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/*
* Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*
*/
/*
* Name: fix_empty_sec_hdr_flags.c
*
* Description: Remove the SHF_ALLOC flag from "empty" section headers.
* An "empty" section header has sh_addr == 0 and sh_size == 0.
*
* This program is adapted from the example program shown on the
* elf(3elf) man page and from code from the Solaris compiler
* driver.
*/
#include <fcntl.h>
#include <stdio.h>
#include <libelf.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
static void failure(void);
void
main(int argc, char ** argv) {
void * ehdr; /* ELF header */
unsigned int i; /* section counter */
int fd; /* descriptor for file */
Elf * elf; /* ELF descriptor */
char * elf_ident; /* ELF identity string */
char * elf_obj; /* elf_obj file */
int fix_count; /* number of flags fixed */
int is_elfclass64; /* is an ELFCLASS64 file? */
Elf_Scn * scn; /* ELF section descriptor */
void * shdr; /* ELF section header */
Elf_Data * shstrtab; /* ELF section header string table */
if (argc != 2) {
(void) fprintf(stderr, "Usage: %s elf_obj\n", argv[0]);
exit(2);
}
/* open the elf_obj */
elf_obj = argv[1];
if ((fd = open(elf_obj, O_RDWR)) == -1) {
(void) fprintf(stderr, "%s: cannot open file.\n", elf_obj);
exit(3);
}
(void) printf("Opening '%s' for update\n", elf_obj);
(void) fflush(stdout);
(void) elf_version(EV_CURRENT); /* coordinate ELF versions */
/* obtain the ELF descriptors from the input file */
if ((elf = elf_begin(fd, ELF_C_RDWR, NULL)) == NULL) {
failure();
}
/* determine if ELFCLASS64 or not? */
elf_ident = elf_getident(elf, NULL);
is_elfclass64 = (elf_ident[EI_CLASS] == ELFCLASS64);
/* get the ELF header */
if (is_elfclass64) {
ehdr = elf64_getehdr(elf);
} else {
ehdr = elf32_getehdr(elf);
}
if (ehdr == NULL) {
failure();
}
/* get the ELF section descriptor */
if (is_elfclass64) {
scn = elf_getscn(elf, ((Elf64_Ehdr *) ehdr)->e_shstrndx);
} else {
scn = elf_getscn(elf, ((Elf32_Ehdr *) ehdr)->e_shstrndx);
}
if (scn == NULL) {
failure();
}
/* get the section header string table */
shstrtab = elf_getdata(scn, NULL);
if (shstrtab == NULL) {
failure();
}
fix_count = 0;
/* traverse the sections of the input file */
for (i = 1, scn = NULL; scn = elf_nextscn(elf, scn); i++) {
int has_flag_set; /* is SHF_ALLOC flag set? */
int is_empty; /* is section empty? */
char * name; /* short hand pointer */
/* get the section header */
if (is_elfclass64) {
shdr = elf64_getshdr(scn);
} else {
shdr = elf32_getshdr(scn);
}
if (shdr == NULL) {
failure();
}
if (is_elfclass64) {
name = (char *)shstrtab->d_buf + ((Elf64_Shdr *) shdr)->sh_name;
} else {
name = (char *)shstrtab->d_buf + ((Elf32_Shdr *) shdr)->sh_name;
}
if (is_elfclass64) {
has_flag_set = ((Elf64_Shdr *) shdr)->sh_flags & SHF_ALLOC;
is_empty = ((Elf64_Shdr *) shdr)->sh_addr == 0 &&
((Elf64_Shdr *) shdr)->sh_size == 0;
} else {
has_flag_set = ((Elf32_Shdr *) shdr)->sh_flags & SHF_ALLOC;
is_empty = ((Elf32_Shdr *) shdr)->sh_addr == 0 &&
((Elf32_Shdr *) shdr)->sh_size == 0;
}
if (is_empty && has_flag_set) {
(void) printf("section[%u] '%s' is empty, "
"but SHF_ALLOC flag is set.\n", i, name);
(void) printf("Clearing the SHF_ALLOC flag.\n");
if (is_elfclass64) {
((Elf64_Shdr *) shdr)->sh_flags &= ~SHF_ALLOC;
} else {
((Elf32_Shdr *) shdr)->sh_flags &= ~SHF_ALLOC;
}
fix_count++;
}
} /* end for each ELF section */
if (fix_count > 0) {
(void) printf("Saving %d updates to '%s'\n", fix_count, elf_obj);
(void) fflush(stdout);
(void) elf_update(elf, ELF_C_NULL); /* recalc ELF memory structures */
(void) elf_update(elf, ELF_C_WRITE); /* write out changes to ELF obj */
} else {
(void) printf("No SHF_ALLOC flags needed to be cleared.\n");
}
(void) elf_end(elf); /* done with ELF obj */
(void) close(fd);
(void) printf("Done %s '%s'\n",
(fix_count > 0) ? "updating" : "with", elf_obj);
(void) fflush(stdout);
exit(0);
} /* end main */
static void
failure() {
(void) fprintf(stderr, "%s\n", elf_errmsg(elf_errno()));
exit(6);
}
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