// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// +build ignore

/*
This program reads a file containing function prototypes
(like syscall_plan9.go) and generates system call bodies.
The prototypes are marked by lines beginning with "//sys"
and read like func declarations if //sys is replaced by func, but:
	* The parameter lists must give a name for each argument.
	  This includes return parameters.
	* The parameter lists must give a type for each argument:
	  the (x, y, z int) shorthand is not allowed.
	* If the return parameter is an error number, it must be named errno.

A line beginning with //sysnb is like //sys, except that the
goroutine will not be suspended during the execution of the system
call.  This must only be used for system calls which can never
block, as otherwise the system call could cause all goroutines to
hang.
*/
package main

import (
	"bufio"
	"flag"
	"fmt"
	"os"
	"regexp"
	"strings"
)

var (
	b32       = flag.Bool("b32", false, "32bit big-endian")
	l32       = flag.Bool("l32", false, "32bit little-endian")
	plan9     = flag.Bool("plan9", false, "plan9")
	openbsd   = flag.Bool("openbsd", false, "openbsd")
	netbsd    = flag.Bool("netbsd", false, "netbsd")
	dragonfly = flag.Bool("dragonfly", false, "dragonfly")
	arm       = flag.Bool("arm", false, "arm") // 64-bit value should use (even, odd)-pair
	tags      = flag.String("tags", "", "build tags")
	filename  = flag.String("output", "", "output file name (standard output if omitted)")
)

// cmdLine returns this programs's commandline arguments
func cmdLine() string {
	return "go run mksyscall.go " + strings.Join(os.Args[1:], " ")
}

// buildTags returns build tags
func buildTags() string {
	return *tags
}

// Param is function parameter
type Param struct {
	Name string
	Type string
}

// usage prints the program usage
func usage() {
	fmt.Fprintf(os.Stderr, "usage: go run mksyscall.go [-b32 | -l32] [-tags x,y] [file ...]\n")
	os.Exit(1)
}

// parseParamList parses parameter list and returns a slice of parameters
func parseParamList(list string) []string {
	list = strings.TrimSpace(list)
	if list == "" {
		return []string{}
	}
	return regexp.MustCompile(`\s*,\s*`).Split(list, -1)
}

// parseParam splits a parameter into name and type
func parseParam(p string) Param {
	ps := regexp.MustCompile(`^(\S*) (\S*)$`).FindStringSubmatch(p)
	if ps == nil {
		fmt.Fprintf(os.Stderr, "malformed parameter: %s\n", p)
		os.Exit(1)
	}
	return Param{ps[1], ps[2]}
}

func main() {
	// Get the OS and architecture (using GOARCH_TARGET if it exists)
	goos := os.Getenv("GOOS")
	goarch := os.Getenv("GOARCH_TARGET")
	if goarch == "" {
		goarch = os.Getenv("GOARCH")
	}

	// Check that we are using the Docker-based build system if we should
	if goos == "linux" {
		if os.Getenv("GOLANG_SYS_BUILD") != "docker" {
			fmt.Fprintf(os.Stderr, "In the Docker-based build system, mksyscall should not be called directly.\n")
			fmt.Fprintf(os.Stderr, "See README.md\n")
			os.Exit(1)
		}
	}

	flag.Usage = usage
	flag.Parse()
	if len(flag.Args()) <= 0 {
		fmt.Fprintf(os.Stderr, "no files to parse provided\n")
		usage()
	}

	endianness := ""
	if *b32 {
		endianness = "big-endian"
	} else if *l32 {
		endianness = "little-endian"
	}

	libc := false
	if goos == "darwin" && strings.Contains(buildTags(), ",go1.12") {
		libc = true
	}
	trampolines := map[string]bool{}

	text := ""
	for _, path := range flag.Args() {
		file, err := os.Open(path)
		if err != nil {
			fmt.Fprintf(os.Stderr, err.Error())
			os.Exit(1)
		}
		s := bufio.NewScanner(file)
		for s.Scan() {
			t := s.Text()
			t = strings.TrimSpace(t)
			t = regexp.MustCompile(`\s+`).ReplaceAllString(t, ` `)
			nonblock := regexp.MustCompile(`^\/\/sysnb `).FindStringSubmatch(t)
			if regexp.MustCompile(`^\/\/sys `).FindStringSubmatch(t) == nil && nonblock == nil {
				continue
			}

			// Line must be of the form
			//	func Open(path string, mode int, perm int) (fd int, errno error)
			// Split into name, in params, out params.
			f := regexp.MustCompile(`^\/\/sys(nb)? (\w+)\(([^()]*)\)\s*(?:\(([^()]+)\))?\s*(?:=\s*((?i)SYS_[A-Z0-9_]+))?$`).FindStringSubmatch(t)
			if f == nil {
				fmt.Fprintf(os.Stderr, "%s:%s\nmalformed //sys declaration\n", path, t)
				os.Exit(1)
			}
			funct, inps, outps, sysname := f[2], f[3], f[4], f[5]

