add minified StartProcess implementation (hacky)

Signed-off-by: leongross <[email protected]>

Author: leongross

src/os/exec.go

@@ -57,8 +57,10 @@ type Process struct {
 	Pid int
 }
 
+// Create a lightweight implementation of execve / syscall.StartProcess
+// Do not save all the proc info as golang does but make some sanity checks
 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) {
@@ -92,3 +94,7 @@ func (p *Process) Release() error {
 func FindProcess(pid int) (*Process, error) {
 	return findProcess(pid)
 }
+
+func ForkExec(argv0 string, argv []string, attr *ProcAttr) (pid int, err error) {
+	return forkExec(argv0, argv, attr)
+}

src/os/exec_posix.go

@@ -9,6 +9,7 @@ package os
 import (
 	"runtime"
 	"syscall"
+	"unsafe"
 )
 
 // The only signal values guaranteed to be present in the os package on all
@@ -33,3 +34,55 @@ func (p *Process) release() error {
 	runtime.SetFinalizer(p, nil)
 	return nil
 }
+
+// Combination of fork and exec, careful to be thread safe.
+
+// https://cs.opensource.google/go/go/+/master:src/syscall/exec_unix.go;l=143?q=forkExec&ss=go%2Fgo
+// losely inspired by the golang implementation
+// This is a hacky fire-and forget implementation without setting any attributes, using pipes or checking for errors
+func forkExec(argv0 string, argv []string, attr *ProcAttr) (pid int, err error) {
+	// Convert args to C form.
+	var (
+		ret uintptr
+	)
+
+	argv0p, err := syscall.BytePtrFromString(argv0)
+	if err != nil {
+		return 0, err
+	}
+	argvp, err := syscall.SlicePtrFromStrings(argv)
+	if err != nil {
+		return 0, err
+	}
+	envvp, err := syscall.SlicePtrFromStrings(attr.Env)
+	if err != nil {
+		return 0, err
+	}
+
+	// pid, _, _ = syscall.Syscall6(syscall.SYS_FORK, 0, 0, 0, 0, 0, 0)
+	// 1. fork
+	ret, _, _ = syscall.Syscall(syscall.SYS_FORK, 0, 0, 0)
+	if ret != 0 {
+		// parent
+		return int(ret), nil
+	} else {
+		// 2. exec
+		ret, _, _ = syscall.Syscall6(syscall.SYS_EXECVE, uintptr(unsafe.Pointer(argv0p)), uintptr(unsafe.Pointer(&argvp[0])), uintptr(unsafe.Pointer(&envvp[0])), 0, 0, 0)
+		if ret != 0 {
+			// exec failed
+			syscall.Exit(1)
+		}
+		// 3. TODO: use pipes to communicate back child status
+		return int(ret), nil
+	}
+}
+
+// in regular go this is where the forkExec thingy comes in play
+func startProcess(name string, argv []string, attr *ProcAttr) (p *Process, err error) {
+	pid, err := ForkExec(name, argv, attr)
+	if err != nil {
+		return nil, err
+	}
+
+	return findProcess(pid)
+}

src/syscall/syscall.go

@@ -2,6 +2,8 @@ package syscall
 
 import (
 	"errors"
+
+	"github.com/tinygo-org/tinygo/src/internal/bytealg"
 )
 
 const (
@@ -10,6 +12,11 @@ const (
 	AF_INET6     = 0xa
 )
 
+const (
+	// #define	EINVAL	22	/* Invalid argument			*/
+	EINVAL = 22
+)
+
 func Exit(code int)
 
 type Rlimit struct {
@@ -20,3 +27,27 @@ type Rlimit struct {
 func Setrlimit(resource int, rlim *Rlimit) error {
 	return errors.New("Setrlimit not implemented")
 }
+
+// ByteSliceFromString returns a NUL-terminated slice of bytes
+// containing the text of s. If s contains a NUL byte at any
+// location, it returns (nil, [EINVAL]).
+// https://cs.opensource.google/go/go/+/master:src/syscall/syscall.go;l=45;drc=94982a07825aec711f11c97283e99e467838d616
+func ByteSliceFromString(s string) ([]byte, error) {
+	if bytealg.IndexByteString(s, 0) != -1 {
+		return nil, errors.New("contains NUL")
+	}
+	a := make([]byte, len(s)+1)
+	copy(a, s)
+	return a, nil
+}
+
+// BytePtrFromString returns a pointer to a NUL-terminated array of
+// bytes containing the text of s. If s contains a NUL byte at any
+// location, it returns (nil, [EINVAL]).
+func BytePtrFromString(s string) (*byte, error) {
+	a, err := ByteSliceFromString(s)
+	if err != nil {
+		return nil, err
+	}
+	return &a[0], nil
+}