Use go:redirect-from directive to map panic to kernel.Panic

All calls (but one) to kernel.Panic have been replaced by calls to
panic. A call to kernel.Panic is still required to prevent the compiler
from treating kernel.Panic as dead code and eliminating it.

kernel/kmain/kmain.go

@@ -8,6 +8,10 @@ import (
 	"github.com/achilleasa/gopher-os/kernel/mem/vmm"
 )
 
+var (
+	errKmainReturned = &kernel.Error{Module: "kmain", Message: "Kmain returned"}
+)
+
 // Kmain is the only Go symbol that is visible (exported) from the rt0 initialization
 // code. This function is invoked by the rt0 assembly code after setting up the GDT
 // and setting up a a minimal g0 struct that allows Go code using the 4K stack
@@ -27,8 +31,12 @@ func Kmain(multibootInfoPtr, kernelStart, kernelEnd uintptr) {
 
 	var err *kernel.Error
 	if err = allocator.Init(kernelStart, kernelEnd); err != nil {
-		kernel.Panic(err)
+		panic(err)
 	} else if err = vmm.Init(); err != nil {
-		kernel.Panic(err)
+		panic(err)
 	}
+
+	// Use kernel.Panic instead of panic to prevent the compiler from
+	// treating kernel.Panic as dead-code and eliminating it.
+	kernel.Panic(errKmainReturned)
 }

kernel/mem/vmm/vmm.go

@@ -16,9 +16,10 @@ var (
 
 	// the following functions are mocked by tests and are automatically
 	// inlined by the compiler.
-	panicFn                   = kernel.Panic
 	handleExceptionWithCodeFn = irq.HandleExceptionWithCode
 	readCR2Fn                 = cpu.ReadCR2
+
+	errUnrecoverableFault = &kernel.Error{Module: "vmm", Message: "page/gpf fault"}
 )
 
 // FrameAllocatorFn is a function that can allocate physical frames.
@@ -78,7 +79,7 @@ func pageFaultHandler(errorCode uint64, frame *irq.Frame, regs *irq.Regs) {
 		}
 	}
 
-	nonRecoverablePageFault(faultAddress, errorCode, frame, regs, nil)
+	nonRecoverablePageFault(faultAddress, errorCode, frame, regs, errUnrecoverableFault)
 }
 
 func nonRecoverablePageFault(faultAddress uintptr, errorCode uint64, frame *irq.Frame, regs *irq.Regs, err *kernel.Error) {
@@ -107,7 +108,7 @@ func nonRecoverablePageFault(faultAddress uintptr, errorCode uint64, frame *irq.
 	frame.Print()
 
 	// TODO: Revisit this when user-mode tasks are implemented
-	panicFn(err)
+	panic(err)
 }
 
 func generalProtectionFaultHandler(_ uint64, frame *irq.Frame, regs *irq.Regs) {
@@ -117,7 +118,7 @@ func generalProtectionFaultHandler(_ uint64, frame *irq.Frame, regs *irq.Regs) {
 	frame.Print()
 
 	// TODO: Revisit this when user-mode tasks are implemented
-	panicFn(nil)
+	panic(errUnrecoverableFault)
 }
 
 // reserveZeroedFrame reserves a physical frame to be used together with

kernel/mem/vmm/vmm_test.go

@@ -2,6 +2,7 @@ package vmm
 
 import (
 	"bytes"
+	"fmt"
 	"strings"
 	"testing"
 	"unsafe"
@@ -19,7 +20,6 @@ func TestRecoverablePageFault(t *testing.T) {
 	var (
 		frame      irq.Frame
 		regs       irq.Regs
-		panicCalled bool
 		pageEntry  pageTableEntry
 		origPage   = make([]byte, mem.PageSize)
 		clonedPage = make([]byte, mem.PageSize)
@@ -28,7 +28,6 @@ func TestRecoverablePageFault(t *testing.T) {
 
 	defer func(origPtePtr func(uintptr) unsafe.Pointer) {
 		ptePtrFn = origPtePtr
-		panicFn = kernel.Panic
 		readCR2Fn = cpu.ReadCR2
 		frameAllocator = nil
 		mapTemporaryFn = MapTemporary
@@ -58,16 +57,31 @@ func TestRecoverablePageFault(t *testing.T) {
 
 	mockTTY()
 
