avr: add support for recover()

You can see that it works with the following command:

    tinygo run -target=simavr ./testdata/recover.go

This also gets the following tests to pass again:

    go test -run=Build -target=simavr -v

Adding support for AVR was a bit more compliated because it's also
necessary to save and restore the Y register.

Author: aykevl

compiler/defer.go

@@ -31,7 +31,7 @@ func (b *builder) supportsRecover() bool {
 		// proposal of WebAssembly:
 		// https://github.com/WebAssembly/exception-handling
 		return false
-	case "avr", "riscv64", "xtensa":
+	case "riscv64", "xtensa":
 		// TODO: add support for these architectures
 		return false
 	default:
@@ -116,8 +116,8 @@ func (b *builder) createInvokeCheckpoint() {
 	//   * The return value (eax, rax, r0, etc) is set to zero in the inline
 	//     assembly but set to an unspecified non-zero value when jumping using
 	//     a longjmp.
-	asmType := llvm.FunctionType(b.uintptrType, []llvm.Type{b.deferFrame.Type()}, false)
 	var asmString, constraints string
+	resultType := b.uintptrType
 	switch b.archFamily() {
 	case "i386":
 		asmString = `
@@ -163,6 +163,21 @@ mov x0, #0
 `
 		constraints = "={x0},{x1},~{x1},~{x2},~{x3},~{x4},~{x5},~{x6},~{x7},~{x8},~{x9},~{x10},~{x11},~{x12},~{x13},~{x14},~{x15},~{x16},~{x17},~{x18},~{x19},~{x20},~{x21},~{x22},~{x23},~{x24},~{x25},~{x26},~{x27},~{x28},~{fp},~{lr},~{q0},~{q1},~{q2},~{q3},~{q4},~{q5},~{q6},~{q7},~{q8},~{q9},~{q10},~{q11},~{q12},~{q13},~{q14},~{q15},~{q16},~{q17},~{q18},~{q19},~{q20},~{q21},~{q22},~{q23},~{q24},~{q25},~{q26},~{q27},~{q28},~{q29},~{q30},~{nzcv},~{ffr},~{vg},~{memory}"
 		// TODO: SVE registers, which we don't use in TinyGo at the moment.
+	case "avr":
+		// Note: the Y register (R28:R29) is a fixed register and therefore
+		// needs to be saved manually. TODO: do this only once per function with
+		// a defer frame, not for every call.
+		resultType = b.ctx.Int8Type()
+		asmString = `
+ldi r24, pm_lo8(1f)
+ldi r25, pm_hi8(1f)
+std z+2, r24
+std z+3, r25
+std z+4, r28
+std z+5, r29
+ldi r24, 0
+1:`
+		constraints = "={r24},z,~{r0},~{r2},~{r3},~{r4},~{r5},~{r6},~{r7},~{r8},~{r9},~{r10},~{r11},~{r12},~{r13},~{r14},~{r15},~{r16},~{r17},~{r18},~{r19},~{r20},~{r21},~{r22},~{r23},~{r25},~{r26},~{r27}"
 	case "riscv32":
 		asmString = `
 la a2, 1f
@@ -174,10 +189,11 @@ li a0, 0
 		// This case should have been handled by b.supportsRecover().
 		b.addError(b.fn.Pos(), "unknown architecture for defer: "+b.archFamily())
 	}
+	asmType := llvm.FunctionType(resultType, []llvm.Type{b.deferFrame.Type()}, false)
 	asm := llvm.InlineAsm(asmType, asmString, constraints, false, false, 0, false)
 	result := b.CreateCall(asm, []llvm.Value{b.deferFrame}, "setjmp")
 	result.AddCallSiteAttribute(-1, b.ctx.CreateEnumAttribute(llvm.AttributeKindID("returns_twice"), 0))
-	isZero := b.CreateICmp(llvm.IntEQ, result, llvm.ConstInt(b.uintptrType, 0, false), "setjmp.result")
+	isZero := b.CreateICmp(llvm.IntEQ, result, llvm.ConstInt(resultType, 0, false), "setjmp.result")
 	continueBB := b.insertBasicBlock("")
 	b.CreateCondBr(isZero, continueBB, b.landingpad)
 	b.SetInsertPointAtEnd(continueBB)

compiler/testdata/defer-cortex-m-qemu.ll

@@ -4,7 +4,7 @@ target datalayout = "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
 target triple = "thumbv7m-unknown-unknown-eabi"
 
 %runtime._defer = type { i32, %runtime._defer* }
-%runtime.deferFrame = type { i8*, i8*, %runtime.deferFrame*, i1, %runtime._interface }
+%runtime.deferFrame = type { i8*, i8*, [0 x i8*], %runtime.deferFrame*, i1, %runtime._interface }
 %runtime._interface = type { i32, i8* }
 
 declare noalias nonnull i8* @runtime.alloc(i32, i8*, i8*) #0

main_test.go

@@ -349,6 +349,7 @@ func runTestWithConfig(name string, t *testing.T, options compileopts.Options, c
 		actual = bytes.Replace(actual, []byte{0x1b, '[', '3', '2', 'm'}, nil, -1)
 		actual = bytes.Replace(actual, []byte{0x1b, '[', '0', 'm'}, nil, -1)
 		actual = bytes.Replace(actual, []byte{'.', '.', '\n'}, []byte{'\n'}, -1)
+		actual = bytes.Replace(actual, []byte{'\n', '.', '\n'}, []byte{'\n', '\n'}, -1)
 	}
 	if name == "testing.go" {
 		// Strip actual time.

