DarwinFindSymbol.cpp

/* Cydia Substrate - Powerful Code Insertion Platform
 * Copyright (C) 2008-2011  Jay Freeman (saurik)
*/

/* GNU Lesser General Public License, Version 3 {{{ */
/*
 * Substrate is free software: you can redistribute it and/or modify it under
 * the terms of the GNU Lesser General Public License as published by the
 * Free Software Foundation, either version 3 of the License, or (at your
 * option) any later version.
 *
 * Substrate is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
**/
/* }}} */

#include <mach/mach.h>
#include <mach/mach_init.h>

#include <mach-o/dyld.h>
#include <mach-o/fat.h>
#include <mach-o/loader.h>

extern "C" {
#include <mach-o/nlist.h>
}

#define BSD_KERNEL_PRIVATE
#include <machine/types.h>
#include <machine/exec.h>

#include <stdio.h>
#include <stdlib.h>

#include "CydiaSubstrate.h"

#define _trace() do { \
    MSLog(MSLogLevelNotice, "_trace(%u)", __LINE__); \
} while (false)

struct MSSymbolData {
    const char *name_;
    uint8_t type_;
    uint8_t sect_;
    int16_t desc_;
    uintptr_t value_;
};

#ifdef __LP64__
typedef struct mach_header_64 mach_header_xx;
typedef struct nlist_64 nlist_xx;
typedef struct segment_command_64 segment_command_xx;

static const uint32_t LC_SEGMENT_XX = LC_SEGMENT_64;
static const uint32_t MH_MAGIC_XX = MH_MAGIC_64;
#else
typedef struct mach_header mach_header_xx;
typedef struct nlist nlist_xx;
typedef struct segment_command segment_command_xx;

static const uint32_t LC_SEGMENT_XX = LC_SEGMENT;
static const uint32_t MH_MAGIC_XX = MH_MAGIC;
#endif

static ssize_t MSMachONameList_(const void *stuff, struct MSSymbolData *list, size_t nreq) {
    // XXX: ok, this is just pathetic; API fail much?
    size_t slide(0);
    for (uint32_t image(0), images(_dyld_image_count()); image != images; ++image)
        if (_dyld_get_image_header(image) == stuff) {
            slide = _dyld_get_image_vmaddr_slide(image);
            goto fat;
        }

    return -1;

  fat:
    const uint8_t *base(reinterpret_cast<const uint8_t *>(stuff));
    const struct exec *buf(reinterpret_cast<const struct exec *>(base));

    if (OSSwapBigToHostInt32(buf->a_magic) == FAT_MAGIC) {
        struct host_basic_info hbi; {
            host_t host(mach_host_self());
            mach_msg_type_number_t count(HOST_BASIC_INFO_COUNT);
            if (host_info(host, HOST_BASIC_INFO, reinterpret_cast<host_info_t>(&hbi), &count) != KERN_SUCCESS)
                return -1;
            mach_port_deallocate(mach_task_self(), host);
        }

        const struct fat_header *fh(reinterpret_cast<const struct fat_header *>(base));
        uint32_t nfat_arch(OSSwapBigToHostInt32(fh->nfat_arch));
        const struct fat_arch *fat_archs(reinterpret_cast<const struct fat_arch *>(fh + 1));

        for (uint32_t i(0); i != nfat_arch; ++i)
            if (static_cast<cpu_type_t>(OSSwapBigToHostInt32(fat_archs[i].cputype)) == hbi.cpu_type) {
                buf = reinterpret_cast<const struct exec *>(base + OSSwapBigToHostInt32(fat_archs[i].offset));
                goto thin;
            }

        return -1;
    }

  thin:
    const nlist_xx *symbols;
    const char *strings;
    size_t n;

    // XXX: this check looks really scary when it fails
    if (buf->a_magic == MH_MAGIC_XX) {
        const mach_header_xx *mh(reinterpret_cast<const mach_header_xx *>(base));
        const struct load_command *load_commands(reinterpret_cast<const struct load_command *>(mh + 1));

        const struct symtab_command *stp(NULL);
        const struct load_command *lcp;

        /* forlc (command, mh, LC_SYMTAB, struct symtab_command) {
            stp = command;
            goto found;
        } */

        lcp = load_commands;
        for (uint32_t i(0); i != mh->ncmds; ++i) {
            if (
                lcp->cmdsize % sizeof(long) != 0 || lcp->cmdsize <= 0 ||
                reinterpret_cast<const uint8_t *>(lcp) + lcp->cmdsize > reinterpret_cast<const uint8_t *>(load_commands) + mh->sizeofcmds
            )
                return -1;

            if (lcp->cmd == LC_SYMTAB) {
                if (lcp->cmdsize != sizeof(struct symtab_command))
                    return -1;
                stp = reinterpret_cast<const struct symtab_command *>(lcp);
                goto found;
            }

            lcp = reinterpret_cast<const struct load_command *>(reinterpret_cast<const uint8_t *>(lcp) + lcp->cmdsize);
        }

        return -1;

      found:
        n = stp->nsyms;

        symbols = NULL;
        strings = NULL;

