elf_update.c

来自「M5,一个功能强大的多处理器系统模拟器.很多针对处理器架构,性能的研究都使用它作」· C语言 代码 · 共 886 行 · 第 1/2 页

        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));
}