Hello Peter,
On Thu, Dec 17, 2009 at 11:24:55AM +0100, Peter Korsgaard wrote:
> >>>>> "Sascha" == Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> writes:
>
> >> > doh! I'm out of brown paper bags.
> >> instead of sizeof("...") - 1, strlen should work.
>
> Sascha> Yes, it works, but adds to the binary space. This doesn't matter in this
> Sascha> case since the binary size does not really matter for the sandbox, but
> Sascha> we don't want other people to copy such things.
>
> Notice that this is in fs/cramfs/crams.c, so not specific to sandbox. I
> would imagine gcc would be smart enough to replace strlen("/dev/") with
> the constant 5, but apparently not:
>
> nm -S fs/cramfs/cramfs.o{.orig,}|grep cramfs_probe
> 0000000000000053 000000000000015d t cramfs_probe
> 0000000000000053 000000000000016f t cramfs_probe
hmmmm, I have here:
ukleinek@cassiopeia:~$ cat test.c
#include <string.h>
size_t strlen(const char *s)
{
return 2;
}
int main(int argc, char **argv)
{
printf("strlen(\"Peter Korsgaard\") = %d\n", strlen("Peter Korsgaard"));
return 0;
}
ukleinek@cassiopeia:~$ gcc test.c -o test
ukleinek@cassiopeia:~$ ./test
strlen("Peter Korsgaard") = 15
So the compiler *is* smart. (Maybe even smarter than most people
expect.)
Compiling that with an arm compiler and disassembling yields:
00000000 <strlen>:
0: e1a0c00d mov ip, sp
4: e92dd800 push {fp, ip, lr, pc}
8: e24cb004 sub fp, ip, #4 ; 0x4
c: e24dd008 sub sp, sp, #8 ; 0x8
10: e50b0010 str r0, [fp, #-16]
14: e3a03002 mov r3, #2 ; 0x2
18: e1a00003 mov r0, r3
1c: e24bd00c sub sp, fp, #12 ; 0xc
20: e89da800 ldm sp, {fp, sp, pc}
00000024 <main>:
24: e1a0c00d mov ip, sp
28: e92dd800 push {fp, ip, lr, pc}
2c: e24cb004 sub fp, ip, #4 ; 0x4
30: e24dd008 sub sp, sp, #8 ; 0x8
34: e50b0010 str r0, [fp, #-16]
38: e50b1014 str r1, [fp, #-20]
3c: e59f0014 ldr r0, [pc, #20] ; 58 <main+0x34>
40: e3a0100f mov r1, #15 ; 0xf
44: ebfffffe bl 0 <printf>
48: e3a03000 mov r3, #0 ; 0x0
4c: e1a00003 mov r0, r3
50: e24bd00c sub sp, fp, #12 ; 0xc
54: e89da800 ldm sp, {fp, sp, pc}
58: 00000000 .word 0x00000000
So the 15 is hardcoded as you can see at address 40.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
_______________________________________________
barebox mailing list
barebox@xxxxxxxxxxxxxxxxxxx
http://lists.infradead.org/mailman/listinfo/barebox
