cmd/link: Go 1.12: depending on source, "go build" generates dynamically linked binaries (uses shared libs)

[jeffkayser2]

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

$ go version
go version go1.12 linux/amd64

Does this issue reproduce with the latest release?

Yes.

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

go env Output

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/jkayser/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/jkayser"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/go1.12"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go1.12/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
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-build474563303=/tmp/go-build -gno-record-gcc-switches"

What did you do?

$ ls -lrt
total 0
-rw-rw-r-- 1 jkayser jkayser 82 Feb 18 14:22 hello.go
-rw-rw-r-- 1 jkayser jkayser 239 Feb 18 14:57 server.go
$ go build hello.go
$ go build server.go
$ file *
hello: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), statically linked, not stripped
hello.go: C source, ASCII text
server: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), not stripped
server.go: C source, ASCII text
$

hello.go: https://play.golang.org/p/ueti2wwyW3N
server.go: https://play.golang.org/p/RzImKo9Men5

What did you expect to see?

All binaries generated by Go to be statically linked.

What did you see instead?

One binary dynamically linked.

[ianlancetaylor]

It's always been true that the Go tool sometimes generates a dynamically linked binary. Is the behavior on your program different than that of 1.11?

In particular, by default, if your program depends on the net or os/user packages, by default you will get a dynamically linked binary. To avoid that, build with -tags "netgo osusergo".

[jeffkayser2]

Go 1.11 also generates a dynamically linked binary. I thought Go always built statically linked binaries. It's a selling feature (you only have to copy the binary to deploy...) Doing a presentation at Oracle Applications Users Group about Go in April. Will need to add the caveat.

[ianlancetaylor]

The problem with the net and os/user packages is that accessing DNS and LDAP data in the exact same way as the local system is in general a very difficult problem. So by default we fall back to the OS support, while providing the netgo and osusergo tags for people who know what they are doing.