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syscall/js: panic in os.Getpid() when called from wasm in a browser #34627

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Stebalien opened this issue Sep 30, 2019 · 7 comments
Closed

syscall/js: panic in os.Getpid() when called from wasm in a browser #34627

Stebalien opened this issue Sep 30, 2019 · 7 comments
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arch-wasm WebAssembly issues FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
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@Stebalien
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What version of Go are you using (go version)?

$ go version
go version go1.13 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="on"
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/steb/.cache/go-build"
GOENV="/home/steb/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/steb/projects/go"
GOPRIVATE=""
GOPROXY="direct"
GOROOT="/usr/lib/go"
GOSUMDB="off"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/steb/projects/go/src/github.com/golang/go/src/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 -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/run/user/1000/tmp/go-build550335201=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Tried to use os.Getpid() from WASM. Gist: https://gist.github.com/Stebalien/4c478e71b0264f9dd66dab9676770511

What did you expect to see?

Either the PID or a faked PID when not applicable (e.g., 1).

What did you see instead?

A panic:

--- FAIL: TestInBrowser (0.00s)
panic: syscall/js: call of Value.Get on undefined [recovered]
	panic: syscall/js: call of Value.Get on undefined

goroutine 8 [running]:
testing.tRunner.func1(0x472100)
	/usr/lib/go/src/testing/testing.go:874 +0x38
panic(0x28ca0, 0x40a0a0)
	/usr/lib/go/src/runtime/panic.go:679 +0x20
syscall/js.Value.Get(0x0, 0x4e818, 0x3, 0x5d928fce)
	/usr/lib/go/src/syscall/js/js.go:252 +0x39
syscall.Getpid(0x15c95b24db15e800)
	/usr/lib/go/src/syscall/syscall_js.go:310 +0x2
os.Getpid(...)
	/usr/lib/go/src/os/exec.go:71
foobar.TestInBrowser(0x472100)
	/home/steb/foobar/foobar_test.go:9 +0x4
testing.tRunner(0x472100, 0x57738)
	/usr/lib/go/src/testing/testing.go:909 +0xe
created by testing.(*T).Run
	/usr/lib/go/src/testing/testing.go:960 +0x2d
FAIL	foobar	0.413s
FAIL

The syscall/js package assumes that all wasm instances have "fs" and "process" globals available.

@Stebalien Stebalien changed the title syscall/js: "process" and "fs" globals shouldn't be assumed to exist syscall/js: panic in os.Getpid() when called from wasm in a browser Sep 30, 2019
Stebalien added a commit to whyrusleeping/go-logging that referenced this issue Sep 30, 2019
os.Getpid() will panic on wasm in browsers (but not in node).

Issue: golang/go#34627
Stebalien added a commit to whyrusleeping/go-logging that referenced this issue Sep 30, 2019
os.Getpid() will panic on wasm in browsers (but not in node).

Issue: golang/go#34627
Stebalien added a commit to whyrusleeping/go-logging that referenced this issue Sep 30, 2019
@agnivade
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agnivade commented Oct 1, 2019

The syscall/js package assumes that all wasm instances have "fs" and "process" globals available.

Correct. The syscall package is not aware of whether it is being called inside a browser or node. Hence it crashes when you try to access the process instance. That is the behavior for all wasm related operations, including the ones in the os package.

@neelance - Do you think it makes sense to add a package level doc mentioning that any function which does not have the corresponding functionality in the target environment will panic ? I think intentional panics should be documented somewhere.

@Stebalien
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If these panics are intentional, they should be an explicit panic("not supported on the current platform") (or something like that).

However, I strongly disagree that they should panic. os.Getuid() doesn't make sense on Windows but it doesn't panic, it just returns -1. I'd expect functions that don't make sense on a platform to return sane values or errors.

@andybons andybons added arch-wasm WebAssembly issues NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels Oct 1, 2019
@andybons andybons added this to the Unplanned milestone Oct 1, 2019
@janpfeifer
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+1 to return some form of error ...

I just found out this broke github.com/golang/glog in wasm :\

@gopherbot
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Change https://golang.org/cl/199357 mentions this issue: syscall: on wasm, do not panic if "process" global is not defined

@gopherbot
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Change https://golang.org/cl/199698 mentions this issue: syscall: on wasm, do not panic if "process" global is not defined

@janpfeifer
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QQ: did the fix made into 1.13.3 ? (sorry, the release notes don't mention it, but I'm not sure how the process works)

@agnivade
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It did not. Patch releases are only for security fixes and serious regressions. You will have to wait for 1.14, or alternatively use tip.

@golang golang locked and limited conversation to collaborators Oct 22, 2020
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