/* -*- mode:c; c-file-style:"k&r"; c-basic-offset: 4; tab-width:4; indent-tabs-mode:nil; mode:auto-fill; fill-column:78; -*- */
/* vim: set ts=4 sw=4 et tw=78 fo=cqt wm=0: */

/* Copyright (C) 2014 OSCAR lab, Stony Brook University
   This file is part of Graphene Library OS.

   Graphene Library OS is free software: you can redistribute it and/or
   modify it under the terms of the GNU General Public License
   as published by the Free Software Foundation, either version 3 of the
   License, or (at your option) any later version.

   Graphene Library OS 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

/*
 * shim_clone.c
 *
 * Implementation of system call "clone". (using "clone" as "fork" is not
 * implemented yet.)
 */

#include <shim_types.h>
#include <shim_internal.h>
#include <shim_table.h>
#include <shim_thread.h>
#include <shim_utils.h>
#include <shim_profile.h>

#include <pal.h>
#include <pal_error.h>

#include <errno.h>
#include <sys/syscall.h>
#include <sys/mman.h>
#include <linux/sched.h>
#include <asm/prctl.h>

/* from **sysdeps/unix/sysv/linux/x86_64/clone.S:
   The userland implementation is:
   int clone (int (*fn)(void *arg), void *child_stack, int flags, void *arg),
   the kernel entry is:
   int clone (long flags, void *child_stack).

   The parameters are passed in register and on the stack from userland:
   rdi: fn
   rsi: child_stack
   rdx: flags
   rcx: arg
   r8d: TID field in parent
   r9d: thread pointer
   %esp+8:	TID field in child

   The kernel expects:
   rax: system call number
   rdi: flags
   rsi: child_stack
   rdx: TID field in parent
   r10: TID field in child
   r8:  thread pointer
*/

/*
 * This Function is a wrapper around the user provided function.
 * Code flow for clone is as follows - 
 * 1) User application allocates stack for child process and  
 *    calls clone. The clone code sets up the user function 
 *    address and the argument address on the child stack.
 * 2)we Hijack the clone call and control flows to shim_clone 
 * 3)In Shim Clone we just call the DK Api to create a thread by providing a 
 *   wrapper function around the user provided function 
 * 4)PAL layer allocates a stack and then invokes the clone syscall
 * 5)PAL runs thread_init function on PAL allocated Stack
 * 6)thread_init calls our wrapper and gives the user provided stack 
 *   address.
 * 7.In the wrapper function ,we just do the stack switch to user 
 *   Provided stack and execute the user Provided function.
 */

int clone_implementation_wrapper(struct clone_args * arg)
{
    //The child thread created by PAL is now running on the
    //PAL allocated stack. We need to switch the stack to use
    //the user provided stack.

    struct clone_args *pcargs = arg;

    DkObjectsWaitAny(1, &pcargs->create_event, NO_TIMEOUT);
    DkObjectClose(pcargs->create_event);

    struct shim_thread * my_thread = pcargs->thread;
    assert(my_thread);
    get_thread(my_thread);

    if (my_thread->set_child_tid) {
        *(my_thread->set_child_tid) = my_thread->tid;
        debug("clone: tid set at %p\n", my_thread->set_child_tid);
    }

    void * stack = pcargs->stack;
    void * return_pc = pcargs->return_pc;

    struct shim_vma * vma = NULL;
    lookup_supervma(ALIGN_DOWN(stack), allocsize, &vma);
    assert(vma);
    my_thread->stack_top = stack;
    my_thread->stack_red = my_thread->stack = vma->addr;

    __libc_tcb_t tcb;
    allocate_tls(&tcb, my_thread);
    debug_setbuf(&tcb.shim_tcb, true);

    /* Don't signal the initialize event until we are actually init-ed */ 
    DkEventSet(pcargs->initialize_event);

    /***** From here down, we are switching to the user-provided stack ****/

    //user_stack_addr[0] ==> user provided function address
    //user_stack_addr[1] ==> arguments to user provided function.

    debug("child swapping stack to %p return %p: %d\n",
          stack, return_pc, my_thread->tid);

    asm volatile("movq %0, %%rsp\r\n"
                 "pushq %1\r\n"
                 "retq\r\n"
                 : : "r"(stack), "r"(return_pc), "a"(0));
    return 0;
}

