Merge pull request #43 from achilleasa/setup-granular-pdt-for-kernel

Setup granular PDT for kernel

src/arch/x86_64/asm/rt0_32.s

@@ -355,6 +355,20 @@ write_string:
 ;------------------------------------------------------------------------------
 bits 64 
 _rt0_64_entry_trampoline:
+	; The currently loaded GDT points to the physical address of gdt0. This
+	; works for now since we identity map the first 8M of the kernel. When
+	; we set up a proper PDT for the VMA address of the kernel, the 0-8M
+	; mapping will be invalid causing a page fault when the CPU tries to
+	; restore the segment registers while returning from the page fault
+	; handler.
+	;
+	; To fix this, we need to update the GDT so it uses the 48-bit virtual 
+	; address of gdt0.
+	mov rax, gdt0_desc
+	mov rbx, gdt0
+	mov qword [rax+2], rbx
+	lgdt [rax]
+
 	mov rsp, stack_top     ; now that paging is enabled we can load the stack 
 			       ; with the virtual address of the allocated stack.
 	

src/arch/x86_64/asm/rt0_64.s

@@ -51,6 +51,8 @@ _rt0_64_entry:
 	extern _kernel_end
 	extern kernel.Kmain
 	
+	mov rax, PAGE_OFFSET
+	push rax
 	mov rax, _kernel_end - PAGE_OFFSET
 	push rax
 	mov rax, _kernel_start - PAGE_OFFSET

src/gopheros/kernel/cpu/cpu_amd64.s

@@ -19,7 +19,8 @@ TEXT ·FlushTLBEntry(SB),NOSPLIT,$0
 
 TEXT ·SwitchPDT(SB),NOSPLIT,$0
 	// loading CR3 also triggers a TLB flush
-	MOVQ pdtPhysAddr+0(FP), CR3
+	MOVQ pdtPhysAddr+0(FP), AX
+	MOVQ AX, CR3
 	RET
 
 TEXT ·ActivePDT(SB),NOSPLIT,$0

src/gopheros/kernel/goruntime/bootstrap.go

@@ -51,6 +51,16 @@ func mSysStatInc(*uint64, uintptr)
 //go:linkname initGoPackages main.init
 func initGoPackages()
 
+// Some of the package init functions (e.g reflect.init) call runtime.init
+// which attempts to create a new process and eventually crashes the kernel.
+// Since the kernel does its own initialization, we can safely redirect
+// runtime.init
+// to this empty stub.
+//go:redirect-from runtime.init
+//go:noinline
+func runtimeInit() {
+}
+
 // sysReserve reserves address space without allocating any memory or
 // establishing any page mappings.
 //
@@ -188,6 +198,7 @@ func init() {
 		zeroPtr  = unsafe.Pointer(uintptr(0))
 	)
 
+	runtimeInit()
 	sysReserve(zeroPtr, 0, &reserved)
 	sysMap(zeroPtr, 0, reserved, &stat)
 	sysAlloc(0, &stat)

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

@@ -9,7 +9,6 @@ import (
 var (
 	infoData  uintptr
 	cmdLineKV map[string]string
-	elfSectionList []*ElfSection
 )
 
 type tagType uint32
@@ -149,7 +148,7 @@ const (
 // 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
+type MemRegionVisitor func(*MemoryMapEntry) bool
 
 // MemoryMapEntry describes a memory region entry, namely its physical address,
 // its length and its type.
@@ -230,63 +229,44 @@ const (
 	ElfSectionExecutable
 )
 
-// ElfSection deefines the name, flags and virtual address of an ELF section
+// ElfSectionVisitor defies a visitor function that gets invoked by VisitElfSections
-// which is part of the kernel image.
+// for rach ELF section that belongs to the loaded kernel image.
-type ElfSection struct {
+type ElfSectionVisitor func(name string, flags ElfSectionFlag, address uintptr, size uint64)
-	// The section name.
-	Name string
-
-	// The list of flags associated with this section
-	Flags ElfSectionFlag
-
-	// The virtual address of this section.
-	Address uintptr
-}
-
-// GetElfSections returns a slice of ElfSections for the loaded kernel image.
-func GetElfSections() []*ElfSection {
-	if elfSectionList != nil {
-		return elfSectionList
-	}
 
