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strlen arm BigEndian glibc bug
From: |
Eric Zerbib |
Subject: |
strlen arm BigEndian glibc bug |
Date: |
Thu, 12 Dec 2002 18:24:44 -0500 |
User-agent: |
KMail/1.4.3 |
I have found a problem with glibc strlen fonction on arm processor with
big-endian
I am using
gcc-2.95.3
I compiled glic.2.2.4 but I think that the bug is already present in the last
2.3.1
the library compile .../glibc-2.2.4/sysdeps/arm/strlen.S
but in with a simple program
----------------------------------
#include "stdio.h"
#include <string.h>
int main(int argc,char **argv)
{
printf ("strlen =%d\n",strlen("123456789"));
}
----------------------------------
the result is
strlen = 8 !!!! instead of 9
Note someone else detect the problem on the net and post the
same remark
here is the link
http://www.geocrawler.com/archives/3/18/2000/3/0/3528870/
Here is the source...
this is the buggy code, but I m not sufficient in arm asm to understand
why this is a buggy code ?
-------------cut here -------------------------------------------------
/* Copyright (C) 1998 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Code contributed by Matthew Wilcox <address@hidden>
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA. */
#include <sysdep.h>
/* size_t strlen(const char *S)
* entry: r0 -> string
* exit: r0 = len
*/
ENTRY(strlen)
bic r1, r0, $3 @ addr of word containing first byte
ldr r2, [r1], $4 @ get the first word
ands r3, r0, $3 @ how many bytes are duff?
rsb r0, r3, $0 @ get - that number into counter.
beq Laligned @ skip into main check routine if no
@ more
#ifdef __ARMEB__
orr r2, r2, $0xff000000 @ set this byte to non-zero
subs r3, r3, $1 @ any more to do?
orrgt r2, r2, $0x00ff0000 @ if so, set this byte
subs r3, r3, $1 @ more?
orrgt r2, r2, $0x0000ff00 @ then set.
#else
orr r2, r2, $0x000000ff @ set this byte to non-zero
subs r3, r3, $1 @ any more to do?
orrgt r2, r2, $0x0000ff00 @ if so, set this byte
subs r3, r3, $1 @ more?
orrgt r2, r2, $0x00ff0000 @ then set.
#endif
Laligned: @ here, we have a word in r2. Does it
tst r2, $0x000000ff @ contain any zeroes?
tstne r2, $0x0000ff00 @
tstne r2, $0x00ff0000 @
tstne r2, $0xff000000 @
addne r0, r0, $4 @ if not, the string is 4 bytes longer
ldrne r2, [r1], $4 @ and we continue to the next word
bne Laligned @
Llastword: @ drop through to here once we find a
tst r2, $0x000000ff @ word that has a zero byte in it
addne r0, r0, $1 @
tstne r2, $0x0000ff00 @ and add up to 3 bytes on to it
addne r0, r0, $1 @
tstne r2, $0x00ff0000 @ (if first three all non-zero, 4th
addne r0, r0, $1 @ must be zero)
RETINSTR(mov,pc,lr)
END(strlen)
----------------------------------------------------------------------------------------------------------
--
Eric Zerbib
TMT Coaxial Networks
address@hidden
Tel: +972 (2) 5328202 ext. 149
- strlen arm BigEndian glibc bug,
Eric Zerbib <=