test code for indirect call elimination in runtime with runtime code generation

runtime_indirect_remover.c

#include <stdlib.h>
#include <stdio.h>
#include <sys/mman.h>
#include <error.h>
#include <stdint.h>

// int mprotect(void *addr, size_t len, int prot);

__attribute__((noinline))
int foo(int a1, int a2, int a3)
{
	return a1 + a2 + a3;
}
int (* const pfoo)(int a1, int a2, int a3) = foo;


__attribute__((noinline))
int indirect(int a1, int a2, int a3)
{
	return pfoo(a1, a2, a3);
}

void unlock_mem(void *ptr)
{
	long vaddr = (long)ptr;
	vaddr = vaddr / 4096 * 4096;

	int res = mprotect((void *)(vaddr), 4096 * 2, PROT_WRITE | PROT_READ | PROT_EXEC);
	if (res) {
		perror("!");
		exit(1);
	}
}


int main()
{
	int64_t stub = (int64_t)&indirect;
	int64_t real = (int64_t)&foo;
	unlock_mem((void *)stub);
	ssize_t diff = stub - real;

	char *pre = (char *)stub;
	pre += 16;
	pre[0] = 0xE9;
	uint32_t *offset = (uint32_t *)(pre + 1);
	offset[0] = diff + 1 + 4;

	fprintf(stderr, "Yep!");

	printf("%i\n", indirect(13, 66, 666));
	return 0;
}