+// VisitElfSections invokes visitor for each ELF entry that belongs to the
+// loaded kernel image.
+func VisitElfSections(visitor ElfSectionVisitor) {
 	curPtr, size := findTagByType(tagElfSymbols)
 	if size == 0 {
-		return nil
+		return
 	}
 
-	ptrElfSections := (*elfSections)(unsafe.Pointer(curPtr))
-	sectionData := *(*[]elfSection64)(unsafe.Pointer(&reflect.SliceHeader{
-		Len:  int(ptrElfSections.numSections),
-		Cap:  int(ptrElfSections.numSections),
-		Data: uintptr(unsafe.Pointer(&ptrElfSections.sectionData)),
-	}))
-
 	var (
-		strTable = *(*[]byte)(unsafe.Pointer(&reflect.SliceHeader{
+		sectionPayload  elfSection64
-			Len:  int(sectionData[ptrElfSections.strtabSectionIndex].size),
+		ptrElfSections  = (*elfSections)(unsafe.Pointer(curPtr))
-			Cap:  int(sectionData[ptrElfSections.strtabSectionIndex].size),
+		secPtr          = uintptr(unsafe.Pointer(&ptrElfSections.sectionData))
-			Data: uintptr(sectionData[ptrElfSections.strtabSectionIndex].address),
+		sizeofSection   = unsafe.Sizeof(sectionPayload)
-		}))
+		strTableSection = (*elfSection64)(unsafe.Pointer(secPtr + uintptr(ptrElfSections.strtabSectionIndex)*sizeofSection))
+		secName         string
+		secNameHeader   = (*reflect.StringHeader)(unsafe.Pointer(&secName))
 	)
 
-	for _, secData := range sectionData {
+	for secIndex := uint16(0); secIndex < ptrElfSections.numSections; secIndex, secPtr = secIndex+1, secPtr+sizeofSection {
+		secData := (*elfSection64)(unsafe.Pointer(secPtr))
 		if secData.size == 0 {
 			continue
 		}
 
 		// String table entries are C-style NULL-terminated strings
-		end := secData.nameIndex
+		end := uintptr(secData.nameIndex)
-		for ; strTable[end] != 0; end++ {
+		for ; *(*byte)(unsafe.Pointer(uintptr(strTableSection.address) + end)) != 0; end++ {
 		}
 
-		elfSectionList = append(elfSectionList, &ElfSection{
+		secNameHeader.Len = int(end - uintptr(secData.nameIndex))
-			Name:    string(strTable[secData.nameIndex:end]),
+		secNameHeader.Data = uintptr(unsafe.Pointer(uintptr(strTableSection.address) + uintptr(secData.nameIndex)))
-			Flags:   ElfSectionFlag(secData.flags),
-			Address: uintptr(secData.address),
-		})
-	}
 
-	return elfSectionList
+		visitor(secName, ElfSectionFlag(secData.flags), uintptr(secData.address), secData.size)
+	}
 }
 
 // SetInfoPtr updates the internal multiboot information pointer to the given

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

@@ -196,9 +196,9 @@ func TestGetBootCmdLine(t *testing.T) {
 func TestGetElfSections(t *testing.T) {
 	SetInfoPtr(uintptr(unsafe.Pointer(&emptyInfoData[0])))
 
-	if GetElfSections() != nil {
+	VisitElfSections(func(_ string, _ ElfSectionFlag, _ uintptr, _ uint64) {
 		t.Fatalf("expected GetElfSections() to return nil when no elf sections tag is present")
-	}
+	})
 
