Question

I need to access an argument from a C function

void printk(char* msg);

and store it into ESI. However I can not do

mov $msg, %esi

or

mov $_msg, %esi

Both return a linker error (Saying that the symbol msg or _msg is undefined. I am pretty sure I could access msg by reading from the stack but it would be easier just to access the symbol msg in my assembly code. Is this even possible in GCC?

Answer 1

You can’t refer to variables like that in GCC inline assembly. I think you want something like:

 asm("mov %[msg], %%esi",
     : /* no outputs */
     : [msg] "r" (msg)
     : "esi");