			// Split argument lists on comma.
			in := parseParamList(inps)
			out := parseParamList(outps)

			// Try in vain to keep people from editing this file.
			// The theory is that they jump into the middle of the file
			// without reading the header.
			text += "// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT\n\n"

			// Go function header.
			outDecl := ""
			if len(out) > 0 {
				outDecl = fmt.Sprintf(" (%s)", strings.Join(out, ", "))
			}
			text += fmt.Sprintf("func %s(%s)%s {\n", funct, strings.Join(in, ", "), outDecl)

			// Check if err return available
			errvar := ""
			for _, param := range out {
				p := parseParam(param)
				if p.Type == "error" {
					errvar = p.Name
					break
				}
			}

			// Prepare arguments to Syscall.
			var args []string
			n := 0
			for _, param := range in {
				p := parseParam(param)
				if regexp.MustCompile(`^\*`).FindStringSubmatch(p.Type) != nil {
					args = append(args, "uintptr(unsafe.Pointer("+p.Name+"))")
				} else if p.Type == "string" && errvar != "" {
					text += fmt.Sprintf("\tvar _p%d *byte\n", n)
					text += fmt.Sprintf("\t_p%d, %s = BytePtrFromString(%s)\n", n, errvar, p.Name)
					text += fmt.Sprintf("\tif %s != nil {\n\t\treturn\n\t}\n", errvar)
					args = append(args, fmt.Sprintf("uintptr(unsafe.Pointer(_p%d))", n))
					n++
				} else if p.Type == "string" {
					fmt.Fprintf(os.Stderr, path+":"+funct+" uses string arguments, but has no error return\n")
					text += fmt.Sprintf("\tvar _p%d *byte\n", n)
					text += fmt.Sprintf("\t_p%d, _ = BytePtrFromString(%s)\n", n, p.Name)
					args = append(args, fmt.Sprintf("uintptr(unsafe.Pointer(_p%d))", n))
					n++
				} else if regexp.MustCompile(`^\[\](.*)`).FindStringSubmatch(p.Type) != nil {
					// Convert slice into pointer, length.
					// Have to be careful not to take address of &a[0] if len == 0:
					// pass dummy pointer in that case.
					// Used to pass nil, but some OSes or simulators reject write(fd, nil, 0).
					text += fmt.Sprintf("\tvar _p%d unsafe.Pointer\n", n)
					text += fmt.Sprintf("\tif len(%s) > 0 {\n\t\t_p%d = unsafe.Pointer(&%s[0])\n\t}", p.Name, n, p.Name)
					text += fmt.Sprintf(" else {\n\t\t_p%d = unsafe.Pointer(&_zero)\n\t}\n", n)
					args = append(args, fmt.Sprintf("uintptr(_p%d)", n), fmt.Sprintf("uintptr(len(%s))", p.Name))
					n++
				} else if p.Type == "int64" && (*openbsd || *netbsd) {
					args = append(args, "0")
					if endianness == "big-endian" {
						args = append(args, fmt.Sprintf("uintptr(%s>>32)", p.Name), fmt.Sprintf("uintptr(%s)", p.Name))
					} else if endianness == "little-endian" {
						args = append(args, fmt.Sprintf("uintptr(%s)", p.Name), fmt.Sprintf("uintptr(%s>>32)", p.Name))
					} else {
						args = append(args, fmt.Sprintf("uintptr(%s)", p.Name))
					}
				} else if p.Type == "int64" && *dragonfly {
					if regexp.MustCompile(`^(?i)extp(read|write)`).FindStringSubmatch(funct) == nil {
						args = append(args, "0")
					}
					if endianness == "big-endian" {
						args = append(args, fmt.Sprintf("uintptr(%s>>32)", p.Name), fmt.Sprintf("uintptr(%s)", p.Name))
					} else if endianness == "little-endian" {
						args = append(args, fmt.Sprintf("uintptr(%s)", p.Name), fmt.Sprintf("uintptr(%s>>32)", p.Name))
					} else {
						args = append(args, fmt.Sprintf("uintptr(%s)", p.Name))
					}
				} else if p.Type == "int64" && endianness != "" {
					if len(args)%2 == 1 && *arm {
						// arm abi specifies 64-bit argument uses
						// (even, odd) pair
						args = append(args, "0")
					}
					if endianness == "big-endian" {
						args = append(args, fmt.Sprintf("uintptr(%s>>32)", p.Name), fmt.Sprintf("uintptr(%s)", p.Name))
					} else {
						args = append(args, fmt.Sprintf("uintptr(%s)", p.Name), fmt.Sprintf("uintptr(%s>>32)", p.Name))
					}
				} else {
					args = append(args, fmt.Sprintf("uintptr(%s)", p.Name))
				}
			}

