/*      $NetBSD: elf_strptr.c,v 1.5 2024/03/03 17:37:33 christos Exp $  */

/*-
* Copyright (c) 2006,2008 Joseph Koshy
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
*    notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
*    notice, this list of conditions and the following disclaimer in the
*    documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/

#if HAVE_NBTOOL_CONFIG_H
# include "nbtool_config.h"
#endif

#include <sys/cdefs.h>
#include <sys/param.h>

#include <assert.h>
#include <gelf.h>

#include "_libelf.h"

__RCSID("$NetBSD: elf_strptr.c,v 1.5 2024/03/03 17:37:33 christos Exp $");

/*
* Convert an ELF section#,offset pair to a string pointer.
*/

char *
elf_strptr(Elf *e, size_t scndx, size_t offset)
{
       Elf_Scn *s;
       Elf_Data *d;
       GElf_Shdr shdr;
       uint64_t alignment, count;

       if (e == NULL || e->e_kind != ELF_K_ELF) {
               LIBELF_SET_ERROR(ARGUMENT, 0);
               return (NULL);
       }

       if ((s = elf_getscn(e, scndx)) == NULL ||
           gelf_getshdr(s, &shdr) == NULL)
               return (NULL);

       if (shdr.sh_type != SHT_STRTAB ||
           offset >= shdr.sh_size) {
               LIBELF_SET_ERROR(ARGUMENT, 0);
               return (NULL);
       }

       d = NULL;
       if (e->e_flags & ELF_F_LAYOUT) {

               /*
                * The application is taking responsibility for the
                * ELF object's layout, so we can directly translate
                * an offset to a `char *' address using the `d_off'
                * members of Elf_Data descriptors.
                */
               while ((d = elf_getdata(s, d)) != NULL) {

                       if (d->d_buf == 0 || d->d_size == 0)
                               continue;

                       if (d->d_type != ELF_T_BYTE) {
                               LIBELF_SET_ERROR(DATA, 0);
                               return (NULL);
                       }

                       if (offset >= d->d_off &&
                           offset < d->d_off + d->d_size)
                               return ((char *) d->d_buf + offset - d->d_off);
               }
       } else {
               /*
                * Otherwise, the `d_off' members are not useable and
                * we need to compute offsets ourselves, taking into
                * account 'holes' in coverage of the section introduced
                * by alignment requirements.
                */
               count = (uint64_t) 0;   /* cumulative count of bytes seen */
               while ((d = elf_getdata(s, d)) != NULL && count <= offset) {

                       if (d->d_buf == NULL || d->d_size == 0)
                               continue;

                       if (d->d_type != ELF_T_BYTE) {
                               LIBELF_SET_ERROR(DATA, 0);
                               return (NULL);
                       }

                       if ((alignment = d->d_align) > 1) {
                               if ((alignment & (alignment - 1)) != 0) {
                                       LIBELF_SET_ERROR(DATA, 0);
                                       return (NULL);
                               }
                               count = roundup2(count, alignment);
                       }

                       if (offset < count) {
                               /* offset starts in the 'hole' */
                               LIBELF_SET_ERROR(ARGUMENT, 0);
                               return (NULL);
                       }

                       if (offset < count + d->d_size) {
                               if (d->d_buf != NULL)
                                       return ((char *) d->d_buf +
                                           offset - count);
                               LIBELF_SET_ERROR(DATA, 0);
                               return (NULL);
                       }

                       count += d->d_size;
               }
       }

       LIBELF_SET_ERROR(ARGUMENT, 0);
       return (NULL);
}