cmd/link: add internal linking support for pie build mode on arm

[hollowaykeanho]

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

$ go version
go version go1.17.5 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
GO111MODULE=""
GOARCH="amd64"
GOBIN="/home/u0/Documents/monteur/.monteurFS/bin/gopath/bin"
GOCACHE="/home/u0/Documents/monteur/.monteurFS/bin/gocache"
GOENV="/home/u0/Documents/monteur/.monteurFS/bin/goenv"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/u0/Documents/monteur/.monteurFS/bin/gopath/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/u0/Documents/monteur/.monteurFS/bin/gopath"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/u0/Documents/monteur/.monteurFS/bin/golang"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/u0/Documents/monteur/.monteurFS/bin/golang/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.17.5"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/u0/Documents/monteur/gopkg/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/user/1000/go-build3616176871=/tmp/go-build -gno-record-gcc-switches"

What did you do?

So I try to cross-compile a pure Go repository to armv7 CPU on amd64 host system with -buildmode=pie, the compiler keeps on seeking for arm based gcc compiler eventhough the entire project does not have cgo codes at all. The command I issued:

GOOS="linux" \
GOARCH="arm" \
GOARM="7" \
go build -buildmode=pie \
-ldflags "-s -w" \
 -o "/home/u0/Documents/monteur/.monteurFS/tmp/build/linux-arm" \
"/home/u0/Documents/monteur/gopkg/app/monteur/main.go"

I even tried to explicitly instruct the compiler that I'm not using Cgo:

CGO_ENABLED=0 \
GOOS="linux" \
GOARCH="arm" \
GOARM="7" \
go build -buildmode=pie \
-ldflags "-s -w" \
 -o "/home/u0/Documents/monteur/.monteurFS/tmp/build/linux-arm" \
"/home/u0/Documents/monteur/gopkg/app/monteur/main.go"

What did you expect to see?

Should be working fine without needing to install arm compiler tool-chain like the workaround (see below).

What did you see instead?

Both the above produced the following outputs:

# command-line-arguments
loadinternal: cannot find runtime/cgo
/home/u0/Documents/monteur/.monteurFS/bin/golang/pkg/tool/linux_amd64/link: running gcc failed: exit status 1
gcc: error: unrecognized command-line option ‘-marm’; did you mean ‘-mabm’?

There are 2 ways to workaround the issue:

Number 1: don't build pie mode

GOOS="linux" \
GOARCH="arm" \
GOARM="7" \
go build \
-ldflags "-s -w" \
 -o "/home/u0/Documents/monteur/.monteurFS/tmp/build/linux-arm" \
"/home/u0/Documents/monteur/gopkg/app/monteur/main.go"

However, some packagers are great at complaining non-pie binary (e.g. debuild).

Number 2: install arm gcc toolchain

On Debian:

$ su
$ apt install gcc-arm-linux-gnueabi binutils-arm-linux-gnueabi -y
$ exit

Then:

CGO_ENABLED=0 \ 
GOOS="linux" \
GOARCH="arm" \
GOARM="7" \
CC=arm-linux-gnueabi-gcc \
go build \
-ldflags "-s -w" \
 -o "/home/u0/Documents/monteur/.monteurFS/tmp/build/linux-arm" \
"/home/u0/Documents/monteur/gopkg/app/monteur/main.go"

Gone through Resources

Gone through the following resources but found no outcome yet... still searching...

1. https://www.reddit.com/r/golang/comments/gszi0d/best_way_to_cross_compile_a_golang_app_onto_a/
2. https://groups.google.com/g/golang-nuts/c/gQ6ArCTlPGU
3. https://stackoverflow.com/questions/61515186/when-using-cgo-enabled-is-must-and-what-happens
4. https://dubo-dubon-duponey.medium.com/a-beginners-guide-to-cross-compiling-static-cgo-pie-binaries-golang-1-16-792eea92d5aa
5. https://groups.google.com/g/golang-nuts/c/cXhRsmNsMwo/m/VUZlLqo9AwAJ
6. https://groups.google.com/g/golang-nuts/c/Jd9tlNc6jUE/m/Z9ldF6vPEAAJ

[seankhliao]

what if you set CGO_ENABLED=0 ?

[hollowaykeanho]

what if you set CGO_ENABLED=0 ?

Same result. See above. Possible Bug?

[ALTree]

-buildmode=pie defaults to external linking except for linux/amd64 and linux/arm64:

The linker now defaults to internal linking mode for -buildmode=pie on linux/amd64 and linux/arm64, so these configurations no longer require a C linker.

arm, which you're targeting, uses external linking, so it requires a cross-compilation toolchain for pie, regardless of cgo usage.

[hollowaykeanho]

arm, which you're targeting, uses external linking, so it requires a cross-compilation toolchain for pie

Noted. Any plans to make the linking internally? It's a very useful tool without depending on external tool-chains. Will close this ticket after the reply.

[ALTree]

I'm not sure if there are any plans to extend internal linking to other GOARCHs, maybe @cherrymui knows.

[erifan]

Will close this ticket after the reply.

Don't need to close the issue, maybe change the title to something like "cmd/link: add internal linking support for pie build mode on arm"

[hollowaykeanho]

Noted. Updated title.

Thanks for the feedback and happy new year @seankhliao, @ALTree , and @erifan. Let's wait after Jan 4th for the quiet week. You guys need it. =)

[cherrymui]

I'm not sure if there are any plans to extend internal linking to other GOARCHs

I'm not aware of any plan. But CLs are always welcome. Thanks.