Add scncopy - like object copy but tries not to change section content
This adds scncopy, which is like objcopy with some differences: - it doesn't try to update section contents, but does try to update program headers and such to correctly reflect the section contents. - it doesn't necessarily try to create a binary eu-elflint will like. If you don't copy a required section, it won't make it for you. TODO: - Make it possible to copy sections to an already existant binary. - Make phdrs only copy if they're needed, and/or modify old phdrs to point to new sections - Make sure nothing is missing from fixup_dynamic() Signed-off-by: Peter Jones <pjones@redhat.com> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Peter Jones
Arnaldo Carvalho de Melo
parent
537db1da2d
commit
29ef465cd8
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@ -0,0 +1,297 @@
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/*
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* Copyright 2009 Red Hat, Inc.
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of version 2 of the GNU General Public License as
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* published by the Free Software Foundation.
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*
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* Author: Peter Jones <pjones@redhat.com>
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*/
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#include <dlfcn.h>
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#include <gelf.h>
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#include <stdio.h>
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#include <strings.h>
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#include <string.h>
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#include <fcntl.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <assert.h>
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#include "elfcreator.h"
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struct elf_creator {
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const char *path;
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int fd;
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Elf *elf;
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GElf_Ehdr *ehdr, ehdr_mem;
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Elf *oldelf;
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/* just because we have to look this up /so/ often... */
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Elf_Scn *dynscn;
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GElf_Shdr *dynshdr, dynshdr_mem;
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Elf_Data *dyndata;
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};
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static void clear(ElfCreator *ctor, int do_unlink)
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{
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if (do_unlink) {
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if (ctor->elf)
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elf_end(ctor->elf);
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if (ctor->fd >= 0)
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close(ctor->fd);
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if (ctor->path)
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unlink(ctor->path);
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} else {
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if (ctor->elf) {
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elf_update(ctor->elf, ELF_C_WRITE_MMAP);
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elf_end(ctor->elf);
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}
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if (ctor->fd >= 0)
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close(ctor->fd);
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}
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memset(ctor, '\0', sizeof(*ctor));
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}
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ElfCreator *elfcreator_begin(char *path, Elf *elf) {
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ElfCreator *ctor = NULL;
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GElf_Ehdr ehdr_mem, *ehdr;
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GElf_Half machine;
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if (!(ctor = calloc(1, sizeof(*ctor))))
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return NULL;
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clear(ctor, 0);
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ctor->path = path;
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ctor->oldelf = elf;
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ehdr = gelf_getehdr(elf, &ehdr_mem);
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machine = ehdr->e_machine;
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if ((ctor->fd = open(path, O_RDWR|O_CREAT|O_TRUNC, 0755)) < 0) {
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err:
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clear(ctor, 1);
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free(ctor);
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return NULL;
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}
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if (!(ctor->elf = elf_begin(ctor->fd, ELF_C_WRITE_MMAP, elf)))
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goto err;
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gelf_newehdr(ctor->elf, gelf_getclass(elf));
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gelf_update_ehdr(ctor->elf, ehdr);
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if (!(ctor->ehdr = gelf_getehdr(ctor->elf, &ctor->ehdr_mem)))
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goto err;
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return ctor;
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}
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static Elf_Scn *get_scn_by_type(ElfCreator *ctor, Elf64_Word sh_type)
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{
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Elf_Scn *scn = NULL;
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while ((scn = elf_nextscn(ctor->elf, scn)) != NULL) {
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GElf_Shdr *shdr, shdr_mem;
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shdr = gelf_getshdr(scn, &shdr_mem);
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if (shdr->sh_type == sh_type)
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return scn;
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}
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return NULL;
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}
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static void update_dyn_cache(ElfCreator *ctor)
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{
