@@ -14,7 +14,6 @@ import (

 	"strings"

 	"sync"

-	"github.com/containerd/containerd/platforms"

 	"github.com/docker/docker/api/server/httputils"

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

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

@@ -24,8 +23,7 @@ import (

 	"github.com/docker/docker/pkg/ioutils"

 	"github.com/docker/docker/pkg/progress"

 	"github.com/docker/docker/pkg/streamformatter"

-	"github.com/docker/docker/pkg/system"

-	"github.com/docker/go-units"

+	units "github.com/docker/go-units"

 	"github.com/pkg/errors"

 	"github.com/sirupsen/logrus"

 )

@@ -72,17 +70,7 @@ func newImageBuildOptions(ctx context.Context, r *http.Request) (*types.ImageBui

 	options.Target = r.FormValue("target")

 	options.RemoteContext = r.FormValue("remote")

 	if versions.GreaterThanOrEqualTo(version, "1.32") {

-		apiPlatform := r.FormValue("platform")

-		if apiPlatform != "" {

-			sp, err := platforms.Parse(apiPlatform)

-			if err != nil {

-				return nil, err

-			}

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

-				return nil, err

-			}

-			options.Platform = &sp

-		}

+		options.Platform = r.FormValue("platform")

 	}

 	if r.Form.Get("shmsize") != "" {

@@ -7,8 +7,7 @@ import (

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

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

-	"github.com/docker/go-units"

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

+	units "github.com/docker/go-units"

 )

 // CheckpointCreateOptions holds parameters to create a checkpoint from a container

@@ -181,7 +180,7 @@ type ImageBuildOptions struct {

 	ExtraHosts  []string // List of extra hosts

 	Target      string

 	SessionID   string

-	Platform    *specs.Platform

+	Platform    string

 	// Version specifies the version of the unerlying builder to use

 	Version BuilderVersion

 	// BuildID is an optional identifier that can be passed together with the

@@ -14,6 +14,7 @@ import (

 	"github.com/docker/docker/builder"

 	"github.com/docker/docker/daemon/images"

 	"github.com/docker/docker/pkg/streamformatter"

+	"github.com/docker/docker/pkg/system"

 	controlapi "github.com/moby/buildkit/api/services/control"

 	"github.com/moby/buildkit/control"

 	"github.com/moby/buildkit/identity"

@@ -208,8 +209,17 @@ func (b *Builder) Build(ctx context.Context, opt backend.BuildConfig) (*builder.

 		frontendAttrs["no-cache"] = ""

 	}

-	if opt.Options.Platform != nil {

-		frontendAttrs["platform"] = platforms.Format(*opt.Options.Platform)

+	if opt.Options.Platform != "" {

+		// same as in newBuilder in builder/dockerfile.builder.go

+		// TODO: remove once opt.Options.Platform is of type specs.Platform

+		sp, err := platforms.Parse(opt.Options.Platform)

+		if err != nil {

+			return nil, err

+		}

+		if err := system.ValidatePlatform(sp); err != nil {

+			return nil, err

+		}

+		frontendAttrs["platform"] = opt.Options.Platform

 	}

 	exporterAttrs := map[string]string{}

@@ -10,6 +10,7 @@ import (

 	"strings"

 	"time"

+	"github.com/containerd/containerd/platforms"

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

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

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

@@ -25,6 +26,7 @@ import (

 	"github.com/moby/buildkit/frontend/dockerfile/parser"

 	"github.com/moby/buildkit/frontend/dockerfile/shell"

 	"github.com/moby/buildkit/session"

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

 	"github.com/pkg/errors"

 	"github.com/sirupsen/logrus"

 	"golang.org/x/sync/syncmap"

@@ -111,7 +113,11 @@ func (bm *BuildManager) Build(ctx context.Context, config backend.BuildConfig) (

 		PathCache:      bm.pathCache,

 		IDMappings:     bm.idMappings,

 	}

-	return newBuilder(ctx, builderOptions).build(source, dockerfile)

+	b, err := newBuilder(ctx, builderOptions)

+	if err != nil {

+		return nil, err

+	}

+	return b.build(source, dockerfile)

 }

 func (bm *BuildManager) initializeClientSession(ctx context.Context, cancel func(), options *types.ImageBuildOptions) (builder.Source, error) {

@@ -175,10 +181,11 @@ type Builder struct {

 	pathCache        pathCache

 	containerManager *containerManager

 	imageProber      ImageProber

+	platform         *specs.Platform

 }

 // newBuilder creates a new Dockerfile builder from an optional dockerfile and a Options.

-func newBuilder(clientCtx context.Context, options builderOptions) *Builder {

+func newBuilder(clientCtx context.Context, options builderOptions) (*Builder, error) {

 	config := options.Options

 	if config == nil {

 		config = new(types.ImageBuildOptions)

@@ -199,7 +206,20 @@ func newBuilder(clientCtx context.Context, options builderOptions) *Builder {

 		containerManager: newContainerManager(options.Backend),

 	}

-	return b

+	// same as in Builder.Build in builder/builder-next/builder.go

+	// TODO: remove once config.Platform is of type specs.Platform

+	if config.Platform != "" {

+		sp, err := platforms.Parse(config.Platform)

+		if err != nil {

+			return nil, err

+		}

+		if err := system.ValidatePlatform(sp); err != nil {

+			return nil, err

+		}

+		b.platform = &sp

+	}

+

+	return b, nil

 }

 // Build 'LABEL' command(s) from '--label' options and add to the last stage

@@ -365,9 +385,12 @@ func BuildFromConfig(config *container.Config, changes []string, os string) (*co

 		return nil, errdefs.InvalidParameter(err)

