cmd/link: fails once more than one function of a .syso file is called

[stapelberg]

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

go version go1.8.1 linux/amd64

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

GOARCH="arm64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/michael/go"
GORACE=""
GOROOT="/home/michael/go1.8.1"
GOTOOLDIR="/home/michael/go1.8.1/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build551212718=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="0"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"

What did you do?

$ head -50 multiple.go both_arm64.s both_arm64.S
==> multiple.go <==
package main

func asm1()

func asm2()

func main() {
	asm1()
	asm2()
}

==> both_arm64.s <==
TEXT ·asm1(SB),$0-0
	JMP asm1ext(SB)

TEXT ·asm2(SB),$0-0
	JMP asm2ext(SB)

==> both_arm64.S <==
.text

.global asm1ext
asm1ext:
    ret

.global asm2ext
asm2ext:
    ret

$ aarch64-linux-gnu-gcc -c -O0 -fPIC -no-pie -o both_arm64.syso both_arm64.S
$ GOARCH=arm64 go build

The issue is reproducible using gcc on an arm64 machine to build the .syso file.

What did you expect to see?

The program should build.

Removing either the call to asm1 or asm2 in the .go file makes it build.

Removing either the JMP asm1ext(SB) or the JMP asm2ext(SB) makes it build.

Adding NOSPLIT to both asm1 and asm2 doesn’t help either.

What did you see instead?

$ GOARCH=arm64 go build
# multiple-syso
asm2ext: call to external function

[ianlancetaylor]

Does it work if you use -ldflags=-linkmode=external?

[stapelberg]

Does it work if you use -ldflags=-linkmode=external?

No:

$ GOARCH=arm64 go build -ldflags=-linkmode=external                 
# multiple-syso
warning: unable to find runtime/cgo.a
asm2ext: call to external function
main.asm1: relocation target asm1ext not defined
main.asm2: relocation target asm2ext not defined
main.asm1: undefined: "asm1ext"
main.asm2: undefined: "asm2ext"

[pwaller]

-linkmode=external giving relocation target * not defined is another issue I have filed: #30890.