dcom.c revision 7c478bd95313f5f23a4c958a745db2134aa03244
/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License, Version 1.0 only
* (the "License"). You may not use this file except in compliance
* with the License.
*
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
* or http://www.opensolaris.org/os/licensing.
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
*
* CDDL HEADER END
*/
/*
* Copyright 2004 Sun Microsystems, Inc. All rights reserved.
* Use is subject to license terms.
*/
#pragma ident "%Z%%M% %I% %E% SMI"
/*
* dcom: Delete Comment
*
* This program demonstrates the use of libelf interface to
* copy the contents of one ELF file to create a new one.
* dcom creates a new ELF file using elf_begin(ELF_C_WRITE).
*
* In order to delete a section from an ELF file you must
* instead create a new ELF file and copy all but the 'selected'
* sections to the new ELF file. This is because libelf is
* unable to delete any sections from an ELF file, it can
* only add them.
*
* NOTE: While this program works fine for simple ELF objects,
* as they get more complex it may not properly update all of the
* fields required. This program is *only* an example of how
* to do this and not a complete program in itself.
*/
#include <stdio.h>
#include <libelf.h>
#include <gelf.h>
#include <fcntl.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/param.h>
static const char *CommentStr = ".comment";
/*
* Build a temporary file name that is in the
* same directory as the elf file being processed.
*/
static char *
mkname(const char *bname)
{
char *ptr;
char buffer[MAXPATHLEN];
ptr = strcpy(buffer, bname);
ptr += strlen(buffer);
while (ptr >= buffer) {
if (*ptr == '/') {
*(ptr + 1) = '\0';
break;
}
ptr--;
}
if (ptr < buffer) {
buffer[0] = '.';
buffer[1] = '\0';
}
return (tempnam(buffer, 0));
}
static void
delete_comment(Elf *elf, int fd, const char *file)
{
GElf_Ehdr ehdr;
Elf_Scn *scn = 0;
char *tfile;
Elf *telf;
int tfd;
GElf_Ehdr tehdr;
GElf_Phdr phdr;
GElf_Phdr tphdr;
size_t shstrndx;
size_t shnum;
int *shndx;
int ndx = 1;
int off = 0;
struct stat sbuf;
if (gelf_getehdr(elf, &ehdr) == 0) {
(void) fprintf(stderr, "%s: elf_getehdr() failed: %s\n",
file, elf_errmsg(0));
return;
}
if (elf_getshnum(elf, &shnum) == 0) {
(void) fprintf(stderr, "%s: elf_getshnum() failed: %s\n",
file, elf_errmsg(0));
return;
}
if (elf_getshstrndx(elf, &shstrndx) == 0) {
(void) fprintf(stderr, "%s: elf_getshstrndx() failed: %s\n",
file, elf_errmsg(0));
return;
}
/*
* shndx is an array used to map the current section
* indexes to the new section indexes.
*/
shndx = calloc(shnum, sizeof (int));
while ((scn = elf_nextscn(elf, scn)) != 0) {
GElf_Shdr shdr;
/*
* Do a string compare to examine each section header
* to see if it is a ".comment" section. If it is then
* this is the section we want to process.
*/
if (gelf_getshdr(scn, &shdr) == 0) {
(void) fprintf(stderr,
"%s: elf_getshdr() failed: %s\n",
file, elf_errmsg(0));
free(shndx);
return;
}
if (strcmp(CommentStr, elf_strptr(elf, shstrndx,
shdr.sh_name)) == 0) {
shndx[ndx] = -1;
off++;
/*
* If the .comment section is part of a loadable
* segment then it can not be delted from the
* ELF file.
*/
if (shdr.sh_addr != 0) {
(void) printf("%s: .comment section is "
"part of a loadable segment, it "
"cannot be deleted.\n", file);
free(shndx);
return;
}
} else
shndx[ndx] = ndx - off;
ndx++;
}
/*
* obtain a unique file name and open a file descriptor
* pointing to that file.
*/
tfile = mkname(file);
if ((tfd = open(tfile, O_RDWR | O_CREAT, 0600)) == -1) {
perror("temp open");
return;
}
/*
* Create a new ELF to duplicate the ELF file into.
*/
if ((telf = elf_begin(tfd, ELF_C_WRITE, 0)) == 0) {
(void) fprintf(stderr, "elf_begin(ELF_C_WRITE) failed: %s\n",
elf_errmsg(0));
return;
}
if (gelf_newehdr(telf, gelf_getclass(elf)) == 0) {
(void) fprintf(stderr, "%s: elf_newehdr() failed: %s\n",
file, elf_errmsg(0));
free(shndx);
return;
}
if (gelf_getehdr(telf, &tehdr) == 0) {
(void) fprintf(stderr, "%s: elf_getehdr() failed: %s\n",
file, elf_errmsg(0));
free(shndx);
return;
}
scn = 0;
ndx = 1;
while ((scn = elf_nextscn(elf, scn)) != 0) {
Elf_Scn * tscn;
Elf_Data * data;
Elf_Data * tdata;
GElf_Shdr shdr;
GElf_Shdr tshdr;
if (shndx[ndx] == -1) {
ndx++;
continue;
}
/*
* Duplicate all but the .comment section in the
* new file.
