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cmd/go: -buildmode=c-shared without specifying output file fails does not add .dll extension on Windows and .so extension on linux #38244

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Sebi2020 opened this issue Apr 4, 2020 · 7 comments
Open

cmd/go: -buildmode=c-shared without specifying output file fails does not add .dll extension on Windows and .so extension on linux #38244

Sebi2020 opened this issue Apr 4, 2020 · 7 comments
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GoCommand cmd/go help wanted NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. OS-Windows
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Backlog

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@Sebi2020
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Sebi2020 commented Apr 4, 2020 •
edited

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

go version go1.14.1 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
set GO111MODULE=auto
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\anon\AppData\Local\go-build
set GOENV=C:\Users\anon\AppData\Roaming\go\env
set GOEXE=.exe
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOINSECURE=
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=C:\Users\anon\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\anon\AppData\Local\Temp\go-build481521658=/tmp/go-build -gno-record-gcc-switches

What did you do?

I tried to build a c-shared library

package main
import "fmt"
import "C"

//export test
func test() {
	fmt.Println("Hello World!")
}

func main() {

}

The archive is linked against a C which just calls test() with:

gcc main.c -L<path to dll folder> -l<dll name without extension> -o test.exe

Executing test.exe does not produce any output.

What did you expect to see?

A valid dll file (standard dynamic library format on windows)

What did you see instead?

The call go build -buildmode=c-shareddoes not yield a valid dll (I think; it does not have any extension by default). It produces a [folder name] file without any extension.

I'm not sure what happens, but if you try to link it against a C mainthe main function does not get executed. The linker does not produce any warnings or errors about the file (after renaming [name] to [name].dll).

If you produce the archive with go build -buildmode=c-shared -o <name>.dll everything works as expected, but go build -buildmode=c-shared should be sufficient, but it isn't.
@Sebi2020 Sebi2020 changed the title Building c-shared and c-archive on windows fails Building c-shared without specifying output file fails Apr 4, 2020
@ianlancetaylor ianlancetaylor changed the title Building c-shared without specifying output file fails cmd/go: -buildmode=c-shared without specifying output file fails does not add .dll extension on Windows Apr 4, 2020
@ianlancetaylor ianlancetaylor added GoCommand cmd/go NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. OS-Windows labels Apr 4, 2020
@ianlancetaylor ianlancetaylor added this to the Backlog milestone Apr 4, 2020
@Sebi2020
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Sebi2020 commented Apr 11, 2020 •
edited

I tested this on linux too. The same behaviour applys to linux. The command generates a extension-less output file.

@Sebi2020 Sebi2020 changed the title cmd/go: -buildmode=c-shared without specifying output file fails does not add .dll extension on Windows cmd/go: -buildmode=c-shared without specifying output file fails does not add .dll extension on Windows and .so extension on linux Apr 11, 2020
@alexbrainman
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@Sebi2020 I think this is working as expected.

If you running

go build -buildmode=c-shared

command, it creates output file without extension.

If you want some particular file name, just use -o parameter. Like so

go build -buildmode=c-shared -o a.dll

Alex

@Sebi2020
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Sebi2020 commented Apr 16, 2020 •
edited

@alexbrainman that was the point of the bug report, because it should output a file with an extension. It's not common for shared objects or dynamic linked libraries to have no extension. On linux the should end with .so and on windows they should (per default) end with .dll.

Apart from this, if you don't specify the name with the -o flag, the compiler does not create a valid .dll on windows (Later linkage fails).

@alexbrainman
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@Sebi2020 I don't disagree with your arguments. But I suggest you use -o flag to solve your problem, instead of letting go command pick file name for your output file.

I haven't used -buildmode=c-shared mode for many years, and I could be wrong. But, I suspect, you will discover, that you cannot rename output files anyway. So you argument is pointless.

Alex

@Sebi2020
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@alexbrainman What do you mean with you cannot rename output files? I think it's a simple code line of the go tool, which must be changed to get file extensions. -o for example could default to [packagename].so instead of [packagename]. on linux and [packagename].dll on windows.

@alexbrainman
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What do you mean with you cannot rename output files?

c:\Users\Alex\dev\src\issue\go\38244>dir
 Volume in drive C has no label.
 Volume Serial Number is 9012-A870

 Directory of c:\Users\Alex\dev\src\issue\go\38244

03/05/2020  06:41 PM    <DIR>          .
03/05/2020  06:41 PM    <DIR>          ..
03/05/2020  06:34 PM               129 main.go
               1 File(s)            129 bytes
               2 Dir(s)  10,984,325,120 bytes free

c:\Users\Alex\dev\src\issue\go\38244>type main.go
package main

import "fmt"
import "C"

//export Test
func Test() {
        fmt.Println("Hello World!")
}

func main() {

}

c:\Users\Alex\dev\src\issue\go\38244>go build -buildmode=c-shared

c:\Users\Alex\dev\src\issue\go\38244>dir
 Volume in drive C has no label.
 Volume Serial Number is 9012-A870

 Directory of c:\Users\Alex\dev\src\issue\go\38244

03/05/2020  06:41 PM    <DIR>          .
03/05/2020  06:41 PM    <DIR>          ..
03/05/2020  06:41 PM         3,651,068 38244
03/05/2020  06:41 PM             1,578 38244.h
03/05/2020  06:34 PM               129 main.go
               3 File(s)      3,652,775 bytes
               2 Dir(s)  10,980,343,808 bytes free

c:\Users\Alex\dev\src\issue\go\38244>copy con main.c
#include "38244.h"
#include <stdio.h>

int main() {
  printf("This is a C Application.\n");
  Test();
  return 0;
}
^Z
        1 file(s) copied.

c:\Users\Alex\dev\src\issue\go\38244>gcc -o a main.c 38244

c:\Users\Alex\dev\src\issue\go\38244>a
This is a C Application.
Hello World!

c:\Users\Alex\dev\src\issue\go\38244>ren 38244 38244.dll

c:\Users\Alex\dev\src\issue\go\38244>gcc -o a main.c 38244.dll

c:\Users\Alex\dev\src\issue\go\38244>a

c:\Users\Alex\dev\src\issue\go\38244>

Running last command brings this box

image

Alex

@Sebi2020
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Yes this occures,because as far as I know the file name is encoded in dlls. You have to use the -o option. But I mean, the command should generate the file with a .dll or .so extension by default.

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