cmd/compile: invalid instruction error for FMOVD when compiling for 387

[NightTsarina]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go version go1.9.1 linux/386

What operating system and processor architecture are you using (go env)?

GOARCH="386"
GOBIN=""
GOEXE=""
GOHOSTARCH="386"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/root/go"
GORACE=""
GOROOT="/usr/lib/go-1.9"
GOTOOLDIR="/usr/lib/go-1.9/pkg/tool/linux_386"
GCCGO="gccgo"
GO386="387"
CC="gcc"
GOGCCFLAGS="-fPIC -m32 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build059883492=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"

What did you do?

I did not try to isolate a minimal test case, as I have no idea what is going on. But at least one package in Debian is failing to build because of this (prometheus).

When compiling the tests, this line fails with the following error:

$ GOPATH=$PWD/build go test -c -v github.com/prometheus/prometheus/storage/local
# github.com/prometheus/prometheus/storage/local
build/src/github.com/prometheus/prometheus/storage/local/storage_test.go:2026:26: invalid instruction: 01483 (/tmp/buildd/prometheus-1.8.1+ds/build/src/github.com/prometheus/prometheus/storage/local/storage_test.go:2027) FMOVD ""..autotmp_78+176(DX)(SP*1), F0

I can't reproduce this problem with go 1.7 or 1.8 from Debian. Disabling optimisations with -gcflags=-N seems to solve the issue.

Looking at #21860, I guess that this could something else than an "invalid instruction", but I have no idea :-)

[ianlancetaylor]

CC @randall77

Tentatively marking as 1.9.3.

[randall77]

@thetincho I'm having trouble reproducing this. There is no local directory in github.com/prometheus/prometheus/storage.
Could you make that available somehow?

[ALTree]

@randall77

$ go get github.com/prometheus/prometheus/cmd/...
$ cd $GOPATH/src/github.com/prometheus/prometheus
$ git checkout release-1.8
$ cat VERSION 
1.8.1  # this is the version that appears in the error log above

I can't reproduce this, anyway:

$ go version
go version go1.9.1 linux/amd64

$ GOARCH=386 go test -c -v github.com/prometheus/prometheus/storage/local

the build command succeeds and the generated test binary runs fine. Not sure what I'm doing wrong.

[randall77]

I can't reproduce yet, but I think I know what is wrong.
The compiler is using SP as an index register in an instruction. That's a no-no in x86 world.
I've seen this before, and we have fixes for it. Maybe those fixes aren't complete for 387?

Normally this happens for ops with indexed addressing mode, and scale==1. Then the order of the base and index registers don't matter to SSA, so they can appear in either order. We have code to swap them during assembly generation, like this (from amd64/ssa.go):

		r := v.Args[0].Reg()
		i := v.Args[1].Reg()
		if i == x86.REG_SP {
			r, i = i, r
		}

I'll prepare a CL. It would be nice to be able to reproduce the OP's problem so we can be sure it is fixed.

[gopherbot]

Change https://golang.org/cl/73551 mentions this issue: cmd/compile: make sure not to use SP as an index register

[randall77]

@thetincho I've uploaded a patch. If you can, please try it and let us know if it fixes your issue.

[randall77]

I concocted a stand-alone repro and added it to the patch.