 	SetInfoPtr(uintptr(unsafe.Pointer(&multibootInfoTestData[0])))
 
@@ -209,9 +209,9 @@ func TestGetElfSections(t *testing.T) {
 		multibootInfoTestData[1660+i] = b
 	}
 
-	sections := GetElfSections()
+	// There are more sections in the test data but we will only focus on these ones for the test
-
+	var (
-	specs := []struct {
+		expSections = []struct {
 			secName  string
 			expFlags ElfSectionFlag
 		}{
@@ -222,30 +222,32 @@ func TestGetElfSections(t *testing.T) {
 			{".rodata", ElfSectionAllocated},
 			{".strtab", 0},
 		}
+		matchedSections int
+	)
 
-	for specIndex, spec := range specs {
+	VisitElfSections(func(secName string, secFlags ElfSectionFlag, _ uintptr, secSize uint64) {
-		var found *ElfSection
+		for secIndex, sec := range expSections {
-		for _, sec := range sections {
+			if secName != sec.secName {
-			if sec.Name == spec.secName {
-				found = sec
-				break
-			}
-		}
-
-		if found == nil {
-			t.Errorf("[spec %d] missing section %q", specIndex, spec.secName)
 				continue
 			}
 
-		if found.Flags != spec.expFlags {
+			if secFlags != sec.expFlags {
-			t.Errorf("[spec %d] expected section flags to be: 0x%x; got 0x%x", specIndex, spec.expFlags, found.Flags)
+				t.Errorf("[section %d] expected section flags to be: 0x%x; got 0x%x", secIndex, sec.expFlags, secFlags)
-		}
+				return
 			}
 
-	// Second call should return the memoized data
+			if secSize == 0 {
-	sections[0].Name = "foo"
+				t.Errorf("[section %d] expected section size to be > 0", secIndex)
-	if sections2 := GetElfSections(); !reflect.DeepEqual(sections2, sections) {
+				return
-		t.Error("expected second call to GetElfSections() to return the memoized section list")
+			}
+
+			matchedSections++
+			return
+		}
+	})
+
+	if exp := len(expSections); matchedSections != exp {
+		t.Fatalf("expected to match %d sections; matched %d", exp, matchedSections)
 	}
 }
 

src/gopheros/kernel/kmain/kmain.go

@@ -20,18 +20,20 @@ var (
 // allocated by the assembly code.
 //
 // The rt0 code passes the address of the multiboot info payload provided by the
-// bootloader as well as the physical addresses for the kernel start/end.
+// bootloader as well as the physical addresses for the kernel start/end. In
+// addition, the start of the kernel virtual address space is passed to the
+// kernelPageOffset argument.
 //
 // Kmain is not expected to return. If it does, the rt0 code will halt the CPU.
 //
 //go:noinline
-func Kmain(multibootInfoPtr, kernelStart, kernelEnd uintptr) {
+func Kmain(multibootInfoPtr, kernelStart, kernelEnd, kernelPageOffset uintptr) {
 	multiboot.SetInfoPtr(multibootInfoPtr)
 
 	var err *kernel.Error
 	if err = allocator.Init(kernelStart, kernelEnd); err != nil {
 		panic(err)
-	} else if err = vmm.Init(); err != nil {
+	} else if err = vmm.Init(kernelPageOffset); err != nil {
 		panic(err)
 	} else if err = goruntime.Init(); err != nil {
 		panic(err)

src/gopheros/kernel/mem/vmm/vmm.go

@@ -3,10 +3,12 @@ package vmm
 import (
 	"gopheros/kernel"
 	"gopheros/kernel/cpu"
+	"gopheros/kernel/hal/multiboot"
 	"gopheros/kernel/irq"
 	"gopheros/kernel/kfmt"
 	"gopheros/kernel/mem"
 	"gopheros/kernel/mem/pmm"
+	"unsafe"
 )
 
 var (
@@ -18,6 +20,8 @@ var (
 	// inlined by the compiler.
 	handleExceptionWithCodeFn = irq.HandleExceptionWithCode
 	readCR2Fn                 = cpu.ReadCR2
+	translateFn               = Translate
+	visitElfSectionsFn        = multiboot.VisitElfSections
 
 	errUnrecoverableFault = &kernel.Error{Module: "vmm", Message: "page/gpf fault"}
 )
@@ -142,9 +146,13 @@ func reserveZeroedFrame() *kernel.Error {
 	return nil
 }
 
