cmd/go: 'go build -race' with a cross-compiled GOOS should not suggest setting CGO_ENABLED

[MasterDimmy]

$ go version
go version go1.13.7 windows/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
set GO111MODULE=

set GOARCH=amd64

set GOBIN=

set GOCACHE=C:\Users\8\AppData\Local\go-build

set GOENV=C:\Users\8\AppData\Roaming\go\env

set GOEXE=.exe

set GOFLAGS=

set GOHOSTARCH=amd64

set GOHOSTOS=windows

set GONOPROXY=

set GONOSUMDB=

set GOOS=windows

set GOPATH=C:\gopath

set GOPRIVATE=

set GOPROXY=https://proxy.golang.org,direct

set GOROOT=C:\Go

set GOSUMDB=sum.golang.org

set GOTMPDIR=

set GOTOOLDIR=C:\Go\pkg\tool\windows_amd64

set GCCGO=gccgo

set AR=ar

set CC=gcc

set CXX=g++

set CGO_ENABLED=1

set GOMOD=C:\Go\src\go.mod

set CGO_CFLAGS=-g -O2

set CGO_CPPFLAGS=

set CGO_CXXFLAGS=-g -O2

set CGO_FFLAGS=-g -O2

set CGO_LDFLAGS=-g -O2

set PKG_CONFIG=pkg-config

set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0 -fdebug-prefix-map=d:\TEMP\go-build345576314=/tmp/go-build -gno-record-gcc-switches

What did you do?

i compile this file for test:

package main

import (
"fmt"
)

func main() {
c := make(chan bool)
m := make(map[string]string)
go func() {
m["1"] = "a" // First conflicting access.
c <- true
}()
m["2"] = "b" // Second conflicting access.
<-c
for k, v := range m {
fmt.Println(k, v)
}
}

with

set CGO_ENABLED=1
set GOOS=linux
set GO_ARCH=amd64
go build -race

What did you expect to see?

success compile

What did you see instead?

# runtime/cgo
gcc_linux_amd64.c: In function '_cgo_sys_thread_start':
gcc_linux_amd64.c:66:2: error: implicit declaration of function 'sigfillset' [-Werror=implicit-function-declaration]
   66 |  sigfillset(&ign);
      |  ^~~~~~~~~~
cc1.exe: all warnings being treated as errors

Note, that

set CGO_ENABLED=1
set GOOS=linux
go build 

is succecced, but i need to compile with "-race" detector. If CGO_ENABLED=0

set CGO_ENABLED=0
set GOOS=linux
go build -race

then i got

go build: -race requires cgo; enable cgo by setting CGO_ENABLED=1

[bcmills]

Cross-compiling programs with C dependencies is generally not supported, and the runtime support for -race mode relies on C dependencies.

If you want to build a race-enabled binary, you need to either compile for GOOS=windows or build the binary on a Linux machine.

[bcmills]

Probably the best we can do here is emit a clearer diagnostic for cross-compiled -race builds. (We should not prompt the user to “enable cgo” if we don't have reason to believe that such a build would succeed.)

CC @jayconrod @matloob

[MasterDimmy]

just try to cross compile this:

package main

import (
"fmt"
)

func main() {
c := make(chan bool)
m := make(map[string]string)
go func() {
m["1"] = "a" // First conflicting access.
c <- true
}()
m["2"] = "b" // Second conflicting access.
<-c
for k, v := range m {
fmt.Println(k, v)
}
}

from windows\amd64 to linux\amd64 with gox

[MasterDimmy]

I think "'go build -race' with a cross-compiled GOOS should not suggest setting CGO_ENABLED" is not what this issue is for, that is another issue\suggestion.

Current issue is unavailability to crosscompile "-race" with gox.

[bcmills]

@MasterDimmy, the fact that go test -race has C dependencies is not something we can feasibly fix. (The race detector uses a fairly extensive C library, and the folks on the Go team are not in a position to rewrite it from scratch in pure Go.)

If you want to volunteer to rewrite the race-detector library in pure Go, you're welcome to do so, but as far as “things we can feasibly plan to fix” are concerned, a better error message for this case is about the limit.

[keyan]

@bcmills I took a stab at just modifying the error message in #38670. I'm just trying getting my feet wet and orient myself in the codebase.

[gopherbot]

Change https://golang.org/cl/230202 mentions this issue: work: add error for cross-compiled -race builds

[ianlancetaylor]

Wait, I'm not following the suggestion here. Cross-compiling cgo code works fine if you have a cross-compiler.

We may want a general fix to do better checking of whether you are using a cross-compiler when doing a cross-build that uses cgo. But that seems separate from the narrow issue of "go build -race", which should work if a cross-compiler is installed.

[keyan]

I misunderstood Bryan's comment:

Cross-compiling programs with C dependencies is generally not supported

If I understand correctly now, the short term move is just to not mention setting CGO_ENABLED because that isn't sufficient on its' own and it is too verbose to explain that you need to have a cross-compiler installed?