Support i386/x86 platforms (#75)

gokrazy · Aug 18, 2024 · de5f76c · de5f76c
1 parent d0d0a0a
commit de5f76c
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Showing 4 changed files with 22 additions and 9 deletions.
diff --git a/internal/packer/packer.go b/internal/packer/packer.go
@@ -1861,7 +1861,7 @@ func (pack *Pack) logic(programName string) error {
 }
 
 // kernelGoarch returns the GOARCH value that corresponds to the provided
-// vmlinuz header. It returns one of "arm64", "arm", "amd64", or the empty
+// vmlinuz header. It returns one of "arm", "arm64", "386", "amd64" or the empty
 // string if not detected.
 func kernelGoarch(hdr []byte) string {
 	// Some constants from the file(1) command's magic.
@@ -1873,17 +1873,23 @@ func kernelGoarch(hdr []byte) string {
 		arm64Magic       = 0x644d5241
 		arm64MagicOffset = 0x38
 		// x86: https://github.com/file/file/blob/65be1904/magic/Magdir/linux#L137-L152
-		x86Magic       = 0xaa55
-		x86MagicOffset = 0x1fe
+		x86Magic            = 0xaa55
+		x86MagicOffset      = 0x1fe
+		x86XloadflagsOffset = 0x236
 	)
 	if len(hdr) >= arm64MagicOffset+4 && binary.LittleEndian.Uint32(hdr[arm64MagicOffset:]) == arm64Magic {
 		return "arm64"
 	}
-	if len(hdr) >= arm64MagicOffset+4 && binary.LittleEndian.Uint32(hdr[arm32MagicOffset:]) == arm32Magic {
+	if len(hdr) >= arm32MagicOffset+4 && binary.LittleEndian.Uint32(hdr[arm32MagicOffset:]) == arm32Magic {
 		return "arm"
 	}
-	if len(hdr) >= arm64MagicOffset+2 && binary.LittleEndian.Uint16(hdr[x86MagicOffset:]) == x86Magic {
-		return "amd64" // we'll assume 386 is unsupported
+	if len(hdr) >= x86XloadflagsOffset+2 && binary.LittleEndian.Uint16(hdr[x86MagicOffset:]) == x86Magic {
+		// XLF0 in arch/x86/boot/header.S
+		if hdr[x86XloadflagsOffset]&1 != 0 {
+			return "amd64"
+		} else {
+			return "386"
+		}
 	}
 	return ""
 }

diff --git a/internal/packer/packer_test.go b/internal/packer/packer_test.go
@@ -6,7 +6,7 @@ import (
 )
 
 func TestKernelGoarch(t *testing.T) {
-	for _, arch := range []string{"arm", "arm64", "amd64"} {
+	for _, arch := range []string{"386", "arm", "arm64", "amd64"} {
 		t.Run(arch, func(t *testing.T) {
 			k, err := os.ReadFile("testdata/kernel." + arch)
 			if err != nil {

diff --git a/internal/packer/testdata/kernel.386 b/internal/packer/testdata/kernel.386
diff --git a/packer/packer.go b/packer/packer.go
@@ -262,6 +262,7 @@ func (p *Pack) writeGPT(w io.Writer, devsize uint64, primary bool) error {
 		partitionTypeLinuxFilesystemData     = "0FC63DAF-8483-4772-8E79-3D69D8477DE4"
 		partitionTypeLinuxRootPartitionAMD64 = "4F68BCE3-E8CD-4DB1-96E7-FBCAF984B709"
 		partitionTypeLinuxRootPartitionARM64 = "B921B045-1DF0-41C3-AF44-4C6F280D3FAE"
+		partitionTypeLinuxRootPartitionX86   = "44479540-f297-41b2-9af7-d131d5f0458a"
 	)
 
 	type partitionEntry struct {
@@ -284,10 +285,16 @@ func (p *Pack) writeGPT(w io.Writer, devsize uint64, primary bool) error {
 	partition3First := partition2Last + 1
 	partition3Last := partition3First + uint64(permSize(p.FirstPartitionOffsetSectors, devsize)) - 1
 
-	rootType := mustParseGUID(partitionTypeLinuxRootPartitionARM64)
-	if os.Getenv("GOARCH") == "amd64" {
+	var rootType [16]byte
+	switch os.Getenv("GOARCH") {
+	case "386":
+		rootType = mustParseGUID(partitionTypeLinuxRootPartitionX86)
+	case "amd64":
 		rootType = mustParseGUID(partitionTypeLinuxRootPartitionAMD64)
+	default:
+		rootType = mustParseGUID(partitionTypeLinuxRootPartitionARM64)
 	}
+
 	partitionEntries := []partitionEntry{
 		{
 			TypeGUID:   mustParseGUID(partitionTypeEFISystemPartition),