/*

 * strptr.c - implementation of the elf_strptr(3) function.

 * Copyright (C) 1995 - 2007 Michael Riepe

 *

 * This library is free software; you can redistribute it and/or

 * modify it under the terms of the GNU Library General Public

 * License as published by the Free Software Foundation; either

 * version 2 of the License, or (at your option) any later version.

 *

 * This library 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

 * Library General Public License for more details.

 *

 * You should have received a copy of the GNU Library General Public

 * License along with this library; if not, write to the Free Software

 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

 */

#include <private.h>

#ifndef lint

static const char rcsid[] = "@(#) $Id: strptr.c,v 1.11 2007/09/07 12:07:59 michael Exp $";

#endif /* lint */

char*

elf_strptr(Elf *elf, size_t section, size_t offset) {

    Elf_Data *data;

    Elf_Scn *scn;

    size_t n;

    char *s;

    if (!elf) {

	return NULL;

    }

    elf_assert(elf->e_magic == ELF_MAGIC);

    if (!(scn = elf_getscn(elf, section))) {

	return NULL;

    }

    if (scn->s_index == SHN_UNDEF) {

	seterr(ERROR_NOSTRTAB);

	return NULL;

    }

    /*

     * checking the section header is more appropriate

     */

    if (elf->e_class == ELFCLASS32) {

	if (scn->s_shdr32.sh_type != SHT_STRTAB) {

	    seterr(ERROR_NOSTRTAB);

	    return NULL;

	}

    }

#if __LIBELF64

    else if (elf->e_class == ELFCLASS64) {

	if (scn->s_shdr64.sh_type != SHT_STRTAB) {

	    seterr(ERROR_NOSTRTAB);

	    return NULL;

	}

    }

#endif /* __LIBELF64 */

    else if (valid_class(elf->e_class)) {

	seterr(ERROR_UNIMPLEMENTED);

	return NULL;

    }

    else {

	seterr(ERROR_UNKNOWN_CLASS);

	return NULL;

    }

    /*

     * Find matching buffer

     */

    n = 0;

    data = NULL;

    if (elf->e_elf_flags & ELF_F_LAYOUT) {

	/*

	 * Programmer is responsible for d_off

	 * Note: buffers may be in any order!

	 */

	while ((data = elf_getdata(scn, data))) {

	    n = data->d_off;

	    if (offset >= n && offset - n < data->d_size) {

		/*

		 * Found it

		 */

		break;

	    }

	}

    }

    else {

	/*

	 * Calculate offsets myself

	 */

	while ((data = elf_getdata(scn, data))) {

	    if (data->d_align > 1) {

		n += data->d_align - 1;

		n -= n % data->d_align;

	    }

	    if (offset < n) {

		/*

		 * Invalid offset: points into a hole

		 */

		seterr(ERROR_BADSTROFF);

		return NULL;

	    }

	    if (offset - n < data->d_size) {

		/*

		 * Found it

		 */

		break;

	    }

	    n += data->d_size;

	}

    }

    if (data == NULL) {

	/*

	 * Not found

	 */

	seterr(ERROR_BADSTROFF);

	return NULL;

    }

    if (data->d_buf == NULL) {

	/*

	 * Buffer is NULL (usually the programmers' fault)

	 */

	seterr(ERROR_NULLBUF);

	return NULL;

    }

    offset -= n;

    s = (char*)data->d_buf;

    if (!(_elf_sanity_checks & SANITY_CHECK_STRPTR)) {

	return s + offset;

    }

    /*

     * Perform extra sanity check

     */

    for (n = offset; n < data->d_size; n++) {

	if (s[n] == '\0') {

	    /*

	     * Return properly NUL terminated string

	     */

	    return s + offset;

	}

    }

    /*

     * String is not NUL terminated

     * Return error to avoid SEGV in application

     */

    seterr(ERROR_UNTERM);

    return NULL;

}