[cfe-dev] Status of stack-protector

[Jean-Daniel Dupas]

My bad. I just read a little more how the stack guard works, and saw that the position of the call is good. 
My problem is elsewhere as the behavior is not the same with GCC and clang. I will dig a little deeper to see what the difference is.

Le 8 janv. 2010 à 15:54, Jean-Daniel Dupas a écrit :

> Hello,
> 
> While I was playing with stack protector option, I found a problem.
> 
> In my test program (x86_64), the call to stack_chk_fail is generated after the 'ret' instruction and so is never reached (I'm not an x86 assembly expert, so correct me if I'm wrong on this point)
> 
> -------------------
> 0000000100000ea4	movq	0xd8(%rbp),%rax
> 0000000100000ea8	movq	(%rax),%rax
> 0000000100000eab	movq	0xf8(%rbp),%rcx
> 0000000100000eaf	cmpq	%rcx,%rax
> 0000000100000eb2	jne	0x00000eba
> 0000000100000eb4	addq	$0x40,%rsp
> 0000000100000eb8	popq	%rbp
> 0000000100000eb9	ret
> 0000000100000eba	callq	0x00000ec0
> 
> The same problem occurs on x86 too. I didn't try other arch.
> 
> Is this a known issue ? 
> 
> This is my test file compiled using 
> 
> clang -fstack-protector-all -o stack stack.c
> 
> ------------- stack.c --------------
> 
> #include <libc.h>
> 
> static
> void test(const char *msg) {
>   char buffer[8];
>   bcopy(msg, buffer, strlen(msg) + 1);
>   fprintf(stderr, "%s\n", buffer);
> }
> 
> int main(int argc, const char **argv) {
>   test("Hello World !");
>   return 0;
> }
> 
> ------------------------
> 
> When compiled with gcc, the execution is properly aborted at the end of the test function, but not when compiled with clang.
> 
> -- Jean-Daniel
> 
> 
> 
> 
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-- Jean-Daniel




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