/*-
 * Copyright (c) 2006-2011 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/stat.h>

#include <assert.h>
#include <errno.h>
#include <gelf.h>
#include <libelf.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "_libelf.h"

#if     ELFTC_HAVE_MMAP
#include <sys/mman.h>
#endif

ELFTC_VCSID("$Id: elf_update.c,v 1.4 2021/09/02 21:12:25 deraadt Exp $");

/*
 * Layout strategy:
 *
 * - Case 1: ELF_F_LAYOUT is asserted
 *     In this case the application has full control over where the
 *     section header table, program header table, and section data
 *     will reside.   The library only perform error checks.
 *
 * - Case 2: ELF_F_LAYOUT is not asserted
 *
 *     The library will do the object layout using the following
 *     ordering:
 *     - The executable header is placed first, are required by the
 *       ELF specification.
 *     - The program header table is placed immediately following the
 *       executable header.
 *     - Section data, if any, is placed after the program header
 *       table, aligned appropriately.
 *     - The section header table, if needed, is placed last.
 *
 *     There are two sub-cases to be taken care of:
 *
 *     - Case 2a: e->e_cmd == ELF_C_READ or ELF_C_RDWR
 *
 *       In this sub-case, the underlying ELF object may already have
 *       content in it, which the application may have modified.  The
 *       library will retrieve content from the existing object as
 *       needed.
 *
 *     - Case 2b: e->e_cmd == ELF_C_WRITE
 *
 *       The ELF object is being created afresh in this sub-case;
 *       there is no pre-existing content in the underlying ELF
 *       object.
 */

/*
 * The types of extents in an ELF object.
 */
enum elf_extent {
        ELF_EXTENT_EHDR,
        ELF_EXTENT_PHDR,
        ELF_EXTENT_SECTION,
        ELF_EXTENT_SHDR
};

/*
 * A extent descriptor, used when laying out an ELF object.
 */
struct _Elf_Extent {
        SLIST_ENTRY(_Elf_Extent) ex_next;
        uint64_t        ex_start; /* Start of the region. */
        uint64_t        ex_size;  /* The size of the region. */
        enum elf_extent ex_type;  /* Type of region. */
        void            *ex_desc; /* Associated descriptor. */
};

SLIST_HEAD(_Elf_Extent_List, _Elf_Extent);

/*
 * Compute the extents of a section, by looking at the data
 * descriptors associated with it.  The function returns 1
 * if successful, or zero if an error was detected.
 */
static int
_libelf_compute_section_extents(Elf *e, Elf_Scn *s, off_t rc)
{
        Elf_Data *d;
        size_t fsz, msz;
        int ec, elftype;
        uint32_t sh_type;
        uint64_t d_align;
        Elf32_Shdr *shdr32;
        Elf64_Shdr *shdr64;
        struct _Libelf_Data *ld;
        uint64_t scn_size, scn_alignment;
        uint64_t sh_align, sh_entsize, sh_offset, sh_size;

        ec = e->e_class;

        shdr32 = &s->s_shdr.s_shdr32;
        shdr64 = &s->s_shdr.s_shdr64;
        if (ec == ELFCLASS32) {
                sh_type    = shdr32->sh_type;
                sh_align   = (uint64_t) shdr32->sh_addralign;
                sh_entsize = (uint64_t) shdr32->sh_entsize;
                sh_offset  = (uint64_t) shdr32->sh_offset;
                sh_size    = (uint64_t) shdr32->sh_size;
        } else {
                sh_type    = shdr64->sh_type;
                sh_align   = shdr64->sh_addralign;
                sh_entsize = shdr64->sh_entsize;
                sh_offset  = shdr64->sh_offset;
                sh_size    = shdr64->sh_size;
        }

        assert(sh_type != SHT_NULL && sh_type != SHT_NOBITS);

        elftype = _libelf_xlate_shtype(sh_type);
        if (elftype < ELF_T_FIRST || elftype > ELF_T_LAST) {
                LIBELF_SET_ERROR(SECTION, 0);
                return (0);
        }

        if (sh_align == 0)
                sh_align = _libelf_falign(elftype, ec);

        /*
         * Compute the section's size and alignment using the data
         * descriptors associated with the section.
         */
        if (STAILQ_EMPTY(&s->s_data)) {
                /*
                 * The section's content (if any) has not been read in
                 * yet.  If section is not dirty marked dirty, we can
                 * reuse the values in the 'sh_size' and 'sh_offset'
                 * fields of the section header.
                 */
                if ((s->s_flags & ELF_F_DIRTY) == 0) {
                        /*
                         * If the library is doing the layout, then we
                         * compute the new start offset for the
                         * section based on the current offset and the
                         * section's alignment needs.
                         *
                         * If the application is doing the layout, we
                         * can use the value in the 'sh_offset' field
                         * in the section header directly.
                         */
                        if (e->e_flags & ELF_F_LAYOUT)
                                goto updatedescriptor;
                        else
                                goto computeoffset;
                }

