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runtime/cgo: the handle pointer is freed during C asynchronous callback #57463

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huskar-t opened this issue Dec 26, 2022 · 3 comments
Closed

runtime/cgo: the handle pointer is freed during C asynchronous callback #57463

huskar-t opened this issue Dec 26, 2022 · 3 comments
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compiler/runtime Issues related to the Go compiler and/or runtime. FrozenDueToAge

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@huskar-t
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What version of Go are you using (go version)?

$ go version
go version go1.19 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=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/root/.cache/go-build"
GOENV="/root/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/root/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/root/go"
GOPRIVATE=""
GOPROXY="https://goproxy.cn,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.19"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
GOWORK=""
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 -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build1056322479=/tmp/go-build -gno-record-gcc-switches"

What did you do?

https://go.dev/play/p/k68Hr3YCWdP
when the C asynchronous callback, the runtime/cgo handle pointer has been freed by the gc, causing the wrong memory to be used during the callback

What did you expect to see?

keep the handle pointer until handle.Delete() is called

What did you see instead?

handle pointer has been freed by the gc
@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label Dec 26, 2022
@doujiang24
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I think it's just a wrong usage.

handle could be GC freed, after C.callback_wrapper returning, it's by design.

according to your code:

func DoAsync() {
	handle := cgo.NewHandle("test")
	pointer := unsafe.Pointer(&handle)
	fmt.Printf("handle:%d,pointer: %v\n", handle, pointer)
	C.callback_wrapper(pointer)
}

@huskar-t
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@doujiang24 I temporarily use sync.map to save the pointer, I'm not sure if cgo handle should provide this feature.This example is just to show the problem I'm having

@seankhliao
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I believe this violates cgo pointer rules https://pkg.go.dev/cmd/cgo#hdr-Passing_pointers
specifically:

C code may not keep a copy of a Go pointer after the call returns.

@seankhliao seankhliao closed this as not planned Won't fix, can't repro, duplicate, stale Dec 26, 2022
@golang golang locked and limited conversation to collaborators Dec 26, 2023
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@doujiang24 @gopherbot @seankhliao @huskar-t