path: root/ext/libelf/elf_update.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/mman.h>
#include <sys/param.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"

/*
 * Update the internal data structures associated with an ELF object.
 * 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 sections are sorted in order of ascending addresses and their
 *   section header table entries updated.   An error is signalled
 *   if an overlap was detected among sections.
 * - All data descriptors associated with a section are sorted in order
 *   of ascending addresses.  Overlaps, if detected, are signalled as
 *   errors.  Other sanity checks for alignments, section types etc. are
 *   made.
 *
 * After a resync_elf() successfully returns, the ELF descriptor is
 * ready for being handed over to _libelf_write_elf().
 *
 * File alignments:
 * PHDR - Addr
 * SHDR - Addr
 *
 * XXX: how do we handle 'flags'.
 */

/*
 * Compute the extents of a section, by looking at the.
 */
static int
_libelf_compute_section_extents(Elf *e, Elf_Scn *s, off_t *rc)
{
        int ec;
        Elf_Data *d, *td;
        unsigned int elftype;
        uint32_t sh_type;
        uint64_t d_align;
        uint64_t sh_align, sh_entsize, sh_offset, sh_size;
        uint64_t scn_size, scn_alignment;

        /*
         * We need to recompute library private data structures if one
         * or more of the following is true:
         * - The underlying Shdr structure has been marked `dirty'.  Significant
         *   fields include: `sh_offset', `sh_type', `sh_size', `sh_addralign'.
         * - The Elf_Data structures part of this section have been marked
         *   `dirty'.  Affected members include `d_align', `d_offset', `d_type',
         *   and `d_size'.
         * - The section as a whole is `dirty', e.g., it has been allocated
         *   using elf_newscn(), or if a new Elf_Data structure was added using
         *   elf_newdata().
         *
         * Each of these conditions would result in the ELF_F_DIRTY bit being
         * set on the section descriptor's `s_flags' field.
         */

        ec = e->e_class;

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

        if (sh_type == SHT_NULL || sh_type == SHT_NOBITS)
                return (1);

        if ((s->s_flags & ELF_F_DIRTY) == 0) {
                if ((size_t) *rc < sh_offset + sh_size)
                        *rc = sh_offset + sh_size;
                return (1);
        }

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

        /*
         * Compute the extent of the data descriptors associated with
         * this section.
         */
        scn_alignment = 0;
        if (sh_align == 0)
                sh_align = _libelf_falign(elftype, ec);

        /* Compute the section alignment. */
        STAILQ_FOREACH(d, &s->s_data, d_next)  {
                if (d->d_type != elftype) {
                        LIBELF_SET_ERROR(DATA, 0);
                        return (0);
                }
                if (d->d_version != e->e_version) {
                        LIBELF_SET_ERROR(VERSION, 0);
                        return (0);
                }
                if ((d_align = d->d_align) % sh_align) {
                        LIBELF_SET_ERROR(LAYOUT, 0);
                        return (0);
                }
                if (d_align == 0 || (d_align & (d_align - 1))) {
                        LIBELF_SET_ERROR(DATA, 0);
                        return (0);
                }
                if (d_align > scn_alignment)
                        scn_alignment = d_align;
        }

        scn_size = 0L;

        STAILQ_FOREACH_SAFE(d, &s->s_data, d_next, td) {
                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 = roundup(scn_size, scn_alignment);
                        d->d_off = scn_size;
                        scn_size += d->d_size;
                }
        }

        /*
         * If the application is requesting full control over the layout
         * of the section, check its values for sanity.
         */
        if (e->e_flags & ELF_F_LAYOUT) {
                if (scn_alignment > sh_align || sh_offset % sh_align ||
                    sh_size < scn_size) {
                        LIBELF_SET_ERROR(LAYOUT, 0);
                        return (0);
                }
        } else {
                /*
                 * Otherwise compute the values in the section header.
                 */