                /*
                 * Otherwise, we need to bring in the section's data
                 * from the underlying ELF object.
                 */
                if (e->e_cmd != ELF_C_WRITE && elf_getdata(s, NULL) == NULL)
                        return (0);
        }

        /*
         * Loop through the section's data descriptors.
         */
        scn_size = 0L;
        scn_alignment = 0;
        STAILQ_FOREACH(ld, &s->s_data, d_next)  {

                d = &ld->d_data;

                /*
                 * The data buffer's type is known.
                 */
                if (d->d_type >= ELF_T_NUM) {
                        LIBELF_SET_ERROR(DATA, 0);
                        return (0);
                }

                /*
                 * The data buffer's version is supported.
                 */
                if (d->d_version != e->e_version) {
                        LIBELF_SET_ERROR(VERSION, 0);
                        return (0);
                }

                /*
                 * The buffer's alignment is non-zero and a power of
                 * two.
                 */
                if ((d_align = d->d_align) == 0 ||
                    (d_align & (d_align - 1))) {
                        LIBELF_SET_ERROR(DATA, 0);
                        return (0);
                }

                /*
                 * The data buffer's ELF type, ELF class and ELF version
                 * should be supported.
                 */
                if ((msz = _libelf_msize(d->d_type, ec, e->e_version)) == 0)
                        return (0);

                /*
                 * The buffer's size should be a multiple of the
                 * memory size of the underlying type.
                 */
                if (d->d_size % msz) {
                        LIBELF_SET_ERROR(DATA, 0);
                        return (0);
                }

                /*
                 * If the application is controlling layout, then the
                 * d_offset field should be compatible with the
                 * buffer's specified alignment.
                 */
                if ((e->e_flags & ELF_F_LAYOUT) &&
                    (d->d_off & (d_align - 1))) {
                        LIBELF_SET_ERROR(LAYOUT, 0);
                        return (0);
                }

                /*
                 * Compute the section's size.
                 */
                if (e->e_flags & ELF_F_LAYOUT) {
                        if ((uint64_t) d->d_off + d->d_size > scn_size)
                                scn_size = d->d_off + d->d_size;
                } else {
                        scn_size = roundup2(scn_size, d->d_align);
                        d->d_off = scn_size;
                        fsz = _libelf_fsize(d->d_type, ec, d->d_version,
                            (size_t) d->d_size / msz);
                        scn_size += fsz;
                }

                /*
                 * The section's alignment is the maximum alignment
                 * needed for its data buffers.
                 */
                if (d_align > scn_alignment)
                        scn_alignment = d_align;
        }


        /*
         * If the application is requesting full control over the
         * layout of the section, check the section's specified size,
         * offsets and alignment for sanity.
         */
        if (e->e_flags & ELF_F_LAYOUT) {
                if (scn_alignment > sh_align ||
                    sh_offset % sh_align ||
                    sh_size < scn_size ||
                    sh_offset % _libelf_falign(elftype, ec)) {
                        LIBELF_SET_ERROR(LAYOUT, 0);
                        return (0);
                }
                goto updatedescriptor;
        }

        /*
         * Otherwise, compute the values in the section header.
         *
         * The section alignment is the maximum alignment for any of
         * its contained data descriptors.
         */
        if (scn_alignment > sh_align)
                sh_align = scn_alignment;

        /*
         * If the section entry size is zero, try and fill in an
         * appropriate entry size.  Per the elf(5) manual page
         * sections without fixed-size entries should have their
         * 'sh_entsize' field set to zero.
         */
        if (sh_entsize == 0 &&
            (sh_entsize = _libelf_fsize(elftype, ec, e->e_version,
                (size_t) 1)) == 1)
                sh_entsize = 0;

        sh_size = scn_size;

computeoffset:
        /*
         * Compute the new offset for the section based on
         * the section's alignment needs.
         */
        sh_offset = roundup((uint64_t) rc, sh_align);

        /*
         * Update the section header.
         */
        if (ec == ELFCLASS32) {
                shdr32->sh_addralign = (uint32_t) sh_align;
                shdr32->sh_entsize   = (uint32_t) sh_entsize;
                shdr32->sh_offset    = (uint32_t) sh_offset;
                shdr32->sh_size      = (uint32_t) sh_size;
        } else {
                shdr64->sh_addralign = sh_align;
                shdr64->sh_entsize   = sh_entsize;
                shdr64->sh_offset    = sh_offset;
                shdr64->sh_size      = sh_size;
        }

updatedescriptor:
        /*
         * Update the section descriptor.
         */
        s->s_size = sh_size;
        s->s_offset = sh_offset;

        return (1);
}

/*
 * Free a list of extent descriptors.
 */

static void
_libelf_release_extents(struct _Elf_Extent_List *extents)
{
        struct _Elf_Extent *ex;

        while ((ex = SLIST_FIRST(extents)) != NULL) {
                SLIST_REMOVE_HEAD(extents, ex_next);
                free(ex);
        }
}

