I'm trying to call a Go function from asm and I'm having trouble figuring
out the details.

(In the past I've always endeavored to avoid this situation and make all my
asm functions be leaf functions, but in my current use case it would be
most helpful to be able to call a Go helper.)

See the demo code at
https://github.com/cespare/misc/tree/master/asm/stackmap or go get

 demo, I have a small function with an append-style API:

func X(b []byte) []byte

This calls a Go helper growSlice.

This code sometimes works, but if I run `go test -count 1000` I'll quickly

runtime: frame github.com/cespare/misc/asm/stackmap.X untyped locals
fatal error: missing stackmap

I've read through the Runtime Coordination section of the
 walkthrough (https://golang.org/doc/asm#runtime) several times, but I
don't see the problem.

Here is my understanding of a few relevant bits of that section (which
might be incorrect):

If the results will hold live pointers during a call instruction, the
> function should start by zeroing the results and then executing the
> pseudo-instruction GO_RESULTS_INITIALIZED.

This doesn't seem to apply to my code because the results aren't populated
until after the CALL.

If a function has no local stack frame, the pointer information can be
> omitted. This is indicated by a local frame size annotation of $0-n on the
> TEXT instruction. The pointer information can also be omitted if the
> function contains no call instructions. Otherwise, the local stack frame
> must not contain pointers, and the assembly must confirm this fact by
> executing the pseudo-instruction NO_LOCAL_POINTERS.

​My function makes a CALL with arguments. But it has to ​have a pointer
(the slice) on the local stack frame in order to pass to that helper. I
don't really understand what this section means.

`go vet` doesn't say anything about my code.

Any ideas?


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