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Extracted from glibc upstream git repository. Changes to the ChangeLog have
been removed. This patch is needed to fix spurious segmentation faults on
i686.
From 3abeeec5f46ff036bd9df60bb096e20314ccd078 Mon Sep 17 00:00:00 2001
From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date: Tue, 14 Mar 2017 14:16:13 -0300
Subject: [PATCH] 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.
---
string/test-memchr.c | 6 ++++++
sysdeps/i386/i686/multiarch/memchr-sse2.S | 2 +-
3 files changed, 15 insertions(+), 1 deletion(-)
diff --git a/string/test-memchr.c b/string/test-memchr.c
index 2403c9242b..669e092e7d 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 910679cfc0..e41f324a77 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
--
2.12.2
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