http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48790
Summary: ARM GCC divide/modulo bug
Product: gcc
Version: 4.3.3
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: c
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: the.me...@gmail.com
I've found a strange gcc bug in the Sourcery G++ Lite 2009q1-203. Invalid
instruction is generated while executing this code:
len = 9;
width = 8;
if ((len % width) == 0)
printf("fail\n");
else
printf("ok\n");
Strange is that if the code was in main, sometimes it passed throught without
any problems, but when I've put the code into function it always fails to
compute 9 modulo 8. I don’t see anything wrong in assembly generated by gcc
(maybe there is some stack handling problem in the __aeabi_idivmod function)
Any ideas what's wrong with the toolchain's gcc would really help...
This is how the assembly looks like (of the testcase function)
testcase:
.fnstart
.LFB2:
@ args = 0, pretend = 0, frame = 16
@ frame_needed = 1, uses_anonymous_args = 0
stmfd sp!, {fp, lr}
.save {fp, lr}
.LCFI0:
.setfp fp, sp, #4
add fp, sp, #4
.LCFI1:
.pad #16
sub sp, sp, #16
.LCFI2:
str r0, [fp, #-8]
str r1, [fp, #-12]
ldr r3, [fp, #-8]
mov r0, r3
ldr r1, [fp, #-12]
bl __aeabi_idivmod
mov r3, r1
cmp r3, #0
bne .L2
ldr r0, .L6
bl puts
b .L5
.L2:
ldr r0, .L6+4
bl puts
.L5:
sub sp, fp, #4
ldmfd sp!, {fp, pc}
.L7:
.align 2
.L6:
.word .LC0
.word .LC1
.LFE2:
.fnend
Full Test example for reproducing the bug (Should write 2 ok into screen, but
it generates Illegal Instruction instead:
#include <stdio.h>
int testcase(int len, int width)
{
/* This generates Illegal instruction (always) */
if ((len % width) == 0)
printf("fail\n");
else
printf("ok\n");
}
int main(int argc, char *argv[])
{
int len, width;
len = 9;
width = 8;
/* This generates Illegal instruction (sometimes ???) */
if ((len % width) == 0)
printf("fail\n");
else
printf("ok\n");
testcase(len, width);
return 0;
}
# arm-none-linux-gnueabi-gcc-4.3.3 --v
Using built-in specs.
Target: arm-none-linux-gnueabi
Configured with:
/scratch/mitchell/builds/4.3-arm-none-linux-gnueabi-respin/src/gcc-4.3/configure
--build=i686-pc-linux-gnu --host=i686-pc-linux-gnu
--target=arm-none-linux-gnueabi --enable-threads --disable-libmudflap
--disable-libssp --disable-libstdcxx-pch --with-gnu-as --with-gnu-ld
--with-specs='%{funwind-tables|fno-unwind-tables|mabi=*|ffreestanding|nostdlib:;:-funwind-tables}'
--enable-languages=c,c++ --enable-shared --enable-symvers=gnu
--enable-__cxa_atexit --with-pkgversion='Sourcery G++ Lite 2009q1-203'
--with-bugurl=https://support.codesourcery.com/GNUToolchain/ --disable-nls
--prefix=/opt/codesourcery
--with-sysroot=/opt/codesourcery/arm-none-linux-gnueabi/libc
--with-build-sysroot=/scratch/mitchell/builds/4.3-arm-none-linux-gnueabi-respin/lite/install/arm-none-linux-gnueabi/libc
--with-gmp=/scratch/mitchell/builds/4.3-arm-none-linux-gnueabi-respin/lite/obj/host-libs-2009q1-203-arm-none-linux-gnueabi-i686-pc-linux-gnu/usr
--with-mpfr=/scratch/mitchell/builds/4.3-arm-none-linux-gnueabi-respin/lite/obj/host-libs-2009q1-203-arm-none-linux-gnueabi-i686-pc-linux-gnu/usr
--disable-libgomp --enable-poison-system-directories
--with-build-time-tools=/scratch/mitchell/builds/4.3-arm-none-linux-gnueabi-respin/lite/install/arm-none-linux-gnueabi/bin
--with-build-time-tools=/scratch/mitchell/builds/4.3-arm-none-linux-gnueabi-respin/lite/install/arm-none-linux-gnueabi/bin
Thread model: posix
gcc version 4.3.3 (Sourcery G++ Lite 2009q1-203)
