Fix source of OS, architecture and variant

This fixes getting of cpu variants for ARM64
Fixes the TestConformance/setuid-file-in-archive test on ARM64.

Signed-off-by: Jan Rodák <[email protected]>

Author: Honny1

config.go

@@ -6,11 +6,11 @@ import (
 	"fmt"
 	"maps"
 	"os"
-	"runtime"
 	"slices"
 	"strings"
 	"time"
 
+	"github.com/containerd/platforms"
 	"github.com/containers/buildah/define"
 	"github.com/containers/buildah/docker"
 	internalUtil "github.com/containers/buildah/internal/util"
@@ -137,18 +137,19 @@ func (b *Builder) fixupConfig(sys *types.SystemContext) {
 	if b.OCIv1.Created == nil || b.OCIv1.Created.IsZero() {
 		b.OCIv1.Created = &now
 	}
+	currentPlatformSpecification := platforms.DefaultSpec()
 	if b.OS() == "" {
 		if sys != nil && sys.OSChoice != "" {
 			b.SetOS(sys.OSChoice)
 		} else {
-			b.SetOS(runtime.GOOS)
+			b.SetOS(currentPlatformSpecification.OS)
 		}
 	}
 	if b.Architecture() == "" {
 		if sys != nil && sys.ArchitectureChoice != "" {
 			b.SetArchitecture(sys.ArchitectureChoice)
 		} else {
-			b.SetArchitecture(runtime.GOARCH)
+			b.SetArchitecture(currentPlatformSpecification.Architecture)
 		}
 		// in case the arch string we started with was shorthand for a known arch+variant pair, normalize it
 		ps := internalUtil.NormalizePlatform(ociv1.Platform{OS: b.OS(), Architecture: b.Architecture(), Variant: b.Variant()})
@@ -158,6 +159,8 @@ func (b *Builder) fixupConfig(sys *types.SystemContext) {
 	if b.Variant() == "" {
 		if sys != nil && sys.VariantChoice != "" {
 			b.SetVariant(sys.VariantChoice)
+		} else {
+			b.SetVariant(currentPlatformSpecification.Variant)
 		}
 		// in case the arch string we started with was shorthand for a known arch+variant pair, normalize it
 		ps := internalUtil.NormalizePlatform(ociv1.Platform{OS: b.OS(), Architecture: b.Architecture(), Variant: b.Variant()})

tests/conformance/conformance_test.go

@@ -2019,6 +2019,16 @@ var internalTestCases = []testCase{
 		compatScratchConfig: types.OptionalBoolTrue,
 	},
 
+	{
+		name: "from-scratch-simple-file", /* Fix On ARM64: fields missing from buildah version: variant */
+		dockerfileContents: strings.Join([]string{
+			"FROM scratch",
+			"COPY file-a.txt /",
+		}, "\n"),
+		contextDir:          "dockerignore/populated",
+		compatScratchConfig: types.OptionalBoolTrue,
+	},
+
 	{
 		name: "setuid-file-in-archive",
 		dockerfileContents: strings.Join([]string{