On Sat, Nov 14, 2009 at 1:00 PM, <sudheer.divakaran@xxxxxxxxx> wrote:
> Hi List,
> Sorry for the off topic question. I think I have better chance of getting a
> solution from this list..
>
>
> I was experimenting with x86 assembly under Linux, I have defined two
> functions (AsmFn1,AsmFn2) in a file named asm.s and my main function (c
> function) calls 'AsmFn1' & it calls AsmFn2 before returning.
>
> Everything works fine if I use the c source as the first file while
> compiling
>
> i.e.,
>
> gcc -g -o good test.c asm.s
>
> but, if I use the assembly file as the first file while compiling, when I
> execute the binary, it is giving SEGFAULT while invoking the Assembly
> function 'AsmFn1'.
>
> i.e.,
> gcc -g -o bad asm.s test.c
>
> ./bad will give segfault.
>
> Why is it behaving like this? I'm using FC11 (32 bit) & the gcc comes along
> with it. I'm pasting the source files below..
>
>
>
> asm.s
> -----
> .text
>
> .globl AsmFn1
> .type AsmFn1, @function
> AsmFn1:
> pushl %ebp
> movl %esp, %ebp
> call AsmFn2
> leave
> ret
> .size AsmFn1, .-AsmFn1
>
>
> .globl AsmFn2
> .type AsmFn2,@function
> AsmFn2:
> pushl %ebp
> movl %esp,%ebp
> leave
> .size AsmFn2,.-AsmFn2
>
>
> test.c
> ------
> extern void AsmFn1(void);
>
> int main(void)
> {
> AsmFn1();
> return 0;
> }
>
>
>
>
>
> TIA,
> --
> Sudheer
>
>
>
>
You have not used "ret" instruction in AsmFn2, I guess it will cause
undefined behavior. I think it has nothing to do with how you compile
the code. It works perfectly after adding ret instruction at the end
of AsmFn2. Correct me if I am missing something here.
-Vinit
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