/*
 * Check if an extent 's' defined by [start..start+size) is free.
 * This routine assumes that the given extent list is sorted in order
 * of ascending extent offsets.
 */

static int
_libelf_extent_is_unused(struct _Elf_Extent_List *extents,
    const uint64_t start, const uint64_t size, struct _Elf_Extent **prevt)
{
        uint64_t tmax, tmin;
        struct _Elf_Extent *t, *pt;
        const uint64_t smax = start + size;

        /* First, look for overlaps with existing extents. */
        pt = NULL;
        SLIST_FOREACH(t, extents, ex_next) {
                tmin = t->ex_start;
                tmax = tmin + t->ex_size;

                if (tmax <= start) {
                        /*
                         * 't' lies entirely before 's': ...| t |...| s |...
                         */
                        pt = t;
                        continue;
                } else if (smax <= tmin) {
                        /*
                         * 's' lies entirely before 't', and after 'pt':
                         *      ...| pt |...| s |...| t |...
                         */
                        assert(pt == NULL ||
                            pt->ex_start + pt->ex_size <= start);
                        break;
                } else
                        /* 's' and 't' overlap. */
                        return (0);
        }

        if (prevt)
                *prevt = pt;
        return (1);
}

/*
 * Insert an extent into the list of extents.
 */

static int
_libelf_insert_extent(struct _Elf_Extent_List *extents, int type,
    uint64_t start, uint64_t size, void *desc)
{
        struct _Elf_Extent *ex, *prevt;

        assert(type >= ELF_EXTENT_EHDR && type <= ELF_EXTENT_SHDR);

        prevt = NULL;

        /*
         * If the requested range overlaps with an existing extent,
         * signal an error.
         */
        if (!_libelf_extent_is_unused(extents, start, size, &prevt)) {
                LIBELF_SET_ERROR(LAYOUT, 0);
                return (0);
        }

        /* Allocate and fill in a new extent descriptor. */
        if ((ex = malloc(sizeof(struct _Elf_Extent))) == NULL) {
                LIBELF_SET_ERROR(RESOURCE, errno);
                return (0);
        }
        ex->ex_start = start;
        ex->ex_size = size;
        ex->ex_desc = desc;
        ex->ex_type = type;

        /* Insert the region descriptor into the list. */
        if (prevt)
                SLIST_INSERT_AFTER(prevt, ex, ex_next);
        else
                SLIST_INSERT_HEAD(extents, ex, ex_next);
        return (1);
}

/*
 * Recompute section layout.
 */

static off_t
_libelf_resync_sections(Elf *e, off_t rc, struct _Elf_Extent_List *extents)
{
        int ec;
        Elf_Scn *s;
        size_t sh_type;

        ec = e->e_class;

        /*
         * Make a pass through sections, computing the extent of each
         * section.
         */
        STAILQ_FOREACH(s, &e->e_u.e_elf.e_scn, s_next) {
                if (ec == ELFCLASS32)
                        sh_type = s->s_shdr.s_shdr32.sh_type;
                else
                        sh_type = s->s_shdr.s_shdr64.sh_type;

                if (sh_type == SHT_NOBITS || sh_type == SHT_NULL)
                        continue;

                if (_libelf_compute_section_extents(e, s, rc) == 0)
                        return ((off_t) -1);

                if (s->s_size == 0)
                        continue;

                if (!_libelf_insert_extent(extents, ELF_EXTENT_SECTION,
                    s->s_offset, s->s_size, s))
                        return ((off_t) -1);

                if ((size_t) rc < s->s_offset + s->s_size)
                        rc = (off_t) (s->s_offset + s->s_size);
        }

        return (rc);
}

/*
 * Recompute the layout of the ELF object and update the internal data
 * structures associated with the ELF descriptor.
 *
 * Returns the size in bytes the ELF object would occupy in its file
 * representation.
 *
 * After a successful call to this function, the following structures
 * are updated:
 *
 * - The ELF header is updated.
 * - All extents in the ELF object are sorted in order of ascending
 *   addresses.  Sections have their section header table entries
 *   updated.  An error is signalled if an overlap was detected among
 *   extents.
 * - Data descriptors associated with sections are checked for valid
 *   types, offsets and alignment.
 *
 * After a resync_elf() successfully returns, the ELF descriptor is
 * ready for being handed over to _libelf_write_elf().
 */

static off_t
_libelf_resync_elf(Elf *e, struct _Elf_Extent_List *extents)
{
        int ec, eh_class;
        unsigned int eh_byteorder, eh_version;
        size_t align, fsz;
        size_t phnum, shnum;
        off_t rc, phoff, shoff;
        void *ehdr, *phdr;
        Elf32_Ehdr *eh32;
        Elf64_Ehdr *eh64;

        rc = 0;

        ec = e->e_class;

        assert(ec == ELFCLASS32 || ec == ELFCLASS64);