        /* forlc (command, mh, LC_SEGMENT_XX, segment_command_xx) {
            stp = command;
            goto found;
        } */

        lcp = load_commands;
        for (uint32_t i(0); i != mh->ncmds; ++i) {
            if (
                lcp->cmdsize % sizeof(long) != 0 || lcp->cmdsize <= 0 ||
                reinterpret_cast<const uint8_t *>(lcp) + lcp->cmdsize > reinterpret_cast<const uint8_t *>(load_commands) + mh->sizeofcmds
            )
                return -1;

            if (lcp->cmd == LC_SEGMENT_XX) {
                if (lcp->cmdsize < sizeof(segment_command_xx))
                    return -1;
                const segment_command_xx *segment(reinterpret_cast<const segment_command_xx *>(lcp));
                if (stp->symoff >= segment->fileoff && stp->symoff < segment->fileoff + segment->filesize)
                    symbols = reinterpret_cast<const nlist_xx *>(stp->symoff - segment->fileoff + segment->vmaddr + slide);
                if (stp->stroff >= segment->fileoff && stp->stroff < segment->fileoff + segment->filesize)
                    strings = reinterpret_cast<const char *>(stp->stroff - segment->fileoff + segment->vmaddr + slide);
            }

            lcp = reinterpret_cast<const struct load_command *>(reinterpret_cast<const uint8_t *>(lcp) + lcp->cmdsize);
        }

        if (symbols == NULL || strings == NULL)
            return -1;
    // XXX: detect a.out somehow?
    } else if (false) {
        /* XXX: is this right anymore?!? */
        symbols = reinterpret_cast<const nlist_xx *>(base + N_SYMOFF(*buf));
        strings = reinterpret_cast<const char *>(reinterpret_cast<const uint8_t *>(symbols) + buf->a_syms);
        n = buf->a_syms / sizeof(nlist_xx);
    } else return -1;

    size_t result(nreq);

    for (size_t m(0); m != n; ++m) {
        const nlist_xx *q(&symbols[m]);
        if (q->n_un.n_strx == 0 || (q->n_type & N_STAB) != 0)
            continue;

        const char *nambuf(strings + q->n_un.n_strx);
        //fprintf(stderr, " == %s\n", nambuf);

        for (size_t item(0); item != nreq; ++item) {
            struct MSSymbolData *p(list + item);
            if (p->name_ == NULL || strcmp(p->name_, nambuf) != 0)
                continue;

            p->name_ = NULL;

            p->value_ = q->n_value;
            if (p->value_ != 0)
                p->value_ += slide;

            p->type_ = q->n_type;
            p->desc_ = q->n_desc;
            p->sect_ = q->n_sect;

            if (--result == 0)
                return 0;
            break;
        }
    }

    return result;
}

_extern MSImageRef MSGetImageByName(const char *file) {
    for (uint32_t image(0), images(_dyld_image_count()); image != images; ++image)
        if (strcmp(_dyld_get_image_name(image), file) == 0)
            return _dyld_get_image_header(image);
    return NULL;
}

static void MSFindSymbols(MSImageRef image, size_t count, const char *names[], void *values[]) {
    MSSymbolData items[count];

    for (size_t index(0); index != count; ++index) {
        MSSymbolData &item(items[index]);

        item.name_ = names[index];
        item.type_ = 0;
        item.sect_ = 0;
        item.desc_ = 0;
        item.value_ = 0;
    }

    if (image != NULL)
        MSMachONameList_(image, items, count);
    else {
        size_t remain(count);

        for (uint32_t image(0), images(_dyld_image_count()); image != images; ++image) {
            //fprintf(stderr, ":: %s\n", _dyld_get_image_name(image));

            ssize_t result(MSMachONameList_(_dyld_get_image_header(image), items, count));
            if (result == -1)
                continue;

            // XXX: maybe avoid this happening at all? a flag to NSMachONameList_?
            for (size_t index(0); index != count; ++index) {
                MSSymbolData &item(items[index]);
                if (item.name_ == NULL && item.value_ == 0) {
                    ++result;
                    item.name_ = names[index];
                }
            }

            remain -= count - result;
            if (remain == 0)
                break;
        }
    }

    for (size_t index(0); index != count; ++index) {
        MSSymbolData &item(items[index]);
        uintptr_t value(item.value_);
#ifdef __arm__
        if ((item.desc_ & N_ARM_THUMB_DEF) != 0)
            value |= 0x00000001;
#endif
        values[index] = reinterpret_cast<void *>(value);
    }
}

_extern void *MSFindSymbol(MSImageRef image, const char *name) {
    void *value;
    MSFindSymbols(image, 1, &name, &value);
    return value;
}

#ifdef __arm__
MSHook(int, nlist, const char *file, struct nlist *names) {
    const void *image(MSGetImageByName(file));
    if (image == NULL)
        return (*_nlist)(file, names);

    size_t count(0);
    for (struct nlist *list(names); list->n_un.n_name != NULL; ++list)
        ++count;

    MSSymbolData items[count];

    for (size_t index(0); index != count; ++index) {
        MSSymbolData &item(items[index]);
        struct nlist &name(names[index]);

        item.name_ = name.n_un.n_name;
        item.type_ = 0;
        item.sect_ = 0;
        item.desc_ = 0;
        item.value_ = 0;
    }

    int result(MSMachONameList_(image, items, count));

    for (size_t index(0); index != count; ++index) {
        MSSymbolData &item(items[index]);
        struct nlist &name(names[index]);

        name.n_type = item.type_;
        name.n_sect = item.sect_;
        name.n_desc = item.desc_;
        name.n_value = item.value_;
    }

    return result;
}

MSInitialize {
    MSHookFunction(&nlist, MSHake(nlist));
}
#endif