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Java example source code file (add_gnu_debuglink.c)

This example Java source code file (add_gnu_debuglink.c) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

adding, crc, elf, elf32_shdr, elf64_shdr, elf_data, elf_scn, elf_t_byte, elfclass64, null, saving, sec_name, shf_exclude, sht_progbits

The add_gnu_debuglink.c Java example source code

/*
 * Copyright (c) 2012, 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:        add_gnu_debuglink.c
 *
 * Description: Add a ".gnu_debuglink" section that refers to the specified
 *     debug_info_path to the specified ELF object.
 *
 *     This program is adapted from the example program shown on the
 *     elf(3elf) man page and from code from the Solaris compiler
 *     driver.
 */

/*
 * needed to define SHF_EXCLUDE
 */
#define ELF_TARGET_ALL

#include <fcntl.h>
#include <stdio.h>
#include <libelf.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

static void failure(void);
static unsigned int gnu_debuglink_crc32(unsigned int crc, unsigned char *buf,
                                        size_t len);

void
main(int argc, char ** argv) {
                                 /* new ELF section name */
    static char SEC_NAME[] = ".gnu_debuglink";

    unsigned char buffer[8 * 1024];  /* I/O buffer */
    int           buffer_len;        /* buffer length */
    char *        debug_info_path;   /* debug info path */
    void *        ehdr;              /* ELF header */
    Elf *         elf;               /* ELF descriptor */
    char *        elf_ident;         /* ELF identity string */
    char *        elf_obj;           /* elf_obj file */
    int           fd;                /* descriptor for files */
    unsigned int  file_crc = 0;      /* CRC for debug info file */
    int           is_elfclass64;     /* is an ELFCLASS64 file? */
    Elf_Data *    link_dat;          /* ELF data for new debug info link */
    Elf_Data *    name_dat;          /* ELF data for new section name */
    Elf_Scn *     new_scn;           /* new ELF section descriptor */
    void *        new_shdr;          /* new ELF section header */
    Elf_Scn *     scn;               /* ELF section descriptor */
    void *        shdr;              /* ELF section header */

    if (argc != 3) {
        (void) fprintf(stderr, "Usage: %s debug_info_path elf_obj\n", argv[0]);
        exit(2);
    }

    debug_info_path = argv[1];  /* save for later */
    if ((fd = open(debug_info_path, O_RDONLY)) == -1) {
        (void) fprintf(stderr, "%s: cannot open file.\n", debug_info_path);
        exit(3);
    }

    (void) printf("Computing CRC for '%s'\n", debug_info_path);
    (void) fflush(stdout);
    /* compute CRC for the debug info file */
    for (;;) {
        int len = read(fd, buffer, sizeof buffer);
        if (len <= 0) {
            break;
        }
        file_crc = gnu_debuglink_crc32(file_crc, buffer, len);
    }
    (void) close(fd);

    /* open the elf_obj */
    elf_obj = argv[2];
    if ((fd = open(elf_obj, O_RDWR)) == -1) {
        (void) fprintf(stderr, "%s: cannot open file.\n", elf_obj);
        exit(4);
    }

    (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 */
    if (is_elfclass64) {
        shdr = elf64_getshdr(scn);
    } else {
        shdr = elf32_getshdr(scn);
    }
    if (shdr == NULL) {
        failure();
    }

    (void) printf("Adding ELF data for new section name\n");
    (void) fflush(stdout);
    name_dat = elf_newdata(scn);
    name_dat->d_buf = (void *) SEC_NAME;
    if (is_elfclass64) {
        name_dat->d_off = ((Elf64_Shdr *) shdr)->sh_size + 1;
    } else {
        name_dat->d_off = ((Elf32_Shdr *) shdr)->sh_size + 1;
    }
    name_dat->d_align = 1;
    name_dat->d_size = strlen(SEC_NAME) + 1;

    new_scn = elf_newscn(elf);

    if (is_elfclass64) {
        new_shdr = elf64_getshdr(new_scn);
        ((Elf64_Shdr *) new_shdr)->sh_flags = SHF_EXCLUDE;
        ((Elf64_Shdr *) new_shdr)->sh_type = SHT_PROGBITS;
        ((Elf64_Shdr *) new_shdr)->sh_name = ((Elf64_Shdr *) shdr)->sh_size;
        ((Elf64_Shdr *) new_shdr)->sh_addralign = 1;
        ((Elf64_Shdr *) shdr)->sh_size += (strlen(SEC_NAME) + 1);
    } else {
        new_shdr = elf32_getshdr(new_scn);
        ((Elf32_Shdr *) new_shdr)->sh_flags = SHF_EXCLUDE;
        ((Elf32_Shdr *) new_shdr)->sh_type = SHT_PROGBITS;
        ((Elf32_Shdr *) new_shdr)->sh_name = ((Elf32_Shdr *) shdr)->sh_size;
        ((Elf32_Shdr *) new_shdr)->sh_addralign = 1;
        ((Elf32_Shdr *) shdr)->sh_size += (strlen(SEC_NAME) + 1);
    }

    (void) printf("Adding ELF data for debug_info_path value\n");
    (void) fflush(stdout);
    (void) memset(buffer, 0, sizeof buffer);
    buffer_len = strlen(debug_info_path) + 1;  /* +1 for NUL */
    (void) strncpy((char *) buffer, debug_info_path, buffer_len);
    if (buffer_len % 4 != 0) {
        /* not on a 4 byte boundary so pad to the next one */
        buffer_len += (4 - buffer_len % 4);
    }
    /* save the CRC */
    (void) memcpy(&buffer[buffer_len], &file_crc, sizeof file_crc);
    buffer_len += sizeof file_crc;

    link_dat = elf_newdata(new_scn);
    link_dat->d_type = ELF_T_BYTE;
    link_dat->d_size = buffer_len;
    link_dat->d_buf = buffer;
    link_dat->d_align = 1;

    (void) printf("Saving updates to '%s'\n", 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 */
    (void) elf_end(elf);                  /* done with ELF obj */
    (void) close(fd);

    (void) printf("Done updating '%s'\n", elf_obj);
    (void) fflush(stdout);
    exit(0);
}  /* end main */


static void
failure() {
    (void) fprintf(stderr, "%s\n", elf_errmsg(elf_errno()));
    exit(5);
}


/*
 * The CRC used in gnu_debuglink, retrieved from
 * http://sourceware.org/gdb/current/onlinedocs/gdb/Separate-Debug-Files.html#Separate-Debug-Files.
 */

static unsigned int
gnu_debuglink_crc32(unsigned int crc, unsigned char *buf, size_t len) {
    static const unsigned int crc32_table[256] = {
        0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419,
        0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4,
        0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07,
        0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
        0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856,
        0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
        0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4,
        0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
        0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3,
        0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a,
        0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599,
        0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
        0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190,
        0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f,
        0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e,
        0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
        0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed,
        0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
        0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3,
        0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
        0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a,
        0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5,
        0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010,
        0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
        0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17,
        0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6,
        0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615,
        0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
        0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344,
        0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
        0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a,
        0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
        0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1,
        0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c,
        0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef,
        0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
        0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe,
        0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31,
        0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c,
        0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
        0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b,
        0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
        0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1,
        0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
        0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278,
        0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7,
        0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66,
        0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
        0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605,
        0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8,
        0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b,
        0x2d02ef8d
    };

    unsigned char *end;

    crc = ~crc & 0xffffffff;
    for (end = buf + len; buf < end; ++buf) {
        crc = crc32_table[(crc ^ *buf) & 0xff] ^ (crc >> 8);
    }
    return ~crc & 0xffffffff;
}

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