@@ -152,7 +152,10 @@ func (d *dispatchRequest) getImageMount(imageRefOrID string) (*imageMount, error

 //

 func initializeStage(d dispatchRequest, cmd *instructions.Stage) error {

 	d.builder.imageProber.Reset()

-	image, err := d.getFromImage(d.shlex, cmd.BaseName, cmd.OperatingSystem)

+	if err := system.ValidatePlatform(&cmd.Platform); err != nil {

+		return err

+	}

+	image, err := d.getFromImage(d.shlex, cmd.BaseName, cmd.Platform.OS)

 	if err != nil {

 		return err

 	}

@@ -215,32 +218,29 @@ func (d *dispatchRequest) getExpandedImageName(shlex *shell.Lex, name string) (s

 // stagePlatform contains the value supplied by optional `--platform=` on

 // a current FROM statement. b.builder.options.Platform contains the operating

 // system part of the optional flag passed in the API call (or CLI flag

-// through `docker build --platform=...`).

-func (d *dispatchRequest) getOsFromFlagsAndStage(stagePlatform string) string {

-	osForPull := ""

-	// First, take the API platform if nothing provided on FROM

-	if stagePlatform == "" && d.builder.options.Platform != "" {

-		osForPull = d.builder.options.Platform

-	}

-	// Next, use the FROM flag if that was provided

-	if osForPull == "" && stagePlatform != "" {

-		osForPull = stagePlatform

-	}

-	// Finally, assume the host OS

-	if osForPull == "" {

-		osForPull = runtime.GOOS

-	}

-	return osForPull

+// through `docker build --platform=...`). Precedence is for an explicit

+// platform indication in the FROM statement.

+func (d *dispatchRequest) getOsFromFlagsAndStage(stageOS string) string {

+	switch {

+	case stageOS != "":

+		return stageOS

+	case d.builder.options.Platform != "":

+		// Note this is API "platform", but by this point, as the daemon is not

+		// multi-arch aware yet, it is guaranteed to only hold the OS part here.

+		return d.builder.options.Platform

+	default:

+		return runtime.GOOS

+	}

 }

-func (d *dispatchRequest) getImageOrStage(name string, stagePlatform string) (builder.Image, error) {

+func (d *dispatchRequest) getImageOrStage(name string, stageOS string) (builder.Image, error) {

 	var localOnly bool

 	if im, ok := d.stages.getByName(name); ok {

 		name = im.Image

 		localOnly = true

 	}

-	os := d.getOsFromFlagsAndStage(stagePlatform)

+	os := d.getOsFromFlagsAndStage(stageOS)

 	// Windows cannot support a container with no base image unless it is LCOW.

 	if name == api.NoBaseImageSpecifier {

@@ -267,12 +267,12 @@ func (d *dispatchRequest) getImageOrStage(name string, stagePlatform string) (bu

 	}

 	return imageMount.Image(), nil

 }

-func (d *dispatchRequest) getFromImage(shlex *shell.Lex, name string, stagePlatform string) (builder.Image, error) {

+func (d *dispatchRequest) getFromImage(shlex *shell.Lex, name string, stageOS string) (builder.Image, error) {

 	name, err := d.getExpandedImageName(shlex, name)

 	if err != nil {

 		return nil, err

 	}

-	return d.getImageOrStage(name, stagePlatform)

+	return d.getImageOrStage(name, stageOS)

 }

 func dispatchOnbuild(d dispatchRequest, c *instructions.OnbuildCommand) error {

@@ -7,6 +7,7 @@ import (

 	"github.com/docker/docker/api/types/container"

 	"github.com/docker/docker/api/types/strslice"

+	specs "github.com/opencontainers/image-spec/specs-go/v1"

 )

 // KeyValuePair represent an arbitrary named value (useful in slice instead of map[string] string to preserve ordering)

@@ -357,11 +358,11 @@ type ShellCommand struct {

 // Stage represents a single stage in a multi-stage build

 type Stage struct {

-	Name            string

-	Commands        []Command

-	BaseName        string

-	SourceCode      string

-	OperatingSystem string

+	Name       string

+	Commands   []Command

+	BaseName   string

+	SourceCode string

+	Platform   specs.Platform

 }

 // AddCommand to the stage

@@ -276,23 +276,13 @@ func parseFrom(req parseRequest) (*Stage, error) {

 	if err := req.flags.Parse(); err != nil {

 		return nil, err

 	}

-	specPlatform := system.ParsePlatform(flPlatform.Value)

-	if err := system.ValidatePlatform(specPlatform); err != nil {

-		return nil, fmt.Errorf("invalid platform %q on FROM", flPlatform.Value)

-	}

-	if specPlatform.OS != "" && !system.IsOSSupported(specPlatform.OS) {

-		return nil, fmt.Errorf("unsupported platform %q on FROM", flPlatform.Value)

-	}

-	if err != nil {

-		return nil, err

-	}

 	code := strings.TrimSpace(req.original)

 	return &Stage{

-		BaseName:        req.args[0],

-		Name:            stageName,

-		SourceCode:      code,

-		Commands:        []Command{},

-		OperatingSystem: specPlatform.OS,

+		BaseName:   req.args[0],

+		Name:       stageName,

+		SourceCode: code,

+		Commands:   []Command{},

+		Platform:   *system.ParsePlatform(flPlatform.Value),

 	}, nil

 }

@@ -1,8 +1,6 @@

 package instructions // import "github.com/docker/docker/builder/dockerfile/instructions"

 import (

-	"fmt"

-	"runtime"

 	"strings"

 	"testing"

@@ -186,16 +184,6 @@ func TestErrorCases(t *testing.T) {

 			dockerfile:    `foo bar`,

 			expectedError: "unknown instruction: FOO",

 		},

-		{

-			name:          "Invalid platform",

-			dockerfile:    `FROM --platform=invalid busybox`,

-			expectedError: `invalid platform "invalid"`,

-		},

-		{

-			name:          "Only OS",

-			dockerfile:    fmt.Sprintf(`FROM --platform=%s/%s busybox`, runtime.GOOS, runtime.GOARCH),

-			expectedError: `invalid platform`,

-		},

 	}

 	for _, c := range cases {

 		r := strings.NewReader(c.dockerfile)