view sources/toys/readelf.c @ 1021:ae5861222322

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author Rob Landley <>
date Mon, 29 Mar 2010 08:17:24 -0500
parents d29edba5582f
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/* vi: set sw=4 ts=4: */
 * A small little readelf implementation for uClibc
 * Copyright (C) 2000-2006 Erik Andersen <>
 * Copyright (C) 2009 Rob Landley <>
 * Several functions in this file (specifically, elf_find_section_type(),
 * elf_find_phdr_type(), and elf_find_dynamic(), were stolen from elflib.c from
 * elfvector ( by John F. Reiser
 * <>, which is copyright 2000 BitWagon Software LLC
 * (GPL2).
 * Licensed under GPLv2

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>

#include <endian.h>
#include <byteswap.h>
#include <elf.h>
#include <link.h>

static int byteswap;
static __inline__ uint32_t byteswap32_to_host(uint32_t value)
    return byteswap ?  bswap_32(value) : value;
static __inline__ uint64_t byteswap64_to_host(uint64_t value)
    return byteswap ? bswap_64(value) : value;
#if __WORDSIZE == 64
# define byteswap_to_host(x) byteswap64_to_host(x)
# define byteswap_to_host(x) byteswap32_to_host(x)

static ElfW(Shdr) * elf_find_section_type( uint32_t key, ElfW(Ehdr) *ehdr)
    int j;
    ElfW(Shdr) *shdr = (ElfW(Shdr) *)(ehdr->e_shoff + (char *)ehdr);
    for (j = ehdr->e_shnum; --j>=0; ++shdr) {
        if (key==byteswap32_to_host(shdr->sh_type)) {
            return shdr;
    return NULL;

static ElfW(Phdr) * elf_find_phdr_type( uint32_t type, ElfW(Ehdr) *ehdr)
    int j;
    ElfW(Phdr) *phdr = (ElfW(Phdr) *)(ehdr->e_phoff + (char *)ehdr);
    for (j = ehdr->e_phnum; --j>=0; ++phdr) {
        if (type==byteswap32_to_host(phdr->p_type)) {
            return phdr;
    return NULL;

/* Returns value if return_val==1, ptr otherwise */
static void * elf_find_dynamic( int64_t const key, ElfW(Dyn) *dynp,
    ElfW(Ehdr) *ehdr, int return_val)
    ElfW(Phdr) *pt_text = elf_find_phdr_type(PT_LOAD, ehdr);
    ElfW(Addr) tx_reloc = byteswap_to_host(pt_text->p_vaddr) - byteswap_to_host(pt_text->p_offset);
    for (; DT_NULL!=byteswap_to_host(dynp->d_tag); ++dynp) {
        if (key == byteswap_to_host(dynp->d_tag)) {
            if (return_val == 1)
                return (void *)byteswap_to_host(dynp->d_un.d_val);
                return (void *)(byteswap_to_host(dynp->d_un.d_val) - tx_reloc + (char *)ehdr );
    return NULL;

static int check_elf_header(ElfW(Ehdr) *const ehdr)
    if (! ehdr || strncmp((void *)ehdr, ELFMAG, SELFMAG) != 0 ||
            (ehdr->e_ident[EI_CLASS] != ELFCLASS32 &&
             ehdr->e_ident[EI_CLASS] != ELFCLASS64) ||
            ehdr->e_ident[EI_VERSION] != EV_CURRENT)
        return 1;

    /* Check if the target endianness matches the host's endianness */
    byteswap = 0;
    if (ehdr->e_ident[5] == ELFDATA2MSB) {
        /* Ick -- we will have to byte-swap everything */
        byteswap = 1;
    if (ehdr->e_ident[5] == ELFDATA2LSB) {
        byteswap = 1;
#error Unknown host byte order!
    /* Be vary lazy, and only byteswap the stuff we use */
    if (byteswap==1) {
    return 0;

static void describe_elf_hdr(ElfW(Ehdr)* ehdr)
    char *tmp, *tmp1;

