Trampoline.t.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 "DarwinThreadInternal.hpp"

#include "Baton.hpp"
#include "CydiaSubstrate.h"

template <typename Type_>
static _finline void dlset(Baton *baton, Type_ &function, const char *name, void *handle = RTLD_DEFAULT) {
    function = reinterpret_cast<Type_>(baton->dlsym(handle, name));
    if (function == NULL)
        baton->dlerror();
}

void *Routine(void *arg) {
    Baton *baton(reinterpret_cast<Baton *>(arg));

    void *(*dlopen)(const char *, int);
    dlset(baton, dlopen, "dlopen");

    void *handle(dlopen(baton->library, RTLD_LAZY | RTLD_LOCAL));
    if (handle == NULL) {
        baton->dlerror();
        return NULL;
    }

    int (*dlclose)(void *);
    dlset(baton, dlclose, "dlclose");

    dlclose(handle);

    return NULL;
}


// I am unable to link against any external functions, so reimplement bzero
// XXX: there might be a gcc builtin for memset/bzero: use it instead?

static void $bzero(void *data, size_t size) {
    char *bytes(reinterpret_cast<char *>(data));
    for (size_t i(0); i != size; ++i)
        bytes[i] = 0;
}


extern "C" void Start(Baton *baton) {
    // XXX: I am not certain if I should deallocate this port (an academic question, as I can't)
    mach_port_t port(baton->mach_thread_self());

    // normally, a pthread has a _pthread associated with it; pthread_t is a pointer to it
    // these are normally initialized by either _pthread_create or _pthread_struct_init
    // however, for our purposes, just initializing it to 0 is reasonably sufficient
    // XXX: look into using _pthread_create instead (_pthread_struct_init is often private)

    struct _pthread self;
    $bzero(&self, sizeof(self));


    // this code comes from _pthread_set_self, which is the startup routine of _pthread_body
    // XXX: __pthread_set_self seems to syscall thread_set_cthread... what does that do?
    // XXX: if we use _pthread_create/_pthread_struct_init, the tsd[0] will be handled

    self.tsd[0] = &self;
    baton->__pthread_set_self(&self);


    // on ARM, a coprocessor register has been allocated to keep track of a thread identifier
    // on iOS << 4.2, this register points at a pthread_t. the tsd table is at +0x48 offset
    // on iOS >= 4.2, this register points at the tsd table, with pthread_t at +0x00 offset

    // here, we need to detect whether the thread register is pointing at a valid table
    // otherwise, later code that attempts to use _pthread_setspecific_direct will crash
    // luckily, on iOS << 4.2, we also do not need to initialize thread local storage!

    bool setspecific;
#ifdef __arm__
    void **tsd;
    __asm__ ("mrc p15, 0, %0, c13, c0, 3\n" : "=r"(tsd));
    setspecific = tsd != NULL;
#else
    setspecific = true;
#endif


    // the current thread identifier is stored in the 0th thread-specific data slot
    // thread-specific data, especially the 0th slot, is often stored in hardware registers
    // the _pthread_setspecific_direct macro allows us to update these static entries
    // we check setspecific, a variable defined above, to see whether this function works

    // note: it is not sufficient to set tsd[0] or to call _pthread_create/__pthread_set_self
    // even more interestingly, calling the full pthread_setspecific(0) doesn't even work

    if (setspecific)
        _pthread_setspecific_direct(0, &self);


    pthread_t thread;
    baton->pthread_create(&thread, NULL, &Routine, baton);

    void *status;
    baton->pthread_join(thread, &status);

    baton->thread_terminate(port);
}