Implement early page allocator

kernel/hal/multiboot/multiboot.go

@@ -101,6 +101,15 @@ const (
 	memUnknown
 )
 
+var (
+	infoData uintptr
+)
+
+// MemRegionVisitor defies a visitor function that gets invoked by VisitMemRegions
+// for each memory region provided by the boot loader. The visitor must return true
+// to continue or false to abort the scan.
+type MemRegionVisitor func(entry *MemoryMapEntry) bool
+
 // MemoryMapEntry describes a memory region entry, namely its physical address,
 // its length and its type.
 type MemoryMapEntry struct {
@@ -114,14 +123,21 @@ type MemoryMapEntry struct {
 	Type MemoryEntryType
 }
 
-var (
-	infoData uintptr
-)
-
-// MemRegionVisitor defies a visitor function that gets invoked by VisitMemRegions
-// for each memory region provided by the boot loader. The visitor must return true
-// to continue or false to abort the scan.
-type MemRegionVisitor func(entry *MemoryMapEntry) bool
+// String implements fmt.Stringer for MemoryEntryType.
+func (t MemoryEntryType) String() string {
+	switch t {
+	case MemAvailable:
+		return "available"
+	case MemReserved:
+		return "reserved"
+	case MemAcpiReclaimable:
+		return "ACPI (reclaimable)"
+	case MemNvs:
+		return "NVS"
+	default:
+		return "unknown"
+	}
+}
 
 // SetInfoPtr updates the internal multiboot information pointer to the given
 // value. This function must be invoked before invoking any other function

kernel/hal/multiboot/multiboot_test.go

@@ -102,6 +102,25 @@ func TestVisitMemRegion(t *testing.T) {
 	}
 }
 
+func TestMemoryEntryTypeStringer(t *testing.T) {
+	specs := []struct {
+		input MemoryEntryType
+		exp   string
+	}{
+		{MemAvailable, "available"},
+		{MemReserved, "reserved"},
+		{MemAcpiReclaimable, "ACPI (reclaimable)"},
+		{MemNvs, "NVS"},
+		{MemoryEntryType(123), "unknown"},
+	}
+
+	for specIndex, spec := range specs {
+		if got := spec.input.String(); got != spec.exp {
+			t.Errorf("[spec %d] expected MemoryEntryType(%d).String() to return %q; got %q", specIndex, spec.input, spec.exp, got)
+		}
+	}
+}
+
 func TestGetFramebufferInfo(t *testing.T) {
 	SetInfoPtr(uintptr(unsafe.Pointer(&emptyInfoData[0])))
 

kernel/kmain.go

@@ -1,11 +1,8 @@
 package kernel
 
 import (
-	_ "unsafe" // required for go:linkname
-
 	"github.com/achilleasa/gopher-os/kernel/hal"
 	"github.com/achilleasa/gopher-os/kernel/hal/multiboot"
-	"github.com/achilleasa/gopher-os/kernel/kfmt/early"
 )
 
 // Kmain is the only Go symbol that is visible (exported) from the rt0 initialization
@@ -25,5 +22,4 @@ func Kmain(multibootInfoPtr uintptr) {
 	// Initialize and clear the terminal
 	hal.InitTerminal()
 	hal.ActiveTerminal.Clear()
-	early.Printf("Starting gopher-os\n")
 }

