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[PATCH] Fix i686 memchr overflow calculation (BZ#21182)
- From: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>
- To: libc-alpha at sourceware dot org
- Date: Tue, 14 Mar 2017 14:28:07 -0300
- Subject: [PATCH] Fix i686 memchr overflow calculation (BZ#21182)
- Authentication-results: sourceware.org; auth=none
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.
[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.
---
ChangeLog | 7 +++++++
string/test-memchr.c | 6 ++++++
sysdeps/i386/i686/multiarch/memchr-sse2.S | 2 +-
3 files changed, 14 insertions(+), 1 deletion(-)
diff --git a/string/test-memchr.c b/string/test-memchr.c
index d64d10c..87a077b 100644
--- a/string/test-memchr.c
+++ b/string/test-memchr.c
@@ -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;
}
diff --git a/sysdeps/i386/i686/multiarch/memchr-sse2.S b/sysdeps/i386/i686/multiarch/memchr-sse2.S
index 910679c..e41f324 100644
--- a/sysdeps/i386/i686/multiarch/memchr-sse2.S
+++ b/sysdeps/i386/i686/multiarch/memchr-sse2.S
@@ -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
--
2.7.4