                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;
                sh_offset = roundup(*rc, sh_align);

                if (ec == ELFCLASS32) {
                        s->s_shdr.s_shdr32.sh_addralign = (uint32_t) sh_align;
                        s->s_shdr.s_shdr32.sh_entsize   = (uint32_t) sh_entsize;
                        s->s_shdr.s_shdr32.sh_offset    = (uint32_t) sh_offset;
                        s->s_shdr.s_shdr32.sh_size      = (uint32_t) sh_size;
                } else {
                        s->s_shdr.s_shdr64.sh_addralign = sh_align;
                        s->s_shdr.s_shdr64.sh_entsize   = sh_entsize;
                        s->s_shdr.s_shdr64.sh_offset    = sh_offset;
                        s->s_shdr.s_shdr64.sh_size      = sh_size;
                }
        }

        if ((size_t) *rc < sh_offset + sh_size)
                *rc = sh_offset + sh_size;

        s->s_size = sh_size;
        s->s_offset = sh_offset;
        return (1);
}


/*
 * Insert a section in ascending order in the list
 */

static int
_libelf_insert_section(Elf *e, Elf_Scn *s)
{
        Elf_Scn *t, *prevt;
        uint64_t smax, smin, tmax, tmin;

        smin = s->s_offset;
        smax = smin + s->s_size;

        prevt = NULL;
        STAILQ_FOREACH(t, &e->e_u.e_elf.e_scn, s_next) {
                tmin = t->s_offset;
                tmax = tmin + t->s_size;

                /* check if there is an overlap */
                if (tmax < smin) {
                        prevt = t;
                        continue;
                } else if (smax < tmin)
                        break;
                else {
                        LIBELF_SET_ERROR(LAYOUT, 0);
                        return (0);
                }
        }

        if (prevt)
                STAILQ_INSERT_AFTER(&e->e_u.e_elf.e_scn, prevt, s, s_next);
        else
                STAILQ_INSERT_HEAD(&e->e_u.e_elf.e_scn, s, s_next);
        return (1);
}

static off_t
_libelf_resync_sections(Elf *e, off_t rc)
{
        int ec;
        off_t nrc;
        size_t sh_type;
        Elf_Scn *s, *ts;

        ec = e->e_class;

        /*
         * Make a pass through sections, computing the extent of each
         * section. Order in increasing order of addresses.
         */

        nrc = rc;
        STAILQ_FOREACH(s, &e->e_u.e_elf.e_scn, s_next)
                if (_libelf_compute_section_extents(e, s, &nrc) == 0)
                        return ((off_t) -1);

        STAILQ_FOREACH_SAFE(s, &e->e_u.e_elf.e_scn, s_next, ts) {
                if (ec == ELFCLASS32)
                        sh_type = s->s_shdr.s_shdr32.sh_type;
                else
                        sh_type = s->s_shdr.s_shdr64.sh_type;

                /* XXX Do we need the 'size' field of an SHT_NOBITS section */
                if (sh_type == SHT_NOBITS || sh_type == SHT_NULL)
                        continue;

                if (s->s_offset < (uint64_t) rc) {
                        if (s->s_offset + s->s_size < (uint64_t) rc) {
                                /*
                                 * Try insert this section in the
                                 * correct place in the list,
                                 * detecting overlaps if any.
                                 */
                                STAILQ_REMOVE(&e->e_u.e_elf.e_scn, s, _Elf_Scn,
                                    s_next);
                                if (_libelf_insert_section(e, s) == 0)
                                        return ((off_t) -1);
                        } else {
                                LIBELF_SET_ERROR(LAYOUT, 0);
                                return ((off_t) -1);
                        }
                } else
                        rc = s->s_offset + s->s_size;
        }

        assert(nrc == rc);

        return (rc);
}

static off_t
_libelf_resync_elf(Elf *e)
{
        int ec, eh_class, eh_type;
        unsigned int eh_byteorder, eh_version;
        size_t align, fsz;
        size_t phnum, shnum;
        off_t rc, phoff, shoff;
        void *ehdr;
        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        = (uint64_t) eh32->e_phoff;
                shoff        = (uint64_t) eh32->e_shoff;
                eh_type      = eh32->e_type;
                eh_version   = eh32->e_version;
        } else {
                eh_byteorder = eh64->e_ident[EI_DATA];
                eh_class     = eh64->e_ident[EI_CLASS];
                phoff        = eh64->e_phoff;
                shoff        = eh64->e_shoff;
                eh_type      = eh64->e_type;
                eh_version   = eh64->e_version;
        }

