Check the validity of the platforms

platforms can still be added but some warning message
will be emitted if the platform cannot pass the validity
check.

Signed-off-by: Dave Chen <dave.chen@arm.com>

cmd/buildkitd/main.go

@@ -558,7 +558,9 @@ func newWorkerController(c *cli.Context, wiOpt workerInitializerOpt) (*worker.Co
 			return nil, err
 		}
 		for _, w := range ws {
-			logrus.Infof("found worker %q, labels=%v, platforms=%v", w.ID(), w.Labels(), formatPlatforms(w.Platforms()))
+			p := formatPlatforms(w.Platforms())
+			logrus.Infof("found worker %q, labels=%v, platforms=%v", w.ID(), w.Labels(), p)
+			binfmt_misc.WarnIfUnsupported(p)
 			if err = wc.Add(w); err != nil {
 				return nil, err
 			}

util/binfmt_misc/amd64_check.go

@@ -2,6 +2,6 @@
 
 package binfmt_misc
 
-func amd64Supported() bool {
-	return check(Binaryamd64) == nil
+func amd64Supported() error {
+	return check(Binaryamd64)
 }

util/binfmt_misc/amd64_check_amd64.go

@@ -2,6 +2,6 @@
 
 package binfmt_misc
 
-func amd64Supported() bool {
-	return true
+func amd64Supported() error {
+	return nil
 }

util/binfmt_misc/arm64_check.go

@@ -2,6 +2,6 @@
 
 package binfmt_misc
 
-func arm64Supported() bool {
-	return check(Binaryarm64) == nil
+func arm64Supported() error {
+	return check(Binaryarm64)
 }

util/binfmt_misc/arm64_check_arm64.go

@@ -2,6 +2,6 @@
 
 package binfmt_misc
 
-func arm64Supported() bool {
-	return true
+func arm64Supported() error {
+	return nil
 }

util/binfmt_misc/arm_check.go

@@ -2,6 +2,6 @@
 
 package binfmt_misc
 
-func armSupported() bool {
-	return check(Binaryarm) == nil
+func armSupported() error {
+	return check(Binaryarm)
 }

util/binfmt_misc/arm_check_arm.go

@@ -2,6 +2,6 @@
 
 package binfmt_misc
 
-func armSupported() bool {
-	return true
+func armSupported() error {
+	return nil
 }

util/binfmt_misc/check.go

@@ -8,6 +8,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"syscall"
 )
 
 func check(bin string) error {
@@ -35,5 +36,10 @@ func check(bin string) error {
 	}
 	f.Close()
 
-	return exec.Command(pp).Run()
+	cmd := exec.Command("/check")
+	cmd.SysProcAttr = &syscall.SysProcAttr{
+		Chroot: tmpdir,
+	}
+	err = cmd.Run()
+	return err
 }

util/binfmt_misc/detect.go

@@ -5,6 +5,7 @@ import (
 	"sync"
 
 	"github.com/containerd/containerd/platforms"
+	"github.com/sirupsen/logrus"
 )
 
 var once sync.Once
@@ -14,19 +15,53 @@ func SupportedPlatforms() []string {
 	once.Do(func() {
 		def := platforms.DefaultString()
 		arr = append(arr, def)
-
-		if p := "linux/amd64"; def != p && amd64Supported() {
+		if p := "linux/amd64"; def != p && amd64Supported() == nil {
 			arr = append(arr, p)
 		}
-		if p := "linux/arm64"; def != p && arm64Supported() {
+		if p := "linux/arm64"; def != p && arm64Supported() == nil {
 			arr = append(arr, p)
 		}
-		if !strings.HasPrefix(def, "linux/arm/") && armSupported() {
+		if !strings.HasPrefix(def, "linux/arm/") && armSupported() == nil {
 			arr = append(arr, "linux/arm/v7", "linux/arm/v6")
 		} else if def == "linux/arm/v7" {
 			arr = append(arr, "linux/arm/v6")
 		}
 	})
-
 	return arr
 }
+
+//WarnIfUnsupported validates the platforms and show warning message if there is,
+//the end user could fix the issue based on those warning, and thus no need to drop
+//the platform from the candidates.
+func WarnIfUnsupported(pfs []string) {
+	def := platforms.DefaultString()
+	for _, p := range pfs {
+		if p != def {
+			if p == "linux/amd64" {
+				if err := amd64Supported(); err != nil {
+					printPlatfromWarning(p, err)
+				}
+			}
+			if p == "linux/arm64" {
+				if err := arm64Supported(); err != nil {
+					printPlatfromWarning(p, err)
+				}
+			}
+			if strings.HasPrefix(p, "linux/arm/v6") || strings.HasPrefix(p, "linux/arm/v7") {
+				if err := armSupported(); err != nil {
+					printPlatfromWarning(p, err)
+				}
+			}
+		}
+	}
+}
+
+func printPlatfromWarning(p string, err error) {
+	if strings.Contains(err.Error(), "exec format error") {
+		logrus.Warnf("platform %s cannot pass the validation, kernel support for miscellaneous binary may have not enabled.", p)
+	} else if strings.Contains(err.Error(), "no such file or directory") {
+		logrus.Warnf("platforms %s cannot pass the validation, '-F' flag might have not set for 'binfmt_misc'.", p)
+	} else {
+		logrus.Warnf("platforms %s cannot pass the validation: %s", p, err.Error())
+	}
+}