*/
if (gelf_getshdr(scn, &shdr) == 0) {
(void) fprintf(stderr,
"%s: elf_getshdr() failed: %s\n",
file, elf_errmsg(0));
free(shndx);
return;
}
if ((tscn = elf_newscn(telf)) == 0) {
(void) fprintf(stderr,
"%s: elf_newscn() failed: %s\n",
file, elf_errmsg(0));
free(shndx);
return;
}
if (gelf_getshdr(tscn, &tshdr) == 0) {
(void) fprintf(stderr,
"%s: elf_getshdr() failed: %s\n",
file, elf_errmsg(0));
free(shndx);
return;
}
tshdr = shdr;
tshdr.sh_link = shndx[shdr.sh_link];
/*
* The relocation sections sh_info field also contains
* a section index that needs to be adjusted. This is
* the only section who's sh_info field contains
* a section index according to the ABI.
*
* If their are non-ABI sections who's sh_info field
* contains section indexes they will not properly
* be updated by this routine.
*/
if (shdr.sh_type == SHT_REL)
tshdr.sh_info = shndx[ndx];
/*
* Flush the changes to the underlying elf32 or elf64
* section header.
*/
gelf_update_shdr(tscn, &tshdr);
if ((data = elf_getdata(scn, 0)) == 0) {
(void) fprintf(stderr,
"%s: elf_getdata() failed: %s\n",
file, elf_errmsg(0));
free(shndx);
return;
}
if ((tdata = elf_newdata(tscn)) == 0) {
(void) fprintf(stderr,
"%s: elf_newdata() failed: %s\n",
file, elf_errmsg(0));
free(shndx);
return;
}
*tdata = *data;
ndx++;
}
tehdr = ehdr;
if (shndx[shstrndx] < SHN_LORESERVE)
tehdr.e_shstrndx = shndx[shstrndx];
else {
Elf_Scn *_scn;
GElf_Shdr shdr0;
/*
* 'ELF Extended Sections' are enabled - we must
* store the shstrndx in Shdr[0].sh_link
*/
if ((_scn = elf_getscn(telf, 0)) == 0) {
(void) fprintf(stderr,
"%s: elf_getscn() failed: %s\n",
file, elf_errmsg(0));
free(shndx);
return;
}
if (gelf_getshdr(_scn, &shdr0) == 0) {
(void) fprintf(stderr,
"%s: elf_getshdr() failed: %s\n",
file, elf_errmsg(0));
free(shndx);
return;
}
tehdr.e_shstrndx = SHN_XINDEX;
shdr0.sh_link = shndx[shstrndx];
gelf_update_shdr(_scn, &shdr0);
}
gelf_update_ehdr(telf, &tehdr);
free(shndx);
/*
* Duplicate all program headers contained in the ELF file.
*/
if (ehdr.e_phnum) {
if (gelf_newphdr(telf, ehdr.e_phnum) == 0) {
(void) fprintf(stderr,
"%s: elf_newphdr() failed: %s\n",
file, elf_errmsg(0));
return;
}
for (ndx = 0; ndx < (int)ehdr.e_phnum; ndx++) {
if (gelf_getphdr(elf, ndx, &phdr) == 0 ||
gelf_getphdr(telf, ndx, &tphdr) == 0) {
(void) fprintf(stderr,
"%s: elf_getphdr() failed: %s\n",
file, elf_errmsg(0));
return;
}
tphdr = phdr;
gelf_update_phdr(telf, ndx, &tphdr);
}
}
/*
* The new Elf file has now been fully described to libelf.
* elf_update() will construct the new Elf file and write
* it out to disk.
*/
if (elf_update(telf, ELF_C_WRITE) == -1) {
(void) fprintf(stderr, "elf_update() failed: %s\n",
elf_errmsg(0));
(void) elf_end(telf);
(void) close(tfd);
return;
}
(void) elf_end(telf);
/*
* set new files permissions to the original files
* permissions.
*/
(void) fstat(fd, &sbuf);
(void) fchmod(tfd, sbuf.st_mode);
(void) close(tfd);
/*
* delete the original file and rename the new file
* to the orignal file.
*/
(void) rename(tfile, file);
}
int
main(int argc, char ** argv)
{
int i;
if (argc < 2) {
(void) printf("usage: %s elf_file ...\n", argv[0]);
return (1);
}
/*
* Initialize the elf library, must be called before elf_begin()
* can be called.
*/
if (elf_version(EV_CURRENT) == EV_NONE) {
(void) fprintf(stderr, "elf_version() failed: %s\n",
elf_errmsg(0));
return (1);
}
for (i = 1; i < argc; i++) {
int fd;
Elf *elf;
char *elf_fname;
elf_fname = argv[i];
if ((fd = open(elf_fname, O_RDONLY)) == -1) {
perror("open");
continue;
}
/*
* Attempt to open an Elf descriptor Read/Write
* for each file.
*/
if ((elf = elf_begin(fd, ELF_C_READ, 0)) == NULL) {
(void) fprintf(stderr, "elf_begin() failed: %s\n",
elf_errmsg(0));
(void) close(fd);
continue;
}
/*
* Determine what kind of elf file this is:
*/
if (elf_kind(elf) != ELF_K_ELF) {
/*
* can only delete comment sections from
* ELF files.
*/
(void) printf("%s not of type ELF_K_ELF. "
"elf_kind == %d\n",
elf_fname, elf_kind(elf));
} else
delete_comment(elf, fd, elf_fname);
(void) elf_end(elf);
(void) close(fd);
}
return (0);
}