//go:build linux || darwin
// +build linux darwin

/*
 * Copyright 2021 ByteDance Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package loader

import (
    `fmt`
    `os`
    `reflect`
    `syscall`
    `unsafe`
)

const (
    _AP = syscall.MAP_ANON  | syscall.MAP_PRIVATE
    _RX = syscall.PROT_READ | syscall.PROT_EXEC
    _RW = syscall.PROT_READ | syscall.PROT_WRITE
)

type Loader   []byte
type Function unsafe.Pointer

func (self Loader) LoadWithFaker(fn string, fp int, args int, faker interface{}) (f Function) {
    p := os.Getpagesize()
    n := (((len(self) - 1) / p) + 1) * p

    /* register the function */
    m := mmap(n)
    v := fmt.Sprintf("runtime.__%s_%x", fn, m)
    argsptr, localsptr := stackMap(faker)
    registerFunction(v, m, uintptr(n), fp, args, uintptr(len(self)), argsptr, localsptr)

    /* reference as a slice */
    s := *(*[]byte)(unsafe.Pointer(&reflect.SliceHeader {
        Data : m,
        Cap  : n,
        Len  : len(self),
    }))

    /* copy the machine code, and make it executable */
    copy(s, self)
    mprotect(m, n)
    return Function(&m)
}

func (self Loader) Load(fn string, fp int, args int) (f Function) {
    return self.LoadWithFaker(fn, fp, args, func(){})
}

func mmap(nb int) uintptr {
    if m, _, e := syscall.RawSyscall6(syscall.SYS_MMAP, 0, uintptr(nb), _RW, _AP, 0, 0); e != 0 {
        panic(e)
    } else {
        return m
    }
}

func mprotect(p uintptr, nb int) {
    if _, _, err := syscall.RawSyscall(syscall.SYS_MPROTECT, p, uintptr(nb), _RX); err != 0 {
        panic(err)
    }
}