-// Init initializes the vmm system and installs paging-related exception
+// Init initializes the vmm system, creates a granular PDT for the kernel and
-// handlers.
+// installs paging-related exception handlers.
-func Init() *kernel.Error {
+func Init(kernelPageOffset uintptr) *kernel.Error {
+	if err := setupPDTForKernel(kernelPageOffset); err != nil {
+		return err
+	}
+
 	if err := reserveZeroedFrame(); err != nil {
 		return err
 	}
@@ -153,3 +161,92 @@ func Init() *kernel.Error {
 	handleExceptionWithCodeFn(irq.GPFException, generalProtectionFaultHandler)
 	return nil
 }
+
+// setupPDTForKernel queries the multiboot package for the ELF sections that
+// correspond to the loaded kernel image and establishes a new granular PDT for
+// the kernel's VMA using the appropriate flags (e.g. NX for data sections, RW
+// for writable sections e.t.c).
+func setupPDTForKernel(kernelPageOffset uintptr) *kernel.Error {
+	var pdt PageDirectoryTable
+
+	// Allocate frame for the page directory and initialize it
+	pdtFrame, err := frameAllocator()
+	if err != nil {
+		return err
+	}
+
+	if err = pdt.Init(pdtFrame); err != nil {
+		return err
+	}
+
+	// Query the ELF sections of the kernel image and establish mappings
+	// for each one using the appropriate flags
+	pageSizeMinus1 := uint64(mem.PageSize - 1)
+	var visitor = func(_ string, secFlags multiboot.ElfSectionFlag, secAddress uintptr, secSize uint64) {
+		// Bail out if we have encountered an error; also ignore sections
+		// not using the kernel's VMA
+		if err != nil || secAddress < kernelPageOffset {
+			return
+		}
+
+		flags := FlagPresent
+
+		if (secFlags & multiboot.ElfSectionExecutable) == 0 {
+			flags |= FlagNoExecute
+		}
+
+		if (secFlags & multiboot.ElfSectionWritable) != 0 {
+			flags |= FlagRW
+		}
+
+		// We assume that all sections are page-aligned by the linker script
+		curPage := PageFromAddress(secAddress)
+		curFrame := pmm.Frame((secAddress - kernelPageOffset) >> mem.PageShift)
+		endFrame := curFrame + pmm.Frame(((secSize+pageSizeMinus1) & ^pageSizeMinus1)>>mem.PageShift)
+		for ; curFrame < endFrame; curFrame, curPage = curFrame+1, curPage+1 {
+			if err = pdt.Map(curPage, curFrame, flags); err != nil {
+				return
+			}
+		}
+	}
+
+	// Use the noescape hack to prevent the compiler from leaking the visitor
+	// function literal to the heap.
+	visitElfSectionsFn(
+		*(*multiboot.ElfSectionVisitor)(noEscape(unsafe.Pointer(&visitor))),
+	)
+
+	// If an error occurred while maping the ELF sections bail out
+	if err != nil {
+		return err
+	}
+
+	// Ensure that any pages mapped by the memory allocator using
+	// EarlyReserveRegion are copied to the new page directory.
+	for rsvAddr := earlyReserveLastUsed; rsvAddr < tempMappingAddr; rsvAddr += uintptr(mem.PageSize) {
+		page := PageFromAddress(rsvAddr)
+
+		frameAddr, err := translateFn(rsvAddr)
+		if err != nil {
+			return err
+		}
+
+		if err = pdt.Map(page, pmm.Frame(frameAddr>>mem.PageShift), FlagPresent|FlagRW); err != nil {
+			return err
+		}
+	}
+
+	// Activate the new PDT. After this point, the identify mapping for the
+	// physical memory addresses where the kernel is loaded becomes invalid.
+	pdt.Activate()
+
+	return nil
+}
+
+// noEscape hides a pointer from escape analysis. This function is copied over
+// from runtime/stubs.go
+//go:nosplit
+func noEscape(p unsafe.Pointer) unsafe.Pointer {
+	x := uintptr(p)
+	return unsafe.Pointer(x ^ 0)
+}

