misc/cgo/testcshared: test failure on Google Pixelbook

[danicat]

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

go version go1.10.3 linux/amd64

Does this issue reproduce with the latest release?

Yes.

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

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/danielapetruzalek/.cache/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/danielapetruzalek/go"
GORACE=""
GOROOT="/usr/local/go"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
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-build074359831=/tmp/go-build -gno-record-gcc-switches"

What did you do?

cd go/src
./all.bash

What did you expect to see?

ALL TESTS PASSED

What did you see instead?

##### ../misc/cgo/testcshared
--- FAIL: TestUnexportedSymbols (0.64s)
    cshared_test.go:353: run: [go build -buildmode=c-shared -installsuffix testcshared -o libgo2.so libgo2]
    cshared_test.go:367: run: [gcc -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build783986620=/tmp/go-build -gno-record-gcc-switches -I pkg/linux_amd64_shared -o testp2 main2.c -Wl,--no-as-needed libgo2.so]
    cshared_test.go:373: run: [./testp2]
    cshared_test.go:376: # NAN ChangeLog
**
FAIL
2018/07/31 23:09:06 Failed: exit status 1

I've tried two other times and the message on the last line (after "cshared_test.go:376") changed all times, suggesting some random values were being read from fd 30. I've tracked this change to the issue #23784 and CL 108537 (https://golang.org/cl/108537).

I've recompiled the binaries to use fd 100 like it was originally and I got the tests to pass.

I'm testing Go on the new Google Pixelbook and it seems that fd 30 is being used already. I wonder if instead of choosing an arbitrary number we could have a more safe way to select the fd? Or use another technique to run this test?

[ianlancetaylor]

Any idea why descriptor 30 is open?

Perhaps we should just close the descriptor first, somehow.

I'm certainly to using another technique if you have any suggestions.

[danicat]

I think I've found something:

$ ls -la /proc/$$/fd
total 0
dr-x------. 2 danielapetruzalek danielapetruzalek  0 Aug  1 01:24 .
dr-xr-xr-x. 9 danielapetruzalek danielapetruzalek  0 Jul 31 22:05 ..
lrwx------. 1 danielapetruzalek danielapetruzalek 64 Aug  1 01:24 0 -> /dev/pts/0
lrwx------. 1 danielapetruzalek danielapetruzalek 64 Aug  1 01:24 1 -> /dev/pts/0
lrwx------. 1 danielapetruzalek danielapetruzalek 64 Aug  1 01:24 2 -> /dev/pts/0
lrwx------. 1 danielapetruzalek danielapetruzalek 64 Aug  1 01:24 255 -> /dev/pts/0
lr-x------. 1 danielapetruzalek danielapetruzalek 64 Aug  1 01:24 30 -> /usr/share/code/resources/app/node_modules.asar
lrwx------. 1 danielapetruzalek danielapetruzalek 64 Aug  1 01:24 35 -> socket:[43689]
lr-x------. 1 danielapetruzalek danielapetruzalek 64 Aug  1 01:24 36 -> /usr/share/code/resources/app/node_modules.asar
lr-x------. 1 danielapetruzalek danielapetruzalek 64 Aug  1 01:24 37 -> /usr/share/code/resources/electron.asar
lr-x------. 1 danielapetruzalek danielapetruzalek 64 Aug  1 01:24 44 -> /usr/share/fonts/truetype/dejavu/DejaVuSansMono.ttf
(...)

It seems that fd 30 is being used by VS Code. I was using the built in terminal in vscode to build the project.

I've ran it in the standalone terminal and it's working as expected -> no use of fd 30:

$ ls -la /proc/$$/fd
total 0
dr-x------. 2 danielapetruzalek danielapetruzalek  0 Aug  1 01:25 .
dr-xr-xr-x. 9 danielapetruzalek danielapetruzalek  0 Aug  1 01:25 ..
lrwx------. 1 danielapetruzalek danielapetruzalek 64 Aug  1 01:25 0 -> /dev/pts/1
lrwx------. 1 danielapetruzalek danielapetruzalek 64 Aug  1 01:25 1 -> /dev/pts/1
lr-x------. 1 danielapetruzalek danielapetruzalek 64 Aug  1 01:25 19 -> anon_inode:inotify
lrwx------. 1 danielapetruzalek danielapetruzalek 64 Aug  1 01:25 2 -> /dev/pts/1
lr-x------. 1 danielapetruzalek danielapetruzalek 64 Aug  1 01:25 20 -> pipe:[2849]
l-wx------. 1 danielapetruzalek danielapetruzalek 64 Aug  1 01:25 21 -> pipe:[2849]
lrwx------. 1 danielapetruzalek danielapetruzalek 64 Aug  1 01:25 255 -> /dev/pts/1

And the build passes:

(...)
##### API check

ALL TESTS PASSED
---
Installed Go for linux/amd64 in /home/danielapetruzalek/golang/go
Installed commands in /home/danielapetruzalek/golang/go/bin
*** You need to add /home/danielapetruzalek/golang/go/bin to your PATH.

That means that this potentially affects anyone using the terminal embedded into VS code. Which leaves the question on how we detect if the fd 30 is being used by another process in runtime. I'm not an expert in OS's, but I'll try to study more about this issue.

[gopherbot]

Change https://golang.org/cl/127395 mentions this issue: misc/cgo/testcshared: force descriptor 30 to be closed when execing test