libelf_ar.c 13.9 KB
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/*-
 * 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 <ar.h>
#include <assert.h>
#include <ctype.h>
#include "libelf.h"
#include <stdlib.h>
#include <string.h>

#include "_libelf.h"

#define	LIBELF_NALLOC_SIZE	16

/*
 * `ar' archive handling.
 *
 * `ar' archives start with signature `ARMAG'.  Each archive member is
 * preceded by a header containing meta-data for the member.  This
 * header is described in <ar.h> (struct ar_hdr).  The header always
 * starts on an even address.  File data is padded with "\n"
 * characters to keep this invariant.
 *
 * Special considerations for `ar' archives:
 *
 * The `ar' header only has space for a 16 character file name.  File
 * names are terminated with a '/', so this effectively leaves 15
 * characters for the actual file name.  In order to accomodate longer
 * file names, names may be stored in a separate 'string table' and
 * referenced indirectly by a member header.  The string table itself
 * appears as an archive member with name "// ".  An indirect file name
 * in an `ar' header matches the pattern "/[0-9]*". The digits form a
 * decimal number that corresponds to a byte offset into the string
 * table where the actual file name of the object starts.  Strings in
 * the string table are padded to start on even addresses.
 *
 * Archives may also have a symbol table (see ranlib(1)), mapping
 * program symbols to object files inside the archive.  A symbol table
 * uses a file name of "/ " in its archive header.  The symbol table
 * is structured as:
 *  - a 4-byte count of entries stored as a binary value, MSB first
 *  - 'n' 4-byte offsets, stored as binary values, MSB first
 *  - 'n' NUL-terminated strings, for ELF symbol names, stored unpadded.
 *
 * If the symbol table and string table are is present in an archive
 * they must be the very first objects and in that order.
 */

/*
 * Convert a string bounded by `start' and `start+sz' (exclusive) to a
 * number in the specified base.
 */
static int
_libelf_ar_get_number(char *s, size_t sz, int base, size_t *ret)
{
        int c, v;
        size_t r;
        char *e;

        assert(base <= 10);

        e = s + sz;

        /* skip leading blanks */
        for (;s < e && (c = *s) == ' '; s++)
                ;

        r = 0L;
        for (;s < e; s++) {
                if ((c = *s) == ' ')
                        break;
                if (c < '0' || c > '9')
                        return (0);
                v = c - '0';
                if (v >= base)		/* Illegal digit. */
                        break;
                r *= base;
                r += v;
        }

        *ret = r;

        return (1);
}

/*
 * Retrieve a string from a name field.  If `rawname' is set, leave
 * ar(1) control characters in.
 */
static char *
_libelf_ar_get_string(const char *buf, size_t bufsize, int rawname)
{
        const char *q;
        char *r;
        size_t sz;

        if (rawname)
                sz = bufsize + 1;
        else {
                /* Skip back over trailing blanks. */
                for (q = buf + bufsize - 1; q >= buf && *q == ' '; --q)
                        ;

                if (q < buf) {
                        /*
                         * If the input buffer only had blanks in it,
                         * return a zero-length string.
                         */
                        buf = "";
                        sz = 1;
                } else {
                        /*
                         * Remove the trailing '/' character, but only
                         * if the name isn't one of the special names
                         * "/" and "//".
                         */
                        if (q > buf + 1 ||
                            (q == (buf + 1) && *buf != '/'))
                                q--;

                        sz = q - buf + 2; /* Space for a trailing NUL. */
                }
        }

        if ((r = malloc(sz)) == NULL) {
                LIBELF_SET_ERROR(RESOURCE, 0);
                return (NULL);
        }

        (void) strncpy(r, buf, sz);
        r[sz - 1] = '\0';

        return (r);
}

/*
 * Retrieve the full name of the archive member.
 */
static char *
_libelf_ar_get_name(char *buf, size_t bufsize, Elf *e)
{
        char c, *q, *r, *s;
        size_t len;
        size_t offset;

        assert(e->e_kind == ELF_K_AR);

        if (buf[0] == '/' && (c = buf[1]) >= '0' && c <= '9') {
                /*
                 * The value in field ar_name is a decimal offset into
                 * the archive string table where the actual name
                 * resides.
                 */
                if (_libelf_ar_get_number(buf + 1, bufsize - 1, 10,
                    &offset) == 0) {
                        LIBELF_SET_ERROR(ARCHIVE, 0);
                        return (NULL);
                }

                if (offset > e->e_u.e_ar.e_rawstrtabsz) {
                        LIBELF_SET_ERROR(ARCHIVE, 0);
                        return (NULL);
                }

                s = q = e->e_u.e_ar.e_rawstrtab + offset;
                r = e->e_u.e_ar.e_rawstrtab + e->e_u.e_ar.e_rawstrtabsz;

                for (s = q; s < r && *s != '/'; s++)
                        ;
                len = s - q + 1; /* space for the trailing NUL */

                if ((s = malloc(len)) == NULL) {
                        LIBELF_SET_ERROR(RESOURCE, 0);
                        return (NULL);
                }

