I want to read the stack pointer register value without writing inline assembly.The reason I want to do this is because I want to assign the stack pointer register value to an element of an array and I find it cumbersome to access an array using inline assembly. So I would want to do something like that.
register "rsp" long rsp_alias; <--- How do I achieve something like that in gcc?
long current_rsp_value[NUM_OF_THREADS];
current_rsp_value[tid] = rsp_alias;
Is there anything like that possible with gcc?
There's a shortcut:
register long rsp asm ("rsp");
Demo:
#include<stdio.h>
void foo(void)
{
register long rsp asm ("rsp");
printf("RSP: %lx\n", rsp);
}
int main()
{
register long rsp asm ("rsp");
printf("RSP: %lx\n", rsp);
foo();
return 0;
}
Gives:
$ gdb ./a.out
GNU gdb (Gentoo 7.2 p1) 7.2
...
Reading symbols from /home/user/tmp/a.out...done.
(gdb) break foo
Breakpoint 1 at 0x400538: file t.c, line 7.
(gdb) r
Starting program: /home/user/tmp/a.out
RSP: 7fffffffdb90
Breakpoint 1, foo () at t.c:7
7 printf("RSP: %lx\n", rsp);
(gdb) info registers
....
rsp 0x7fffffffdb80 0x7fffffffdb80
....
(gdb) n
RSP: 7fffffffdb80
8 }
Taken from the Variables in Specified Registers documentation.
register const long rsp_alias asm volatile("rsp");
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