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ctor->dynscn = get_scn_by_type(ctor, SHT_DYNAMIC);
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if (ctor->dynscn == NULL)
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return;
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ctor->dynshdr = gelf_getshdr(ctor->dynscn, &ctor->dynshdr_mem);
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ctor->dyndata = elf_getdata(ctor->dynscn, NULL);
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}
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void elfcreator_copy_scn(ElfCreator *ctor, Elf *src, Elf_Scn *scn)
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{
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Elf_Scn *newscn;
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Elf_Data *indata, *outdata;
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GElf_Shdr *oldshdr, oldshdr_mem;
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GElf_Shdr *newshdr, newshdr_mem;
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newscn = elf_newscn(ctor->elf);
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newshdr = gelf_getshdr(newscn, &newshdr_mem);
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oldshdr = gelf_getshdr(scn, &oldshdr_mem);
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memmove(newshdr, oldshdr, sizeof(*newshdr));
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gelf_update_shdr(newscn, newshdr);
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indata = NULL;
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while ((indata = elf_getdata(scn, indata)) != NULL) {
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outdata = elf_newdata(newscn);
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*outdata = *indata;
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}
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if (newshdr->sh_type == SHT_DYNAMIC)
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update_dyn_cache(ctor);
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}
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static GElf_Dyn *get_dyn_by_tag(ElfCreator *ctor, Elf64_Sxword d_tag,
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GElf_Dyn *mem, size_t *idx)
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{
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size_t cnt;
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if (!ctor->dyndata)
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return NULL;
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for (cnt = 1; cnt < ctor->dynshdr->sh_size / ctor->dynshdr->sh_entsize;
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cnt++) {
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GElf_Dyn *dyn;
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if ((dyn = gelf_getdyn(ctor->dyndata, cnt, mem)) == NULL)
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break;
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if (dyn->d_tag == d_tag) {
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*idx = cnt;
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return dyn;
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}
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}
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return NULL;
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}
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static void remove_dyn(ElfCreator *ctor, size_t idx)
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{
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size_t cnt;
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for (cnt = idx; cnt < ctor->dynshdr->sh_size/ctor->dynshdr->sh_entsize;
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cnt++) {
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GElf_Dyn *dyn, dyn_mem;
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if (cnt+1 == ctor->dynshdr->sh_size/ctor->dynshdr->sh_entsize) {
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memset(&dyn_mem, '\0', sizeof(dyn_mem));
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gelf_update_dyn(ctor->dyndata, cnt, &dyn_mem);
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break;
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}
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dyn = gelf_getdyn(ctor->dyndata, cnt+1, &dyn_mem);
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gelf_update_dyn(ctor->dyndata, cnt, dyn);
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}
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ctor->dynshdr->sh_size--;
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gelf_update_shdr(ctor->dynscn, ctor->dynshdr);
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update_dyn_cache(ctor);
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}
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typedef void (*dyn_fixup_fn)(ElfCreator *ctor, Elf64_Sxword d_tag, Elf_Scn *scn);
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static void generic_dyn_fixup_fn(ElfCreator *ctor, Elf64_Sxword d_tag, Elf_Scn *scn)
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{
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GElf_Shdr *shdr, shdr_mem;
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GElf_Dyn *dyn, dyn_mem;
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size_t idx;
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dyn = get_dyn_by_tag(ctor, d_tag, &dyn_mem, &idx);
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shdr = gelf_getshdr(scn, &shdr_mem);
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if (shdr) {
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dyn->d_un.d_ptr = shdr->sh_addr;
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gelf_update_dyn(ctor->dyndata, idx, dyn);
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} else {
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remove_dyn(ctor, idx);
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}
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}
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static void rela_dyn_fixup_fn(ElfCreator *ctor, Elf64_Sxword d_tag, Elf_Scn *scn)
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{
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GElf_Shdr *shdr, shdr_mem;
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GElf_Dyn *dyn, dyn_mem;
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size_t idx;
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dyn = get_dyn_by_tag(ctor, d_tag, &dyn_mem, &idx);
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shdr = gelf_getshdr(scn, &shdr_mem);
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if (shdr) {
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dyn->d_un.d_ptr = shdr->sh_addr;
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gelf_update_dyn(ctor->dyndata, idx, dyn);
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} else {
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remove_dyn(ctor, idx);
