some quesion about assembly when calling fork
Ben Dooks
ben-linux at fluff.org
Wed Sep 16 10:30:59 EDT 2009
On Wed, Sep 16, 2009 at 10:23:40PM +0800, loody wrote:
> Dear all:
> i copy the assembly code as below, I use uclibc.
>
> if ((pid = fork()) < 0) {
> 84b4: ebffffb5 bl 8390 <.text-0x48>
> 84b8: e1a03000 mov r3, r0
> 84bc: e50b3010 str r3, [fp, #-16] xx1
> 84c0: e51b3010 ldr r3, [fp, #-16] xx2
> 84c4: e3530000 cmp r3, #0 ; 0x0
> 84c8: aa000002 bge 84d8 <main+0x3c>
> printf("fork error");
> 84cc: e59f0040 ldr r0, [pc, #64] ; 8514 <.text
> +0x13c>
> 84d0: ebffffba bl 83c0 <.text-0x18>
> 84d4: ea00000b b 8508 <main+0x6c>
>
> why we store r3 and ld it back at the same place in xx1 and xx2.
> does that have any relationship with fork?
> appreciate your help,
It is possible that the compiler is not being told to optimise enough
and that it is failing to spot that it can fold those together, or that
it think there is somewhere else in the code that could branch back
here.
--
Ben
Q: What's a light-year?
A: One-third less calories than a regular year.
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