How to get the VDSO and see what's inside

getvdso.c

#include <sys/auxv.h>
#include <stdlib.h>
#include <unistd.h>
#include <elf.h>

#ifdef __LP64__
typedef Elf64_auxv_t Elf_auxv_t;
typedef Elf64_Ehdr Elf_Ehdr;
typedef Elf64_Phdr Elf_Phdr;
#else
typedef Elf32_auxv_t Elf_auxv_t;
typedef Elf32_Ehdr Elf_Ehdr;
typedef Elf32_Phdr Elf_Phdr;
#endif

int
main(int argc, char *argv[], char **environ)
{
    // First, skip the environment.
    void **vpp = (void **)environ;
    while (*vpp++)
        ;
    // vpp now points to the first auxv entry.
    for (Elf_auxv_t *auxvp = (Elf_auxv_t *)vpp; auxvp->a_type != AT_NULL; ++auxvp) {
        if (auxvp->a_type == AT_SYSINFO_EHDR) {
            // Find the end of the executable, either the end of the last segment,
            // or the end of the section headers.
            char *exebase = (char *)auxvp->a_un.a_val;
            Elf_Ehdr *ehdr = (Elf_Ehdr *)exebase;
            Elf_Phdr *phdr = (Elf_Phdr *)(exebase + ehdr->e_phoff);
            size_t i;
            size_t size = 0;

            for (i = 0; i < ehdr->e_phnum; ++i) {
                size_t hdrend = phdr[i].p_offset + phdr[i].p_filesz;
                if (hdrend > size)
                    size = hdrend;
            }

            size_t section_end = ehdr->e_shoff + ehdr->e_shnum * ehdr->e_shentsize;
            if (section_end > size)
               size = section_end;

            while (size) {
                ssize_t chunk = write(1, exebase, size);
                if (chunk == -1)
                    abort();
                size -= chunk;
                exebase += chunk;
            }
            break;
        }
    }
}