src/runtime/arch_386.go

@@ -5,6 +5,8 @@ const GOARCH = "386"
 // The bitness of the CPU (e.g. 8, 32, 64).
 const TargetBits = 32
 
+const deferExtraRegs = 0
+
 // Align on word boundary.
 func align(ptr uintptr) uintptr {
 	return (ptr + 15) &^ 15

src/runtime/arch_amd64.go

@@ -5,6 +5,8 @@ const GOARCH = "amd64"
 // The bitness of the CPU (e.g. 8, 32, 64).
 const TargetBits = 64
 
+const deferExtraRegs = 0
+
 // Align a pointer.
 // Note that some amd64 instructions (like movaps) expect 16-byte aligned
 // memory, thus the result must be 16-byte aligned.

src/runtime/arch_arm.go

@@ -8,6 +8,8 @@ const GOARCH = "arm"
 // The bitness of the CPU (e.g. 8, 32, 64).
 const TargetBits = 32
 
+const deferExtraRegs = 0
+
 // Align on word boundary.
 func align(ptr uintptr) uintptr {
 	return (ptr + 3) &^ 3

src/runtime/arch_arm64.go

@@ -5,6 +5,8 @@ const GOARCH = "arm64"
 // The bitness of the CPU (e.g. 8, 32, 64).
 const TargetBits = 64
 
+const deferExtraRegs = 0
+
 // Align on word boundary.
 func align(ptr uintptr) uintptr {
 	return (ptr + 7) &^ 7

src/runtime/arch_avr.go

@@ -10,6 +10,8 @@ const GOARCH = "arm" // avr pretends to be arm
 // The bitness of the CPU (e.g. 8, 32, 64).
 const TargetBits = 8
 
+const deferExtraRegs = 1 // the frame pointer (Y register) also needs to be stored
+
 // Align on a word boundary.
 func align(ptr uintptr) uintptr {
 	// No alignment necessary on the AVR.

src/runtime/arch_cortexm.go

@@ -12,6 +12,8 @@ const GOARCH = "arm"
 // The bitness of the CPU (e.g. 8, 32, 64).
 const TargetBits = 32
 
+const deferExtraRegs = 0
+
 // Align on word boundary.
 func align(ptr uintptr) uintptr {
 	return (ptr + 3) &^ 3

src/runtime/arch_tinygoriscv.go

@@ -5,6 +5,8 @@ package runtime
 
 import "device/riscv"
 
+const deferExtraRegs = 0
+
 func getCurrentStackPointer() uintptr {
 	return uintptr(stacksave())
 }

src/runtime/arch_tinygowasm.go

@@ -12,6 +12,8 @@ const GOARCH = "wasm"
 // The bitness of the CPU (e.g. 8, 32, 64).
 const TargetBits = 32
 
+const deferExtraRegs = 0
+
 //go:extern __heap_base
 var heapStartSymbol [0]byte
 

src/runtime/arch_xtensa.go

@@ -8,6 +8,8 @@ const GOARCH = "arm" // xtensa pretends to be arm
 // The bitness of the CPU (e.g. 8, 32, 64).
 const TargetBits = 32
 
+const deferExtraRegs = 0
+
 // Align on a word boundary.
 func align(ptr uintptr) uintptr {
 	return (ptr + 3) &^ 3

src/runtime/asm_avr.S

@@ -50,3 +50,33 @@ tinygo_scanCurrentStack:
     pop r17
     pop r28 // Y
     pop r29 // Y
+
+
+.section .text.tinygo_longjmp
+.global tinygo_longjmp
+tinygo_longjmp:
+    ; Move the *DeferFrame pointer to the X register.
+    mov r26, r24
+    mov r27, r25
+
+    ; Load the stack pointer
+    ld r24, X+
+    ld r25, X+
+
+    ; Switch to the given stack pointer.
+    in r0, 0x3f   ; SREG
+    cli           ; disable interrupts
+    out 0x3d, r24 ; SPL
+    out 0x3f, r0  ; re-enable interrupts (with one instruction delay)
+    out 0x3e, r25 ; SPH
+
+    ; Load the new PC
+    ld r30, X+
+    ld r31, X+
+
+    ; Load the new Y register
+    ld r28, X+
+    ld r29, X+
+
+    ; Jump to the PC (stored in the Z register)
+    icall

src/runtime/panic.go

@@ -25,11 +25,12 @@ func supportsRecover() bool
 // The compiler knows about the JumpPC struct offset, so it should not be moved
 // without also updating compiler/defer.go.
 type deferFrame struct {
-	JumpSP     unsafe.Pointer // stack pointer to return to
-	JumpPC     unsafe.Pointer // pc to return to
-	Previous   *deferFrame    // previous recover buffer pointer
-	Panicking  bool           // true iff this defer frame is panicking
-	PanicValue interface{}    // panic value, might be nil for panic(nil) for example
+	JumpSP     unsafe.Pointer                 // stack pointer to return to
+	JumpPC     unsafe.Pointer                 // pc to return to
+	ExtraRegs  [deferExtraRegs]unsafe.Pointer // extra registers (depending on the architecture)
+	Previous   *deferFrame                    // previous recover buffer pointer
+	Panicking  bool                           // true iff this defer frame is panicking
+	PanicValue interface{}                    // panic value, might be nil for panic(nil) for example
 }
 
 // Builtin function panic(msg), used as a compiler intrinsic.