/cc @thanm

@danderson, any chance you could reproduce both at 4435fcf and just before 4435fcf?

I don't have a local go tip installation right now - I'll get one set up and try, though y'all may beat me to it.

No worries. I'll try to repro locally first.

I can reproduce the crash at tip.

It works at dbb1d19 (which is the parent of 4435fcf).

As predicted, you beat me to it :)

Yup, this crash begins at 4435fcf.

All yours, @thanm! :)

I will take a look.

FWIW I've seen that assert in cases where you have a mix of Go objects (some object files bulit by previous versions of the compiler), but I'll see what I can find out.

@thanm, such things shouldn't happen anymore with the new cmd/go content-based caching. Your change is well past the cmd/go changes.

I've reproduce the issue. Still not 100% sure, but I think it has to do with an interaction between the new DWARF stuff and the linker's dead code pass (the one of the type symbols referred to by a DWARF abstract function appears to be mysteriously missing).

If this is holding anyone up, let me know and I can disable the feature with a flag flip while I work on it.

FWIW, it's not blocking me, I just disabled testing on go tip in my automation until it's fixed.

Smaller reproduce:

p/p.go

package p

import "q"

type T struct {
	X *q.P
}

func F(in, out *T) {
	*out = *in
	if in.X != nil {
		in, out := &in.X, &out.X
		if *in == nil {
			*out = nil
		} else {
			*out = new(q.P)
			**out = **in
		}
	}
	return
}

//go:noinline
func G(x, y *T) {
	F(x, y)
}

q/q.go

package q

type P int

main/main.go

package main

import "p"

func main() {
	p.G(nil, nil)
}

It seems that when compiling p, it generates the abstract function DIE of F with references to go.info.**q.P, for the locals in and out (in the inner scope). When the linker sees go.info.**q.P, it tries to make the type DIE from type.**q.P, which is, however, not generated by the compiler.

The variables in the inner scope (in, out in F) are optimized by the compiler, so the type symbols for them are not created.

Change https://golang.org/cl/81415 mentions this issue: cmd/compile: fix DWARF type symbol buglet