        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 {					\
                (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] = (EC);				\
                (E)->e_ident[EI_VERSION] = (V);				\
                (E)->e_ehsize = _libelf_fsize(ELF_T_EHDR, (EC), (V),	\
                    (size_t) 1);					\
                (E)->e_phentsize = _libelf_fsize(ELF_T_PHDR, (EC), (V),	\
                    (size_t) 1);					\
                (E)->e_shentsize = _libelf_fsize(ELF_T_SHDR, (EC), (V),	\
                    (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 += _libelf_fsize(ELF_T_EHDR, ec, eh_version, (size_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(HEADER, 0);
                                return ((off_t) -1);
                        }

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

                } else
                        phoff = roundup(rc, align);

                rc = phoff + fsz;
        } else
                phoff = 0;

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

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

        /*
         * Compute the space taken up by the section header table, if
         * one is needed.
         */
        if (shnum) {
                fsz = _libelf_fsize(ELF_T_SHDR, ec, eh_version, (size_t) 1);
                align = _libelf_falign(ELF_T_SHDR, ec);

                if (e->e_flags & ELF_F_LAYOUT) {
                        if (rc > shoff) {
                                LIBELF_SET_ERROR(HEADER, 0);
                                return ((off_t) -1);
                        }

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

                rc = shoff + fsz * shnum;
        } 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 a section.
 */

static off_t
_libelf_write_scn(Elf *e, char *nf, Elf_Scn *s, off_t rc)
{
        int ec;
        size_t fsz, msz, nobjects;
        uint32_t sh_type;
        uint64_t sh_off;
        int elftype;
        Elf_Data *d, dst;

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

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


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

        msz = _libelf_msize(elftype, ec, e->e_version);

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

        /*
         * 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(d, &s->s_rawdata, d_next) {
                        if ((uint64_t) rc < sh_off + d->d_off)
                                (void) memset(nf + rc,
                                    LIBELF_PRIVATE(fillchar), sh_off +
                                    d->d_off - rc);
                        rc = 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, d->d_size);

                        rc += 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(d, &s->s_data, d_next) {

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

                rc = sh_off + d->d_off;

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

                nobjects = d->d_size / msz;

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

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

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

                rc += fsz;
        }

        return ((off_t) rc);
}

/*
 * 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)
{
        int ec;
        off_t rc;
        size_t fsz, msz, phnum, shnum;
        uint64_t phoff, shoff;
        void *ehdr;
        char *newfile;
        Elf_Data dst, src;
        Elf_Scn *scn, *tscn;
        Elf32_Ehdr *eh32;
        Elf64_Ehdr *eh64;

        assert(e->e_kind == ELF_K_ELF);
        assert(e->e_cmd != ELF_C_READ);
        assert(e->e_fd >= 0);

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

        ec = e->e_class;

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

        phnum = e->e_u.e_elf.e_nphdr;

        if (ec == ELFCLASS32) {
                eh32 = (Elf32_Ehdr *) ehdr;

                phoff = (uint64_t) eh32->e_phoff;
                shnum = eh32->e_shnum;
                shoff = (uint64_t) eh32->e_shoff;
        } else {
                eh64 = (Elf64_Ehdr *) ehdr;

                phoff = eh64->e_phoff;
                shnum = eh64->e_shnum;
                shoff = eh64->e_shoff;
        }

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

        (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;

        rc = 0;