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dyn = get_dyn_by_tag(ctor, DT_RELASZ, &dyn_mem, &idx);
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if (dyn) {
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dyn->d_un.d_val = 0;
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gelf_update_dyn(ctor->dyndata, idx, dyn);
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}
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}
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}
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static void rel_dyn_fixup_fn(ElfCreator *ctor, Elf64_Sxword d_tag, Elf_Scn *scn)
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{
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GElf_Shdr *shdr, shdr_mem;
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GElf_Dyn *dyn, dyn_mem;
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size_t idx;
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dyn = get_dyn_by_tag(ctor, d_tag, &dyn_mem, &idx);
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shdr = gelf_getshdr(scn, &shdr_mem);
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if (shdr) {
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dyn->d_un.d_ptr = shdr->sh_addr;
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gelf_update_dyn(ctor->dyndata, idx, dyn);
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} else {
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remove_dyn(ctor, idx);
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dyn = get_dyn_by_tag(ctor, DT_RELSZ, &dyn_mem, &idx);
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if (dyn) {
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dyn->d_un.d_val = 0;
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gelf_update_dyn(ctor->dyndata, idx, dyn);
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}
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}
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}
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static void fixup_dynamic(ElfCreator *ctor)
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{
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struct {
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Elf64_Sxword d_tag;
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Elf64_Word sh_type;
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dyn_fixup_fn fn;
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} fixups[] = {
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{ DT_HASH, SHT_HASH, NULL },
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{ DT_STRTAB, SHT_STRTAB, NULL },
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{ DT_SYMTAB, SHT_SYMTAB, NULL },
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{ DT_RELA, SHT_RELA, rela_dyn_fixup_fn},
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{ DT_REL, SHT_REL, rel_dyn_fixup_fn},
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{ DT_GNU_HASH, SHT_GNU_HASH, NULL },
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{ DT_NULL, SHT_NULL, NULL }
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};
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int i;
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for (i = 0; fixups[i].d_tag != DT_NULL; i++) {
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Elf_Scn *scn;
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scn = get_scn_by_type(ctor, fixups[i].sh_type);
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if (fixups[i].fn)
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fixups[i].fn(ctor, fixups[i].d_tag, scn);
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else
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generic_dyn_fixup_fn(ctor, fixups[i].d_tag, scn);
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}
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}
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void elfcreator_end(ElfCreator *ctor)
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{
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GElf_Phdr phdr_mem, *phdr;
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int m,n;
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for (m = 0; (phdr = gelf_getphdr(ctor->oldelf, m, &phdr_mem)) != NULL; m++)
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/* XXX this should check if an entry is needed */;
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gelf_newphdr(ctor->elf, m);
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elf_update(ctor->elf, ELF_C_NULL);
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update_dyn_cache(ctor);
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for (n = 0; n < m; n++) {
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/* XXX this should check if an entry is needed */
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phdr = gelf_getphdr(ctor->oldelf, n, &phdr_mem);
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if (ctor->dynshdr && phdr->p_type == PT_DYNAMIC)
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phdr->p_offset = ctor->dynshdr->sh_offset;
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gelf_update_phdr(ctor->elf, n, phdr);
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}
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fixup_dynamic(ctor);
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clear(ctor, 0);
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free(ctor);
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}
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@ -0,0 +1,20 @@
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/*
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* Copyright 2009 Red Hat, Inc.
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of version 2 of the GNU General Public License as
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* published by the Free Software Foundation.
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*
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* Author: Peter Jones <pjones@redhat.com>
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*/
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#ifndef ELFCREATOR_H
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#define ELFCREATOR_H 1
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#include <gelf.h>
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typedef struct elf_creator ElfCreator;
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extern ElfCreator *elfcreator_begin(char *path, Elf *elf);
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extern void elfcreator_copy_scn(ElfCreator *ctor, Elf *src, Elf_Scn *scn);
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extern void elfcreator_end(ElfCreator *ctor);
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#endif /* ELFCREATOR_H */
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@ -0,0 +1,125 @@
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/*
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* Copyright 2009 Red Hat, Inc.
