debugger_jit_test.m

#import <Foundation/Foundation.h>
#import <mach/mach.h>
#import <stdio.h>
#import <stdlib.h>
#import <string.h>

#define PAGE 0x4000

__attribute__((section("__TEXT,__nop_section"), aligned(PAGE)))
static const uint32_t nop_page[PAGE / sizeof(uint32_t)] = {
    [0 ... (PAGE / sizeof(uint32_t)) - 1] = 0x1F2003D5 // nop
};

typedef int (*JitFunction)(void);

void write_instructions(void *page) {
    uint32_t instructions[] = {
        0x52800540, // mov w0, #42
        0xD65F03C0  // ret
    };

    memcpy(page, instructions, sizeof(instructions));
}

int main(int argc, char *argv[]) {
    void *page = (void *)nop_page;
    printf("NOP page address: %p\n", page);
    
    // Set page to RW (PROT_READ | PROT_WRITE | PROT_COPY)
    kern_return_t kr = vm_protect(mach_task_self_, (mach_vm_address_t)page, PAGE, FALSE, VM_PROT_READ | VM_PROT_WRITE | VM_PROT_COPY);
    if (kr != KERN_SUCCESS) {
        fprintf(stderr, "Failed to set RW protection: %d\n", kr);
        return 1;
    }

    // Write new instructions
    write_instructions(page);
    
    // Set page to RX (PROT_READ | PROT_EXEC)
    kr = vm_protect(mach_task_self_, (mach_vm_address_t)page, PAGE, FALSE, VM_PROT_READ | VM_PROT_EXECUTE);
    if (kr != KERN_SUCCESS) {
        fprintf(stderr, "Failed to set RX protection: %d\n", kr);
        return 1;
    }

    JitFunction func = (JitFunction)page;
    int result = func();
    printf("Executed JIT-ed function, result: %d\n", result); // Should print 42

    return 0;
}