go: syscall: (*LazyProc).Call does not keep arguments alive (anymore)

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

$ go version
go version go1.13 windows/amd64

Does this issue reproduce with the latest release?

Yes

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

$ go env
set GO111MODULE=                                                                                                                                        set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\elias\AppData\Local\go-build
set GOENV=C:\Users\elias\AppData\Roaming\go\env
set GOEXE=.exe
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=C:\Users\elias\go
set GOPRIVATE=
set GOPROXY=https://proxy.golang.org,direct
set GOROOT=c:\go
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLDIR=c:\go\pkg\tool\windows_amd64
set GCCGO=gccgo
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0 -fdebug-prefix-map=C:\Users\elias\AppData\Local\Temp\go-build579976134=/tmp/go-build -gno-record-gcc-switches

What did you do?

On my Windows 10, run the program from https://play.golang.org/p/2JzHDalGN7Q.

What did you expect to see?

No errors.

What did you see instead?

$ go run .
panic: finalized message before returning from window proc!
goroutine 1 [running, locked to thread]:
main.windowProc(0xb04c8, 0x31f, 0x1, 0x0, 0x7bfc48)
        C:/Users/elias/syscallcrash/crash.go:157 +0x186
syscall.Syscall(0x7ffec53f6020, 0x1, 0xc000044000, 0x0, 0x0, 0x0, 0x0, 0x0)
        c:/go/src/runtime/syscall_windows.go:184 +0xfa
syscall.(*Proc).Call(0xc0000045c0, 0xc000094028, 0x1, 0x1, 0x8, 0x4becc0, 0x4b7001, 0xc000094028)
        c:/go/src/syscall/dll_windows.go:171 +0x136
syscall.(*LazyProc).Call(0xc00006c390, 0xc000094028, 0x1, 0x1, 0x4, 0x4, 0x1, 0x0)
        c:/go/src/syscall/dll_windows.go:328 +0x66
main.dispatchMessage(0xc000044000)
        C:/Users/elias/syscallcrash/crash.go:207 +0xde
main.CreateWindow(0x1, 0xc000056058)
        C:/Users/elias/syscallcrash/crash.go:87 +0x128
main.main()
        C:/Users/elias/syscallcrash/crash.go:72 +0x29
exit status 2

Which means that the m *msg argument to dispatchMessage was finalized before the call to the window procedure callback returned, indicating that the _DispatchMessage.Call didn’t keep its argument alive.

On my machine, I can comment out the panic and get a native crash instead:

$ go run .
Exception 0xc0000005 0x1 0xc000044010 0x7ffec53f622d
PC=0x7ffec53f622d

syscall.Syscall(0x7ffec53f6020, 0x1, 0xc000044000, 0x0, 0x0, 0x0, 0x0, 0x0)
        c:/go/src/runtime/syscall_windows.go:184 +0xfa
syscall.(*Proc).Call(0xc0000045c0, 0xc000010038, 0x1, 0x1, 0x8, 0x4becc0, 0x4b7001, 0xc000010038)
        c:/go/src/syscall/dll_windows.go:171 +0x136
syscall.(*LazyProc).Call(0xc00006c390, 0xc000010038, 0x1, 0x1, 0x4, 0x4, 0x1, 0x0)
        c:/go/src/syscall/dll_windows.go:328 +0x66
main.dispatchMessage(0xc000044000)
        C:/Users/elias/syscallcrash/crash.go:207 +0xde
main.CreateWindow(0x1, 0xc000056058)
        C:/Users/elias/syscallcrash/crash.go:87 +0x128
main.main()
        C:/Users/elias/syscallcrash/crash.go:72 +0x29

goroutine 6 [chan receive]:
main.init.0.func1()
        C:/Users/elias/syscallcrash/crash.go:126 +0x74
created by main.init.0
        C:/Users/elias/syscallcrash/crash.go:125 +0x3c
rax     0x0
rbx     0x25ed820
rcx     0x151040
rdi     0x45c640
rsi     0xc000044000
rbp     0xc000049cc0
rsp     0x7bfd90
r8      0x7bfc90
r9      0x7ffec089e2a8
r10     0x0
r11     0x7bfd60
r12     0x4cfe20
r13     0x0
r14     0x1
r15     0x0
rip     0x7ffec53f622d
rflags  0x10246
cs      0x33
fs      0x53
gs      0x2b
exit status 2

This issue seems like a variant of https://github.com/golang/go/issues/16035. And sure enough, adding runtime.KeepAlive(m) to dispatchMessage does fix the native crash above.