// run -gcflags=-d=maymorestack=main.mayMoreStack

// Copyright 2021 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Test the maymorestack testing hook by injecting a hook that counts
// how many times it is called and checking that count.

package main

import "runtime"

var count uint32

//go:nosplit
func mayMoreStack() {
	count++

}

// mayMoreStackPreempt is a maymorestack hook that forces a preemption
// at every possible cooperative preemption point.
//
// This is valuable to apply to the runtime, which can be sensitive to
// preemption points. To apply this to all preemption points in the
// runtime and runtime-like code, use the following in bash or zsh:
//
//	X=(-{gc,asm}flags={runtime/...,reflect,sync}=-d=maymorestack=runtime.mayMoreStackPreempt) GOFLAGS=${X[@]}

	Importpath = flag.String("p", obj.UnlinkablePkg, "set expected package import to path")
	Spectre    = flag.String("spectre", "", "enable spectre mitigations in `list` (all, ret)")
)

var DebugFlags struct {
	MayMoreStack string `help:"call named function before all stack growth checks"`
	PCTab        string `help:"print named pc-value table\nOne of: pctospadj, pctofile, pctoline, pctoinline, pctopcdata"`
}

var (
	D        MultiFlag

	ctxt.Debugvlog = flags.DebugV
	ctxt.Flag_dynlink = *flags.Dynlink
	ctxt.Flag_linkshared = *flags.Linkshared
	ctxt.Flag_shared = *flags.Shared || *flags.Dynlink
	ctxt.Flag_maymorestack = flags.DebugFlags.MayMoreStack
	ctxt.Debugpcln = flags.DebugFlags.PCTab
	ctxt.IsAsm = true
	ctxt.Pkgpath = *flags.Importpath
	switch *flags.Spectre {
	default:
		log.Printf("unknown setting -spectre=%s", *flags.Spectre)
		os.Exit(2)

	// generated function.
	needMoreStack := framesize > 0 && !s.Func().Text.From.Sym.NoSplit()

	// If the maymorestack debug option is enabled, insert the
	// call to maymorestack *before* processing resume points so
	// we can construct a resume point after maymorestack for
	// morestack to resume at.
	var pMorestack = s.Func().Text
	if needMoreStack && ctxt.Flag_maymorestack != "" {
		p := pMorestack

		// SEH unwind information don't support prologues that are more than 255 bytes long.
		// These are very rare, but still possible, e.g., when compiling functions with many
		// parameters with -gcflags=-d=maymorestack=runtime.mayMoreStackPreempt.
		// Return without reporting an error.
		return
	}

	// Reference:
	// https://learn.microsoft.com/en-us/cpp/build/exception-handling-x64#struct-unwind_info

	const (

	// already quite long and mayMoreStackMove makes it about
	// twice as slow.
	if !t.compileOnly && !t.short {
		// hooks is the set of maymorestack hooks to test with.
		hooks := []string{"mayMoreStackPreempt", "mayMoreStackMove"}
		// hookPkgs is the set of package patterns to apply
		// the maymorestack hook to.
		hookPkgs := []string{"runtime/...", "reflect", "sync"}
		// unhookPkgs is the set of package patterns to

	if c.ctxt.Flag_maymorestack != "" {
		if c.ctxt.Flag_shared || c.ctxt.Flag_dynlink {
			// See the call to morestack for why these are
			// complicated to support.
			c.ctxt.Diag("maymorestack with -shared or -dynlink is not supported")
		}

		// Spill arguments. This has to happen before we open
		// any more frame space.
		p = c.cursym.Func().SpillRegisterArgs(p, c.newprog)

		p = obj.Appendp(p, c.newprog)
		p.As = add
		p.From.Type = obj.TYPE_CONST
		p.From.Offset = int64(-frameSize)
		p.To.Type = obj.TYPE_REG
		p.To.Reg = REGSP
		p.Spadj = int32(frameSize)

		// JAL	maymorestack
		p = obj.Appendp(p, c.newprog)
		p.As = AJAL
		p.To.Type = obj.TYPE_BRANCH
		// See ../x86/obj6.go
		p.To.Sym = c.ctxt.LookupABI(c.ctxt.Flag_maymorestack, c.cursym.ABI())
		p.Mark |= BRANCH

		// MOVW REGCTXT, 4(SP)
		p = obj.Appendp(p, c.newprog)
		p.As = AMOVW
		p.From.Type = obj.TYPE_REG
		p.From.Reg = REGCTXT
		p.To.Type = obj.TYPE_MEM
		p.To.Offset = 4
		p.To.Reg = REGSP

		// CALL maymorestack
		p = obj.Appendp(p, c.newprog)
		p.As = obj.ACALL
		p.To.Type = obj.TYPE_BRANCH
		// See ../x86/obj6.go
		p.To.Sym = c.ctxt.LookupABI(c.ctxt.Flag_maymorestack, c.cursym.ABI())

		// Restore REGCTXT and LR.