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cmd/link: trying to get a C function pointer from Go breaks if the function is stdcall #47992

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Keithcat1 opened this issue Aug 26, 2021 · 0 comments

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@Keithcat1
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@Keithcat1 Keithcat1 commented Aug 26, 2021

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

$ go version
go version go1.17 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 GO111MODULE=auto
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\keith\AppData\Local\go-build
set GOENV=C:\Users\keith\AppData\Roaming\go\env
set GOEXE=.exe
set GOEXPERIMENT=
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOINSECURE=
set GOMODCACHE=C:\py\go\pkg\mod
set GONOPROXY=github.com/keithcat1/nvgo
set GONOSUMDB=github.com/keithcat1/nvgo
set GOOS=windows
set GOPATH=C:\py\go
set GOPRIVATE=github.com/keithcat1/nvgo
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 GOVCS=
set GOVERSION=go1.17
set GCCGO=gccgo
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=C:\py\go\player\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=-m64 -mthreads -fmessage-length=0 -fdebug-prefix-map=C:\Users\keith\AppData\Local\Temp\go-build1242204174=/tmp/go-build -gno-record-gcc-switches

What did you do?

I was working over on github.com/keithcat1/gobass, adding a way for users to pass Go functions as a C callback. This involves creating a Go wrapper function which calls the user-provided callback. My problem is that BASS requires its callbacks to have the CALLBACK attribute. On windows this boils down to __stdcall.
On Windows/386 I get a linker error when trying to get the pointer to a stdcall function from Go. I think this is because stdcall functions have their name changed from for example 'add' to '_add@8' and Go can't account for this.
Here is an example:
example.zip
Get either a 32-bit MinGW toolchain from something like https://www.winlibs.com Extract or LLVM MinGW, cd into the example, set GOARCH=386 and go build. If using GCC you'll get a warning about stdcall fixups, and if using Clang the linking process will fail entirely.
The way to get around this for me was to make functions that returned the C function pointers so that the C comppiler could do the right thing.

@toothrot toothrot changed the title CGO: trying to get a C function pointer from Go breaks if the function is stdcall cmd/link: trying to get a C function pointer from Go breaks if the function is stdcall Aug 27, 2021
@toothrot toothrot added this to the Backlog milestone Aug 27, 2021
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