cmd/go: -compiler=gccgo: -buildmode=c-archive can't produce an archive with statically linked libgo

[andreybokhanko]

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

$ go version
go version go1.18 gollvm LLVM 15.0.0git 20230721 (experimental) 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="off"
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/abokhanko/.cache/go-build"
GOENV="/home/abokhanko/.config/go/env"
GOEXE=""
GOEXPERIMENT="fieldtrack,regabiwrappers"
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/abokhanko/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/abokhanko/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/abokhanko/gollvm/bin"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/abokhanko/gollvm/tools"
GOVCS=""
GOVERSION="go1.18 gollvm LLVM 15.0.0git 20230721 (experimental)"
GCCGO="/home/abokhanko/gollvm/bin/llvm-goc"
GOAMD64="v1"
AR="ar"
CC="/usr/bin/cc"
CXX="/usr/bin/c++"
CGO_ENABLED="1"
GOMOD=""
GOWORK=""
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-build2805243357=/tmp/go-build -gno-record-gcc-switches -funwind-tables"

What did you do?

$ cat >example10.go <<.
package main

import "C"
import "fmt"

//export Bar
func Bar() C.int {
fmt.Println("Hello!")
return C.int(1)
}

func main() {}
.
$ cat >example10.c <<.
#include "example10.h"

int main(int argc, char **argv) {
return Bar();
}
.
$ go build -gccgoflags=-static-libgo -buildmode=c-archive example10.go
$ clang example10.c example10.a -lpthread

What did you expect to see?

The program compiles and then executes without errors. This is what happens when using the standard "gc" compiler.

What did you see instead?

$ clang example10.c example10.a -lpthread
/usr/bin/ld: example10.a(a.out.a.o): in function `_cgo_c9ae4c457df7_Cfunc_CString':
./cgo-c-prolog-gccgo:27: undefined reference to `runtime_throw'
...
/usr/bin/ld: example10.a(a.out.a.o):(.data.DW.ref.__gccgo_personality_v0[DW.ref.__gccgo_personality_v0]+0x0): undefined reference to `__gccgo_personality_v0'
clang: error: linker command failed with exit code 1 (use -v to see invocation)

The created archive size is much smaller than archive created by "gc" (100634 vs 4876006 bytes on my machine). This clearly indicates that "-gccgoflags=-static-libgo" option got ignored.

[ianlancetaylor]

There should perhaps be some way to do this, but it won't be via -gccgoflags. That is a flag to pass to gccgo/GoLLVM, but the key step here is not being executed by gccgo/GoLLVM at all.

It may be difficult to implement this. There is a comment in the cmd/go code that says:

		// The user remains responsible for linking against
		// -lgo -lpthread -lm in the final link. We can't use
		// -r to pick them up because we can't combine
		// split-stack and non-split-stack code in a single -r
		// link, and libgo picks up non-split-stack code from
		// libffi.

But it may be possible for cmd/go to use the ar program to add all of libgo.a to the generated archive.