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

$ go version
go version devel +14c3692502 Sat Mar 16 14:16:39 2019 +0000 linux/amd64

(Also tested with go1.12 and go1.12.1).

Does this issue reproduce with the latest release?

Yes.

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

$ go env
GOARCH="amd64"
GOBIN="/home/pwaller/.local/bin"
GOCACHE="/home/pwaller/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/pwaller/go"
GOPROXY=""
GORACE=""
GOROOT="/home/pwaller/sdk/go1.12"
GOTMPDIR=""
GOTOOLDIR="/home/pwaller/sdk/go1.12/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/pwaller/.local/src/github.com/pwaller/bench-syso-broken/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build380714510=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Tried to use the toolchain trick described in "Use syso file to embed arbitrary self-contained C code".

1. Put code.go, code.s and code.syso in a package with the following described below.
2. Run go build.

code.syso

I generated a .syso file in the same directory as the package with the following command: gcc -x c -c -o code.syso - <<<'void nop1() {}'. Note, I'm aware of the limitations of syso files with respect to calling convention, I'm just using this as an easy way to get an object file for purposes of demonstrating that linking is not working as I'd expect.

code.go

package main

// Comment out this line, and the main binary compiles successfully(!?).
import _ "golang.org/x/sys/unix"

func main() {
	nop()
}

func nop()

code.s

TEXT ·nop(SB),$0-0
  JMP nop1(SB)

Then I ran go build.

What did you expect to see?

A successfully compiled binary.

What did you see instead?

# github.com/pwaller/syso-broken
main.nop: relocation target nop1 not defined

Additional notes

• If I remove the otherwise unused import of golang.org/x/sys/unix, then the binary compiles.
• I can reproduce with both old-style GOPATH or modules.

/cc @ianlancetaylor for the linker.

@gopherbot label needsinvestigation