): Change to memcpy.

6
string/test-memchr.c
View File

@ -210,6 +210,12 @@ test_main (void)
do_test (0, i, i + 1, i + 1, 0);
}
/* BZ#21182 - wrong overflow calculation for i686 implementation
with address near end of the page. */
for (i = 2; i < 16; ++i)
/* page_size is in fact getpagesize() * 2. */
do_test (page_size / 2 - i, i, i, 1, 0x9B);
do_random_tests ();
return ret;
}

2
sysdeps/i386/i686/multiarch/memchr-sse2.S
View File

@ -117,7 +117,6 @@ L(crosscache):
# ifndef USE_AS_RAWMEMCHR
jnz L(match_case2_prolog1)
lea -16(%edx), %edx
/* Calculate the last acceptable address and check for possible
addition overflow by using satured math:
edx = ecx + edx
@ -125,6 +124,7 @@ L(crosscache):
add %ecx, %edx
sbb %eax, %eax
or %eax, %edx
sub $16, %edx
jbe L(return_null)
lea 16(%edi), %edi
# else