                (void) strncpy(s, q, len);
                s[len - 1] = '\0';

                return (s);
        }

        /*
         * Normal 'name'
         */
        return (_libelf_ar_get_string(buf, bufsize, 0));
}


Elf_Arhdr *
_libelf_ar_gethdr(Elf *e)
{
        Elf *parent;
        struct ar_hdr *arh;
        Elf_Arhdr *eh;
        size_t n;

        if ((parent = e->e_parent) == NULL) {
                LIBELF_SET_ERROR(ARGUMENT, 0);
                return (NULL);
        }

        arh = (struct ar_hdr *) ((uintptr_t) e->e_rawfile - sizeof(struct ar_hdr));

        assert((uintptr_t) arh >= (uintptr_t) parent->e_rawfile + SARMAG);
        assert((uintptr_t) arh <= (uintptr_t) parent->e_rawfile + parent->e_rawsize -
            sizeof(struct ar_hdr));

        if ((eh = malloc(sizeof(Elf_Arhdr))) == NULL) {
                LIBELF_SET_ERROR(RESOURCE, 0);
                return (NULL);
        }

        e->e_arhdr = eh;
        eh->ar_name = eh->ar_rawname = NULL;

        if ((eh->ar_name = _libelf_ar_get_name(arh->ar_name, sizeof(arh->ar_name),
                 parent)) == NULL)
                goto error;

        if (_libelf_ar_get_number(arh->ar_uid, sizeof(arh->ar_uid), 10, &n) == 0)
                goto error;
        eh->ar_uid = (uid_t) n;

        if (_libelf_ar_get_number(arh->ar_gid, sizeof(arh->ar_gid), 10, &n) == 0)
                goto error;
        eh->ar_gid = (gid_t) n;

        if (_libelf_ar_get_number(arh->ar_mode, sizeof(arh->ar_mode), 8, &n) == 0)
                goto error;
        eh->ar_mode = (mode_t) n;

        if (_libelf_ar_get_number(arh->ar_size, sizeof(arh->ar_size), 10, &n) == 0)
                goto error;
        eh->ar_size = n;

        if ((eh->ar_rawname = _libelf_ar_get_string(arh->ar_name,
                 sizeof(arh->ar_name), 1)) == NULL)
                goto error;

        return (eh);

 error:
        if (eh) {
                if (eh->ar_name)
                        free(eh->ar_name);
                if (eh->ar_rawname)
                        free(eh->ar_rawname);
                free(eh);
        }
        e->e_arhdr = NULL;

        return (NULL);
}

Elf *
_libelf_ar_open_member(int fd, Elf_Cmd c, Elf *elf)
{
        Elf *e;
        off_t next;
        struct ar_hdr *arh;
        size_t sz;

        assert(elf->e_kind == ELF_K_AR);

        next = elf->e_u.e_ar.e_next;

        /*
         * `next' is only set to zero by elf_next() when the last
         * member of an archive is processed.
         */
        if (next == (off_t) 0)
                return (NULL);

        assert((next & 1) == 0);

        arh = (struct ar_hdr *) (elf->e_rawfile + next);

        if (_libelf_ar_get_number(arh->ar_size, sizeof(arh->ar_size), 10, &sz) == 0) {
                LIBELF_SET_ERROR(ARCHIVE, 0);
                return (NULL);
        }

        assert(sz > 0);

        arh++;	/* skip over archive member header */

        if ((e = elf_memory((char *) arh, sz)) == NULL)
                return (NULL);

        e->e_fd = fd;
        e->e_cmd = c;

        elf->e_u.e_ar.e_nchildren++;
        e->e_parent = elf;

        return (e);
}

Elf *
_libelf_ar_open(Elf *e)
{
        int i;
        char *s, *end;
        size_t sz;
        struct ar_hdr arh;

        e->e_kind = ELF_K_AR;
        e->e_u.e_ar.e_nchildren = 0;
        e->e_u.e_ar.e_next = (off_t) -1;