src/gopheros/kernel/mem/vmm/vmm_test.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"gopheros/kernel"
 	"gopheros/kernel/cpu"
+	"gopheros/kernel/hal/multiboot"
 	"gopheros/kernel/irq"
 	"gopheros/kernel/kfmt"
 	"gopheros/kernel/mem"
@@ -165,7 +166,7 @@ func TestNonRecoverablePageFault(t *testing.T) {
 	}
 }
 
-func TestGPtHandler(t *testing.T) {
+func TestGPFHandler(t *testing.T) {
 	defer func() {
 		readCR2Fn = cpu.ReadCR2
 	}()
@@ -191,6 +192,9 @@ func TestGPtHandler(t *testing.T) {
 func TestInit(t *testing.T) {
 	defer func() {
 		frameAllocator = nil
+		activePDTFn = cpu.ActivePDT
+		switchPDTFn = cpu.SwitchPDT
+		translateFn = Translate
 		mapTemporaryFn = MapTemporary
 		unmapFn = Unmap
 		handleExceptionWithCodeFn = irq.HandleExceptionWithCode
@@ -199,6 +203,8 @@ func TestInit(t *testing.T) {
 	// reserve space for an allocated page
 	reservedPage := make([]byte, mem.PageSize)
 
+	multiboot.SetInfoPtr(uintptr(unsafe.Pointer(&emptyInfoData[0])))
+
 	t.Run("success", func(t *testing.T) {
 		// fill page with junk
 		for i := 0; i < len(reservedPage); i++ {
@@ -209,11 +215,15 @@ func TestInit(t *testing.T) {
 			addr := uintptr(unsafe.Pointer(&reservedPage[0]))
 			return pmm.Frame(addr >> mem.PageShift), nil
 		})
+		activePDTFn = func() uintptr {
+			return uintptr(unsafe.Pointer(&reservedPage[0]))
+		}
+		switchPDTFn = func(_ uintptr) {}
 		unmapFn = func(p Page) *kernel.Error { return nil }
 		mapTemporaryFn = func(f pmm.Frame) (Page, *kernel.Error) { return Page(f), nil }
 		handleExceptionWithCodeFn = func(_ irq.ExceptionNum, _ irq.ExceptionHandlerWithCode) {}
 
-		if err := Init(); err != nil {
+		if err := Init(0); err != nil {
 			t.Fatal(err)
 		}
 
@@ -225,15 +235,45 @@ func TestInit(t *testing.T) {
 		}
 	})
 
+	t.Run("setupPDT fails", func(t *testing.T) {
+		expErr := &kernel.Error{Module: "test", Message: "out of memory"}
+
+		// Allow the PDT allocation to succeed and then return an error when
+		// trying to allocate the blank fram
+		SetFrameAllocator(func() (pmm.Frame, *kernel.Error) {
+			return pmm.InvalidFrame, expErr
+		})
+
+		if err := Init(0); err != expErr {
+			t.Fatalf("expected error: %v; got %v", expErr, err)
+		}
+	})
+
 	t.Run("blank page allocation error", func(t *testing.T) {
 		expErr := &kernel.Error{Module: "test", Message: "out of memory"}
 
