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cmd/go: document system setup for cross compiling between linux architectures #47175

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Link512 opened this issue Jul 13, 2021 · 5 comments
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@Link512
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@Link512 Link512 commented Jul 13, 2021

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

$ go version
1.16.6

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="arm64"
GOBIN=""
GOCACHE="/root/.cache/go-build"
GOENV="/root/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_arm64"
GOVCS=""
GOVERSION="go1.16.6"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build1439812787=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Trying to cross compile a simple program that uses github.com/mattn/go-sqlite3 (which requires CGO) from linux/arm64 to linux/amd64 using docker on an M1 macbook, fails due to an incorrect flag passed to gcc

Some extra info:

Host OS: macOS 11.4
Host processor: Apple M1
Docker desktop version: 3.5.2 (66501)
Docker engine version: 20.10.7
gcc version: gcc (Alpine 10.3.1_git20210424) 10.3.1 20210424

The program

package main

import (
	"database/sql"

	_ "github.com/mattn/go-sqlite3"
)

func main() {
	db, err := sql.Open("sqlite3", "tmp.sqlite3")
	if err != nil {
		panic(err)
	}
	_, err = db.Exec("SELECT 1")
	if err != nil {
		panic(err)
	}
}

The dockerfile

FROM golang:1.16.6-alpine3.14

WORKDIR /app

RUN apk --no-cache add gcc libc-dev

COPY . .
RUN go mod download

RUN GOOS=linux GOARCH=amd64 CGO_ENABLED=1 go build -o main .

What did you expect to see?

The compilation succeed

What did you see instead?

[6/6] RUN GOOS=linux GOARCH=amd64 CGO_ENABLED=1 go build -o main .:
#10 0.294 # runtime/cgo
#10 0.294 gcc: error: unrecognized command-line option '-m64'

@bcmills
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@bcmills bcmills commented Jul 13, 2021

@cherrymui, do you have any insight on building amd64 code from an M1?

@golang/release, my understanding is that we have a native arm64 builder for macOS — should we add a builder (perhaps just a misc-compile builder?) to test building for amd64 on arm64 hardware?

@bcmills bcmills changed the title Invalid gcc flag when cross compiling from linux/arm64 for linux/amd64 cmd/go: Invalid gcc flag when cross compiling from linux/arm64 for linux/amd64 Jul 13, 2021
@cherrymui
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@cherrymui cherrymui commented Jul 13, 2021

@cherrymui, do you have any insight on building amd64 code from an M1?

I don't think this is related to M1. The OP is using a linux-arm64 container.

@Link512 for cross-compiling, I think you need to use a cross C compiler that targets linux/amd64. Is your gcc a cross compiler? Thanks.

@Link512
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@Link512 Link512 commented Jul 13, 2021

@Link512 for cross-compiling, I think you need to use a cross C compiler that targets linux/amd64. Is your gcc a cross compiler? Thanks.

Good question, I believe that is the underlying issue. The default arm64 gcc installed by alpine linux seems to not support amd64 cross compilation.

@bcmills
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@bcmills bcmills commented Jul 13, 2021

I'm inclined to say that this is a documentation issue: we probably ought to have instructions for setting up a cross-compiling environment on Linux. (I see https://golang.org/wiki/GccgoCrossCompilation and https://golang.org/wiki/WindowsCrossCompiling, but only third-party resources for cross-compiling from one Linux arch to another.)

@bcmills bcmills changed the title cmd/go: Invalid gcc flag when cross compiling from linux/arm64 for linux/amd64 cmd/go: document system setup for cross compiling between linux architectures Jul 13, 2021
@bcmills bcmills added this to the Backlog milestone Jul 13, 2021
@ALTree
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@ALTree ALTree commented Jul 13, 2021

This is mentioned in the cgo documentation:

When cross-compiling, you must specify a C cross-compiler for cgo to use. You can do this by setting the generic CC_FOR_TARGET or the more specific CC_FOR_${GOOS}_${GOARCH} (for example, CC_FOR_linux_arm) environment variable when building the toolchain using make.bash, or you can set the CC environment variable any time you run the go tool.

But I guess a general wiki page on cross-compilation wouldn't hurt, since many people probably wouldn't think to read the cgo doc page before trying to cross-compile.

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