假设我想在C中进行JIT编译。我反汇编函数并将其代码插入到我的程序中的内存中:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
void* alloc_executable_memory(size_t size) {
void *ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
if (ptr == MAP_FAILED) {
fprintf(stderr, "%s\n", "mmap failed");
return NULL;
}
return ptr;
}
void push_code_into_memory(unsigned char *memory) {
unsigned char code[] = {
0x48, 0x89, 0xf8, // mov %rdi, %rax
0,48, 0x83, 0xc0, 0x04, // add $4, %rax
0xc3 // ret
};
memcpy(memory, code, sizeof(code));
}
int make_memory_executable(void* memory, size_t size) {
if (mprotect(memory, size, PROT_READ | PROT_EXEC) == -1) {
fprintf(stderr, "%s\n", "mprotect failed");
return -1;
}
return 0;
}
const size_t SIZE = 512;
typedef long (*jitFunc)(long);
int main(int argc, char const *argv[]) {
void *mem = alloc_executable_memory(SIZE);
push_code_into_memory((unsigned char *)mem);
make_memory_executable(mem, SIZE);
jitFunc foo = (jitFunc)mem;
int res = foo(2);
printf("%d\n", res);
return 0;
}
但是,在调用foo之后,我总是得到段错11(macOS)。这段代码有什么问题?首先,我认为问题出在访问权限上,但标志似乎设置正确。
答案 0 :(得分:6)
想想我找到了它:
0,48, 0x83, 0xc0, 0x04
应该是
0x48, 0x83, 0xc0, 0x04