[cfe-dev] Status of stack-protector

[Jean-Daniel Dupas]

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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