/*
 * 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);
}