usr/src/cmd/sgs/libelf/demo/acom.c

   1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License (the "License").
   6  * You may not use this file except in compliance with the License.
   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21 /*
  22  * Copyright (c) 1995, 2010, Oracle and/or its affiliates. All rights reserved.
  23  */
  24
  25 /*
  26  * acom: Append Comment
  27  *
  28  * This program demonstrates the use of the libelf interface to
  29  * modify a ELF file. This program will open an ELF file and
  30  * either modify an existing .comment section and/or append
  31  * a new .comment section to an existing ELF file.
  32  */
  33
  34 #include <stdio.h>
  35 #include <libelf.h>
  36 #include <gelf.h>
  37 #include <fcntl.h>
  38 #include <unistd.h>
  39 #include <stdlib.h>
  40 #include <string.h>
  41
  42
  43 static const char       *CommentStr =   ".comment";
  44
  45 static void
  46 update_comment(Elf *elf, const char *file, const char *comment)
  47 {
  48         Elf_Scn         *scn = NULL;
  49         GElf_Shdr       shdr;
  50         Elf_Data        *data;
  51         size_t          shstrndx;
  52
  53         if (elf_getshdrstrndx(elf, &shstrndx) == -1) {
  54                 (void) fprintf(stderr, "%s: gelf_getshdrstrdx() failed: %s\n",
  55                     file, elf_errmsg(0));
  56                 return;
  57         }
  58
  59         while ((scn = elf_nextscn(elf, scn)) != NULL) {
  60                 /*
  61                  * Do a string compare to examine each section header
  62                  * to see if it is a ".comment" section.  If it is then
  63                  * this is the section we want to process.
  64                  */
  65                 if (gelf_getshdr(scn, &shdr) == NULL) {
  66                         (void) fprintf(stderr, "%s: elf_getshdr() failed: %s\n",
  67                             file, elf_errmsg(0));
  68                         return;
  69                 }
  70                 if (strcmp(CommentStr, elf_strptr(elf, shstrndx,
  71                     shdr.sh_name)) == 0)
  72                         break;
  73         }
  74
  75         if (scn == NULL) {
  76                 int     ndx;
  77
  78                 (void) printf("%s has no .comment section.  "
  79                     "Creating one...\n", file);
  80                 /*
  81                  * First add the ".comment" string to the string table
  82                  */
  83                 if ((scn = elf_getscn(elf, shstrndx)) == NULL) {
  84                         (void) fprintf(stderr, "%s: elf_getscn() failed: %s\n",
  85                             file, elf_errmsg(0));
  86                         return;
  87                 }
  88                 if ((data = elf_getdata(scn, NULL)) == NULL) {
  89                         (void) fprintf(stderr, "%s: elf_getdata() failed: %s\n",
  90                             file, elf_errmsg(0));
  91                         return;
  92                 }
  93                 ndx = data->d_off + data->d_size;
  94                 if ((data = elf_newdata(scn)) == NULL) {
  95                         (void) fprintf(stderr, "%s: elf_newdata() failed: %s\n",
  96                             file, elf_errmsg(0));
  97                         return;
  98                 }
  99                 data->d_buf = (void *)CommentStr;
 100                 data->d_size = strlen(CommentStr) + 1;
 101                 data->d_align = 1;
 102
 103                 /*
 104                  * Add the ".comment" section to the end of the file.
 105                  * Initialize the fields in the Section Header that
 106                  * libelf will not fill in.
 107                  */
 108                 if ((scn = elf_newscn(elf)) == NULL) {
 109                         (void) fprintf(stderr, "%s: elf_newscn() failed: %s\n",
 110                             file, elf_errmsg(0));
 111                         return;
 112                 }
 113                 if (gelf_getshdr(scn, &shdr) == NULL) {
 114                         (void) fprintf(stderr, "%s: elf_getshdr() failed: %s\n",
 115                             file, elf_errmsg(0));
 116                         return;
 117                 }
 118                 shdr.sh_name = ndx;
 119                 shdr.sh_type = SHT_PROGBITS;
 120                 shdr.sh_flags = 0;
 121                 shdr.sh_addr = 0;
 122                 shdr.sh_link = 0;
 123                 shdr.sh_info = 0;
 124
 125                 /*
 126                  * Flush the changes to the underlying elf32 or elf64
 127                  * section header.
 128                  */
 129                 (void) gelf_update_shdr(scn, &shdr);
 130         }
 131
 132         if (shdr.sh_addr != 0) {
 133                 (void) printf("%s: .comment section is part of a "
 134                     "loadable segment, it cannot be changed.\n", file);
 135                 return;
 136         }
 137
 138         if ((data = elf_newdata(scn)) == NULL) {
 139                 (void) fprintf(stderr, "%s: elf_getdata() failed: %s\n",
 140                     file, elf_errmsg(0));
 141                 return;
 142         }
 143         data->d_buf = (void *)comment;
 144         data->d_size = strlen(comment) + 1;
 145         data->d_align = 1;
 146
 147         if (elf_update(elf, ELF_C_WRITE) == -1)
 148                 (void) fprintf(stderr, "%s: elf_update() failed: %s\n", file,
 149                     elf_errmsg(0));
 150 }
 151
 152 int
 153 main(int argc, char **argv)
 154 {
 155         int     i;
 156         char    *new_comment;
 157
 158
 159         if (argc < 3) {
 160                 (void) printf("usage: %s <new comment> elf_file ...\n",
 161                     argv[0]);
 162                 return (1);
 163         }
 164
 165         /*
 166          * Initialize the elf library, must be called before elf_begin()
 167          * can be called.
 168          */
 169         if (elf_version(EV_CURRENT) == EV_NONE) {
 170                 (void) fprintf(stderr, "elf_version() failed: %s\n",
 171                     elf_errmsg(0));
 172                 return (1);
 173         }
 174
 175         /*
 176          * The new comment is passed in through the command line.
 177          * This string will be used to update the .comment section of
 178          * the specified ELF files.
 179          */
 180         new_comment = argv[1];
 181         for (i = 2; i < argc; i++) {
 182                 int     fd;
 183                 Elf     *elf;
 184                 char    *elf_fname;
 185
 186                 elf_fname = argv[i];
 187                 if ((fd = open(elf_fname, O_RDWR)) == -1) {
 188                         perror("open");
 189                         continue;
 190                 }
 191
 192                 /*
 193                  * Attempt to open an Elf descriptor Read/Write
 194                  * for each file.
 195                  */
 196                 if ((elf = elf_begin(fd, ELF_C_RDWR, 0)) == NULL) {
 197                         (void) fprintf(stderr, "elf_begin() failed: %s\n",
 198                             elf_errmsg(0));
 199                         (void) close(fd);
 200                         continue;
 201                 }
 202                 /*
 203                  * Determine what kind of elf file this is:
 204                  */
 205                 if (elf_kind(elf) == ELF_K_ELF)
 206                         update_comment(elf, elf_fname, new_comment);
 207                 else
 208                         (void) printf("%s not of type ELF_K_ELF.  "
 209                             "elf_kind == %d\n", elf_fname, elf_kind(elf));
 210
 211                 (void) elf_end(elf);
 212                 (void) close(fd);
 213         }
 214
 215         return (0);
 216 }