    switch (ehdr->e_type) {
        case ET_NONE:    tmp = "None"; tmp1 = "NONE"; break;
        case ET_REL:    tmp = "Relocatable File"; tmp1 = "REL"; break;
        case ET_EXEC:    tmp = "Executable file"; tmp1 = "EXEC"; break;
        case ET_DYN:    tmp = "Shared object file"; tmp1 = "DYN"; break;
        case ET_CORE:    tmp = "Core file"; tmp1 = "CORE"; break;
                        tmp = tmp1 = "Unknown";
    printf( "Type:\t\t%s (%s)\n", tmp1, tmp);

    switch (ehdr->e_machine) {
        case EM_NONE:        tmp="No machine"; break;
        case EM_M32:        tmp="AT&T WE 32100"; break;
        case EM_SPARC:        tmp="SUN SPARC"; break;
        case EM_386:        tmp="Intel 80386"; break;
        case EM_68K:        tmp="Motorola m68k family"; break;
        case EM_88K:        tmp="Motorola m88k family"; break;
//        case EM_486:        tmp="Intel 80486"; break;
        case EM_860:        tmp="Intel 80860"; break;
        case EM_MIPS:        tmp="MIPS R3000 big-endian"; break;
        case EM_S370:        tmp="IBM System/370"; break;
        case EM_MIPS_RS3_LE:    tmp="MIPS R3000 little-endian"; break;
//        case EM_OLD_SPARCV9:    tmp="Sparc v9 (old)"; break;
        case EM_PARISC:        tmp="HPPA"; break;
        /*case EM_PPC_OLD:    tmp="Power PC (old)"; break;  conflicts with EM_VPP500 */
        case EM_SPARC32PLUS:    tmp="Sun's v8plus"; break;
        case EM_960:        tmp="Intel 80960"; break;
        case EM_PPC:        tmp="PowerPC"; break;
        case EM_PPC64:        tmp="PowerPC 64-bit"; break;
        case EM_V800:        tmp="NEC V800 series"; break;
        case EM_FR20:        tmp="Fujitsu FR20"; break;
        case EM_RH32:        tmp="TRW RH-32"; break;
//        case EM_MCORE:        tmp="MCORE"; break;
        case EM_ARM:        tmp="ARM"; break;
        case EM_FAKE_ALPHA:    tmp="Digital Alpha"; break;
        case EM_SH:            tmp="Renesas SH"; break;
        case EM_SPARCV9:    tmp="SPARC v9 64-bit"; break;
        case EM_TRICORE:    tmp="Siemens Tricore"; break;
        case EM_ARC:        tmp="Argonaut RISC Core"; break;
        case EM_H8_300:        tmp="Renesas H8/300"; break;
        case EM_H8_300H:    tmp="Renesas H8/300H"; break;
        case EM_H8S:        tmp="Renesas H8S"; break;
        case EM_H8_500:        tmp="Renesas H8/500"; break;
        case EM_IA_64:        tmp="Intel Merced"; break;
        case EM_MIPS_X:        tmp="Stanford MIPS-X"; break;
        case EM_COLDFIRE:    tmp="Motorola Coldfire"; break;
        case EM_68HC12:        tmp="Motorola M68HC12"; break;
        case EM_ALPHA:        tmp="Alpha"; break;
//        case EM_CYGNUS_D10V:
        case EM_D10V:        tmp="Mitsubishi D10V"; break;
//        case EM_CYGNUS_D30V:
        case EM_D30V:        tmp="Mitsubishi D30V"; break;
//        case EM_CYGNUS_M32R:
        case EM_M32R:        tmp="Renesas M32R (formerly Mitsubishi M32r)"; break;
//        case EM_CYGNUS_V850:
        case EM_V850:        tmp="NEC v850"; break;
//        case EM_CYGNUS_MN10300:
        case EM_MN10300:    tmp="Matsushita MN10300"; break;
//        case EM_CYGNUS_MN10200:
        case EM_MN10200:    tmp="Matsushita MN10200"; break;
//        case EM_CYGNUS_FR30:
        case EM_FR30:        tmp="Fujitsu FR30"; break;
