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Baby's First JIT
#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <sys/mman.h>
#include <unistd.h>
#include <err.h>
#include <sysexits.h>
typedef int32_t (*fptr)(int32_t);
int main(int argc, char *argv[]) {
int page = getpagesize();
uint8_t *code = mmap(NULL, page, PROT_READ | PROT_WRITE, MAP_ANON | MAP_PRIVATE, -1, 0);
if (code == MAP_FAILED) err(EX_OSERR, "mmap");
if (argc < 2) return EX_USAGE;
int32_t term = (int32_t)strtol(argv[1], NULL, 10);
code[0] = 0x48;
code[1] = 0xc7;
code[2] = 0xc0;
code[3] = (uint8_t)term;
code[4] = (uint8_t)(term >> 8);
code[5] = (uint8_t)(term >> 16);
code[6] = (uint8_t)(term >> 24);
code[7] = 0x48;
code[8] = 0x01;
code[9] = 0xf8;
code[10] = 0xc3;
int error = mprotect(code, page, PROT_READ | PROT_EXEC);
if (error) err(EX_OSERR, "mprotect");
fptr fn = (fptr)code;
printf("%d %d %d\n", fn(1), fn(2), fn(3));
return EX_OK;
}
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