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/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License (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 (c) 1995, 2010, Oracle and/or its affiliates. All rights reserved.
*/
/*
* acom: Append Comment
*
* This program demonstrates the use of the libelf interface to
* modify a ELF file. This program will open an ELF file and
* either modify an existing .comment section and/or append
* a new .comment section to an existing ELF file.
*/
#include <stdio.h>
#include <libelf.h>
#include <gelf.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
static const char *CommentStr = ".comment";
static void
update_comment(Elf *elf, const char *file, const char *comment)
{
Elf_Scn *scn = NULL;
GElf_Shdr shdr;
Elf_Data *data;
size_t shstrndx;
if (elf_getshdrstrndx(elf, &shstrndx) == -1) {
(void) fprintf(stderr, "%s: gelf_getshdrstrdx() failed: %s\n",
file, elf_errmsg(0));
return;
}
while ((scn = elf_nextscn(elf, scn)) != NULL) {
/*
* 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) == NULL) {
(void) fprintf(stderr, "%s: elf_getshdr() failed: %s\n",
file, elf_errmsg(0));
return;
}
if (strcmp(CommentStr, elf_strptr(elf, shstrndx,
shdr.sh_name)) == 0)
break;
}
if (scn == NULL) {
int ndx;
(void) printf("%s has no .comment section. "
"Creating one...\n", file);
/*
* First add the ".comment" string to the string table
*/
if ((scn = elf_getscn(elf, shstrndx)) == NULL) {
(void) fprintf(stderr, "%s: elf_getscn() failed: %s\n",
file, elf_errmsg(0));
return;
}
if ((data = elf_getdata(scn, NULL)) == NULL) {
(void) fprintf(stderr, "%s: elf_getdata() failed: %s\n",
file, elf_errmsg(0));
return;
}
ndx = data->d_off + data->d_size;
if ((data = elf_newdata(scn)) == NULL) {
(void) fprintf(stderr, "%s: elf_newdata() failed: %s\n",
file, elf_errmsg(0));
return;
}
data->d_buf = (void *)CommentStr;
data->d_size = strlen(CommentStr) + 1;
data->d_align = 1;
/*
* Add the ".comment" section to the end of the file.
* Initialize the fields in the Section Header that
* libelf will not fill in.
*/
if ((scn = elf_newscn(elf)) == NULL) {
(void) fprintf(stderr, "%s: elf_newscn() failed: %s\n",
file, elf_errmsg(0));
return;
}
if (gelf_getshdr(scn, &shdr) == NULL) {
(void) fprintf(stderr, "%s: elf_getshdr() failed: %s\n",
file, elf_errmsg(0));
return;
}
shdr.sh_name = ndx;
shdr.sh_type = SHT_PROGBITS;
shdr.sh_flags = 0;
shdr.sh_addr = 0;
shdr.sh_link = 0;
shdr.sh_info = 0;
/*
* Flush the changes to the underlying elf32 or elf64
* section header.
*/
(void) gelf_update_shdr(scn, &shdr);
}
if (shdr.sh_addr != 0) {
(void) printf("%s: .comment section is part of a "
"loadable segment, it cannot be changed.\n", file);
return;
}
if ((data = elf_newdata(scn)) == NULL) {
(void) fprintf(stderr, "%s: elf_getdata() failed: %s\n",
file, elf_errmsg(0));
return;
}
data->d_buf = (void *)comment;
data->d_size = strlen(comment) + 1;
data->d_align = 1;
if (elf_update(elf, ELF_C_WRITE) == -1)
(void) fprintf(stderr, "%s: elf_update() failed: %s\n", file,
elf_errmsg(0));
}
int
main(int argc, char **argv)
{
int i;
char *new_comment;
if (argc < 3) {
(void) printf("usage: %s <new comment> 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);
}
/*
* The new comment is passed in through the command line.
* This string will be used to update the .comment section of
* the specified ELF files.
*/
new_comment = argv[1];
for (i = 2; i < argc; i++) {
int fd;
Elf *elf;
char *elf_fname;
elf_fname = argv[i];
if ((fd = open(elf_fname, O_RDWR)) == -1) {
perror("open");
continue;
}
/*
* Attempt to open an Elf descriptor Read/Write
* for each file.
*/
if ((elf = elf_begin(fd, ELF_C_RDWR, 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)
update_comment(elf, elf_fname, new_comment);
else
(void) printf("%s not of type ELF_K_ELF. "
"elf_kind == %d\n", elf_fname, elf_kind(elf));
(void) elf_end(elf);
(void) close(fd);
}
return (0);
}
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