-		SetFrameAllocator(func() (pmm.Frame, *kernel.Error) { return pmm.InvalidFrame, expErr })
+		// Allow the PDT allocation to succeed and then return an error when
+		// trying to allocate the blank fram
+		var allocCount int
+		SetFrameAllocator(func() (pmm.Frame, *kernel.Error) {
+			defer func() { allocCount++ }()
+
+			if allocCount == 0 {
+				addr := uintptr(unsafe.Pointer(&reservedPage[0]))
+				return pmm.Frame(addr >> mem.PageShift), nil
+			}
+
+			return pmm.InvalidFrame, expErr
+		})
+		activePDTFn = func() uintptr {
+			return uintptr(unsafe.Pointer(&reservedPage[0]))
+		}
+		switchPDTFn = func(_ uintptr) {}
 		unmapFn = func(p Page) *kernel.Error { return nil }
 		mapTemporaryFn = func(f pmm.Frame) (Page, *kernel.Error) { return Page(f), nil }
 		handleExceptionWithCodeFn = func(_ irq.ExceptionNum, _ irq.ExceptionHandlerWithCode) {}
 
-		if err := Init(); err != expErr {
+		if err := Init(0); err != expErr {
 			t.Fatalf("expected error: %v; got %v", expErr, err)
 		}
 	})
@@ -245,12 +285,207 @@ func TestInit(t *testing.T) {
 			addr := uintptr(unsafe.Pointer(&reservedPage[0]))
 			return pmm.Frame(addr >> mem.PageShift), nil
 		})
+		activePDTFn = func() uintptr {
+			return uintptr(unsafe.Pointer(&reservedPage[0]))
+		}
+		switchPDTFn = func(_ uintptr) {}
 		unmapFn = func(p Page) *kernel.Error { return nil }
 		mapTemporaryFn = func(f pmm.Frame) (Page, *kernel.Error) { return Page(f), expErr }
 		handleExceptionWithCodeFn = func(_ irq.ExceptionNum, _ irq.ExceptionHandlerWithCode) {}
 