//        case EM_CYGNUS_FRV:
//        case EM_PJ_OLD:
        case EM_PJ:            tmp="picoJava"; break;
        case EM_MMA:        tmp="Fujitsu MMA Multimedia Accelerator"; break;
        case EM_PCP:        tmp="Siemens PCP"; break;
        case EM_NCPU:        tmp="Sony nCPU embeeded RISC"; break;
        case EM_NDR1:        tmp="Denso NDR1 microprocessor"; break;
        case EM_STARCORE:    tmp="Motorola Start*Core processor"; break;
        case EM_ME16:        tmp="Toyota ME16 processor"; break;
        case EM_ST100:        tmp="STMicroelectronic ST100 processor"; break;
        case EM_TINYJ:        tmp="Advanced Logic Corp. Tinyj emb.fam"; break;
        case EM_FX66:        tmp="Siemens FX66 microcontroller"; break;
        case EM_ST9PLUS:    tmp="STMicroelectronics ST9+ 8/16 mc"; break;
        case EM_ST7:        tmp="STmicroelectronics ST7 8 bit mc"; break;
        case EM_68HC16:        tmp="Motorola MC68HC16 microcontroller"; break;
        case EM_68HC11:        tmp="Motorola MC68HC11 microcontroller"; break;
        case EM_68HC08:        tmp="Motorola MC68HC08 microcontroller"; break;
        case EM_68HC05:        tmp="Motorola MC68HC05 microcontroller"; break;
        case EM_SVX:        tmp="Silicon Graphics SVx"; break;
        case EM_ST19:        tmp="STMicroelectronics ST19 8 bit mc"; break;
        case EM_VAX:        tmp="Digital VAX"; break;
//        case EM_AVR_OLD:
        case EM_AVR:        tmp="Atmel AVR 8-bit microcontroller"; break;
        case EM_CRIS:        tmp="Axis Communications 32-bit embedded processor"; break;
        case EM_JAVELIN:    tmp="Infineon Technologies 32-bit embedded processor"; break;
        case EM_FIREPATH:    tmp="Element 14 64-bit DSP Processor"; break;
        case EM_ZSP:        tmp="LSI Logic 16-bit DSP Processor"; break;
        case EM_MMIX:        tmp="Donald Knuth's educational 64-bit processor"; break;
        case EM_HUANY:        tmp="Harvard University machine-independent object files"; break;
        case EM_PRISM:        tmp="SiTera Prism"; break;
        case EM_X86_64:        tmp="AMD x86-64 architecture"; break;
//        case EM_S390_OLD:
        case EM_S390:        tmp="IBM S390"; break;
//        case EM_XSTORMY16:    tmp="Sanyo Xstormy16 CPU core"; break;
        case EM_OPENRISC:
//        case EM_OR32:        tmp="OpenRISC"; break;
//        case EM_CRX:        tmp="National Semiconductor CRX microprocessor"; break;
//        case EM_DLX:        tmp="OpenDLX"; break;
//        case EM_IP2K_OLD:
//        case EM_IP2K:        tmp="Ubicom IP2xxx 8-bit microcontrollers"; break;
//        case EM_IQ2000:        tmp="Vitesse IQ2000"; break;
//        case EM_XTENSA_OLD:
        case EM_XTENSA:        tmp="Tensilica Xtensa Processor"; break;
//        case EM_M32C:        tmp="Renesas M32c"; break;
//        case EM_MT:            tmp="Morpho Techologies MT processor"; break;
//        case EM_BLACKFIN:    tmp="Analog Devices Blackfin"; break;
//        case EM_NIOS32:        tmp="Altera Nios 32"; break;
//        case EM_ALTERA_NIOS2:    tmp="Altera Nios II"; break;
        case EM_VPP500:        tmp="Fujitsu VPP500"; break;
        case EM_PDSP:        tmp="Sony DSP Processor"; break;
        default:            tmp="unknown";
    printf( "Machine:\t%s\n", tmp);

