ext/libelf/elf_strptr.c

/*-
 * Copyright (c) 2006 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.
 */


#include <sys/param.h>
#ifdef __sun
#include <sys/sysmacros.h>
#endif

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

#include "_libelf.h"

/*
 * 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;
        size_t alignment, count;
        GElf_Shdr shdr;

        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 = (size_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 = roundup(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);
}