golang musl libc shared object constructor reproducer

build-and-run-container.sh

#!/bin/sh
docker build -t golang-alpine . && docker run --tty --interactive -h golang-alpine golang-alpine

Dockerfile

FROM golang:1.11.2-alpine

USER root
RUN apk update && apk add musl-dbg gcc libc-dev
COPY preload.c /go
COPY gogo.go /go
COPY runtest.sh /go
RUN gcc -ggdb -fPIC -shared -o libpreload.so preload.c && go build -o gogo-int-linker gogo.go && go build -ldflags '-linkmode external' -o gogo-ext-linker gogo.go

ENTRYPOINT [ "/bin/sh" ]

gogo.go

package main

import (
	"fmt"
	"net/http"
)

func main() {

	// add explicit reference to net/http to enforce dynamic linking
	rc := http.StatusOK
	rc *= 2
	fmt.Println("hi there")
}

preload.c

#include <unistd.h>

// ----------------------------------------------------------------------------
__attribute__((constructor)) void doInit(void) {
	static const char msg[] = "---> your preloaded shared object says hey <---\n";
	write(1, msg, sizeof(msg) - 1);
}

runtest.sh

#!/bin/sh

LIB=libpreload.so

run() {
	echo LD_LIBRARY_PATH=$PWD LD_PRELOAD=$LIB $1
	LD_LIBRARY_PATH=$PWD LD_PRELOAD=$LIB $1
}

echo 'running gogo (built with internal linker'
run ./gogo-int-linker

echo
echo 'running /go/gogo-ext-linker (built with external linker)'
run ./gogo-ext-linker