-		if err := Init(); err != expErr {
+		if err := Init(0); err != expErr {
 			t.Fatalf("expected error: %v; got %v", expErr, err)
 		}
 	})
 }
+
+func TestSetupPDTForKernel(t *testing.T) {
+	defer func() {
+		frameAllocator = nil
+		activePDTFn = cpu.ActivePDT
+		switchPDTFn = cpu.SwitchPDT
+		translateFn = Translate
+		mapFn = Map
+		mapTemporaryFn = MapTemporary
+		unmapFn = Unmap
+		earlyReserveLastUsed = tempMappingAddr
+	}()
+
+	// reserve space for an allocated page
+	reservedPage := make([]byte, mem.PageSize)
+
+	multiboot.SetInfoPtr(uintptr(unsafe.Pointer(&emptyInfoData[0])))
+
+	t.Run("map kernel sections", func(t *testing.T) {
+		defer func() { visitElfSectionsFn = multiboot.VisitElfSections }()
+
+		SetFrameAllocator(func() (pmm.Frame, *kernel.Error) {
+			addr := uintptr(unsafe.Pointer(&reservedPage[0]))
+			return pmm.Frame(addr >> mem.PageShift), nil
+		})
+		activePDTFn = func() uintptr {
+			return uintptr(unsafe.Pointer(&reservedPage[0]))
+		}
+		switchPDTFn = func(_ uintptr) {}
+		translateFn = func(_ uintptr) (uintptr, *kernel.Error) { return 0xbadf00d000, nil }
+		mapTemporaryFn = func(f pmm.Frame) (Page, *kernel.Error) { return Page(f), nil }
+		visitElfSectionsFn = func(v multiboot.ElfSectionVisitor) {
+			v(".debug", 0, 0, uint64(mem.PageSize>>1)) // address < VMA; should be ignored
+			v(".text", multiboot.ElfSectionExecutable, 0xbadc0ffee, uint64(mem.PageSize>>1))
+			v(".data", multiboot.ElfSectionWritable, 0xbadc0ffee, uint64(mem.PageSize))
+			v(".rodata", 0, 0xbadc0ffee, uint64(mem.PageSize<<1))
+		}
+		mapCount := 0
+		mapFn = func(page Page, frame pmm.Frame, flags PageTableEntryFlag) *kernel.Error {
+			defer func() { mapCount++ }()
+
+			var expFlags PageTableEntryFlag
+
+			switch mapCount {
+			case 0:
+				expFlags = FlagPresent
+			case 1:
+				expFlags = FlagPresent | FlagNoExecute | FlagRW
+			case 2, 3:
+				expFlags = FlagPresent | FlagNoExecute
+			}
+
+			if (flags & expFlags) != expFlags {
+				t.Errorf("[map call %d] expected flags to be %d; got %d", mapCount, expFlags, flags)
+			}
+
+			return nil
+		}
+
+		if err := setupPDTForKernel(0x123); err != nil {
+			t.Fatal(err)
+		}
+
+		if exp := 4; mapCount != exp {
+			t.Errorf("expected Map to be called %d times; got %d", exp, mapCount)
+		}
+	})
+
+	t.Run("map of kernel sections fials", func(t *testing.T) {
+		defer func() { visitElfSectionsFn = multiboot.VisitElfSections }()
+		expErr := &kernel.Error{Module: "test", Message: "map failed"}
+
+		SetFrameAllocator(func() (pmm.Frame, *kernel.Error) {
+			addr := uintptr(unsafe.Pointer(&reservedPage[0]))
+			return pmm.Frame(addr >> mem.PageShift), nil
+		})
+		activePDTFn = func() uintptr {
+			return uintptr(unsafe.Pointer(&reservedPage[0]))
+		}
+		switchPDTFn = func(_ uintptr) {}
+		translateFn = func(_ uintptr) (uintptr, *kernel.Error) { return 0xbadf00d000, nil }
+		mapTemporaryFn = func(f pmm.Frame) (Page, *kernel.Error) { return Page(f), nil }
+		visitElfSectionsFn = func(v multiboot.ElfSectionVisitor) {
+			v(".text", multiboot.ElfSectionExecutable, 0xbadc0ffee, uint64(mem.PageSize>>1))
+		}
+		mapFn = func(page Page, frame pmm.Frame, flags PageTableEntryFlag) *kernel.Error {
+			return expErr
+		}
+
+		if err := setupPDTForKernel(0); err != expErr {
+			t.Fatalf("expected error: %v; got %v", expErr, err)
+		}
+	})
+
+	t.Run("copy allocator reservations to PDT", func(t *testing.T) {
+		earlyReserveLastUsed = tempMappingAddr - uintptr(mem.PageSize)
+		SetFrameAllocator(func() (pmm.Frame, *kernel.Error) {
+			addr := uintptr(unsafe.Pointer(&reservedPage[0]))
