https://linux.die.net/man/3/dl_iterate_phdr (opens new window)

通过dl_iterate_phdr遍历so的linkmap，获取so加载地址

elf_utils.h

#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
#include <stdio.h>
#include <link.h>
#include <string.h>

/**
 * ref: 
 *    https://stackoverflow.com/questions/19451791/get-loaded-address-of-a-elf-binary-dlopen-is-not-working-as-expected
 *    https://linux.die.net/man/3/dl_iterate_phdr
 * 
**/

typedef struct CbData_t {
    char in_so_name[1024]; //input
    void *so_addr; //output
    size_t so_size; //output
}CbData;

extern "C" int __libc_csu_init(); //near 0x400920
extern "C" int __libc_start_main(); //__libc_start_main@GLIBC_2.2.5
extern "C" int _start(); //near 0x400610


// iterator all shared objects, or iterator unitl this callback return none 0
static int dl_iter_callback(struct dl_phdr_info *info, size_t size, void *data)
{
    CbData *cbdata = (CbData *)data;
    printf("======dl_iter_callback: %s @ %#lx\n", info->dlpi_name, (unsigned long)info->dlpi_addr);
    if(strstr(info->dlpi_name, cbdata->in_so_name)) {
        cbdata->so_addr = (char *)info->dlpi_addr;
    }

    int j;
    const char *main_addr = (const char *)&_start;
    const char *base = (const char *)info->dlpi_addr;
    const ElfW(Phdr) *first_load = NULL;

    for (j = 0; j < info->dlpi_phnum; j++) {
      const ElfW(Phdr) *phdr = &info->dlpi_phdr[j];

      if (phdr->p_type == PT_LOAD) {
        const char *begin = base + phdr->p_vaddr;
        const char *end = begin + phdr->p_memsz;

        printf("    in [%s] load %p->%p size=%ld\n", info->dlpi_name, begin, end, end-begin);

        if (first_load == NULL) first_load = phdr;
        if (begin <= main_addr && main_addr < end) {
          // Found PT_LOAD that "covers" callback().
          printf("    --main ELF header is at %p, image linked at 0x%zx, relocation: 0x%zx\n",
                base + first_load->p_vaddr, first_load->p_vaddr, info->dlpi_addr); 
                //elf_header=0x400000, image_link=0x400000, relocation: 0x0
          // return 0;
        }
      }
    }

    return 0;
}


// get so load addr. so_name should be smaller than 1024
__attribute__((visibility("default")))
void *get_so_addr(const char *so_name) {
    if(!so_name) return NULL;
    CbData cbdata;
    bzero(&cbdata, sizeof(CbData));
    strncpy(cbdata.in_so_name, so_name, sizeof(cbdata.so_addr));
    dl_iterate_phdr(&dl_iter_callback, &cbdata);
    if(cbdata.so_addr) {
        return cbdata.so_addr;
    }
    return nullptr;
}



int main(int argc, char *argv[])
{
    void *addr = get_so_addr("libc.so.6");
    printf("\nget addr of libc.so.6: %p\n", addr);

    addr = get_so_addr("libgcc");
    printf("\nget addr of libgcc: %p\n", addr);

    printf("main end\n");
    getchar();  //  cat /proc/`pgrep demo`/maps
    return 0;
}