        /*
         * Prepare the EHDR.
         */
        if ((ehdr = _libelf_ehdr(e, ec, 0)) == NULL)
                return ((off_t) -1);

        eh32 = ehdr;
        eh64 = ehdr;

        if (ec == ELFCLASS32) {
                eh_byteorder = eh32->e_ident[EI_DATA];
                eh_class     = eh32->e_ident[EI_CLASS];
                phoff        = (off_t) eh32->e_phoff;
                shoff        = (off_t) eh32->e_shoff;
                eh_version   = eh32->e_version;
        } else {
                eh_byteorder = eh64->e_ident[EI_DATA];
                eh_class     = eh64->e_ident[EI_CLASS];
                phoff        = (off_t) eh64->e_phoff;
                shoff        = (off_t) eh64->e_shoff;
                eh_version   = eh64->e_version;
        }

        if (phoff < 0 || shoff < 0) {
                LIBELF_SET_ERROR(HEADER, 0);
                return ((off_t) -1);
        }

        if (eh_version == EV_NONE)
                eh_version = EV_CURRENT;

        if (eh_version != e->e_version) {       /* always EV_CURRENT */
                LIBELF_SET_ERROR(VERSION, 0);
                return ((off_t) -1);
        }

        if (eh_class != e->e_class) {
                LIBELF_SET_ERROR(CLASS, 0);
                return ((off_t) -1);
        }

        if (e->e_cmd != ELF_C_WRITE && eh_byteorder != e->e_byteorder) {
                LIBELF_SET_ERROR(HEADER, 0);
                return ((off_t) -1);
        }

        shnum = e->e_u.e_elf.e_nscn;
        phnum = e->e_u.e_elf.e_nphdr;

        e->e_byteorder = eh_byteorder;

#define INITIALIZE_EHDR(E,EC,V) do {                                    \
                unsigned int _version = (unsigned int) (V);             \
                (E)->e_ident[EI_MAG0] = ELFMAG0;                        \
                (E)->e_ident[EI_MAG1] = ELFMAG1;                        \
                (E)->e_ident[EI_MAG2] = ELFMAG2;                        \
                (E)->e_ident[EI_MAG3] = ELFMAG3;                        \
                (E)->e_ident[EI_CLASS] = (unsigned char) (EC);          \
                (E)->e_ident[EI_VERSION] = (_version & 0xFFU);          \
                (E)->e_ehsize = (uint16_t) _libelf_fsize(ELF_T_EHDR,    \
                    (EC), _version, (size_t) 1);                        \
                (E)->e_phentsize = (uint16_t) ((phnum == 0) ? 0 :       \
                    _libelf_fsize(ELF_T_PHDR, (EC), _version,           \
                        (size_t) 1));                                   \
                (E)->e_shentsize = (uint16_t) _libelf_fsize(ELF_T_SHDR, \
                    (EC), _version, (size_t) 1);                        \
        } while (0)

        if (ec == ELFCLASS32)
                INITIALIZE_EHDR(eh32, ec, eh_version);
        else
                INITIALIZE_EHDR(eh64, ec, eh_version);

        (void) elf_flagehdr(e, ELF_C_SET, ELF_F_DIRTY);

        rc += (off_t) _libelf_fsize(ELF_T_EHDR, ec, eh_version, (size_t) 1);

        if (!_libelf_insert_extent(extents, ELF_EXTENT_EHDR, 0, (uint64_t) rc,
                ehdr))
                return ((off_t) -1);

        /*
         * Compute the layout the program header table, if one is
         * present.  The program header table needs to be aligned to a
         * `natural' boundary.
         */
        if (phnum) {
                fsz = _libelf_fsize(ELF_T_PHDR, ec, eh_version, phnum);
                align = _libelf_falign(ELF_T_PHDR, ec);

                if (e->e_flags & ELF_F_LAYOUT) {
                        /*
                         * Check offsets for sanity.
                         */
                        if (rc > phoff) {
                                LIBELF_SET_ERROR(LAYOUT, 0);
                                return ((off_t) -1);
                        }

                        if (phoff % (off_t) align) {
                                LIBELF_SET_ERROR(LAYOUT, 0);
                                return ((off_t) -1);
                        }

                } else
                        phoff = roundup(rc, (off_t) align);

                rc = phoff + (off_t) fsz;

                phdr = _libelf_getphdr(e, ec);

                if (!_libelf_insert_extent(extents, ELF_EXTENT_PHDR,
                        (uint64_t) phoff, fsz, phdr))
                        return ((off_t) -1);
        } else
                phoff = 0;

