Mail Archives: cygwin/1999/11/09/16:15:32
In article <upuxjq1tj DOT fsf AT 1c DOT ru>, Vadim Egorov <egorovv AT 1c DOT ru> wrote:
>Hello,
>While porting ElectricFence to cygwin I encountered a problem
>with strchr implementation in newlib.
>When it finds character occurance near the end of string it seems
>to access (sometimes) memory past the end of string. When the memory
>just after the end of string is unaccessible it causes access violation.
>This can be reproduced by the following program:
>
>-------------- test.cc --------------
>#include <string.h>
>#include <windows.h>
>char pattern[] = "::\0";
>
>int main()
>{
> DWORD dw;
> int len = 4;
> if (sizeof(pattern) != len)
> return 1;
> char* base = (char*)VirtualAlloc(0, 0x10000, MEM_COMMIT, PAGE_READWRITE);
> char* end = base + 4096;
> if (!VirtualProtect(end, 4096, PAGE_NOACCESS, &dw))
> return 1;
> char* p = end - len;
> memcpy(p, pattern, len);
> p++;
> p = strchr(p, ':');
> return 0;
>}
>-------------- test.cc --------------
>
>What confuses is that it happens only when optimization is turned on:
>gcc test.cc -O2 -o test
>I tried it with gcc 2.95 and 2.95.2 and recent cygwin snapshots.
>Any idea?
Thanks for the bug report and especially for the test case. I've
forwarded this to our newlib development team and they've come up
with a fix. It is below.
This will show up in the next snapshot as well.
-chris
----- Forwarded message from J. Johnston" <jjohnstn AT cygnus DOT com> -----
To: Chris Faylor <cgf AT cygnus DOT com>
Subject: Re: [egorovv AT 1c DOT ru: strchr bug?]
Chris,
I have identified the problem in newlib/libc/machine/i386/strchr.S
and have checked a patch into devo. I have attached the patch
if you need to send it to the user prior to your nightly build.
-- Jeff J.
> ----- Forwarded message from Vadim Egorov <egorovv AT 1c DOT ru> -----
> [snip]
>
> ----- End forwarded message -----
--------------851B2C2FBABC35E4F80FBDE7
Content-Type: text/plain; charset=us-ascii;
name="strchr.patch"
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
filename="strchr.patch"
Index: strchr.S
===================================================================
RCS file: /cvs/cvsfiles/devo/newlib/libc/machine/i386/strchr.S,v
retrieving revision 1.1
diff -c -p -r1.1 strchr.S
*** strchr.S 1998/11/30 22:03:46 1.1
--- strchr.S 1999/11/09 17:23:21
*************** SYM (strchr):
*** 24,30 ****
#ifndef __OPTIMIZE_SIZE__
/* check if string is aligned, if not do check one byte at a time */
! testb $3,al
jne L9
/* create 4 byte mask which is just the desired byte repeated 4 times */
--- 24,30 ----
#ifndef __OPTIMIZE_SIZE__
/* check if string is aligned, if not do check one byte at a time */
! test $3,edi
jne L9
/* create 4 byte mask which is just the desired byte repeated 4 times */
--------------851B2C2FBABC35E4F80FBDE7--
--
cgf AT cygnus DOT com
http://www.cygnus.com/
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