-	panicFn = func(_ *kernel.Error) {
-		panicCalled = true
-	}
-
 	ptePtrFn = func(entry uintptr) unsafe.Pointer { return unsafe.Pointer(&pageEntry) }
 	readCR2Fn = func() uint64 { return uint64(uintptr(unsafe.Pointer(&origPage[0]))) }
 	unmapFn = func(_ Page) *kernel.Error { return nil }
 	flushTLBEntryFn = func(_ uintptr) {}
 
 	for specIndex, spec := range specs {
+		t.Run(fmt.Sprint(specIndex), func(t *testing.T) {
+			defer func() {
+				err := recover()
+				if spec.expPanic && err == nil {
+					t.Error("expected a panic")
+				} else if !spec.expPanic {
+					if err != nil {
+						t.Error("unexpected panic")
+						return
+					}
+
+					for i := 0; i < len(origPage); i++ {
+						if origPage[i] != clonedPage[i] {
+							t.Errorf("expected clone page to be a copy of the original page; mismatch at index %d", i)
+						}
+					}
+				}
+			}()
+
 			mapTemporaryFn = func(f pmm.Frame) (Page, *kernel.Error) { return Page(f), spec.mapError }
 			SetFrameAllocator(func() (pmm.Frame, *kernel.Error) {
 				addr := uintptr(unsafe.Pointer(&clonedPage[0]))
@@ -79,76 +93,51 @@ func TestRecoverablePageFault(t *testing.T) {
 				clonedPage[i] = 0
 			}
 
-		panicCalled = false
 			pageEntry = 0
 			pageEntry.SetFlags(spec.pteFlags)
 
 			pageFaultHandler(2, &frame, &regs)
-
+		})
-		if spec.expPanic != panicCalled {
-			t.Errorf("[spec %d] expected panic %t; got %t", specIndex, spec.expPanic, panicCalled)
-		}
-
-		if !spec.expPanic {
-			for i := 0; i < len(origPage); i++ {
-				if origPage[i] != clonedPage[i] {
-					t.Errorf("[spec %d] expected clone page to be a copy of the original page; mismatch at index %d", specIndex, i)
-				}
-			}
-		}
 	}
 
 }
 
 func TestNonRecoverablePageFault(t *testing.T) {
-	defer func() {
-		panicFn = kernel.Panic
-	}()
-
 	specs := []struct {
 		errCode   uint64
 		expReason string
-		expPanic  bool
 	}{
 		{
 			0,
 			"read from non-present page",
-			true,
 		},
 		{
 			1,
 			"page protection violation (read)",
-			true,
 		},
 		{
 			2,
 			"write to non-present page",
-			true,
 		},
 		{
 			3,
 			"page protection violation (write)",
-			true,
 		},
 		{
 			4,
 			"page-fault in user-mode",
-			true,
 		},
 		{
 			8,
 			"page table has reserved bit set",
-			true,
 		},
 		{
 			16,
 			"instruction fetch",
-			true,
 		},
 		{
 			0xf00,
 			"unknown",
-			true,
 		},
 	}
 
@@ -157,58 +146,45 @@ func TestNonRecoverablePageFault(t *testing.T) {
 		frame irq.Frame
 	)
 
-	panicCalled := false
-	panicFn = func(_ *kernel.Error) {
-		panicCalled = true
-	}
-
 	for specIndex, spec := range specs {
+		t.Run(fmt.Sprint(specIndex), func(t *testing.T) {
+			defer func() {
+				if err := recover(); err != errUnrecoverableFault {
+					t.Errorf("expected a panic with errUnrecoverableFault; got %v", err)
+				}
+			}()
 			fb := mockTTY()
-		panicCalled = false
 
-		nonRecoverablePageFault(0xbadf00d000, spec.errCode, &frame, &regs, nil)
+			nonRecoverablePageFault(0xbadf00d000, spec.errCode, &frame, &regs, errUnrecoverableFault)
 			if got := readTTY(fb); !strings.Contains(got, spec.expReason) {
-			t.Errorf("[spec %d] expected reason %q; got output:\n%q", specIndex, spec.expReason, got)
+				t.Errorf("expected reason %q; got output:\n%q", spec.expReason, got)
-			continue
-		}
-
-		if spec.expPanic != panicCalled {
-			t.Errorf("[spec %d] expected panic %t; got %t", specIndex, spec.expPanic, panicCalled)
 			}
+		})
 	}
 }
 
 func TestGPtHandler(t *testing.T) {
 	defer func() {
-		panicFn = kernel.Panic
 		readCR2Fn = cpu.ReadCR2
 	}()
 
 	var (
 		regs  irq.Regs
 		frame irq.Frame
-		fb    = mockTTY()
 	)
 
 	readCR2Fn = func() uint64 {
 		return 0xbadf00d000
 	}
 
-	panicCalled := false
+	defer func() {
-	panicFn = func(_ *kernel.Error) {
+		if err := recover(); err != errUnrecoverableFault {
-		panicCalled = true
+			t.Errorf("expected a panic with errUnrecoverableFault; got %v", err)
 		}
+	}()
 
