runtime: native callback on Windows only returns 32 bit result on 64 bit platform #29331

rixtox · 2018-12-19T06:33:24Z

What version of Go are you using?

$ go version
go version go1.11.4 windows/amd64

Problem

I'm calling a DLL function, that takes a callback function, where the callback function returns a pointer to some data structure, and the DLL will perform some action on the data structure.

package main

import (
    "golang.org/x/sys/windows"
    "unsafe"
)

type A struct {}
var a = &A{}

func Callback() uintptr {
    ptr := uintptr(unsafe.Pointer(a))
    fmt.Printf("Address: 0x%X\n", ptr)
    return ptr
}

func main() {
    dll := windows.MustLoadDLL("some.dll")
    init := dll.MustFindProc("init")
    init.Call(windows.NewCallback(Callback))
    fmt.Printf("This never get prints\n")
}

I'm running Go on Windows 64-bit machine, the DLL is also 64-bit. The above code will print the address of the pointer, which is 0xC000080018, but the call to the DLL will fail silently.

Cause

I don't have the source code to the DLL so I can't make it print the value it gets. So I used IDA pro to dynamically debug the program, and I found that the Go callback function is actually returning 32-bit value instead of 64-bit value. This is the final code of the Go callback routine before it returns back to the DLL:

main.exe:00000000004537E7     mov     eax, [rcx+rdx-8]
main.exe:00000000004537EB     pop     qword ptr [rcx+rdx-8]
main.exe:00000000004537EF     retn

As you can see Go is writing the return value in eax instead of rax, which will discard the higher address, therefore the DLL will only get 0x80018 and caused errors.

Possible fix?

I've done some digging into Go's implementation of the callback, and found the assembly code at src/runtime/sys_windows_amd64.s. I noticed that in runtime·callbackasm1, the return value is set using MOVL instead of MOVQ. So I changed it to MOVQ and everything worked.

I'm not sure if it's a bug or actually intended, so I'm opening an issue first.

The text was updated successfully, but these errors were encountered:

bcmills · 2018-12-19T16:46:54Z

CC @alexbrainman @bradfitz

alexbrainman · 2018-12-29T00:33:57Z

@rixtox

Thank you for reporting this issue. I am pretty sure, it is a bug to use MOVL instead of MOVQ in that code. windows/386 was first version of Go, and then windows/amd64 was created later. I suspect 386 code was copied onto amd64, and we did not adjusted that line. We also obviously do not have the test for that code.

I will try and write new test, and change this code, and see if anything gets affected in a bad way. We won't be able to make this change until after go1.12 is released. It has been broken forever, so it cannot be urgent.

If you want to try and implement the change yourself, let me know. This https://golang.org/doc/contribute.html is how to contribute.

Alex

OliverZou · 2019-01-16T15:05:32Z

o no,I met the like problem when go64exe load 64dll which call a callback function imp in go under windows10 x64.after c function call the callback ,the go program stop at asm_amd64.s cgocallback_gofunc.i hope these bugs are fiexed as soon as possible.thanks. (by the workround mentioned here ,i modified file and rebuilt a go.exe,but it dont work for me)

gopherbot · 2019-01-25T08:15:04Z

Change https://golang.org/cl/159579 mentions this issue: runtime: allow for syscall.NewCallback function return uintptr values

alexbrainman · 2019-01-25T08:18:22Z

@rixtox and @OliverZou please try https://golang.org/cl/159579 see if it fixes your problem. https://golang.org/cl/159579 fixes syscall package, not golang.org/x/sys/windows. So just replace golang.org/x/sys/windows with syscall in your test program. If syscall fix works, I will copy that code into golang.org/x/sys/windows.

Thank you.

Alex

rixtox · 2019-01-26T01:12:23Z

@alexbrainman The fix works for me.

alexbrainman · 2019-01-27T03:53:26Z

The fix works for me.

Thanks for confirming. Now we need for someone to review my change (I made a note there to wait until go1.12 is released).

Alex

odeke-em · 2019-01-30T19:58:55Z

Thanks for confirming. Now we need for someone to review my change (I made a note there to wait until go1.12 is released).

Cool, thanks for the CL @alexbrainman! @randall77 and I reviewed and approved your CL, and there is a small pending update to the test.
I've also updated this issue's title to reflect where the change is to be made, i.e. in the runtime.

alexbrainman · 2019-03-03T00:17:31Z

If syscall fix works, I will copy that code into golang.org/x/sys/windows.

I tried copying CL 159579 into golang.org/x/sys/windows, but there is nothing to do. CL 159579 inly changed src/runtime/sys_windows_amd64.s file, that lives in runtime (not syscall) package.

Let me know, if I am mistaken.

Alex

rixtox · 2019-03-03T08:14:22Z

@alexbrainman You are right. golang.org/x/sys/windows delegates NewCallback to syscall.NewCallback, which eventually fallback to runtime code. See follows:

https://github.com/golang/sys/blob/master/windows/syscall_windows.go#L116

bcmills changed the title ~~Windows native callback only returns 32 bit result on 64 bit platform~~ x/sys/windows: native callback only returns 32 bit result on 64 bit platform Dec 19, 2018

gopherbot added this to the Unreleased milestone Dec 19, 2018

bcmills added OS-Windows NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels Dec 19, 2018

odeke-em changed the title ~~x/sys/windows: native callback only returns 32 bit result on 64 bit platform~~ runtime: native callback on Windows only returns 32 bit result on 64 bit platform Jan 30, 2019

odeke-em modified the milestones: Unreleased, Go1.13 Jan 30, 2019

odeke-em added NeedsFix The path to resolution is known, but the work has not been done. and removed NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels Jan 30, 2019

odeke-em assigned alexbrainman Jan 30, 2019

gopherbot closed this as completed in 5cf4e44 Feb 26, 2019

golang locked and limited conversation to collaborators Mar 2, 2020

gopherbot added the FrozenDueToAge label Mar 2, 2020

rsc unassigned alexbrainman Jun 23, 2022

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runtime: native callback on Windows only returns 32 bit result on 64 bit platform #29331

runtime: native callback on Windows only returns 32 bit result on 64 bit platform #29331

rixtox commented Dec 19, 2018 •

edited

bcmills commented Dec 19, 2018

alexbrainman commented Dec 29, 2018

OliverZou commented Jan 16, 2019

gopherbot commented Jan 25, 2019

alexbrainman commented Jan 25, 2019

rixtox commented Jan 26, 2019

alexbrainman commented Jan 27, 2019

odeke-em commented Jan 30, 2019

alexbrainman commented Mar 3, 2019

rixtox commented Mar 3, 2019

runtime: native callback on Windows only returns 32 bit result on 64 bit platform #29331

runtime: native callback on Windows only returns 32 bit result on 64 bit platform #29331

Comments

rixtox commented Dec 19, 2018 • edited

What version of Go are you using?

Problem

Cause

Possible fix?

bcmills commented Dec 19, 2018

alexbrainman commented Dec 29, 2018

OliverZou commented Jan 16, 2019

gopherbot commented Jan 25, 2019

alexbrainman commented Jan 25, 2019

rixtox commented Jan 26, 2019

alexbrainman commented Jan 27, 2019

odeke-em commented Jan 30, 2019

alexbrainman commented Mar 3, 2019

rixtox commented Mar 3, 2019

rixtox commented Dec 19, 2018 •

edited