kernel/mem/pfn/bootmem_allocator.go

@@ -0,0 +1,120 @@
+package pfn
+
+import (
+	"github.com/achilleasa/gopher-os/kernel/hal/multiboot"
+	"github.com/achilleasa/gopher-os/kernel/kfmt/early"
+	"github.com/achilleasa/gopher-os/kernel/mem"
+)
+
+var (
+	// EarlyAllocator points to a static instance of the boot memory allocator
+	// which is used to bootstrap the kernel before initializing a more
+	// advanced memory allocator.
+	EarlyAllocator BootMemAllocator
+)
+
+// BootMemAllocator implements a rudimentary physical memory allocator which is used
+// to bootstrap the kernel.
+//
+// The allocator implementation uses the memory region information provided by
+// the bootloader to detect free memory blocks and return the next available
+// free frame.
+//
+// Allocations are tracked via an internal counter that contains the last
+// allocated frame index.  The system memory regions are mapped into a linear
+// page index by aligning the region start address to the system's page size
+// and then dividing by the page size.
+//
+// Due to the way that the allocator works, it is not possible to free
+// allocated pages. Once the kernel is properly initialized, the allocated
+// blocks will be handed over to a more advanced memory allocator that does
+// support freeing.
+type BootMemAllocator struct {
+	initialized bool
+
+	// allocCount tracks the total number of allocated frames.
+	allocCount uint64
+
+	// lastAllocIndex tracks the last allocated frame index.
+	lastAllocIndex int64
+}
+
+// init sets up the boot memory allocator internal state and prints out the
+// system memory map.
+func (alloc *BootMemAllocator) init() {
+	alloc.lastAllocIndex = -1
+	alloc.initialized = true
+
+	early.Printf("[boot_mem_alloc] system memory map:\n")
+	var totalFree mem.Size
+	multiboot.VisitMemRegions(func(region *multiboot.MemoryMapEntry) bool {
+		early.Printf("\t[0x%10x - 0x%10x], size: %10d, type: %s\n", region.PhysAddress, region.PhysAddress+region.Length, region.Length, region.Type.String())
+
+		if region.Type == multiboot.MemAvailable {
+			totalFree += mem.Size(region.Length)
+		}
+		return true
+	})
+	early.Printf("[boot_mem_alloc] free memory: %dKb\n", uint64(totalFree/mem.Kb))
+}
+
+// AllocFrame scans the system memory regions reported by the bootloader and
+// reseves the next available free frame. AllocFrame returns false if no more
+// memory can be allocated.
+//
+// The allocator only supports allocating blocks equal to the page size.
+// Requests for a page order > 0 will cause the allocator to return false.
+//
+// The use of a bool return value is intentional; if this method returned an
+// error then the compiler would call runtime.convT2I which in turn invokes the
+// yet uninitialized Go allocator.
+func (alloc *BootMemAllocator) AllocFrame(order mem.PageOrder) (Frame, bool) {
+	if !alloc.initialized {
+		alloc.init()
+	}
+
+	if order > 0 {
+		return InvalidFrame, false
+	}
+
+	var (
+		foundPageIndex                           int64 = -1
+		regionStartPageIndex, regionEndPageIndex int64
+	)
+	multiboot.VisitMemRegions(func(region *multiboot.MemoryMapEntry) bool {
+		if region.Type != multiboot.MemAvailable {
+			return true
+		}
+
+		// Align region start address to a page boundary and find the start
+		// and end page indices for the region
+		regionStartPageIndex = int64(((mem.Size(region.PhysAddress) + (mem.PageSize - 1)) & ^(mem.PageSize - 1)) >> mem.PageShift)
+		regionEndPageIndex = int64(((mem.Size(region.PhysAddress+region.Length) - (mem.PageSize - 1)) & ^(mem.PageSize - 1)) >> mem.PageShift)
+
+		// Ignore already allocated regions
+		if alloc.lastAllocIndex >= regionEndPageIndex {
+			return true
+		}
+
+		// We found a block that can be allocated. The last allocated
+		// index will be either pointing to a previous region or will
+		// point inside this region. In the first case we just need to
+		// select the regionStartPageIndex. In the latter case we can
+		// simply select the next available page in the current region.
+		if alloc.lastAllocIndex < regionStartPageIndex {
+			foundPageIndex = regionStartPageIndex
+		} else {
+			foundPageIndex = alloc.lastAllocIndex + 1
+		}
+		return false
+	})
+
+	if foundPageIndex == -1 {
+		return InvalidFrame, false
+	}
+
+	alloc.allocCount++
+	alloc.lastAllocIndex = foundPageIndex
+
+	return Frame(foundPageIndex), true
+}