        /*
         * Compute the layout of the sections associated with the
         * file.
         */

        if (e->e_cmd != ELF_C_WRITE &&
            (e->e_flags & LIBELF_F_SHDRS_LOADED) == 0 &&
            _libelf_load_section_headers(e, ehdr) == 0)
                return ((off_t) -1);

        if ((rc = _libelf_resync_sections(e, rc, extents)) < 0)
                return ((off_t) -1);

        /*
         * Compute the space taken up by the section header table, if
         * one is needed.
         *
         * If ELF_F_LAYOUT has been asserted, the application may have
         * placed the section header table in between existing
         * sections, so the net size of the file need not increase due
         * to the presence of the section header table.
         *
         * If the library is responsible for laying out the object,
         * the section header table is placed after section data.
         */
        if (shnum) {
                fsz = _libelf_fsize(ELF_T_SHDR, ec, eh_version, shnum);
                align = _libelf_falign(ELF_T_SHDR, ec);

                if (e->e_flags & ELF_F_LAYOUT) {
                        if (shoff % (off_t) align) {
                                LIBELF_SET_ERROR(LAYOUT, 0);
                                return ((off_t) -1);
                        }
                } else
                        shoff = roundup(rc, (off_t) align);

                if (shoff + (off_t) fsz > rc)
                        rc = shoff + (off_t) fsz;

                if (!_libelf_insert_extent(extents, ELF_EXTENT_SHDR,
                        (uint64_t) shoff, fsz, NULL))
                        return ((off_t) -1);
        } else
                shoff = 0;

        /*
         * Set the fields of the Executable Header that could potentially use
         * extended numbering.
         */
        _libelf_setphnum(e, ehdr, ec, phnum);
        _libelf_setshnum(e, ehdr, ec, shnum);

        /*
         * Update the `e_phoff' and `e_shoff' fields if the library is
         * doing the layout.
         */
        if ((e->e_flags & ELF_F_LAYOUT) == 0) {
                if (ec == ELFCLASS32) {
                        eh32->e_phoff = (uint32_t) phoff;
                        eh32->e_shoff = (uint32_t) shoff;
                } else {
                        eh64->e_phoff = (uint64_t) phoff;
                        eh64->e_shoff = (uint64_t) shoff;
                }
        }

        return (rc);
}

/*
 * Write out the contents of an ELF section.
 */

static off_t
_libelf_write_scn(Elf *e, unsigned char *nf, struct _Elf_Extent *ex)
{
        off_t rc;
        int ec, em;
        Elf_Scn *s;
        int elftype;
        Elf_Data *d, dst;
        uint32_t sh_type;
        struct _Libelf_Data *ld;
        uint64_t sh_off, sh_size;
        size_t fsz, msz, nobjects;

        assert(ex->ex_type == ELF_EXTENT_SECTION);

        s = ex->ex_desc;
        rc = (off_t) ex->ex_start;

        if ((ec = e->e_class) == ELFCLASS32) {
                sh_type = s->s_shdr.s_shdr32.sh_type;
                sh_size = (uint64_t) s->s_shdr.s_shdr32.sh_size;
        } else {
                sh_type = s->s_shdr.s_shdr64.sh_type;
                sh_size = s->s_shdr.s_shdr64.sh_size;
        }

        /*
         * Ignore sections that do not allocate space in the file.
         */
        if (sh_type == SHT_NOBITS || sh_type == SHT_NULL || sh_size == 0)
                return (rc);

        elftype = _libelf_xlate_shtype(sh_type);
        assert(elftype >= ELF_T_FIRST && elftype <= ELF_T_LAST);

        sh_off = s->s_offset;
        assert(sh_off % _libelf_falign(elftype, ec) == 0);

        em = _libelf_elfmachine(e);
        assert(em >= EM_NONE && em < EM__LAST__);

        /*
         * If the section has a `rawdata' descriptor, and the section
         * contents have not been modified, use its contents directly.
         * The `s_rawoff' member contains the offset into the original
         * file, while `s_offset' contains its new location in the
         * destination.
         */

        if (STAILQ_EMPTY(&s->s_data)) {

                if ((d = elf_rawdata(s, NULL)) == NULL)
                        return ((off_t) -1);

                STAILQ_FOREACH(ld, &s->s_rawdata, d_next) {

                        d = &ld->d_data;

                        if ((uint64_t) rc < sh_off + d->d_off)
                                (void) memset(nf + rc,
                                    LIBELF_PRIVATE(fillchar),
                                    (size_t) (sh_off + d->d_off -
                                        (uint64_t) rc));
                        rc = (off_t) (sh_off + d->d_off);

