gcc canaries : undefined reference to __stack_chk_guard

Provide __stack_chk_guard with a random value in c file, avoid using regular values like all zero's or FF's because the stack can easily get these values during any memory operation. Wiki on providing magic number implementation. This __stack_chk_guard will be placed at the top and bottom of the stack, which will be checked during every stack access. Any change in the value implies a corrupted stack and returns with error providing the stack protection.

unsigned long __stack_chk_guard;
void __stack_chk_guard_setup(void)
{
     __stack_chk_guard = 0xBAAAAAAD;//provide some magic numbers
}

void __stack_chk_fail(void)                         
{
 /* Error message */                                 
}// will be called when guard variable is corrupted 

It would appear that the -mstack-protector-guard option is only for backwards compatibility with how the stack protector worked in the past. In the past the canary was in a global variable. Later it was switched to TLS. It would appear that the operating system / libc you use either removed or never had support for the global variable canary, so only TLS works.

Don't touch the -mstack-protector-guard option and everything should work. The default should be fine when you use -fstack-protector-all.