cmd/go: buildmode=c-shared broken /w libmusl

[nicolai86]

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

1.8rc3, 1.7.5

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

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/go"
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build694367367=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"
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?

I tried to use a go shared library from a C program on alpine-linux (libmusl).

To reproduce:

$ docker run --rm -it golang:1.8-alpine sh
# apk add -U build-base
# cat > sum.go
// sum.go
package main

import "C"

//export sum
func sum(x, y int) int {
    return x + y
}

func main() {}
^C
# cat > sum.c
#include <stdio.h>
#include "sum.h"

int main(void) {

    int z = sum(1, 2);
    printf("1+2=%d\n", z);

    return 0;
}
^C
# go build -buildmode=c-shared -o sum.so
# gcc sum.c ./sum.so -o sum && ./sum
Segmentation fault

the same happens with the golang:1.7.5-alpine image. I did not test with older versions.

Using gdb I get the following core dump:

# apk add -U gdb
# ulimit -c unlimited
# gcc sum.c ./sum.so -o sum && ./sum
# gdb ./sum core
(gdb) bt
#0  runtime.raise () at /usr/local/go/src/runtime/sys_linux_amd64.s:110
#1  0x00007fadef86cddb in runtime.dieFromSignal (sig=11) at /usr/local/go/src/runtime/signal_unix.go:323
#2  0x00007fadef86d2a1 in runtime.sigfwdgo (sig=11, info=0x7fadefd88130, ctx=0x7fadefd88000, ~r3=false) at /usr/local/go/src/runtime/signal_unix.go:501
#3  0x00007fadef86c70b in runtime.sigtrampgo (sig=11, info=0x7fadefd88130, ctx=0x7fadefd88000) at /usr/local/go/src/runtime/signal_unix.go:200
#4  0x00007fadef883133 in runtime.sigtramp () at /usr/local/go/src/runtime/sys_linux_amd64.s:262
#5  <signal handler called>
#6  0x00007fadef85a02c in runtime.sysargs (argc=-273804016, argv=0x0) at /usr/local/go/src/runtime/os_linux.go:199
#7  0x00007fadef86962c in runtime.args (c=-273804016, v=0x0) at /usr/local/go/src/runtime/runtime1.go:64
#8  0x00007fadef87f60b in runtime.rt0_go () at /usr/local/go/src/runtime/asm_amd64.s:156
#9  0x00000000efae1510 in ?? ()
#10 0x0000000000000000 in ?? ()

What did you expect to see?

I expect the binary to work and print 1+2=3

What did you see instead?

Segmentation fault

[bradfitz]

We don't really have CI coverage for either build-shared or musl/alpine by themselves, much less together.

/cc @crawshaw @jessfraz (for #17891)

[bradfitz]

Update to my Feb 9th comment: we do have an Alpine builder as of recently which we're trying to get green. So this is at least easily debuggable by people now.

[ALTree]

Closing this as an exact dup of #13492 (which has more discussion and people in it).