tinygo/src/runtime/panic.go

package runtime

import (
	"internal/task"
	"unsafe"
)

// trap is a compiler hint that this function cannot be executed. It is
// translated into either a trap instruction or a call to abort().
//
//export llvm.trap
func trap()

// Inline assembly stub. It is essentially C longjmp but modified a bit for the
// purposes of TinyGo. It restores the stack pointer and jumps to the given pc.
//
//export tinygo_longjmp
func tinygo_longjmp(frame *deferFrame)

// Compiler intrinsic.
// Returns whether recover is supported on the current architecture.
func supportsRecover() bool

const (
	panicStrategyPrint = 1
	panicStrategyTrap  = 2
)

// Compile intrinsic.
// Returns which strategy is used. This is usually "print" but can be changed
// using the -panic= compiler flag.
func panicStrategy() uint8

// DeferFrame is a stack allocated object that stores information for the
// current "defer frame", which is used in functions that use the `defer`
// keyword.
// 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
	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.
func _panic(message interface{}) {
	if panicStrategy() == panicStrategyTrap {
		trap()
	}
	if supportsRecover() {
		frame := (*deferFrame)(task.Current().DeferFrame)
		if frame != nil {
			frame.PanicValue = message
			frame.Panicking = true
			tinygo_longjmp(frame)
			// unreachable
		}
	}
	printstring("panic: ")
	printitf(message)
	printnl()
	abort()
}

// Cause a runtime panic, which is (currently) always a string.
func runtimePanic(msg string) {
	// As long as this function is inined, llvm.returnaddress(0) will return
	// something sensible.
	runtimePanicAt(returnAddress(0), msg)
}

func runtimePanicAt(addr unsafe.Pointer, msg string) {
	if panicStrategy() == panicStrategyTrap {
		trap()
	}
	if hasReturnAddr {
		printstring("panic: runtime error at ")
		printptr(uintptr(addr) - callInstSize)
		printstring(": ")
	} else {
		printstring("panic: runtime error: ")
	}
	println(msg)
	abort()
}

// Called at the start of a function that includes a deferred call.
// It gets passed in the stack-allocated defer frame and configures it.
// Note that the frame is not zeroed yet, so we need to initialize all values
// that will be used.
//
//go:inline
//go:nobounds
func setupDeferFrame(frame *deferFrame, jumpSP unsafe.Pointer) {
	currentTask := task.Current()
	frame.Previous = (*deferFrame)(currentTask.DeferFrame)
	frame.JumpSP = jumpSP
	frame.Panicking = false
	currentTask.DeferFrame = unsafe.Pointer(frame)
}

// Called right before the return instruction. It pops the defer frame from the
// linked list of defer frames. It also re-raises a panic if the goroutine is
// still panicking.
//
//go:inline
//go:nobounds
func destroyDeferFrame(frame *deferFrame) {
	task.Current().DeferFrame = unsafe.Pointer(frame.Previous)
	if frame.Panicking {
		// We're still panicking!
		// Re-raise the panic now.
		_panic(frame.PanicValue)
	}
}

// _recover is the built-in recover() function. It tries to recover a currently
// panicking goroutine.
// useParentFrame is set when the caller of runtime._recover has a defer frame
// itself. In that case, recover() shouldn't check that frame but one frame up.
func _recover(useParentFrame bool) interface{} {
	if !supportsRecover() {
		// Compiling without stack unwinding support, so make this a no-op.
		return nil
	}
	// TODO: somehow check that recover() is called directly by a deferred
	// function in a panicking goroutine. Maybe this can be done by comparing
	// the frame pointer?
	frame := (*deferFrame)(task.Current().DeferFrame)
	if useParentFrame {
		// Don't recover panic from the current frame (which can't be panicking
		// already), but instead from the previous frame.
		frame = frame.Previous
	}
	if frame != nil && frame.Panicking {
		// Only the first call to recover returns the panic value. It also stops
		// the panicking sequence, hence setting panicking to false.
		frame.Panicking = false
		return frame.PanicValue
	}
	// Not panicking, so return a nil interface.
	return nil
}

// Panic when trying to dereference a nil pointer.
func nilPanic() {
	runtimePanicAt(returnAddress(0), "nil pointer dereference")
}

// Panic when trying to add an entry to a nil map
func nilMapPanic() {
	runtimePanicAt(returnAddress(0), "assignment to entry in nil map")
}

// Panic when trying to acces an array or slice out of bounds.
func lookupPanic() {
	runtimePanicAt(returnAddress(0), "index out of range")
}

// Panic when trying to slice a slice out of bounds.
func slicePanic() {
	runtimePanicAt(returnAddress(0), "slice out of range")
}

// Panic when trying to convert a slice to an array pointer (Go 1.17+) and the
// slice is shorter than the array.
func sliceToArrayPointerPanic() {
	runtimePanicAt(returnAddress(0), "slice smaller than array")
}

// Panic when calling unsafe.Slice() (Go 1.17+) or unsafe.String() (Go 1.20+)
// with a len that's too large (which includes if the ptr is nil and len is
// nonzero).
func unsafeSlicePanic() {
	runtimePanicAt(returnAddress(0), "unsafe.Slice/String: len out of range")
}

// Panic when trying to create a new channel that is too big.
func chanMakePanic() {
	runtimePanicAt(returnAddress(0), "new channel is too big")
}

// Panic when a shift value is negative.
func negativeShiftPanic() {
	runtimePanicAt(returnAddress(0), "negative shift")
}

// Panic when there is a divide by zero.
func divideByZeroPanic() {
	runtimePanicAt(returnAddress(0), "divide by zero")
}

func blockingPanic() {
	runtimePanicAt(returnAddress(0), "trying to do blocking operation in exported function")
}