Show the hints when buildkit is on multi-arch mode

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_containerd_worker.go

@@ -10,6 +10,7 @@ import (
 
 	ctd "github.com/containerd/containerd"
 	"github.com/moby/buildkit/cmd/buildkitd/config"
+	"github.com/moby/buildkit/util/binfmt_misc"
 	"github.com/moby/buildkit/worker"
 	"github.com/moby/buildkit/worker/base"
 	"github.com/moby/buildkit/worker/containerd"
@@ -142,6 +143,10 @@ func applyContainerdFlags(c *cli.Context, cfg *config.Config) error {
 	}
 
 	if platforms := c.GlobalStringSlice("containerd-worker-platform"); len(platforms) != 0 {
+		supported := binfmt_misc.ValidatePlatforms(platforms)
+		if !supported {
+			logrus.Warn("cross-platfrom build may fail, please consdier to configure 'F' flag for 'binfmt_misc'.")
+		}
 		cfg.Workers.Containerd.Platforms = platforms
 	}
 

cmd/buildkitd/main_oci_worker.go

@@ -11,6 +11,7 @@ import (
 	"github.com/containerd/containerd/snapshots/overlay"
 	"github.com/moby/buildkit/cmd/buildkitd/config"
 	"github.com/moby/buildkit/executor/oci"
+	"github.com/moby/buildkit/util/binfmt_misc"
 	"github.com/moby/buildkit/worker"
 	"github.com/moby/buildkit/worker/base"
 	"github.com/moby/buildkit/worker/runc"
@@ -142,6 +143,10 @@ func applyOCIFlags(c *cli.Context, cfg *config.Config) error {
 	}
 
 	if platforms := c.GlobalStringSlice("oci-worker-platform"); len(platforms) != 0 {
+		supported := binfmt_misc.ValidatePlatforms(platforms)
+		if !supported {
+			logrus.Warn("cross-platfrom build may fail, please consdier to configure 'F' flag for 'binfmt_misc'.")
+		}
 		cfg.Workers.OCI.Platforms = platforms
 	}
 

util/binfmt_misc/detect.go

@@ -30,3 +30,22 @@ func SupportedPlatforms() []string {
 
 	return arr
 }
+
+func ValidatePlatforms(pf []string) bool {
+	def := platforms.DefaultString()
+	var supported bool = true
+	for _, p := range pf {
+		if p != def {
+			if p == "linux/amd64" && !amd64Supported() {
+				supported = false
+			}
+			if p == "linux/arm64" && !arm64Supported() {
+				supported = false
+			}
+			if (strings.HasPrefix(p, "linux/arm/v6") || strings.HasPrefix(p, "linux/arm/v7")) && !armSupported() {
+				supported = false
+			}
+		}
+	}
+	return supported
+}