x/sys/windows: call 32bit dll in 64bit windows panic when pass float64(double) parameter

[winxxp]

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

$ go version
go version go1.11.2 windows/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
set GOARCH=386
set GOBIN=
set GOCACHE=C:\Users\1\AppData\Local\go-build
set GOEXE=.exe
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOOS=windows
set GOPATH=D:\Golib
set GOPROXY=
set GORACE=
set GOROOT=D:\Go
set GOTMPDIR=
set GOTOOLDIR=D:\Go\pkg\tool\windows_amd64
set GCCGO=gccgo
set GO386=sse2
set CC=gcc
set CXX=g++
set CGO_ENABLED=0
set GOMOD=E:\workspace\998-source\gowork\src\github.com\go.mod
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=-m32 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=T:\Temp\go-build953563306=/tmp/go-build -gno-record-gcc-switches

What did you do?

https://play.golang.org/p/roPsAJFuQpU

What did you expect to see?

f32: 3f800000, f64: 3ff0000000000000
out = 1

What did you see instead?

In Windows DebugView: [20868] f32 3f800000, f64:1105008000000000

Output

GOROOT=D:\Go #gosetup
GOPATH=D:\Golib #gosetup
D:\Go\bin\go.exe build -o T:\Temp\___go_build_m_go.exe E:/workspace/998-source/gowork/src/github.com/winxxp/dll/ex/m.go #gosetup
"D:\Program Files\JetBrains\IntelliJ IDEA 2018.3\bin\runnerw64.exe" T:\Temp\___go_build_m_go.exe #gosetup
f32: 3f800000, f64: 3ff0000000000000
Exception 0xc0000005 0x1 0x446b0e 0x8213e7
PC=0x8213e7
syscall.Syscall(0x821320, 0x3, 0x3f800000, 0x0, 0x11050080, 0x0, 0x0, 0x0)

D:/Go/src/runtime/syscall_windows.go:172 +0xcf

golang.org/x/sys/windows.(*Proc).Call(0x1104e120, 0x110500c0, 0x3, 0x3, 0x10, 0x494040, 0x1, 0x110500c0)

D:/Golib/pkg/mod/golang.org/x/sys@v0.0.0-20180830151530-49385e6e1522/windows/dll_windows.go:135 +0x21e

golang.org/x/sys/windows.(*LazyProc).Call(0x110754a0, 0x110500c0, 0x3, 0x3, 0x2, 0x25, 0x0, 0x0)

D:/Golib/pkg/mod/golang.org/x/sys@v0.0.0-20180830151530-49385e6e1522/windows/dll_windows.go:309 +0x48

main.main()

E:/workspace/998-source/gowork/src/github.com/winxxp/dll/ex/m.go:22 +0x192

eax     0x1

ebx     0x535994

ecx     0xc5327b32

edx     0x0

edi     0x446b0e

esi     0x76cb5a30

ebp     0x19fea8

esp     0x19fd40

eip     0x8213e7

eflags  0x10246

cs      0x23

fs      0x53

gs      0x2b
Process finished with exit code 2

[tklauser]

/cc @alexbrainman

[alexbrainman]

@winxxp

When you call any function, your arguments must match function parameters. I think, some of yours do not match.

From https://play.golang.org/p/roPsAJFuQpU

C has

DllExport int DllFunc(float f32, double f64, float* f32out)

and Go passes

r1, _, err := dllFunc.Call(
uintptr(f32),
uintptr(f64),
uintptr(unsafe.Pointer(&out)),
)

First C f32 parameter looks OK, because (according to https://docs.microsoft.com/en-us/previous-versions/cc953fe1(v=vs.140) ) C float expects 4 bytes, and you pass uintptr (4 bytes). So match here.

But C f64 takes 8 bytes, while Go parameter is uintptr (4 bytes). This is not allowed. I think you want to split Go f64 into 2 uintptr values (upper and lower 4 bytes), and pass them to dllFunc.Call as separate parameters.

I did not look passed C f64, but similar logic would apply.

I do not have Visual C to build your DLL, and you did not provide the DLL source, so I cannot verify my theory. But I don't think there is anything to fix here - this is all working as expected. Let me know, if I am wrong.

Thank you.

Alex

[alexbrainman]

There is TestFloatArgs in runtime package, if anyone wants to play with this.

Alex

[winxxp]

@alexbrainman

1. change to call 64bit dll, passed
2. double split into 2 uint32, passed (https://play.golang.org/p/mfsa_RzDRpz)