        /*
         * Look for special members.
         */

        s = e->e_rawfile + SARMAG;
        end = e->e_rawfile + e->e_rawsize;

        assert(e->e_rawsize > 0);

        /*
         * Look for magic names "/ " and "// " in the first two entries
         * of the archive.
         */
        for (i = 0; i < 2; i++) {

                if (s + sizeof(arh) > end) {
                        LIBELF_SET_ERROR(ARCHIVE, 0);
                        return (NULL);
                }

                (void) memcpy(&arh, s, sizeof(arh));

                if (arh.ar_fmag[0] != '`' || arh.ar_fmag[1] != '\n') {
                        LIBELF_SET_ERROR(ARCHIVE, 0);
                        return (NULL);
                }

                if (arh.ar_name[0] != '/')	/* not a special symbol */
                        break;

                if (_libelf_ar_get_number(arh.ar_size, sizeof(arh.ar_size), 10, &sz) == 0) {
                        LIBELF_SET_ERROR(ARCHIVE, 0);
                        return (NULL);
                }

                assert(sz > 0);

                s += sizeof(arh);

                if (arh.ar_name[1] == ' ') {	/* "/ " => symbol table */

                        e->e_u.e_ar.e_rawsymtab = s;
                        e->e_u.e_ar.e_rawsymtabsz = sz;

                } else if (arh.ar_name[1] == '/' && arh.ar_name[2] == ' ') {

                        /* "// " => string table for long file names */
                        e->e_u.e_ar.e_rawstrtab = s;
                        e->e_u.e_ar.e_rawstrtabsz = sz;
                }

                sz = LIBELF_ADJUST_AR_SIZE(sz);

                s += sz;
        }

        e->e_u.e_ar.e_next = (off_t) (s - e->e_rawfile);

        return (e);
}

/*
 * An ar(1) symbol table has the following layout:
 *
 * The first 4 bytes are a binary count of the number of entries in the
 * symbol table, stored MSB-first.
 *
 * Then there are 'n' 4-byte binary offsets, also stored MSB first.
 *
 * Following this, there are 'n' null-terminated strings.
 */

#define	GET_WORD(P, V) do {			\
                (V) = 0;			\
                (V) = (P)[0]; (V) <<= 8;	\
                (V) += (P)[1]; (V) <<= 8;	\
                (V) += (P)[2]; (V) <<= 8;	\
                (V) += (P)[3];			\
        } while (0)

#define	INTSZ	4

Elf_Arsym *
_libelf_ar_process_symtab(Elf *e, size_t *count)
{
        size_t n, nentries, off;
        Elf_Arsym *symtab, *sym;
        char *p, *s, *end;

        assert(e != NULL);
        assert(count != NULL);

        if (e->e_u.e_ar.e_rawsymtabsz < INTSZ) {
                LIBELF_SET_ERROR(ARCHIVE, 0);
                return (NULL);
        }

        p = e->e_u.e_ar.e_rawsymtab;
        end = p + e->e_u.e_ar.e_rawsymtabsz;

        GET_WORD(p, nentries);
        p += INTSZ;

        if (nentries == 0 || p + nentries * INTSZ >= end) {
                LIBELF_SET_ERROR(ARCHIVE, 0);
                return (NULL);
        }

        /* Allocate space for a nentries + a sentinel. */
        if ((symtab = malloc(sizeof(Elf_Arsym) * (nentries+1))) == NULL) {
                LIBELF_SET_ERROR(RESOURCE, 0);
                return (NULL);
        }

        s = p + (nentries * INTSZ); /* start of the string table. */

        for (n = nentries, sym = symtab; n > 0; n--) {
                off = 0;

                GET_WORD(p, off);

                sym->as_off = off;
                sym->as_hash = elf_hash(s);
                sym->as_name = s;

                p += INTSZ;
                sym++;

                for (; s < end && *s++ != '\0';) /* skip to next string */
                        ;
                if (s > end) {
                        LIBELF_SET_ERROR(ARCHIVE, 0);
                        free(symtab);
                        return (NULL);
                }
        }

        /* Fill up the sentinel entry. */
        sym->as_name = NULL;
        sym->as_hash = ~0UL;
        sym->as_off = (off_t) 0;

        *count = e->e_u.e_ar.e_symtabsz = nentries + 1;
        e->e_u.e_ar.e_symtab = symtab;

        return (symtab);
}