cmd/link: -buildmode=c-shared not supported on linux/mips64le

[Mengkzhaoyun]

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

$ go version
1.15.6

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="mips64le"
GOBIN=""
GOCACHE="/root/.cache/go-build"
GOENV="/root/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="mips64le"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/go"
GOPRIVATE=""
GOPROXY="https://goproxy.cn,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_mips64le"
GCCGO="gccgo"
GOMIPS64="hardfloat"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/go/src/github.com/cilium/cilium/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 -mabi=64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build215838537=/tmp/go-build -gno-record-gcc-switches"

What did you do?

When I tried to migrate Cilium to the mips64le (loongnix) platform, I got an error, among others, when I compiled a class library, Proxylib, and found that Cilium was handling it as a .so file.
Here is the compile command

$ CGO_ENABLED=1 go build -mod=vendor -ldflags ' -X "github.com/cilium/cilium/pkg/version.ciliumVersion=1.9.1 6857a8d2a 2020-12-18T01 :24:42+08:00" -s -w -X "github.com/cilium/cilium/pkg/envoy.RequestedEnvoyVersionSHA=1177896bebde79915fe5f9092409bf0254084b4e" -X " github.com/cilium/cilium/pkg/datapath/loader.DatapathSHA=3d9461ac3d8ae0b334f319c93e10ddea336d8617" -extldflags -Wl,-soname, libcilium.so.1' -tags=osusergo -o libcilium.so.1 -buildmode=c-shared
-buildmode=c-shared support on linux/mips64le

Since -buildmod=c-shared is used, this buildmod prompt does not support building on linux/mips64le, does anyone have any good solutions?

What did you expect to see?

-buildmode=c-shared support on linux/mips64le

What did you see instead?

-buildmode=c-shared not supported on linux/mips64le

[XiaodongLoong]

I have analyzed this issue, and I try to develop this feature, but I have not completed it yet.
I will do it.

[hellocloudnative]

我也遇到了编译so文件，不支持的问题。这个问题如何解决呢

[ianlancetaylor]

@XiaodongLoong Thanks.

[XiaodongLoong]

@ianlancetaylor I meet a issue when I develop the -buildmod=c-shared featrue on linux/mips64le port. Could you give me a hint to fix this issule?
I just open some switches that intercept the feature on linux/mips64le port, and execute go build -a -x -work -buildmod=c-shared xxx.go the following error occors:

/root/go/pkg/tool/linux_mips64le/link -o $WORK/b001/exe/a.out -importcfg $WORK/b001/importcfg.link -installsuffix shared -buildmode=c-shared -buildid=7oc0eGeuITC04x1PL6YA/zGmTkGzcjMksVKPwtCJC/FipDBPEiHap1g6M81mW7/7oc0eGeuITC04x1PL6YA -extld=gcc $WORK/b001/_pkg_.a
# command-line-arguments
/root/go/pkg/tool/linux_mips64le/link: running gcc failed: exit status 1
collect2: fatal error: ld terminated with signal 10 [Bus error], core dumped
compilation terminated.
/usr/bin/ld: /tmp/go-link-020946183/go.o: relocation R_MIPS_26 against `a local symbol' can not be used when making a shared object; recompile with -fPIC
/usr/bin/ld: BFD (GNU Binutils for Debian) 2.31.1 assertion fail ../../bfd/elfxx-mips.c:6550
/usr/bin/ld: BFD (GNU Binutils for Debian) 2.31.1 assertion fail ../../bfd/elfxx-mips.c:6550
/usr/bin/ld: BFD (GNU Binutils for Debian) 2.31.1 assertion fail ../../bfd/elfxx-mips.c:6550

[ianlancetaylor]

This is only a guess, but my first thought would be that (*ctxt0).asmout in cmd/internal/obj/mips/asm0.go needs to check c.ctxt.Flag_shared, and, if that is true, not set rel.Type to objabi.R_CALLMIPS. It needs to generate a position independent relocation instead. Look at C code and see how the assembly differs when using -fPIC; the code in mips/asm0.go will likely need to do something similar. Also look at how other cmd/internal/obj/ARCH/asm*.go files handle Flag_shared.

[gopherbot]

Change https://golang.org/cl/339049 mentions this issue: cmd/internal: support -buildmode=c-shared on linux/mips64le

[gopherbot]

Change https://golang.org/cl/339051 mentions this issue: runtime: support -buildmode=c-shared on linux/mips64le