                        assert(d->d_buf != NULL);
                        assert(d->d_type == ELF_T_BYTE);
                        assert(d->d_version == e->e_version);

                        (void) memcpy(nf + rc,
                            e->e_rawfile + s->s_rawoff + d->d_off,
                            (size_t) d->d_size);

                        rc += (off_t) d->d_size;
                }

                return (rc);
        }

        /*
         * Iterate over the set of data descriptors for this section.
         * The prior call to _libelf_resync_elf() would have setup the
         * descriptors for this step.
         */

        dst.d_version = e->e_version;

        STAILQ_FOREACH(ld, &s->s_data, d_next) {

                d = &ld->d_data;

                if ((msz = _libelf_msize(d->d_type, ec, e->e_version)) == 0)
                        return ((off_t) -1);

                if ((uint64_t) rc < sh_off + d->d_off)
                        (void) memset(nf + rc,
                            LIBELF_PRIVATE(fillchar),
                            (size_t) (sh_off + d->d_off - (uint64_t) rc));

                rc = (off_t) (sh_off + d->d_off);

                assert(d->d_buf != NULL);
                assert(d->d_version == e->e_version);
                assert(d->d_size % msz == 0);
                assert(msz != 0);

                nobjects = (size_t) (d->d_size / msz);

                fsz = _libelf_fsize(d->d_type, ec, e->e_version, nobjects);

                dst.d_buf    = nf + rc;
                dst.d_size   = fsz;

                if (_libelf_xlate(&dst, d, e->e_byteorder, ec, em, ELF_TOFILE)
                    == NULL)
                        return ((off_t) -1);

                rc += (off_t) fsz;
        }

        return (rc);
}

/*
 * Write out an ELF Executable Header.
 */

static off_t
_libelf_write_ehdr(Elf *e, unsigned char *nf, struct _Elf_Extent *ex)
{
        int ec, em;
        void *ehdr;
        size_t fsz, msz;
        Elf_Data dst, src;

        assert(ex->ex_type == ELF_EXTENT_EHDR);
        assert(ex->ex_start == 0); /* Ehdr always comes first. */

        ec = e->e_class;

        ehdr = _libelf_ehdr(e, ec, 0);
        assert(ehdr != NULL);

        fsz = _libelf_fsize(ELF_T_EHDR, ec, e->e_version, (size_t) 1);
        if ((msz = _libelf_msize(ELF_T_EHDR, ec, e->e_version)) == 0)
                return ((off_t) -1);

        em = _libelf_elfmachine(e);

        (void) memset(&dst, 0, sizeof(dst));
        (void) memset(&src, 0, sizeof(src));

        src.d_buf     = ehdr;
        src.d_size    = msz;
        src.d_type    = ELF_T_EHDR;
        src.d_version = dst.d_version = e->e_version;

        dst.d_buf     = nf;
        dst.d_size    = fsz;

        if (_libelf_xlate(&dst, &src, e->e_byteorder, ec, em, ELF_TOFILE) ==
            NULL)
                return ((off_t) -1);

        return ((off_t) fsz);
}

/*
 * Write out an ELF program header table.
 */

static off_t
_libelf_write_phdr(Elf *e, unsigned char *nf, struct _Elf_Extent *ex)
{
        int ec, em;
        void *ehdr;
        Elf32_Ehdr *eh32;
        Elf64_Ehdr *eh64;
        Elf_Data dst, src;
        size_t fsz, msz, phnum;
        uint64_t phoff;

        assert(ex->ex_type == ELF_EXTENT_PHDR);

        ec = e->e_class;

        ehdr = _libelf_ehdr(e, ec, 0);
        assert(ehdr != NULL);

        phnum = e->e_u.e_elf.e_nphdr;
        assert(phnum > 0);

        if (ec == ELFCLASS32) {
                eh32 = (Elf32_Ehdr *) ehdr;
                phoff = (uint64_t) eh32->e_phoff;
        } else {
                eh64 = (Elf64_Ehdr *) ehdr;
                phoff = eh64->e_phoff;
        }

        em = _libelf_elfmachine(e);

        assert(phoff > 0);
        assert(ex->ex_start == phoff);
        assert(phoff % _libelf_falign(ELF_T_PHDR, ec) == 0);

