Hi there :-)
Im building on a project with the STM32. So using the GCC V 4.3.0
(WinARM_20080331_testing) I got into the following problem:
the usual
while( a <50){
++a;
}
works just fine! Then one time I used :
{
++a;
}while( a<50 );
of course with much more useful contend, than just incrementing a :-)
The result was: it didn't work. But wait: I debugged it with
Insight/OOCD and it went like this:
# entered loop
# executed statements (like ++a;) (checked with memory watch)
# checked condition (which was true, thus not quitting loop)
# DID NOT EXECUTE LOOP AGAIN ????
I did some research and found out, that the jump-mark, to which he
should jump on re-doing the loop was not the beginning of the loop but
the end, thus executing while for infinity (because the condition was
always true).
I thought "OK may be there was something wrong with my setup" so I tried
this:
made 'test.c' with the following contend (and really nothing else):
-------------------------------------------------------------------
int main(){
int b=4;
{
++b;
}while( b<100);
return b;
}
-------------------------------------------------------------------
below you will find the disambling done with insight. You can see that
the jump-mark ('<main+20>')is pointing to the beginning of 'while' not
the beginning of the loop. The cmd to compile was the following:
'arm-eabi-gcc-4.3.0 -mthumb -mcpu=cortex-m3 -g -c test.c -o test.o'
-------------------------------------------------------------------
4 int main(){
- 0x0 <main>: push {r7}
- 0x2 <main+2>: sub sp, #12
- 0x4 <main+4>: add r7, sp, #0
5 int b=4;
- 0x6 <main+6>: mov.w r3, #4 ; 0x4
- 0xa <main+10>: str r3, [r7, #4]
6
7 {
8 ++b;
- 0xc <main+12>: ldr r3, [r7, #4]
- 0xe <main+14>: add.w r3, r3, #1 ; 0x1
- 0x12 <main+18>: str r3, [r7, #4]
9 }while( b<100);
- 0x14 <main+20>: ldr r3, [r7, #4]
- 0x16 <main+22>: cmp r3, #99
- 0x18 <main+24>: ble.n 0x14 <main+20>
10
11 return b;
- 0x1a <main+26>: ldr r3, [r7, #4]
- 0x1c <main+28>: mov r0, r3
- 0x1e <main+30>: add.w r7, r7, #12 ; 0xc
- 0x22 <main+34>: mov sp, r7
- 0x24 <main+36>: pop {r7}
- 0x26 <main+38>: bx lr
-------------------------------------------------------------------
Is this a bug in GCC (I searched the bug list but couldn't find
anything). I cannot imagine that nobody found that before ???
Btw. the sourcery g++ version of GCC did exactly the same.
HELP :-)