 1// By GPT-4; slightly modified
 2
 3#include <stdio.h>
 4#include <stdint.h>
 5#include <stdlib.h>
 6#include <fcntl.h>
 7#include <unistd.h>
 8#include <dlfcn.h>
 9
10#define PAGE_SHIFT 12
11#define PAGEMAP_LENGTH 8
12
13void *get_physical_address(void *va) {
14    int pagemap_fd;
15    uint64_t value;
16    uint64_t file_offset = ((uint64_t)va / (1ULL << PAGE_SHIFT)) * PAGEMAP_LENGTH;
17    char pagemap_file[64];
18
19    sprintf(pagemap_file, "/proc/%d/pagemap", getpid());
20    pagemap_fd = open(pagemap_file, O_RDONLY);
21    if (pagemap_fd < 0) {
22        perror("Error opening pagemap file");
23        return NULL;
24    }
25
26    if (pread(pagemap_fd, &value, PAGEMAP_LENGTH, file_offset) != PAGEMAP_LENGTH) {
27        perror("Error reading pagemap");
28        close(pagemap_fd);
29        return NULL;
30    }
31
32    close(pagemap_fd);
33
34    if (value & (1ULL << 63)) {
35        return (void*)(((value & ((1ULL << 55) - 1)) << PAGE_SHIFT)
36          + ((uint64_t)va & ((1ULL << PAGE_SHIFT) - 1)));
37    } else {
38        return NULL;
39    }
40}
41
42int main() {
43    void *handle;
44    void (*printf_ptr)(const char *, ...);
45
46    // Load the libc library
47    handle = dlopen("libc.so.6", RTLD_LAZY);
48    if (!handle) {
49        fprintf(stderr, "Error: %s\n", dlerror());
50        return 1;
51    }
52
53    // Get the address of printf
54    printf_ptr = dlsym(handle, "printf");
55    if (!printf_ptr) {
56        fprintf(stderr, "Error: %s\n", dlerror());
57        dlclose(handle);
58        return 1;
59    }
60
61    // Close the library handle
62    dlclose(handle);
63
64    char *ptr = malloc(1);
65
66    printf("ptr: %p -> %p\n", ptr, get_physical_address(ptr));
67    printf("main: %p -> %p\n", main, get_physical_address(main));
68    printf("printf: %p -> %p\n", printf_ptr, get_physical_address(printf_ptr));
69
70    free(ptr);
71
72    while (1) {
73      sleep(1);
74    }
75
76    return 0;
77}
24. 进程的实现¶

Take-away Messages¶

1. 阅读材料¶