        (void) memset(&dst, 0, sizeof(dst));
        (void) memset(&src, 0, sizeof(src));

        if ((msz = _libelf_msize(ELF_T_PHDR, ec, e->e_version)) == 0)
                return ((off_t) -1);
        fsz = _libelf_fsize(ELF_T_PHDR, ec, e->e_version, phnum);
        assert(fsz > 0);

        src.d_buf = _libelf_getphdr(e, ec);
        src.d_version = dst.d_version = e->e_version;
        src.d_type = ELF_T_PHDR;
        src.d_size = phnum * msz;

        dst.d_size = fsz;
        dst.d_buf = nf + ex->ex_start;

        if (_libelf_xlate(&dst, &src, e->e_byteorder, ec, em, ELF_TOFILE) ==
            NULL)
                return ((off_t) -1);

        return ((off_t) (phoff + fsz));
}

/*
 * Write out an ELF section header table.
 */

static off_t
_libelf_write_shdr(Elf *e, unsigned char *nf, struct _Elf_Extent *ex)
{
        int ec, em;
        void *ehdr;
        Elf_Scn *scn;
        uint64_t shoff;
        Elf32_Ehdr *eh32;
        Elf64_Ehdr *eh64;
        size_t fsz, msz, nscn;
        Elf_Data dst, src;

        assert(ex->ex_type == ELF_EXTENT_SHDR);

        ec = e->e_class;

        ehdr = _libelf_ehdr(e, ec, 0);
        assert(ehdr != NULL);

        nscn = e->e_u.e_elf.e_nscn;

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

        em = _libelf_elfmachine(e);

        assert(nscn > 0);
        assert(shoff % _libelf_falign(ELF_T_SHDR, ec) == 0);
        assert(ex->ex_start == shoff);

        (void) memset(&dst, 0, sizeof(dst));
        (void) memset(&src, 0, sizeof(src));

        if ((msz = _libelf_msize(ELF_T_SHDR, ec, e->e_version)) == 0)
                return ((off_t) -1);

        src.d_type = ELF_T_SHDR;
        src.d_size = msz;
        src.d_version = dst.d_version = e->e_version;

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

        STAILQ_FOREACH(scn, &e->e_u.e_elf.e_scn, s_next) {
                if (ec == ELFCLASS32)
                        src.d_buf = &scn->s_shdr.s_shdr32;
                else
                        src.d_buf = &scn->s_shdr.s_shdr64;

                dst.d_size = fsz;
                dst.d_buf = nf + ex->ex_start + scn->s_ndx * fsz;

                if (_libelf_xlate(&dst, &src, e->e_byteorder, ec, em,
                        ELF_TOFILE) == NULL)
                        return ((off_t) -1);
        }

        return ((off_t) (ex->ex_start + nscn * fsz));
}

/*
 * Write out the file image.
 *
 * The original file could have been mapped in with an ELF_C_RDWR
 * command and the application could have added new content or
 * re-arranged its sections before calling elf_update().  Consequently
 * its not safe to work `in place' on the original file.  So we
 * malloc() the required space for the updated ELF object and build
 * the object there and write it out to the underlying file at the
 * end.  Note that the application may have opened the underlying file
 * in ELF_C_RDWR and only retrieved/modified a few sections.  We take
 * care to avoid translating file sections unnecessarily.
 *
 * Gaps in the coverage of the file by the file's sections will be
 * filled with the fill character set by elf_fill(3).
 */

static off_t
_libelf_write_elf(Elf *e, off_t newsize, struct _Elf_Extent_List *extents)
{
        off_t nrc, rc;
        Elf_Scn *scn, *tscn;
        struct _Elf_Extent *ex;
        unsigned char *newfile;

        assert(e->e_kind == ELF_K_ELF);
        assert(e->e_cmd == ELF_C_RDWR || e->e_cmd == ELF_C_WRITE);
        assert(e->e_fd >= 0);

        if ((newfile = malloc((size_t) newsize)) == NULL) {
                LIBELF_SET_ERROR(RESOURCE, errno);
                return ((off_t) -1);
        }

        nrc = rc = 0;
        SLIST_FOREACH(ex, extents, ex_next) {

                /* Fill inter-extent gaps. */
                if (ex->ex_start > (size_t) rc)
                        (void) memset(newfile + rc, LIBELF_PRIVATE(fillchar),
                            (size_t) (ex->ex_start - (uint64_t) rc));

                switch (ex->ex_type) {
                case ELF_EXTENT_EHDR:
                        if ((nrc = _libelf_write_ehdr(e, newfile, ex)) < 0)
                                goto error;
                        break;

                case ELF_EXTENT_PHDR:
                        if ((nrc = _libelf_write_phdr(e, newfile, ex)) < 0)
                                goto error;
                        break;

                case ELF_EXTENT_SECTION:
                        if ((nrc = _libelf_write_scn(e, newfile, ex)) < 0)
                                goto error;
                        break;

                case ELF_EXTENT_SHDR:
                        if ((nrc = _libelf_write_shdr(e, newfile, ex)) < 0)
                                goto error;
                        break;

                default:
                        assert(0);
                        break;
                }

                assert(ex->ex_start + ex->ex_size == (size_t) nrc);
                assert(rc < nrc);

                rc = nrc;
        }

        assert(rc == newsize);

