From de5f76c8837898ee4005dee5df58b7aba09a3d3a Mon Sep 17 00:00:00 2001
From: George Hopkins <george-hopkins@null.net>
Date: Sun, 18 Aug 2024 16:15:51 +0200
Subject: [PATCH] Support i386/x86 platforms (#75)

---
 internal/packer/packer.go           |  18 ++++++++++++------
 internal/packer/packer_test.go      |   2 +-
 internal/packer/testdata/kernel.386 | Bin 0 -> 1024 bytes
 packer/packer.go                    |  11 +++++++++--
 4 files changed, 22 insertions(+), 9 deletions(-)
 create mode 100644 internal/packer/testdata/kernel.386

diff --git a/internal/packer/packer.go b/internal/packer/packer.go
index 146e9c8..b7e639b 100644
--- 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
index d836505..e5a18e5 100644
--- 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
new file mode 100644
index 0000000000000000000000000000000000000000..3859b78520c530054895505492c0e251014b11f7
GIT binary patch
literal 1024
zcmaFG%5Z?a=S1I)z5{(144?e|vrm^{jlzKv&Mkbq*%{6Xy#8c(;H=nL$yXo#Gkgdw
zPE|-$NXpMIQOL<pOi3-$<K^NCO3lqLOI1k8EY4O)%u7)yC`v6Z2C^y@vQsM+O7azo
zQb9WO^ni*PM!~>_!2kc!j11?3nSrkO|DS;&bk*xDkCdWdekQQ91RfYOFfueSFbJTy
z@_`S8`~Uy{daxWXP&Ye@5{613cguGZWI;wS$6y(lI$~+c&;v|le|j!i9_oBlBDU*+
z*EcpnriK!hZZQ?6#zPD&#Y~2mnjifsW#0AYf8T{P{_T%`%VjKPI-S;N7hxW{Dk`c}
ze1C%Z&c|M9h6gl%9(>94Ic;^?i?cw-r0uv1^ikT24?wHFy#8y!_MfSQb<uyO*9>WM
z_!sc6NK0sbqtkh<^Z8D0hR<nB(-Qet@-JkUPn&xds6dVlqT~<I#wU=RkltOR;-dJ!
zgroBrL`U-x9f+p1xoL;f!qS4%fCi>@9!_ii!BxtWwgcz}p!JV|0hHGHAnnCvaR!F;
z<1Q)!>|jcQks<w<i;65?TIap=ju;i0G{ci=osZIXfPy*gg)c~3v)vpIh7ygmouFt*
z>lT~ik=A)Rt@#k^n-vNroN1jO(mHRwd(DyNS@QYwgxB}dKrV_-ivzkQ80e1lH2!_e
zEeA@t(wx&?!~o5E{T3*DnB6a5p*Xdqv_PRaGd(Y{q_ikiAuYc&F9nzxxfs%REofr|
E08O3w+5i9m

literal 0
HcmV?d00001

diff --git a/packer/packer.go b/packer/packer.go
index ee6fc10..611662c 100644
--- 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),