			// Determine which form to use; pad args with zeros.
			asm := "Syscall"
			if nonblock != nil {
				if errvar == "" && goos == "linux" {
					asm = "RawSyscallNoError"
				} else {
					asm = "RawSyscall"
				}
			} else {
				if errvar == "" && goos == "linux" {
					asm = "SyscallNoError"
				}
			}
			if len(args) <= 3 {
				for len(args) < 3 {
					args = append(args, "0")
				}
			} else if len(args) <= 6 {
				asm += "6"
				for len(args) < 6 {
					args = append(args, "0")
				}
			} else if len(args) <= 9 {
				asm += "9"
				for len(args) < 9 {
					args = append(args, "0")
				}
			} else {
				fmt.Fprintf(os.Stderr, "%s:%s too many arguments to system call\n", path, funct)
			}

			// System call number.
			if sysname == "" {
				sysname = "SYS_" + funct
				sysname = regexp.MustCompile(`([a-z])([A-Z])`).ReplaceAllString(sysname, `${1}_$2`)
				sysname = strings.ToUpper(sysname)
			}

			var libcFn string
			if libc {
				asm = "syscall_" + strings.ToLower(asm[:1]) + asm[1:] // internal syscall call
				sysname = strings.TrimPrefix(sysname, "SYS_")         // remove SYS_
				sysname = strings.ToLower(sysname)                    // lowercase
				if sysname == "getdirentries64" {
					// Special case - libSystem name and
					// raw syscall name don't match.
					sysname = "__getdirentries64"
				}
				libcFn = sysname
				sysname = "funcPC(libc_" + sysname + "_trampoline)"
			}

			// Actual call.
			arglist := strings.Join(args, ", ")
			call := fmt.Sprintf("%s(%s, %s)", asm, sysname, arglist)

			// Assign return values.
			body := ""
			ret := []string{"_", "_", "_"}
			doErrno := false
			for i := 0; i < len(out); i++ {
				p := parseParam(out[i])
				reg := ""
				if p.Name == "err" && !*plan9 {
					reg = "e1"
					ret[2] = reg
					doErrno = true
				} else if p.Name == "err" && *plan9 {
					ret[0] = "r0"
					ret[2] = "e1"
					break
				} else {
					reg = fmt.Sprintf("r%d", i)
					ret[i] = reg
				}
				if p.Type == "bool" {
					reg = fmt.Sprintf("%s != 0", reg)
				}
				if p.Type == "int64" && endianness != "" {
					// 64-bit number in r1:r0 or r0:r1.
					if i+2 > len(out) {
						fmt.Fprintf(os.Stderr, "%s:%s not enough registers for int64 return\n", path, funct)
					}
					if endianness == "big-endian" {
						reg = fmt.Sprintf("int64(r%d)<<32 | int64(r%d)", i, i+1)
					} else {
						reg = fmt.Sprintf("int64(r%d)<<32 | int64(r%d)", i+1, i)
					}
					ret[i] = fmt.Sprintf("r%d", i)
					ret[i+1] = fmt.Sprintf("r%d", i+1)
				}
				if reg != "e1" || *plan9 {
					body += fmt.Sprintf("\t%s = %s(%s)\n", p.Name, p.Type, reg)
				}
			}
			if ret[0] == "_" && ret[1] == "_" && ret[2] == "_" {
				text += fmt.Sprintf("\t%s\n", call)
			} else {
				if errvar == "" && goos == "linux" {
					// raw syscall without error on Linux, see golang.org/issue/22924
					text += fmt.Sprintf("\t%s, %s := %s\n", ret[0], ret[1], call)
				} else {
					text += fmt.Sprintf("\t%s, %s, %s := %s\n", ret[0], ret[1], ret[2], call)
				}
			}
			text += body

			if *plan9 && ret[2] == "e1" {
				text += "\tif int32(r0) == -1 {\n"
				text += "\t\terr = e1\n"
				text += "\t}\n"
			} else if doErrno {
				text += "\tif e1 != 0 {\n"
				text += "\t\terr = errnoErr(e1)\n"
				text += "\t}\n"
			}
			text += "\treturn\n"
			text += "}\n\n"

			if libc && !trampolines[libcFn] {
				// some system calls share a trampoline, like read and readlen.
				trampolines[libcFn] = true
				// Declare assembly trampoline.
				text += fmt.Sprintf("func libc_%s_trampoline()\n", libcFn)
				// Assembly trampoline calls the libc_* function, which this magic
				// redirects to use the function from libSystem.
				text += fmt.Sprintf("//go:linkname libc_%s libc_%s\n", libcFn, libcFn)
				text += fmt.Sprintf("//go:cgo_import_dynamic libc_%s %s \"/usr/lib/libSystem.B.dylib\"\n", libcFn, libcFn)
				text += "\n"
			}
		}
		if err := s.Err(); err != nil {
			fmt.Fprintf(os.Stderr, err.Error())
			os.Exit(1)
		}
		file.Close()
	}
	fmt.Printf(srcTemplate, cmdLine(), buildTags(), text)
}

const srcTemplate = `// %s
// Code generated by the command above; see README.md. DO NOT EDIT.

// +build %s

package plan9

import "unsafe"

%s
`