+			return pmm.Frame(addr >> mem.PageShift), nil
+		})
+		activePDTFn = func() uintptr {
+			return uintptr(unsafe.Pointer(&reservedPage[0]))
+		}
+		switchPDTFn = func(_ uintptr) {}
+		translateFn = func(_ uintptr) (uintptr, *kernel.Error) { return 0xbadf00d000, nil }
+		unmapFn = func(p Page) *kernel.Error { return nil }
+		mapTemporaryFn = func(f pmm.Frame) (Page, *kernel.Error) { return Page(f), nil }
+		mapFn = func(page Page, frame pmm.Frame, flags PageTableEntryFlag) *kernel.Error {
+			if exp := PageFromAddress(earlyReserveLastUsed); page != exp {
+				t.Errorf("expected Map to be called with page %d; got %d", exp, page)
+			}
+
+			if exp := pmm.Frame(0xbadf00d000 >> mem.PageShift); frame != exp {
+				t.Errorf("expected Map to be called with frame %d; got %d", exp, frame)
+			}
+
+			if flags&(FlagPresent|FlagRW) != (FlagPresent | FlagRW) {
+				t.Error("expected Map to be called FlagPresent | FlagRW")
+			}
+			return nil
+		}
+
+		if err := setupPDTForKernel(0); err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	t.Run("pdt init fails", func(t *testing.T) {
+		expErr := &kernel.Error{Module: "test", Message: "translate failed"}
+
+		SetFrameAllocator(func() (pmm.Frame, *kernel.Error) {
+			addr := uintptr(unsafe.Pointer(&reservedPage[0]))
+			return pmm.Frame(addr >> mem.PageShift), nil
+		})
+		activePDTFn = func() uintptr { return 0 }
+		mapTemporaryFn = func(f pmm.Frame) (Page, *kernel.Error) { return 0, expErr }
+
+		if err := setupPDTForKernel(0); err != expErr {
+			t.Fatalf("expected error: %v; got %v", expErr, err)
+		}
+	})
+
+	t.Run("translation fails for page in reserved address space", func(t *testing.T) {
+		expErr := &kernel.Error{Module: "test", Message: "translate failed"}
+
+		earlyReserveLastUsed = tempMappingAddr - uintptr(mem.PageSize)
+		SetFrameAllocator(func() (pmm.Frame, *kernel.Error) {
+			addr := uintptr(unsafe.Pointer(&reservedPage[0]))
+			return pmm.Frame(addr >> mem.PageShift), nil
+		})
+		activePDTFn = func() uintptr {
+			return uintptr(unsafe.Pointer(&reservedPage[0]))
+		}
+		translateFn = func(_ uintptr) (uintptr, *kernel.Error) {
+			return 0, expErr
+		}
+
+		if err := setupPDTForKernel(0); err != expErr {
+			t.Fatalf("expected error: %v; got %v", expErr, err)
+		}
+	})
+
+	t.Run("map fails for page in reserved address space", func(t *testing.T) {
+		expErr := &kernel.Error{Module: "test", Message: "map failed"}
+
+		earlyReserveLastUsed = tempMappingAddr - uintptr(mem.PageSize)
+		SetFrameAllocator(func() (pmm.Frame, *kernel.Error) {
+			addr := uintptr(unsafe.Pointer(&reservedPage[0]))
+			return pmm.Frame(addr >> mem.PageShift), nil
+		})
+		activePDTFn = func() uintptr {
+			return uintptr(unsafe.Pointer(&reservedPage[0]))
+		}
+		translateFn = func(_ uintptr) (uintptr, *kernel.Error) { return 0xbadf00d000, nil }
+		mapTemporaryFn = func(f pmm.Frame) (Page, *kernel.Error) { return Page(f), nil }
+		mapFn = func(page Page, frame pmm.Frame, flags PageTableEntryFlag) *kernel.Error { return expErr }
+
+		if err := setupPDTForKernel(0); err != expErr {
+			t.Fatalf("expected error: %v; got %v", expErr, err)
+		}
+	})
+}
+
+var (
+	emptyInfoData = []byte{
+		0, 0, 0, 0, // size
+		0, 0, 0, 0, // reserved
+		0, 0, 0, 0, // tag with type zero and length zero
+		0, 0, 0, 0,
+	}
+)

src/gopheros/stub.go

@@ -11,5 +11,5 @@ var multibootInfoPtr uintptr
 // A global variable is passed as an argument to Kmain to prevent the compiler
 // from inlining the actual call and removing Kmain from the generated .o file.
 func main() {
-	kmain.Kmain(multibootInfoPtr, 0, 0)
+	kmain.Kmain(multibootInfoPtr, 0, 0, 0)
 }