    switch (ehdr->e_ident[EI_CLASS]) {
        case ELFCLASSNONE: tmp = "Invalid class";  break;
        case ELFCLASS32:   tmp = "ELF32"; break;
        case ELFCLASS64:   tmp = "ELF64"; break;
        default:           tmp = "Unknown";
    printf( "Class:\t\t%s\n", tmp);

    switch (ehdr->e_ident[EI_DATA]) {
        case ELFDATANONE:  tmp = "Invalid data encoding"; break;
        case ELFDATA2LSB:  tmp = "2's complement, little endian"; break;
        case ELFDATA2MSB:  tmp = "2's complement, big endian"; break;
        default:           tmp = "Unknown";
    printf( "Data:\t\t%s\n", tmp);

    printf( "Version:\t%d %s\n", ehdr->e_ident[EI_VERSION],
            "(current)" : "(unknown: %lx)");

    switch (ehdr->e_ident[EI_OSABI]) {
        case ELFOSABI_SYSV:       tmp ="UNIX - System V"; break;
        case ELFOSABI_HPUX:       tmp ="UNIX - HP-UX"; break;
        case ELFOSABI_NETBSD:     tmp ="UNIX - NetBSD"; break;
        case ELFOSABI_LINUX:      tmp ="UNIX - Linux"; break;
//        case ELFOSABI_HURD:       tmp ="GNU/Hurd"; break;
        case ELFOSABI_SOLARIS:    tmp ="UNIX - Solaris"; break;
        case ELFOSABI_AIX:        tmp ="UNIX - AIX"; break;
        case ELFOSABI_IRIX:       tmp ="UNIX - IRIX"; break;
        case ELFOSABI_FREEBSD:    tmp ="UNIX - FreeBSD"; break;
        case ELFOSABI_TRU64:      tmp ="UNIX - TRU64"; break;
        case ELFOSABI_MODESTO:    tmp ="Novell - Modesto"; break;
        case ELFOSABI_OPENBSD:    tmp ="UNIX - OpenBSD"; break;
        case ELFOSABI_STANDALONE: tmp ="Standalone App"; break;
        case ELFOSABI_ARM:        tmp ="ARM"; break;
        default:                  tmp = "Unknown";
    printf( "OS/ABI:\t\t%s\n", tmp);

    printf( "ABI Version:\t%d\n", ehdr->e_ident[EI_ABIVERSION]);

static void list_needed_libraries(ElfW(Dyn)* dynamic, char *strtab)
    ElfW(Dyn)  *dyns;

    for (dyns=dynamic; byteswap_to_host(dyns->d_tag)!=DT_NULL; ++dyns) {
        if (dyns->d_tag == DT_NEEDED) {
            printf("\t%s\n", (char*)strtab + byteswap_to_host(dyns->d_un.d_val));

static void describe_elf_interpreter(ElfW(Ehdr)* ehdr)
    ElfW(Phdr) *phdr;
    phdr = elf_find_phdr_type(PT_INTERP, ehdr);
    if (phdr) {
        printf("Interpreter:\t%s\n", (char*)ehdr + byteswap_to_host(phdr->p_offset));

int main( int argc, char** argv)
    /* map the .so, and locate interesting pieces */
    char *dynstr;
    char *thefilename = argv[1];
    FILE *thefile;
    struct stat statbuf;
    ElfW(Ehdr) *ehdr = 0;
    ElfW(Shdr) *dynsec;
    ElfW(Dyn) *dynamic;

    if (!thefilename) {
        fprintf(stderr, "Usage: readelf FILENAME\n");
    if (!(thefile = fopen(thefilename, "r"))) {
    if (fstat(fileno(thefile), &statbuf) < 0) {

    if ((size_t)statbuf.st_size < sizeof(ElfW(Ehdr)))
        goto foo;

    /* mmap the file to make reading stuff from it effortless */
    ehdr = (ElfW(Ehdr) *)mmap(0, statbuf.st_size,
            PROT_READ|PROT_WRITE, MAP_PRIVATE, fileno(thefile), 0);

    /* Check if this looks legit */
    if (check_elf_header(ehdr)) {
        fprintf(stderr, "This does not appear to be an ELF file.\n");

    dynsec = elf_find_section_type(SHT_DYNAMIC, ehdr);
    if (dynsec) {
        dynamic = (ElfW(Dyn)*)(byteswap_to_host(dynsec->sh_offset) + (char *)ehdr);
        dynstr = (char *)elf_find_dynamic(DT_STRTAB, dynamic, ehdr, 0);
        list_needed_libraries(dynamic, dynstr);

    return 0;