kernel/mem/pfn/bootmem_allocator_test.go

@@ -0,0 +1,93 @@
+package pfn
+
+import (
+	"testing"
+	"unsafe"
+
+	"github.com/achilleasa/gopher-os/kernel/driver/video/console"
+	"github.com/achilleasa/gopher-os/kernel/hal"
+	"github.com/achilleasa/gopher-os/kernel/hal/multiboot"
+	"github.com/achilleasa/gopher-os/kernel/mem"
+)
+
+func TestBootMemoryAllocator(t *testing.T) {
+	// Mock a tty to handle early.Printf output
+	mockConsoleFb := make([]byte, 160*25)
+	mockConsole := &console.Ega{}
+	mockConsole.Init(80, 25, uintptr(unsafe.Pointer(&mockConsoleFb[0])))
+	hal.ActiveTerminal.AttachTo(mockConsole)
+
+	multiboot.SetInfoPtr(uintptr(unsafe.Pointer(&multibootMemoryMap[0])))
+
+	var totalFreeFrames uint64
+	multiboot.VisitMemRegions(func(region *multiboot.MemoryMapEntry) bool {
+		if region.Type == multiboot.MemAvailable {
+			regionStartFrameIndex := uint64(((mem.Size(region.PhysAddress) + (mem.PageSize - 1)) & ^(mem.PageSize - 1)) >> mem.PageShift)
+			regionEndFrameIndex := uint64(((mem.Size(region.PhysAddress+region.Length) - (mem.PageSize - 1)) & ^(mem.PageSize - 1)) >> mem.PageShift)
+
+			totalFreeFrames += regionEndFrameIndex - regionStartFrameIndex + 1
+		}
+
+		return true
+	})
+
+	var (
+		alloc           BootMemAllocator
+		allocFrameCount uint64
+	)
+	for ; ; allocFrameCount++ {
+		frame, ok := alloc.AllocFrame(mem.PageOrder(0))
+		if !ok {
+			break
+		}
+
+		expAddress := uintptr(uint64(alloc.lastAllocIndex) * uint64(mem.PageSize))
+		if got := frame.Address(); got != expAddress {
+			t.Errorf("[frame %d] expected frame address to be 0x%x; got 0x%x", allocFrameCount, expAddress, got)
+		}
+
+		if !frame.IsValid() {
+			t.Errorf("[frame %d] expected IsValid() to return true", allocFrameCount)
+		}
+
+		if got := frame.PageOrder(); got != mem.PageOrder(0) {
+			t.Errorf("[frame %d] expected allocated frame page order to be 0; got %d", allocFrameCount, got)
+		}
+
+		if got := frame.Size(); got != mem.PageSize {
+			t.Errorf("[frame %d] expected allocated frame size to be %d; got %d", allocFrameCount, mem.PageSize, got)
+		}
+	}
+
+	if allocFrameCount != totalFreeFrames {
+		t.Fatalf("expected allocator to allocate %d frames; allocated %d", totalFreeFrames, allocFrameCount)
+	}
+
+	// This allocator only works with order(0) blocks
+	if frame, ok := alloc.AllocFrame(mem.PageOrder(1)); ok || frame.IsValid() {
+		t.Fatalf("expected allocator to return false and an invalid frame when requested to allocate a block with order > 0; got %t, %v", ok, frame)
+	}
+}
+
+var (
+	// A dump of multiboot data when running under qemu containing only the memory region tag.
+	multibootMemoryMap = []byte{
+		72, 5, 0, 0, 0, 0, 0, 0,
+		6, 0, 0, 0, 160, 0, 0, 0, 24, 0, 0, 0, 0, 0, 0, 0,
+		0, 0, 0, 0, 0, 0, 0, 0, 0, 252, 9, 0, 0, 0, 0, 0,
+		1, 0, 0, 0, 0, 0, 0, 0, 0, 252, 9, 0, 0, 0, 0, 0,
+		0, 4, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0,
+		0, 0, 15, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
+		2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 16, 0, 0, 0, 0, 0,
+		0, 0, 238, 7, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0,
+		0, 0, 254, 7, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0,
+		2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 252, 255, 0, 0, 0, 0,
+		0, 0, 4, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0,
+		9, 0, 0, 0, 212, 3, 0, 0, 24, 0, 0, 0, 40, 0, 0, 0,
+		21, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 27, 0, 0, 0,
+		1, 0, 0, 0, 2, 0, 0, 0, 0, 0, 16, 0, 0, 16, 0, 0,
+		24, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	}
+)