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of version 2 of the GNU General Public License as
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* published by the Free Software Foundation.
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*
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* Author: Peter Jones <pjones@redhat.com>
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*/
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#include <gelf.h>
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#include <stdio.h>
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#include <strings.h>
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#include <string.h>
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#include <fcntl.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include "elfcreator.h"
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#include "dutil.h"
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static int should_copy_scn(Elf *elf, GElf_Shdr *shdr, struct strlist *scns)
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{
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char *name;
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size_t shstrndx;
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if (elf_getshdrstrndx(elf, &shstrndx) < 0)
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return 0;
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name = elf_strptr(elf, shstrndx, shdr->sh_name);
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if (name == NULL)
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return 0;
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if (strlist__has_entry(scns, name))
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return 1;
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return 0;
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}
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int main(int argc, char *argv[])
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{
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int n;
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struct strlist *sections;
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char *infile = NULL, *outfile = NULL;
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int fd;
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Elf *elf;
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Elf_Scn *scn;
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int copy_all_sections = 0;
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ElfCreator *ctor;
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sections = strlist__new(false);
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for (n = 1; n < argc; n++) {
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if (!strcmp(argv[n], "-a")) {
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copy_all_sections = 1;
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} else if (!strcmp(argv[n], "-s")) {
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if (n == argc-1) {
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fprintf(stderr, "Missing argument to -s\n");
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return -1;
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}
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n++;
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strlist__add(sections, argv[n]);
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continue;
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} else if (!strcmp(argv[n], "-o")) {
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if (n == argc-1) {
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fprintf(stderr, "Missing argument to -o\n");
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return -1;
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}
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n++;
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outfile = argv[n];
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continue;
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} else if (!strcmp(argv[n], "-?") || !strcmp(argv[n],"--usage")) {
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printf("usage: pjoc -s section 0 [[-s section1] ... -s sectionN] -o outfile infile\n");
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return 0;
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} else if (n == argc-1) {
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infile = argv[n];
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} else {
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fprintf(stderr, "usage: pjoc -s section 0 [[-s section1] ... -s sectionN] -o outfile infile\n");
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return 1;
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}
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}
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if (!infile || !outfile) {
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fprintf(stderr, "usage: pjoc -s section 0 [[-s section1] ... -s sectionN] -o outfile infile\n");
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return 1;
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}
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if (!(fd = open(infile, O_RDONLY))) {
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fprintf(stderr, "Could not open \"%s\" for reading: %m\n", infile);
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return 1;
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}
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elf_version(EV_CURRENT);
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if ((elf = elf_begin(fd, ELF_C_READ_MMAP_PRIVATE, NULL)) == NULL) {
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fprintf(stderr, "cannot get elf descriptor for \"%s\": %s\n",
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infile, elf_errmsg(-1));
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close(fd);
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return 1;
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}
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if (elf_kind(elf) != ELF_K_ELF) {
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fprintf(stderr, "\"%s\" is not an ELF file\n", infile);
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err:
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elf_end(elf);
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close(fd);
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return 1;
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}
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if ((ctor = elfcreator_begin(outfile, elf)) == NULL) {
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fprintf(stderr, "could not initialize ELF creator\n");
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goto err;
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}
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scn = NULL;
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while ((scn = elf_nextscn(elf, scn)) != NULL) {
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GElf_Shdr shdr_mem, *shdr;
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shdr = gelf_getshdr(scn, &shdr_mem);
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if (shdr == NULL)
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continue;
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if (!should_copy_scn(elf, shdr, sections) && !copy_all_sections)
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continue;
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elfcreator_copy_scn(ctor, elf, scn);
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}
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elfcreator_end(ctor);
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return 0;
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}
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