/*  long int __arg0 - flags
 *  long int __arg1 - 16 bytes ( 2 words ) offset into the child stack allocated
 *                    by the parent     */

int shim_do_clone (int flags, void * user_stack_addr, int * parent_tidptr,
                   void * tls, int * child_tidptr)
{
    //The Clone Implementation in glibc has setup the child's stack
    //with the function pointer and the argument to the funciton.
    INC_PROFILE_OCCURENCE(syscall_use_ipc);
    struct shim_thread * self = get_cur_thread();
    assert(self);
    struct clone_args * new_args = __alloca(sizeof(struct clone_args));
    memset(new_args, 0, sizeof(struct clone_args));
    int ret = 0;

    assert((flags & ~(CLONE_PARENT_SETTID|CLONE_CHILD_SETTID|
                      CLONE_CHILD_CLEARTID|CLONE_SETTLS|
                      CLONE_VM|CLONE_FILES|
                      CLONE_FS|CLONE_SIGHAND|CLONE_THREAD|
                      CLONE_DETACHED| // Unused
#ifdef CLONE_PTRACE
                      CLONE_PTRACE| // Unused
#endif
                      CLONE_SYSVSEM|CSIGNAL)) == 0);

    new_args->create_event = DkNotificationEventCreate(0);
    if (!new_args->create_event) {
        ret = -PAL_ERRNO;
        goto failed;
    }

    new_args->initialize_event = DkNotificationEventCreate(0);
    if (!new_args->initialize_event) {
        ret = -PAL_ERRNO;
        goto failed;
    }

    new_args->thread = get_new_thread(0);
    if (!new_args->thread) {
        ret = -ENOMEM;
        goto failed;
    }

    new_args->stack     = user_stack_addr;
    new_args->return_pc = *(void **) user_stack_addr;

    if (flags & CLONE_PARENT_SETTID)
        new_args->thread->set_child_tid = parent_tidptr;

    if ((flags & CLONE_CHILD_SETTID) && (flags & CLONE_CHILD_CLEARTID)) {
        ret = -EINVAL;
        goto failed;
    }

    if (flags & CLONE_CHILD_SETTID)
        new_args->thread->set_child_tid = child_tidptr;

    if (flags & CLONE_CHILD_CLEARTID)
        /* Implemented in shim_futex.c: release_clear_child_id */
        new_args->thread->clear_child_tid = parent_tidptr;

    if (flags & CLONE_SETTLS) {
        new_args->thread->tcb = tls;
    } else {
        new_args->thread->tcb = NULL;
    }

    if ((flags & CLONE_VM) != CLONE_VM)
        debug("Fork-like behavior is not yet implemented in clone\n");

    if ((flags & CLONE_FS) != CLONE_FS)
        debug("clone without CLONE_FS is not yet implemented\n");

    if ((flags & CLONE_SIGHAND) != CLONE_SIGHAND)
        debug("clone without CLONE_SIGHAND is not yet implemented\n");

    if ((flags & CLONE_SYSVSEM) != CLONE_SYSVSEM)
        debug("clone without CLONE_SYSVSEM is not yet implemented\n");

    if ((flags & CLONE_THREAD) != CLONE_THREAD)
        new_args->thread->tgid = new_args->thread->tid;

    struct shim_handle_map * handle_map = get_cur_handle_map(self);

    if (flags & CLONE_FILES) {
        set_handle_map(new_args->thread, handle_map);
    } else {
        /* if CLONE_FILES is not given, the new thread should receive
           a copy of current descriptor table */
        struct shim_handle_map * new_map = NULL;

        get_handle_map(handle_map);
        dup_handle_map(&new_map, handle_map);
        set_handle_map(new_args->thread, new_map);
        put_handle_map(handle_map);
    }

    // Invoke DkThreadCreate to spawn off a child process using the actual 
    // "clone" system call. DkThreadCreate allocates a stack for the child 
    // and then runs the given function on that stack However, we want our 
    // child to run on the Parent allocated stack , so once the DkThreadCreate 
    // returns .The parent comes back here - however, the child is Happily 
    // running the function we gave to DkThreadCreate.
    PAL_HANDLE pal_handle = thread_create(clone_implementation_wrapper,
                                          new_args, flags);
    if (!pal_handle) {
        ret = -PAL_ERRNO;
        goto failed;
    }

    new_args->thread->pal_handle = pal_handle;

    new_args->thread->in_vm = new_args->thread->is_alive = true;
    add_thread(new_args->thread);
    set_as_child(NULL, new_args->thread);
    put_thread(new_args->thread);

    if (new_args->thread->set_child_tid)
        *new_args->thread->set_child_tid = new_args->thread->tid;

    DkEventSet(new_args->create_event);

    DkObjectsWaitAny(1, &new_args->initialize_event, NO_TIMEOUT);
    DkObjectClose(new_args->initialize_event);

    return new_args->thread->tid;

failed:
    if (new_args->create_event)
        DkObjectClose(new_args->create_event);
    if (new_args->initialize_event)
        DkObjectClose(new_args->initialize_event);
    if (new_args->thread)
        put_thread(new_args->thread);
    return ret;
}