+	mockTTY()
 	generalProtectionFaultHandler(0, &frame, &regs)
-
-	exp := "\nGeneral protection fault while accessing address: 0xbadf00d000\nRegisters:\nRAX = 0000000000000000 RBX = 0000000000000000\nRCX = 0000000000000000 RDX = 0000000000000000\nRSI = 0000000000000000 RDI = 0000000000000000\nRBP = 0000000000000000\nR8  = 0000000000000000 R9  = 0000000000000000\nR10 = 0000000000000000 R11 = 0000000000000000\nR12 = 0000000000000000 R13 = 0000000000000000\nR14 = 0000000000000000 R15 = 0000000000000000\nRIP = 0000000000000000 CS  = 0000000000000000\nRSP = 0000000000000000 SS  = 0000000000000000\nRFL = 0000000000000000"
-	if got := readTTY(fb); got != exp {
-		t.Errorf("expected output:\n%q\ngot:\n%q", exp, got)
-	}
-
-	if !panicCalled {
-		t.Error("expected kernel.Panic to be called")
-	}
 }
 
 func TestInit(t *testing.T) {

kernel/panic.go

@@ -8,11 +8,28 @@ import (
 var (
 	// cpuHaltFn is mocked by tests and is automatically inlined by the compiler.
 	cpuHaltFn = cpu.Halt
+
+	errRuntimePanic = &Error{Module: "rt", Message: "unknown cause"}
 )
 
 // Panic outputs the supplied error (if not nil) to the console and halts the
-// CPU. Calls to Panic never return.
+// CPU. Calls to Panic never return. Panic also works as a redirection target
-func Panic(err *Error) {
+// for calls to panic() (resolved via runtime.gopanic)
+//go:redirect-from runtime.gopanic
+func Panic(e interface{}) {
+	var err *Error
+
+	switch t := e.(type) {
+	case *Error:
+		err = t
+	case string:
+		errRuntimePanic.Message = t
+		err = errRuntimePanic
+	case error:
+		errRuntimePanic.Message = t.Error()
+		err = errRuntimePanic
+	}
+
 	early.Printf("\n-----------------------------------\n")
 	if err != nil {
 		early.Printf("[%s] unrecoverable error: %s\n", err.Module, err.Message)

kernel/panic_test.go

@@ -2,6 +2,7 @@ package kernel
 
 import (
 	"bytes"
+	"errors"
 	"testing"
 	"unsafe"
 
@@ -20,7 +21,7 @@ func TestPanic(t *testing.T) {
 		cpuHaltCalled = true
 	}
 
-	t.Run("with error", func(t *testing.T) {
+	t.Run("with *kernel.Error", func(t *testing.T) {
 		cpuHaltCalled = false
 		fb := mockTTY()
 		err := &Error{Module: "test", Message: "panic test"}
@@ -38,6 +39,42 @@ func TestPanic(t *testing.T) {
 		}
 	})
 
+	t.Run("with error", func(t *testing.T) {
+		cpuHaltCalled = false
+		fb := mockTTY()
+		err := errors.New("go error")
+
+		Panic(err)
+
+		exp := "\n-----------------------------------\n[rt] unrecoverable error: go error\n*** kernel panic: system halted ***\n-----------------------------------"
+
+		if got := readTTY(fb); got != exp {
+			t.Fatalf("expected to get:\n%q\ngot:\n%q", exp, got)
+		}
+
+		if !cpuHaltCalled {
+			t.Fatal("expected cpu.Halt() to be called by Panic")
+		}
+	})
+
+	t.Run("with string", func(t *testing.T) {
+		cpuHaltCalled = false
+		fb := mockTTY()
+		err := "string error"
+
+		Panic(err)
+
+		exp := "\n-----------------------------------\n[rt] unrecoverable error: string error\n*** kernel panic: system halted ***\n-----------------------------------"
+
+		if got := readTTY(fb); got != exp {
+			t.Fatalf("expected to get:\n%q\ngot:\n%q", exp, got)
+		}
+
+		if !cpuHaltCalled {
+			t.Fatal("expected cpu.Halt() to be called by Panic")
+		}
+	})
+
 	t.Run("without error", func(t *testing.T) {
 		cpuHaltCalled = false
 		fb := mockTTY()