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

        if (_libelf_xlate(&dst, &src, e->e_byteorder, ec, ELF_TOFILE) ==
            NULL)
                goto error;

        rc += fsz;

        /*
         * Write the program header table if present.
         */

        if (phnum != 0 && phoff != 0) {
                assert((unsigned) rc <= phoff);

                fsz = _libelf_fsize(ELF_T_PHDR, ec, e->e_version, phnum);

                assert(phoff % _libelf_falign(ELF_T_PHDR, ec) == 0);
                assert(fsz > 0);

                src.d_version = dst.d_version = e->e_version;
                src.d_type = ELF_T_PHDR;

                if (ec == ELFCLASS32)
                        src.d_buf = e->e_u.e_elf.e_phdr.e_phdr32;
                else
                        src.d_buf = e->e_u.e_elf.e_phdr.e_phdr64;

                src.d_size = phnum * _libelf_msize(ELF_T_PHDR, ec,
                    e->e_version);

                dst.d_size = fsz;

                if ((uint64_t) rc < phoff)
                        (void) memset(newfile + rc,
                            LIBELF_PRIVATE(fillchar), phoff - rc);

                dst.d_buf = newfile + rc;

                if (_libelf_xlate(&dst, &src, e->e_byteorder, ec, ELF_TOFILE) ==
                    NULL)
                        goto error;

                rc = phoff + fsz;
        }

        /*
         * Write out individual sections.
         */

        STAILQ_FOREACH(scn, &e->e_u.e_elf.e_scn, s_next)
                if ((rc = _libelf_write_scn(e, newfile, scn, rc)) < 0)
                        goto error;

        /*
         * Write out the section header table, if required.
         */

        if (shnum != 0 && shoff != 0) {
                assert((unsigned) rc <= shoff);

                if ((uint64_t) rc < shoff)
                        (void) memset(newfile + rc,
                            LIBELF_PRIVATE(fillchar), shoff - rc);

                rc = shoff;

                assert(rc % _libelf_falign(ELF_T_SHDR, ec) == 0);

                src.d_type = ELF_T_SHDR;
                src.d_size = _libelf_msize(ELF_T_SHDR, ec, e->e_version);
                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 = newfile + rc;

                        if (_libelf_xlate(&dst, &src, e->e_byteorder, ec,
                                ELF_TOFILE) != &dst)
                                goto error;

                        rc += fsz;
                }
        }

        /*
         */

        assert(rc == newsize);

        /*
         * Write out the constructed contents and remap the file in
         * read-only.
         */

        if (e->e_rawfile && munmap(e->e_rawfile, e->e_rawsize) < 0) {
                LIBELF_SET_ERROR(IO, errno);
                goto error;
        }

        if (write(e->e_fd, newfile, (size_t) newsize) != newsize ||
            lseek(e->e_fd, (off_t) 0, SEEK_SET) < 0) {
                LIBELF_SET_ERROR(IO, errno);
                goto error;
        }

        if (e->e_cmd != ELF_C_WRITE) {
                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;
                }
                e->e_rawsize = newsize;
        }

        /*
         * 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 (ec == 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;
        }

        return (rc);

 error:
        if (newfile)
                free(newfile);
        return ((off_t) -1);
}

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

        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);
        }

        if ((rc = _libelf_resync_elf(e)) < 0)
                return (rc);

        if (c == ELF_C_NULL)
                return (rc);

        if (e->e_cmd == ELF_C_READ) {
                /*
                 * This descriptor was opened in read-only mode or by
                 * elf_memory().
                 */
                if (e->e_fd)
                        LIBELF_SET_ERROR(MODE, 0);
                else
                        LIBELF_SET_ERROR(ARGUMENT, 0);
                return ((off_t) -1);
        }

        if (e->e_fd < 0) {
                LIBELF_SET_ERROR(SEQUENCE, 0);
                return ((off_t) -1);
        }

        return (_libelf_write_elf(e, rc));
}