tinygo/src/runtime/gc_stack_portable.go

//go:build gc.conservative && tinygo.wasm
// +build gc.conservative,tinygo.wasm

package runtime

import (
	"unsafe"
)

//go:extern runtime.stackChainStart
var stackChainStart *stackChainObject

type stackChainObject struct {
	parent   *stackChainObject
	numSlots uintptr
}

// markStack marks all root pointers found on the stack.
//
// This implementation is conservative and relies on the compiler inserting code
// to manually push/pop stack objects that are stored in a linked list starting
// with stackChainStart. Manually keeping track of stack values is _much_ more
// expensive than letting the compiler do it and it inhibits a few important
// optimizations, but it has the big advantage of being portable to basically
// any ISA, including WebAssembly.
func markStack() {
	stackObject := stackChainStart
	for stackObject != nil {
		start := uintptr(unsafe.Pointer(stackObject)) + unsafe.Sizeof(uintptr(0))*2
		end := start + stackObject.numSlots*unsafe.Alignof(uintptr(0))
		markRoots(start, end)
		stackObject = stackObject.parent
	}
}

// trackPointer is a stub function call inserted by the compiler during IR
// construction. Calls to it are later replaced with regular stack bookkeeping
// code.
func trackPointer(ptr unsafe.Pointer)

// swapStackChain swaps the stack chain.
// This is called from internal/task when switching goroutines.
func swapStackChain(dst **stackChainObject) {
	*dst, stackChainStart = stackChainStart, *dst
}