 	}

-	b := newBuilder(context.Background(), builderOptions{

+	b, err := newBuilder(context.Background(), builderOptions{

 		Options: &types.ImageBuildOptions{NoCache: true},

 	})

+	if err != nil {

+		return nil, err

+	}

 	// ensure that the commands are valid

 	for _, n := range dockerfile.AST.Children {

@@ -87,7 +87,7 @@ func copierFromDispatchRequest(req dispatchRequest, download sourceDownloader, i

 		pathCache:   req.builder.pathCache,

 		download:    download,

 		imageSource: imageSource,

-		platform:    req.builder.options.Platform,

+		platform:    req.builder.platform,

 	}

 }

@@ -146,7 +146,7 @@ func (d *dispatchRequest) getImageMount(imageRefOrID string) (*imageMount, error

 		imageRefOrID = stage.Image

 		localOnly = true

 	}

-	return d.builder.imageSources.Get(imageRefOrID, localOnly, d.builder.options.Platform)

+	return d.builder.imageSources.Get(imageRefOrID, localOnly, d.builder.platform)

 }

 // FROM [--platform=platform] imagename[:tag | @digest] [AS build-stage-name]

@@ -238,7 +238,7 @@ func (d *dispatchRequest) getImageOrStage(name string, platform *specs.Platform)

 	}

 	if platform == nil {

-		platform = d.builder.options.Platform

+		platform = d.builder.platform

 	}

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

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

 	"runtime"

 	"testing"

-	"github.com/containerd/containerd/platforms"

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

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

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

@@ -23,8 +22,7 @@ import (

 func newBuilderWithMockBackend() *Builder {

 	mockBackend := &MockBackend{}

-	defaultPlatform := platforms.DefaultSpec()

-	opts := &types.ImageBuildOptions{Platform: &defaultPlatform}

+	opts := &types.ImageBuildOptions{}

 	ctx := context.Background()

 	b := &Builder{

 		options:       opts,

@@ -116,7 +114,7 @@ func TestFromScratch(t *testing.T) {

 	err := initializeStage(sb, cmd)

 	if runtime.GOOS == "windows" && !system.LCOWSupported() {

-		assert.Check(t, is.Error(err, "Windows does not support FROM scratch"))

+		assert.Check(t, is.Error(err, "Linux containers are not supported on this system"))

 		return

 	}

@@ -169,7 +169,7 @@ func (b *Builder) performCopy(req dispatchRequest, inst copyInstruction) error {

 		return err

 	}

-	imageMount, err := b.imageSources.Get(state.imageID, true, req.builder.options.Platform)

+	imageMount, err := b.imageSources.Get(state.imageID, true, req.builder.platform)

 	if err != nil {

 		return errors.Wrapf(err, "failed to get destination image %q", state.imageID)

 	}

@@ -416,7 +416,9 @@ func (b *Builder) probeAndCreate(dispatchState *dispatchState, runConfig *contai

 func (b *Builder) create(runConfig *container.Config) (string, error) {

 	logrus.Debugf("[BUILDER] Command to be executed: %v", runConfig.Cmd)

-	hostConfig := hostConfigFromOptions(b.options)

+

+	isWCOW := runtime.GOOS == "windows" && b.platform != nil && b.platform.OS == "windows"

+	hostConfig := hostConfigFromOptions(b.options, isWCOW)

 	container, err := b.containerManager.Create(runConfig, hostConfig)

 	if err != nil {

 		return "", err

@@ -429,7 +431,7 @@ func (b *Builder) create(runConfig *container.Config) (string, error) {

 	return container.ID, nil

 }

-func hostConfigFromOptions(options *types.ImageBuildOptions) *container.HostConfig {

+func hostConfigFromOptions(options *types.ImageBuildOptions, isWCOW bool) *container.HostConfig {

 	resources := container.Resources{

 		CgroupParent: options.CgroupParent,

 		CPUShares:    options.CPUShares,

@@ -457,7 +459,7 @@ func hostConfigFromOptions(options *types.ImageBuildOptions) *container.HostConf

 	// is too small for builder scenarios where many users are

 	// using RUN statements to install large amounts of data.

 	// Use 127GB as that's the default size of a VHD in Hyper-V.

-	if runtime.GOOS == "windows" && options.Platform != nil && options.Platform.OS == "windows" {

+	if isWCOW {

 		hc.StorageOpt = make(map[string]string)

 		hc.StorageOpt["size"] = "127GB"

 	}

@@ -8,8 +8,8 @@ import (

 	"net/http"

 	"net/url"

 	"strconv"

+	"strings"

-	"github.com/containerd/containerd/platforms"

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

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

 )

@@ -30,12 +30,6 @@ func (cli *Client) ImageBuild(ctx context.Context, buildContext io.Reader, optio

 	}

 	headers.Add("X-Registry-Config", base64.URLEncoding.EncodeToString(buf))

-	if options.Platform != nil {

-		if err := cli.NewVersionError("1.32", "platform"); err != nil {

-			return types.ImageBuildResponse{}, err

-		}

-		query.Set("platform", platforms.Format(*options.Platform))

-	}

 	headers.Set("Content-Type", "application/x-tar")

 	serverResp, err := cli.postRaw(ctx, "/build", query, buildContext, headers)

@@ -130,8 +124,11 @@ func (cli *Client) imageBuildOptionsToQuery(options types.ImageBuildOptions) (ur

 	if options.SessionID != "" {

 		query.Set("session", options.SessionID)

 	}

-	if options.Platform != nil {

-		query.Set("platform", platforms.Format(*options.Platform))

+	if options.Platform != "" {

+		if err := cli.NewVersionError("1.32", "platform"); err != nil {

+			return query, err

+		}

+		query.Set("platform", strings.ToLower(options.Platform))

 	}

 	if options.BuildID != "" {

 		query.Set("buildid", options.BuildID)