Go version
go version go1.24.1 darwin/arm64; go version go1.24.1 windows/arm64
Output of go env in your module/workspace:
AR='ar'
CC='clang'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='clang++'
GCCGO='gccgo'
GO111MODULE=''
GOARCH='arm64'
GOARM64='v8.0'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/Users/traduality/Library/Caches/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/Users/traduality/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/l4/p1_djmc55xq5rxlpmdxqfb8c0000gp/T/go-build2536227112=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMOD='/Users/traduality/Projects/Traduality/go.mod'
GOMODCACHE='/Users/traduality/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/traduality/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/nix/store/jp3z5jp9gaxsw7fdzbqn29aabmrxq62j-go-1.24.1/share/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='on'
GOTELEMETRYDIR='/Users/traduality/Library/Application Support/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/nix/store/jp3z5jp9gaxsw7fdzbqn29aabmrxq62j-go-1.24.1/share/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.24.1'
GOWORK=''
PKG_CONFIG='pkg-config'
What did you do?
Run this program (requires CGo):
package main
import (
"runtime"
)
/*
typedef struct {
void *p;
} Engine;
void foo(Engine* e) {
e->p = e;
}
*/
import "C"
type State struct {
dummy *int
engine C.Engine
}
func main() {
var state *State = &State{}
var d int = 42
state.dummy = &d
var pinner runtime.Pinner = runtime.Pinner{}
pinner.Pin(state)
//pinner.Pin(state.dummy)
defer pinner.Unpin()
C.foo(&state.engine)
C.foo(&state.engine)
}
What did you see happen?
The program crashes:
$ go run ./test/
panic: runtime error: cgo argument has Go pointer to unpinned Go pointer
goroutine 1 [running]:
main.main.func2(...)
/Users/traduality/Projects/Traduality/beedo/beedovsm/cmd/test/main.go:35
main.main()
/Users/traduality/Projects/Traduality/beedo/beedovsm/cmd/test/main.go:35 +0x104
exit status 2
What did you expect to see?
I expect no crash.
If I uncomment the pinner.Pin(state.dummy) line, then I see no crash. However, this is surprising. I am not passing &state to C.foo(); I am passing &state.engine which cannot [easily] access state.dummy.
Go's current checking seems to contradict the CGo docs:
Go code may pass a Go pointer to C provided the memory to which it points does not contain any Go pointers to memory that is unpinned. When passing a pointer to a field in a struct, the Go memory in question is the memory occupied by the field, not the entire struct. When passing a pointer to an element in an array or slice, the Go memory in question is the entire array or the entire backing array of the slice.
Comment From: strager
Possible duplicate of: https://github.com/golang/go/issues/28606 (but I'm not sure)
Comment From: seankhliao
same as #63460
Comment From: gabyhelp
Related Issues
- runtime: broken for global struct objects #74116
- cmd/cgo: sometimes when passing a struct to C containing a go pointer to a struct field, the entire go struct is checked for go pointers instead of just the field #63460 (closed)
- runtime: issue confused about the use of pin #64735 (closed)
- cgo: wrapping a C pointer as uintptr gives "cgo argument has Go pointer to Go pointer" after some time #24269 (closed)
- cmd/cgo: spurious pointer check for pointer to `int` struct field #30245 (closed)
- runtime: provide Pinner API for object pinning #46787 (closed)
- cmd/cgo: a type alias of unsafe.Pointer is not treated as unsafe.Pointer #67333
- cmd/cgo: false cgo "Go pointer to Go pointer" #18184 (closed)
Related Documentation
(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)