os: implement StartProcess

Signed-off-by: leongross <leon.gross@9elements.com>

Author: leongross

GNUmakefile

@@ -941,6 +941,7 @@ endif
 	@cp -rp lib/musl/src/thread          build/release/tinygo/lib/musl/src
 	@cp -rp lib/musl/src/time            build/release/tinygo/lib/musl/src
 	@cp -rp lib/musl/src/unistd          build/release/tinygo/lib/musl/src
+	@cp -rp lib/musl/src/process         build/release/tinygo/lib/musl/src
 	@cp -rp lib/mingw-w64/mingw-w64-crt/def-include                 build/release/tinygo/lib/mingw-w64/mingw-w64-crt
 	@cp -rp lib/mingw-w64/mingw-w64-crt/lib-common/api-ms-win-crt-* build/release/tinygo/lib/mingw-w64/mingw-w64-crt/lib-common
 	@cp -rp lib/mingw-w64/mingw-w64-crt/lib-common/kernel32.def.in  build/release/tinygo/lib/mingw-w64/mingw-w64-crt/lib-common

builder/musl.go

@@ -136,12 +136,20 @@ var libMusl = Library{
 			"thread/*.c",
 			"time/*.c",
 			"unistd/*.c",
+			"process/*.c",
 		}
+
 		if arch == "arm" {
 			// These files need to be added to the start for some reason.
 			globs = append([]string{"thread/arm/*.c"}, globs...)
 		}
 
+		if arch != "aarch64" && arch != "mips" {
+			//aarch64 and mips have no architecture specific code, either they
+			// are not supported or don't need any?
+			globs = append([]string{"process/" + arch + "/*.s"}, globs...)
+		}
+
 		var sources []string
 		seenSources := map[string]struct{}{}
 		basepath := goenv.Get("TINYGOROOT") + "/lib/musl/src/"

src/os/exec.go

@@ -5,6 +5,12 @@ import (
 	"syscall"
 )
 
+var (
+	ErrNotImplementedDir   = errors.New("directory setting not implemented")
+	ErrNotImplementedSys   = errors.New("sys setting not implemented")
+	ErrNotImplementedFiles = errors.New("files setting not implemented")
+)
+
 type Signal interface {
 	String() string
 	Signal() // to distinguish from other Stringers
@@ -47,6 +53,10 @@ func (p *ProcessState) Sys() interface{} {
 	return nil // TODO
 }
 
+func (p *ProcessState) Exited() bool {
+	return false // TODO
+}
+
 // ExitCode returns the exit code of the exited process, or -1
 // if the process hasn't exited or was terminated by a signal.
 func (p *ProcessState) ExitCode() int {
@@ -57,8 +67,10 @@ type Process struct {
 	Pid int
 }
 
+// StartProcess starts a new process with the program, arguments and attributes specified by name, argv and attr.
+// Arguments to the process (os.Args) are passed via argv.
 func StartProcess(name string, argv []string, attr *ProcAttr) (*Process, error) {
-	return nil, &PathError{Op: "fork/exec", Path: name, Err: ErrNotImplemented}
+	return startProcess(name, argv, attr)
 }
 
