runtime/coverage: covcounters not written in -buildmode=c-shared

[spacewander]

Go version

go version go1.21.4 linux/arm64

Reproducibility

• Does this issue reproduce with the latest release?

What operating system and processor architecture are you using (go env)?

GO111MODULE=''
GOARCH='arm64'
GOBIN=''
GOCACHE='/root/.cache/go-build'
GOENV='/root/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/go'
GOPRIVATE=''
GOPROXY='https://goproxy.cn'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='local'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_arm64'
GOVCS=''
GOVERSION='go1.21.4'
GCCGO='gccgo'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/go/src/mosn.io/moe/go.mod'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build681226605=/tmp/go-build -gno-record-gcc-switches'

What did you do?

1. built Go program into a shared library by using CGO_ENABLED=1 go build -cover --buildmode=c-shared -o libgolang.so.
2. Run a process with env variable GOCOVERDIR set, the process will load the libgolang.so.
3. The process exited.
4. I checked the GOCOVERDIR, only covmeta file is generated.

What did you expect to see?

Both covmeta and covcounters file should be generated.

What did you see instead?

Only covmeta file is generated.
Look like when Go code runs as a shared library, the covcounters file is not flushed when the host process exits.

Currently, I work around this by calling coverage.WriteCounters manually.

[dmitshur]

CC @thanm.

[thanm]

Thanks for the report.

If you could please post a complete example, that would be helpful. In particular, does your example program invoke os.Exit() when it terminates?

[spacewander]

does your example program invoke os.Exit() when it terminates?

No, it can't. The program loads the Go shared library is a C++ program, so it won't invoke os.Exit() when it terminates.

If you could please post a complete example, that would be helpful.

It is a Go plugin running inside Envoy: https://www.envoyproxy.io/docs/envoy/latest/configuration/http/http_filters/golang_filter.html#golang.

It would require knowledge about Envoy (a network proxy) to run the example. I am glad to give you help if you need.

[thanm]

No, it can't. The program loads the Go shared library is a C++ program, so it won't invoke os.Exit() when it terminates.

Thanks for that.

Given that the Go code is running as a plugin of some sort and is only invoked at the behest of the main process, and isn't being notified when the program terminates, how exactly would you imagine it would be possible to write out coverage counters?

Unless the Go runtime within the plugin has some idea that the program is complete, it doesn't seem as though there's much the runtime can do. I think this is a case where it needs a bit of help from the main program, would you not agree?

[spacewander]

No, it can't. The program loads the Go shared library is a C++ program, so it won't invoke os.Exit() when it terminates.

Thanks for that.

Given that the Go code is running as a plugin of some sort and is only invoked at the behest of the main process, and isn't being notified when the program terminates, how exactly would you imagine it would be possible to write out coverage counters?

Unless the Go runtime within the plugin has some idea that the program is complete, it doesn't seem as though there's much the runtime can do. I think this is a case where it needs a bit of help from the main program, would you not agree?

Thanks for your reply.
Is it possible that Go can register something like atexit or add hook to dlclose, so that when the program is gone, the Go code can be noticed and flush the counter?