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cmd/vet: reports sync.Mutex copy in unsafe.Sizeof #21800

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achille-roussel opened this issue Sep 8, 2017 · 1 comment

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@achille-roussel
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commented Sep 8, 2017

Please answer these questions before submitting your issue. Thanks!

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

go version go1.9 darwin/amd64

Does this issue reproduce with the latest release?

Yes

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

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/achilleroussel/dev"
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/0p/tfjq063j4hdcjnm0_9qb4bww0000gn/T/go-build312584611=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
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"

What did you do?

go vet gives a false positive when using unsafe.Sizeof on an expression that would copy a sync.Mutex, here's a minimal example:

package main

import (
	"sync"
	"unsafe"
)

func main() {
	mu := sync.Mutex{}
	println(unsafe.Sizeof(mu))
}
$ go vet ./test.go
test.go:10: call of unsafe.Sizeof copies lock value: sync.Mutex
exit status 1

What did you expect to see?

I would expect go vet to not report unsafe.Sizeof as an unsafe operation since it's resolved at compile time and therefore doesn't cause a copy. It should also return 0 in the program given as example.

What did you see instead?

go vet returns 1 to indicate a failure because it misinterpreted the call to unsafe.Sizeof as making a copy of a mutex.

@ianlancetaylor ianlancetaylor added this to the Go1.10 milestone Sep 8, 2017

@gopherbot

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commented Sep 26, 2017

Change https://golang.org/cl/66210 mentions this issue: cmd/vet: fix copylocks false positive on unsafe.Sizeof(mutex)

@gopherbot gopherbot closed this in 9a84e52 Oct 18, 2017

@golang golang locked and limited conversation to collaborators Oct 18, 2018

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