kernel/mem/pfn/frame.go

@@ -0,0 +1,39 @@
+// Package pfn provides physical memory allocator implementations that allow
+// allocations of physical memory frames.
+package pfn
+
+import (
+	"math"
+
+	"github.com/achilleasa/gopher-os/kernel/mem"
+)
+
+// Frame describes a physical memory page index.
+type Frame uint64
+
+const (
+	// InvalidFrame is returned by page allocators when
+	// they fail to reserve the requested frame.
+	InvalidFrame = Frame(math.MaxUint64)
+)
+
+// IsValid returns true if this is a valid frame.
+func (f Frame) IsValid() bool {
+	return f != InvalidFrame
+}
+
+// Address returns a pointer to the physical memory address pointed to by this Frame.
+func (f Frame) Address() uintptr {
+	return uintptr(f << mem.PageShift)
+}
+
+// PageOrder returns the page order of this frame. The page order is encoded in the
+// 8 MSB of the frame number.
+func (f Frame) PageOrder() mem.PageOrder {
+	return mem.PageOrder((f >> 56) & 0xFF)
+}
+
+// Size returns the size of this frame.
+func (f Frame) Size() mem.Size {
+	return mem.PageSize << ((f >> 56) & 0xFF)
+}

kernel/mem/pfn/frame_test.go

@@ -0,0 +1,31 @@
+package pfn
+
+import (
+	"testing"
+
+	"github.com/achilleasa/gopher-os/kernel/mem"
+)
+
+func TestFrameMethods(t *testing.T) {
+	for order := mem.PageOrder(0); order < mem.PageOrder(10); order++ {
+		for frameIndex := uint64(0); frameIndex < 128; frameIndex++ {
+			frame := Frame(frameIndex | (uint64(order) << 56))
+
+			if !frame.IsValid() {
+				t.Errorf("[order %d] expected frame %d to be valid", order, frameIndex)
+			}
+
+			if got := frame.PageOrder(); got != order {
+				t.Errorf("[order %d] expected frame (%d, index: %d) call to PageOrder() to return %d; got %d", order, frame, frameIndex, order, got)
+			}
+
+			if exp, got := uintptr(frameIndex<<mem.PageShift), frame.Address(); got != exp {
+				t.Errorf("[order %d] expected frame (%d, index: %d) call to Address() to return %x; got %x", order, frame, frameIndex, exp, got)
+			}
+
+			if exp, got := mem.Size(mem.PageSize<<order), frame.Size(); got != exp {
+				t.Errorf("[order %d] expected frame (%d, index: %d) call to Size() to return %d; got %d", order, frame, frameIndex, exp, got)
+			}
+		}
+	}
+}

kernel/mem/size.go

@@ -10,3 +10,11 @@ const (
 	Mb        = 1024 * Kb
 	Gb        = 1024 * Mb
 )
+
+// PageOrder represents a power-of-two multiple of the base page size and is
+// used as an argument to page-based memory allocators.
+//
+// PageOrder(0) refers to a page with size PageSize << 0
+// PageOrder(1) refers to a page with size PageSize << 1
+// ...
+type PageOrder uint8