ext/libelf/elf_scn.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 <assert.h>
#include <errno.h>
#include <stddef.h>
#include <stdlib.h>

#include "gelf.h"
#include "libelf.h"
#include "_libelf.h"

/*
 * Load an ELF section table and create a list of Elf_Scn structures.
 */
static int
_libelf_load_scn(Elf *e, void *ehdr)
{
        int ec, swapbytes;
        size_t fsz, i, shnum;
        uint64_t shoff;
        char *src;
        Elf32_Ehdr *eh32;
        Elf64_Ehdr *eh64;
        Elf_Scn *scn;
        void (*xlator)(char *_d, char *_s, size_t _c, int _swap);

        assert(e != NULL);
        assert(ehdr != NULL);
        assert((e->e_flags & LIBELF_F_SHDRS_LOADED) == 0);

#define	CHECK_EHDR(E,EH)	do {				\
                if (fsz != (EH)->e_shentsize ||			\
                    shoff + fsz * shnum > e->e_rawsize) {	\
                        LIBELF_SET_ERROR(HEADER, 0);		\
                        return (0);				\
                }						\
        } while (0)

        ec = e->e_class;
        fsz = _libelf_fsize(ELF_T_SHDR, ec, e->e_version, (size_t) 1);
        assert(fsz > 0);

        shnum = e->e_u.e_elf.e_nscn;

        if (ec == ELFCLASS32) {
                eh32 = (Elf32_Ehdr *) ehdr;
                shoff = (uint64_t) eh32->e_shoff;
                CHECK_EHDR(e, eh32);
        } else {
                eh64 = (Elf64_Ehdr *) ehdr;
                shoff = eh64->e_shoff;
                CHECK_EHDR(e, eh64);
        }

        xlator = _libelf_get_translator(ELF_T_SHDR, ELF_TOMEMORY, ec);

        swapbytes = e->e_byteorder != LIBELF_PRIVATE(byteorder);
        src = e->e_rawfile + shoff;

        /*
         * If the file is using extended numbering then section #0
         * would have already been read in.
         */

        i = 0;
        if (!STAILQ_EMPTY(&e->e_u.e_elf.e_scn)) {
                assert(STAILQ_FIRST(&e->e_u.e_elf.e_scn) ==
                    STAILQ_LAST(&e->e_u.e_elf.e_scn, _Elf_Scn, s_next));

                i = 1;
                src += fsz;
        }

        for (; i < shnum; i++, src += fsz) {
                if ((scn = _libelf_allocate_scn(e, i)) == NULL)
                        return (0);

                (*xlator)((char *) &scn->s_shdr, src, (size_t) 1, swapbytes);

                if (ec == ELFCLASS32) {
                        scn->s_offset = scn->s_rawoff =
                            scn->s_shdr.s_shdr32.sh_offset;
                        scn->s_size = scn->s_shdr.s_shdr32.sh_size;
                } else {
                        scn->s_offset = scn->s_rawoff =
                            scn->s_shdr.s_shdr64.sh_offset;
                        scn->s_size = scn->s_shdr.s_shdr64.sh_size;
                }
        }

        e->e_flags |= LIBELF_F_SHDRS_LOADED;

        return (1);
}


Elf_Scn *
elf_getscn(Elf *e, size_t index)
{
        int ec;
        void *ehdr;
        Elf_Scn *s;

        if (e == NULL || e->e_kind != ELF_K_ELF ||
            ((ec = e->e_class) != ELFCLASS32 && ec != ELFCLASS64)) {
                LIBELF_SET_ERROR(ARGUMENT, 0);
                return (NULL);
        }

        if ((ehdr = _libelf_ehdr(e, ec, 0)) == NULL)
                return (NULL);

        if (e->e_cmd != ELF_C_WRITE &&
            (e->e_flags & LIBELF_F_SHDRS_LOADED) == 0 &&
            _libelf_load_scn(e, ehdr) == 0)
                return (NULL);

        STAILQ_FOREACH(s, &e->e_u.e_elf.e_scn, s_next)
                if (s->s_ndx == index)
                        return (s);

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

size_t
elf_ndxscn(Elf_Scn *s)
{
        if (s == NULL) {
                LIBELF_SET_ERROR(ARGUMENT, 0);
                return (SHN_UNDEF);
        }
        return (s->s_ndx);
}

Elf_Scn *
elf_newscn(Elf *e)
{
        int ec;
        void *ehdr;
        Elf_Scn *scn;

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

        if ((ec = e->e_class) != ELFCLASS32 && ec != ELFCLASS64) {
                LIBELF_SET_ERROR(CLASS, 0);
                return (NULL);
        }

        if ((ehdr = _libelf_ehdr(e, ec, 0)) == NULL)
                return (NULL);

        /*
         * The application may be asking for a new section descriptor
         * on an ELF object opened with ELF_C_RDWR or ELF_C_READ.  We
         * need to bring in the existing section information before
         * appending a new one to the list.
         *
         * Per the ELF(3) API, an application is allowed to open a
         * file using ELF_C_READ, mess with its internal structure and
         * use elf_update(...,ELF_C_NULL) to compute its new layout.
         */
        if (e->e_cmd != ELF_C_WRITE &&
            (e->e_flags & LIBELF_F_SHDRS_LOADED) == 0 &&
            _libelf_load_scn(e, ehdr) == 0)
                return (NULL);

        if (STAILQ_EMPTY(&e->e_u.e_elf.e_scn)) {
                assert(e->e_u.e_elf.e_nscn == 0);
                if ((scn = _libelf_allocate_scn(e, (size_t) SHN_UNDEF)) ==
                    NULL)
                        return (NULL);
                e->e_u.e_elf.e_nscn++;
        }

        assert(e->e_u.e_elf.e_nscn > 0);

        if ((scn = _libelf_allocate_scn(e, e->e_u.e_elf.e_nscn)) == NULL)
                return (NULL);

        e->e_u.e_elf.e_nscn++;

        (void) elf_flagscn(scn, ELF_C_SET, ELF_F_DIRTY);

        return (scn);
}

Elf_Scn *
elf_nextscn(Elf *e, Elf_Scn *s)
{
        if (e == NULL || (e->e_kind != ELF_K_ELF) ||
            (s && s->s_elf != e)) {
                LIBELF_SET_ERROR(ARGUMENT, 0);
                return (NULL);
        }

        return (s == NULL ? elf_getscn(e, (size_t) 1) :
            STAILQ_NEXT(s, s_next));
}