 func (p *Process) Wait() (*ProcessState, error) {

src/os/exec_linux.go

@@ -0,0 +1,103 @@
+// Copyright 2009 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.
+
+//go:build linux && !baremetal && !tinygo.wasm
+
+package os
+
+import (
+	"errors"
+	"runtime"
+	"syscall"
+)
+
+// The only signal values guaranteed to be present in the os package on all
+// systems are os.Interrupt (send the process an interrupt) and os.Kill (force
+// the process to exit). On Windows, sending os.Interrupt to a process with
+// os.Process.Signal is not implemented; it will return an error instead of
+// sending a signal.
+var (
+	Interrupt Signal = syscall.SIGINT
+	Kill      Signal = syscall.SIGKILL
+)
+
+// Keep compatible with golang and always succeed and return new proc with pid on Linux.
+func findProcess(pid int) (*Process, error) {
+	return &Process{Pid: pid}, nil
+}
+
+func (p *Process) release() error {
+	// NOOP for unix.
+	p.Pid = -1
+	// no need for a finalizer anymore
+	runtime.SetFinalizer(p, nil)
+	return nil
+}
+
+// This function is a wrapper around the forkExec function, which is a wrapper around the fork and execve system calls.
+// The StartProcess function creates a new process by forking the current process and then calling execve to replace the current process with the new process.
+// It thereby replaces the newly created process with the specified command and arguments.
+// Differences to upstream golang implementation (https://cs.opensource.google/go/go/+/master:src/syscall/exec_unix.go;l=143):
+// * No setting of Process Attributes
+// * Ignoring Ctty
+// * No ForkLocking (might be introduced by #4273)
+// * No parent-child communication via pipes (TODO)
+// * No waiting for crashes child processes to prohibit zombie process accumulation / Wait status checking (TODO)
+func forkExec(argv0 string, argv []string, attr *ProcAttr) (pid int, err error) {
+	if argv == nil {
+		return 0, errors.New("exec: no argv")
+	}
+
+	if len(argv) == 0 {
+		return 0, errors.New("exec: no argv")
+	}
+
+	if attr == nil {
+		attr = new(ProcAttr)
+	}
+
+	p, err := fork()
+	pid = int(p)
+
+	if err != nil {
+		return 0, err
+	}
+
+	// else code runs in child, which then should exec the new process
+	err = execve(argv0, argv, attr.Env)
+	if err != nil {
+		// exec failed
+		return 0, err
+	}
+	// 3. TODO: use pipes to communicate back child status
+	return pid, nil
+}
+
+// In Golang, the idiomatic way to create a new process is to use the StartProcess function.
+// Since the Model of operating system processes in tinygo differs from the one in Golang, we need to implement the StartProcess function differently.
+// The startProcess function is a wrapper around the forkExec function, which is a wrapper around the fork and execve system calls.
+// The StartProcess function creates a new process by forking the current process and then calling execve to replace the current process with the new process.
+// It thereby replaces the newly created process with the specified command and arguments.
+func startProcess(name string, argv []string, attr *ProcAttr) (p *Process, err error) {
+	if attr != nil {
+		if attr.Dir != "" {
+			return nil, ErrNotImplementedDir
+		}
+
+		if attr.Sys != nil {
+			return nil, ErrNotImplementedSys
+		}
+
+		if len(attr.Files) != 0 {
+			return nil, ErrNotImplementedFiles
+		}
+	}
+
+	pid, err := forkExec(name, argv, attr)
+	if err != nil {
+		return nil, err
+	}
+
+	return findProcess(pid)
+}

src/os/exec_linux_test.go

@@ -0,0 +1,78 @@
+//go:build linux && !baremetal && !tinygo.wasm
+
+package os_test
+
+import (
+	"errors"
+	. "os"
+	"runtime"
+	"syscall"
+	"testing"
+)
+
+// Test the functionality of the forkExec function, which is used to fork and exec a new process.
+// This test is not run on Windows, as forkExec is not supported on Windows.
+// This test is not run on Plan 9, as forkExec is not supported on Plan 9.
+func TestForkExec(t *testing.T) {
+	if runtime.GOOS != "linux" {
+		t.Logf("skipping test on %s", runtime.GOOS)
+		return
+	}
+
+	proc, err := StartProcess("/bin/echo", []string{"hello", "world"}, &ProcAttr{})
+	if !errors.Is(err, nil) {
+		t.Fatalf("forkExec failed: %v", err)
+	}
+
+	if proc == nil {
+		t.Fatalf("proc is nil")
+	}
+
+	if proc.Pid == 0 {
+		t.Fatalf("forkExec failed: new process has pid 0")
+	}
+}
+
+func TestForkExecErrNotExist(t *testing.T) {
+	proc, err := StartProcess("invalid", []string{"invalid"}, &ProcAttr{})
+	if !errors.Is(err, ErrNotExist) {
+		t.Fatalf("wanted ErrNotExist, got %s\n", err)
+	}
+
+	if proc != nil {
+		t.Fatalf("wanted nil, got %v\n", proc)
+	}
+}
+
+func TestForkExecProcDir(t *testing.T) {
+	proc, err := StartProcess("/bin/echo", []string{"hello", "world"}, &ProcAttr{Dir: "dir"})
+	if !errors.Is(err, ErrNotImplementedDir) {
+		t.Fatalf("wanted ErrNotImplementedDir, got %v\n", err)
+	}
+
+	if proc != nil {
+		t.Fatalf("wanted nil, got %v\n", proc)
+	}
+}
+
+func TestForkExecProcSys(t *testing.T) {
+	proc, err := StartProcess("/bin/echo", []string{"hello", "world"}, &ProcAttr{Sys: &syscall.SysProcAttr{}})
+	if !errors.Is(err, ErrNotImplementedSys) {
+		t.Fatalf("wanted ErrNotImplementedSys, got %v\n", err)
+	}
+
+	if proc != nil {
+		t.Fatalf("wanted nil, got %v\n", proc)
+	}
+}
+
+func TestForkExecProcFiles(t *testing.T) {
+	proc, err := StartProcess("/bin/echo", []string{"hello", "world"}, &ProcAttr{Files: []*File{}})
+	if !errors.Is(err, ErrNotImplementedFiles) {
+		t.Fatalf("wanted ErrNotImplementedFiles, got %v\n", err)
+	}
+
+	if proc != nil {
+		t.Fatalf("wanted nil, got %v\n", proc)
+	}
+}

