Hello everybody!
We've just pointed out a strange problem with gcc 3.4.0: we use it for
generating ARM 7 processor thumb code.
This strange behavior was pointed out with a function taking 5 parameters (the
fifth one is passed through stack according to the abi spec).
We use the following "test.c" code:
#include <stdio.h>
void trace(int p1, int p2, int p3, int p4, char * message)
{ char temp[512];
printf("msg is: %s", message);
}
the command line for gcc (3.4.0 or 3.4.6) is
gcc.exe -g test.c -o test.o -Os -mcpu=arm7tdmi -mthumb -c
disassembling the output gives:
test.o: file format elf32-littlearm
Disassembly of section .text:
00000000 <trace>:
#include <stdio.h>
void trace(int p1, int p2, int p3, int p4, char * message)
{ char temp[512];
0: b580 push {r7, r14} ==> r7 and r14 are pushed to the
stack
2: 46bc mov r12, r7 ==> r12 = r7
4: 4f05 ldr r7, [pc, #20] (1c <.text+0x1c>) ==> r7 =
-512
6: 44bd add r13, r7 ==> sp += -512
printf("msg is: %s", message);
8: 9981 ldr r1, [sp, #516] ==> /!\ r1 = sp + 516, but
since r7 and r14 were pushed, it should be r1 = sp + 520 /!\
a: 4805 ldr r0, [pc, #20] (20 <.text+0x20>)
c: 4667 mov r7, r12
e: f7ff fffe bl 0 <op_printf>
12: 2380 movs r3, #128
14: 009b lsls r3, r3, #2
16: 449d add r13, r3
18: bd80 pop {r7, r15}
1a: 0000 lsls r0, r0, #0
1c: fe00 ffff mcr2 15, 0, r15, cr0, cr15, {7}
20: 0000 lsls r0, r0, #0
...
When -O2 is used, the output is also wrong, but when compiling with -O1 we get
void trace(int p1, int p2, int p3, int p4, char * message)
{ char temp[512];
0: b500 push {r14}
2: 46bc mov r12, r7
4: 4f05 ldr r7, [pc, #20] (1c <.text+0x1c>)
6: 44bd add r13, r7
8: 4667 mov r7, r12
printf("msg is: %s", message);
a: 4805 ldr r0, [pc, #20] (20 <.text+0x20>)
c: 9981 ldr r1, [sp, #516] ==> r1 = sp + 516, this time
it's good, since only r14 has been pushed!
e: f7ff fffe bl 0 <op_printf>
}
12: 2380 movs r3, #128
14: 009b lsls r3, r3, #2
16: 449d add r13, r3
18: bd00 pop {r15}
1a: 0000 lsls r0, r0, #0
1c: fe00 ffff mcr2 15, 0, r15, cr0, cr15, {7}
20: 0000 lsls r0, r0, #0
...
I've built the gcc 3.4.6 for arm target, and I get the same results. I've
tracked bugzilla entries for such an issue, without success: maybe it's a side
effect of another issue I don't know, but when compiling to generate ARM code,
the output is ok, so it seems particular to thumb mode...
Did someone already encountered this issue? Am I doing something wrong (ok ok,
allocating a 512 bytes buffer on the stack is quite dirty ;=) )?
Should I post a bug entry?
Thx for your attention,
Best regards,
Mick.
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