        /*
         * For regular files, throw away existing file content and
         * unmap any existing mappings.
         */
        if ((e->e_flags & LIBELF_F_SPECIAL_FILE) == 0) {
                if (ftruncate(e->e_fd, (off_t) 0) < 0 ||
                    lseek(e->e_fd, (off_t) 0, SEEK_SET)) {
                        LIBELF_SET_ERROR(IO, errno);
                        goto error;
                }
#if     ELFTC_HAVE_MMAP
                if (e->e_flags & LIBELF_F_RAWFILE_MMAP) {
                        assert(e->e_rawfile != NULL);
                        assert(e->e_cmd == ELF_C_RDWR);
                        if (munmap(e->e_rawfile, (size_t) e->e_rawsize) < 0) {
                                LIBELF_SET_ERROR(IO, errno);
                                goto error;
                        }
                }
#endif
        }

        /*
         * Write out the new contents.
         */
        if (write(e->e_fd, newfile, (size_t) newsize) != newsize) {
                LIBELF_SET_ERROR(IO, errno);
                goto error;
        }

        /*
         * For files opened in ELF_C_RDWR mode, set up the new 'raw'
         * contents.
         */
        if (e->e_cmd == ELF_C_RDWR) {
                assert(e->e_rawfile != NULL);
                assert((e->e_flags & LIBELF_F_RAWFILE_MALLOC) ||
                    (e->e_flags & LIBELF_F_RAWFILE_MMAP));
                if (e->e_flags & LIBELF_F_RAWFILE_MALLOC) {
                        assert((e->e_flags & LIBELF_F_RAWFILE_MMAP) == 0);
                        free(e->e_rawfile);
                        e->e_rawfile = newfile;
                        newfile = NULL;
                }
#if     ELFTC_HAVE_MMAP
                else if (e->e_flags & LIBELF_F_RAWFILE_MMAP) {
                        assert((e->e_flags & LIBELF_F_RAWFILE_MALLOC) == 0);
                        if ((e->e_rawfile = mmap(NULL, (size_t) newsize,
                            PROT_READ, MAP_PRIVATE, e->e_fd, (off_t) 0)) ==
                            MAP_FAILED) {
                                LIBELF_SET_ERROR(IO, errno);
                                goto error;
                        }
                }
#endif  /* ELFTC_HAVE_MMAP */

                /* Record the new size of the file. */
                e->e_rawsize = newsize;
        } else {
                /* File opened in ELF_C_WRITE mode. */
                assert(e->e_rawfile == NULL);
        }

        /*
         * Reset flags, remove existing section descriptors and
         * {E,P}HDR pointers so that a subsequent elf_get{e,p}hdr()
         * and elf_getscn() will function correctly.
         */

        e->e_flags &= ~ELF_F_DIRTY;

        STAILQ_FOREACH_SAFE(scn, &e->e_u.e_elf.e_scn, s_next, tscn)
                _libelf_release_scn(scn);

        if (e->e_class == ELFCLASS32) {
                free(e->e_u.e_elf.e_ehdr.e_ehdr32);
                if (e->e_u.e_elf.e_phdr.e_phdr32)
                        free(e->e_u.e_elf.e_phdr.e_phdr32);

                e->e_u.e_elf.e_ehdr.e_ehdr32 = NULL;
                e->e_u.e_elf.e_phdr.e_phdr32 = NULL;
        } else {
                free(e->e_u.e_elf.e_ehdr.e_ehdr64);
                if (e->e_u.e_elf.e_phdr.e_phdr64)
                        free(e->e_u.e_elf.e_phdr.e_phdr64);

                e->e_u.e_elf.e_ehdr.e_ehdr64 = NULL;
                e->e_u.e_elf.e_phdr.e_phdr64 = NULL;
        }

        /* Free the temporary buffer. */
        if (newfile)
                free(newfile);

        return (rc);

 error:
        free(newfile);

        return ((off_t) -1);
}

/*
 * Update an ELF object.
 */

off_t
elf_update(Elf *e, Elf_Cmd c)
{
        int ec;
        off_t rc;
        struct _Elf_Extent_List extents;

        rc = (off_t) -1;

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

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

        if (e->e_version == EV_NONE)
                e->e_version = EV_CURRENT;

        if (c == ELF_C_WRITE && e->e_cmd == ELF_C_READ) {
                LIBELF_SET_ERROR(MODE, 0);
                return (rc);
        }

        SLIST_INIT(&extents);

        if ((rc = _libelf_resync_elf(e, &extents)) < 0)
                goto done;

        if (c == ELF_C_NULL)
                goto done;

        if (e->e_fd < 0) {
                rc = (off_t) -1;
                LIBELF_SET_ERROR(SEQUENCE, 0);
                goto done;
        }

        rc = _libelf_write_elf(e, rc, &extents);

done:
        _libelf_release_extents(&extents);
        return (rc);
}