libc/bionic/dl_iterate_phdr_static.c

/*
 * Copyright (C) 2006 The Android Open Source Project
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *  * Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *  * Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <elf.h>
#include <sys/auxv.h>
#include <sys/types.h>
#include <link.h>

/* ld provides this to us in the default link script */
extern void* __executable_start;

int dl_iterate_phdr(int (*cb)(struct dl_phdr_info* info, size_t size, void* data), void* data) {
    Elf32_Ehdr* ehdr = (Elf32_Ehdr*) &__executable_start;

    // TODO: again, copied from linker.c. Find a better home for this later.
    if (ehdr->e_ident[EI_MAG0] != ELFMAG0) return -1;
    if (ehdr->e_ident[EI_MAG1] != ELFMAG1) return -1;
    if (ehdr->e_ident[EI_MAG2] != ELFMAG2) return -1;
    if (ehdr->e_ident[EI_MAG3] != ELFMAG3) return -1;

    // Dynamic binaries get their dl_iterate_phdr from the dynamic linker, but
    // static binaries get this. We don't have a list of shared objects to
    // iterate over, since there's really only a single monolithic blob of
    // code/data, plus optionally a VDSO.

    struct dl_phdr_info exe_info;
    exe_info.dlpi_addr = 0;
    exe_info.dlpi_name = NULL;
    exe_info.dlpi_phdr = (Elf32_Phdr*) ((unsigned long) ehdr + ehdr->e_phoff);
    exe_info.dlpi_phnum = ehdr->e_phnum;

#ifdef AT_SYSINFO_EHDR
    // Try the executable first.
    int rc = cb(&exe_info, sizeof(exe_info), data);
    if (rc != 0) {
        return rc;
    }

    // Try the VDSO if that didn't work.
    Elf32_Ehdr* ehdr_vdso = (Elf32_Ehdr*) getauxval(AT_SYSINFO_EHDR);
    struct dl_phdr_info vdso_info;
    vdso_info.dlpi_addr = 0;
    vdso_info.dlpi_name = NULL;
    vdso_info.dlpi_phdr = (Elf32_Phdr*) ((char*) ehdr_vdso + ehdr_vdso->e_phoff);
    vdso_info.dlpi_phnum = ehdr_vdso->e_phnum;
    for (size_t i = 0; i < vdso_info.dlpi_phnum; ++i) {
        if (vdso_info.dlpi_phdr[i].p_type == PT_LOAD) {
            vdso_info.dlpi_addr = (Elf32_Addr) ehdr_vdso - vdso_info.dlpi_phdr[i].p_vaddr;
            break;
        }
    }
    return cb(&vdso_info, sizeof(vdso_info), data);
#else
    // There's only the executable to try.
    return cb(&exe_info, sizeof(exe_info), data);
#endif
}