Support extraction of boot cmdline off the multiboot data

src/gopheros/kernel/hal/multiboot/multiboot.go

@@ -1,6 +1,10 @@
 package multiboot
 
-import "unsafe"
+import (
+	"reflect"
+	"strings"
+	"unsafe"
+)
 
 type tagType uint32
 
@@ -137,7 +141,8 @@ const (
 )
 
 var (
-	infoData uintptr
+	infoData  uintptr
+	cmdLineKV map[string]string
 )
 
 // MemRegionVisitor defies a visitor function that gets invoked by VisitMemRegions
@@ -224,6 +229,39 @@ func GetFramebufferInfo() *FramebufferInfo {
 	return info
 }
 
+// GetBootCmdLine returns the command line key-value pairs passed to the
+// kernel.  This function must only be invoked after bootstrapping the memory
+// allocator.
+func GetBootCmdLine() map[string]string {
+	if cmdLineKV != nil {
+		return cmdLineKV
+	}
+
+	cmdLineKV = make(map[string]string)
+
+	curPtr, size := findTagByType(tagBootCmdLine)
+	if size != 0 {
+		// The command line is a C-style NULL-terminated string
+		cmdLine := *(*[]byte)(unsafe.Pointer(&reflect.SliceHeader{
+			Len:  int(size - 1),
+			Cap:  int(size - 1),
+			Data: curPtr,
+		}))
+		pairs := strings.Fields(string(cmdLine))
+		for _, pair := range pairs {
+			kv := strings.Split(pair, "=")
+			switch len(kv) {
+			case 2: // foo=bar
+				cmdLineKV[kv[0]] = kv[1]
+			case 1: // nofoo
+				cmdLineKV[kv[0]] = kv[0]
+			}
+		}
+	}
+
+	return cmdLineKV
+}
+
 // findTagByType scans the multiboot info data looking for the start of of the
 // specified type. It returns a pointer to the tag contents start offset and
 // the content length exluding the tag header.

src/gopheros/kernel/hal/multiboot/multiboot_test.go

@@ -1,6 +1,7 @@
 package multiboot
 
 import (
+	"reflect"
 	"testing"
 	"unsafe"
 )
@@ -170,6 +171,26 @@ func TestGetFramebufferInfo(t *testing.T) {
 	}
 }
 
+func TestGetBootCmdLine(t *testing.T) {
+	SetInfoPtr(uintptr(unsafe.Pointer(&multibootInfoTestData[0])))
+
+	expKV := map[string]string{
+		"param1": "param1", // "param1" (no value)
+		"param2": "value2", // "param2=value2"
+	}
+
+	kv := GetBootCmdLine()
+	if !reflect.DeepEqual(kv, expKV) {
+		t.Errorf("expected to get: %v; got %v", expKV, kv)
+	}
+
+	// Second call should return the memoized data
+	cmdLineKV["foo"] = "bar"
+	if kv2 := GetBootCmdLine(); !reflect.DeepEqual(kv2, kv) {
+		t.Error("expected second call to GetBootCmdLine() to return the memoized KV pairs")
+	}
+}
+
 var (
 	emptyInfoData = []byte{
 		0, 0, 0, 0, // size
@@ -181,7 +202,7 @@ var (
 	// A dump of multiboot data when running under qemu.
 	multibootInfoTestData = []byte{
 		0xb8, 0x0a, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x24, 0x00, 0x00, 0x00,
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