Created
October 13, 2016 03:09
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Baby's First JIT
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| #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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