src/os/exec_other.go

@@ -0,0 +1,27 @@
+//go:build (!aix && !android && !freebsd && !linux && !netbsd && !openbsd && !plan9 && !solaris) || baremetal || tinygo.wasm
+
+package os
+
+import "syscall"
+
+var (
+	Interrupt Signal = syscall.SIGINT
+	Kill      Signal = syscall.SIGKILL
+)
+
+func findProcess(pid int) (*Process, error) {
+	return &Process{Pid: pid}, nil
+}
+
+func (p *Process) release() error {
+	p.Pid = -1
+	return nil
+}
+
+func forkExec(_ string, _ []string, _ *ProcAttr) (pid int, err error) {
+	return 0, ErrNotImplemented
+}
+
+func startProcess(_ string, _ []string, _ *ProcAttr) (proc *Process, err error) {
+	return &Process{Pid: 0}, ErrNotImplemented
+}

src/os/exec_posix.go

@@ -0,0 +1,58 @@
+//go:build linux && !baremetal && !tinygo.wasm
+
+package os
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+func fork() (pid int32, err error) {
+	pid = libc_fork()
+	if pid != 0 {
+		if errno := *libc_errno(); errno != 0 {
+			err = syscall.Errno(*libc_errno())
+		}
+	}
+	return
+}
+
+// the golang standard library does not expose interfaces for execve and fork, so we define them here the same way via the libc wrapper
+func execve(pathname string, argv []string, envv []string) error {
+	argv0 := cstring(pathname)
+
+	// transform argv and envv into the format expected by execve
+	argv1 := make([]*byte, len(argv)+1)
+	for i, arg := range argv {
+		argv1[i] = &cstring(arg)[0]
+	}
+	argv1[len(argv)] = nil
+
+	env1 := make([]*byte, len(envv)+1)
+	for i, env := range envv {
+		env1[i] = &cstring(env)[0]
+	}
+	env1[len(envv)] = nil
+
+	ret, _, err := syscall.Syscall(syscall.SYS_EXECVE, uintptr(unsafe.Pointer(&argv0[0])), uintptr(unsafe.Pointer(&argv1[0])), uintptr(unsafe.Pointer(&env1[0])))
+	if int(ret) != 0 {
+		return err
+	}
+
+	return nil
+}
+
+func cstring(s string) []byte {
+	data := make([]byte, len(s)+1)
+	copy(data, s)
+	// final byte should be zero from the initial allocation
+	return data
+}
+
+//export fork
+func libc_fork() int32
+
+// Internal musl function to get the C errno pointer.
+//
+//export __errno_location
+func libc_errno() *int32

src/os/osexec.go

@@ -233,6 +233,11 @@ func (w WaitStatus) Continued() bool    { return false }
 func (w WaitStatus) StopSignal() Signal { return 0 }
 func (w WaitStatus) TrapCause() int     { return 0 }
 
+// since rusage is quite a big struct and we stub it out anyway no need to define it here
+func Wait4(pid int, wstatus *WaitStatus, options int, rusage uintptr) (wpid int, err error) {
+	return 0, ENOSYS // TODO
+}
+
 func Getenv(key string) (value string, found bool) {
 	data := cstring(key)
 	raw := libc_getenv(&data[0])

src/syscall/syscall_libc.go

@@ -1,3 +1,5 @@
+//go:build linux || unix
+
 package syscall
 
 func Exec(argv0 string, argv []string, envv []string) (err error)