[cgo ] Export go function to C - illegal character

[nicolas...@yahoo.fr]

Hello,

I need some assistance to export a GO dll function to a C program.

The C program (wich i m not the author) required to call a function with this name: _RVExtension@12

so, i simply declare my go function like this:

//export _RVExtension@12
func _RVExtension@12(output *C.char, outputsize C.size_t, input *C.char) {Saisissez le code ici...

but when i try to compile it, it returns an illegal character U+0040 '@' error.

Do you know if there is a workaround about this ? I m not familiar with C code and i don't understand why there is @12 in the function name.

note: for the 64 bits the entry point is simple : RVExtension and it works perfectly well.


[Jason E. Aten]

The @12 part isn't legal as part of a function name, as the compiler is telling you. You must remove it.

[nicolas...@yahoo.fr]

thanks you for your answer. I will check for this :)

[nicolas...@yahoo.fr]

the dll is build but the entry point not works correctly :(

[nicolas...@yahoo.fr]

as asked by Jason, i give more information.

I build a 32 bits .dll and there was no error message. When i launch the dll with the c program, the c program return a generic error message "method is not recognized" wich happens when the entry point name is wrong.

So the C program expected a function named _RVExtension@12 and go returns

#ifdef __cplusplus
extern "C" {
#endif


extern void _RVExtensionVersion(char* p0, size_t p1);

extern void _RVExtensionArgs(char* p0, size_t p1, char* p2, char** p3, int p4);

extern void _RVExtension(char* p0, size_t p1, char* p2);

#ifdef __cplusplus
}
#endif

[Kurtis Rader]

On Sun, Jun 23, 2019 at 4:49 AM nicolas_boiteux via golang-nuts <golan...@googlegroups.com> wrote:

I need some assistance to export a GO dll function to a C program.

The C program (wich i m not the author) required to call a function with this name: _RVExtension@12

That is not a valid symbol (i.e., function name) in either C or Go. In other words the following C is invalid:

    extern int _RVExtension@12();

    int main() {

        _RVExtension@12();

    }

Your question has nothing to do with Go or C as such. What does the "@12" represent? Is it an API version number? In any event your question is really about a specific build toolchain on a specific platform. And you didn't even bother to tell us what platform you are using. I'm guessing MS Windows but we shouldn't have to make such guesses.

--

Kurtis Rader

Caretaker of the exceptional canines Junior and Hank

[nicolas...@yahoo.fr]

Hello Kurtis,

Precisly, i don't know what is this @12, and nobody can explain this :( It's for a windows build and the dll is load by arma game.

more informations at this place:

https://community.bistudio.com/wiki/Extensions

in c#, i used this line for export 32 bits dll

[DllExport("_RVExtension@12", CallingConvention = CallingConvention.Winapi)]

[Marvin Renich]

* nicolas_boiteux via golang-nuts <golan...@googlegroups.com> [190623 15:33]:

> Precisly, i don't know what is this @12, and nobody can explain this :(
> It's for a windows build and the dll is load by arma game.

The leading '_' and trailing '@' followed by a number is the __stdcall
decoration for a C name in the produced object symbol table. I do not
know what calling conventions cgo recognizes or how to tell cgo what
calling convention to use. Hopefully someone else can help with that.

See https://docs.microsoft.com/en-us/cpp/build/reference/decorated-names?view=vs-2019

...Marvin

[Jason E. Aten]

remove the _ underscore.

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[nicolas...@yahoo.fr]

thanks you Marvin for this interesting article. You point the real problem :)

[ono...@gmail.com]

We are trying to make the x32 version of the extension, as shown in the link below.

https://community.bistudio.com/wiki/Extensions#C.2FC.2B.2B

How we see, for x64 we must use entry points 

• RVExtension
• RVExtensionArgs
• RVExtensionVersion

but for x32 

• _RVExtension@12
• _RVExtensionArgs@20
• _RVExtensionVersion@8

It is very hard for me to explain to you exactly what we need, because I am new to this language, and C doesn’t know at all. I really hope that you understand what I mean.

воскресенье, 23 июня 2019 г., 22:20:53 UTC+3 пользователь Kurtis Rader написал:

[Alexander Kapshuk]

If I understand it correctly, cgo should have generated a
_cgo_export.h header with a declaration for your exported function.
Can you please post the generated declaration?

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[nicolas...@yahoo.fr]

Hello Alexander,

from my understanding, we need to build a GO 32 bits DLL for a C software.

To load this DLL, the C software loads an entry point function called _RVExtension@12 wich is a decorated/mangle C name/

It seems that cgo doesn't accept to export functions with '@' in name composition wich is accepted by convention in C

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[Alexander Kapshuk]

Or was this it?

#ifdef __cplusplus
extern "C" {
#endif
extern void _RVExtensionVersion(char* p0, size_t p1);
extern void _RVExtensionArgs(char* p0, size_t p1, char* p2, char** p3, int p4);
extern void _RVExtension(char* p0, size_t p1, char* p2);
#ifdef __cplusplus
}
#endif

The 32-bit exports listed here,
https://community.bistudio.com/wiki/Extensions, are most likely what
is listed in the module-definition file ending in .def.
Can you please try using the following declaration:
//export RVExtension
func RVExtension(output *C.char, outputsize C.size_t, input *C.char) {...}

Compile your dll and post the output of dumpbin.exe /EXPORTS
/path/to/slib.dll showing the listing of your exported symbols?

[ono...@gmail.com]

/* Code generated by cmd/cgo; DO NOT EDIT. */

/* package _/F_/Git/returnHWID-Arma */

#line 1 "cgo-builtin-export-prolog"

#include <stddef.h> /* for ptrdiff_t below */

#ifndef GO_CGO_EXPORT_PROLOGUE_H

#define GO_CGO_EXPORT_PROLOGUE_H

#ifndef GO_CGO_GOSTRING_TYPEDEF

typedef struct { const char *p; ptrdiff_t n; } _GoString_;

#endif

#endif

/* Start of preamble from import "C" comments.  */

#line 3 "main.go"

#include <stdlib.h>

#include <stdio.h>

#include <string.h>

#line 1 "cgo-generated-wrapper"

/* End of preamble from import "C" comments.  */

/* Start of boilerplate cgo prologue.  */

#line 1 "cgo-gcc-export-header-prolog"

#ifndef GO_CGO_PROLOGUE_H

#define GO_CGO_PROLOGUE_H

typedef signed char GoInt8;

typedef unsigned char GoUint8;

typedef short GoInt16;

typedef unsigned short GoUint16;

typedef int GoInt32;

typedef unsigned int GoUint32;

typedef long long GoInt64;

typedef unsigned long long GoUint64;

typedef GoInt64 GoInt;

typedef GoUint64 GoUint;

typedef __SIZE_TYPE__ GoUintptr;

typedef float GoFloat32;

typedef double GoFloat64;

typedef float _Complex GoComplex64;

typedef double _Complex GoComplex128;

/*

  static assertion to make sure the file is being used on architecture

  at least with matching size of GoInt.

*/

typedef char _check_for_64_bit_pointer_matching_GoInt[sizeof(void*)==64/8 ? 1:-1];

#ifndef GO_CGO_GOSTRING_TYPEDEF

typedef _GoString_ GoString;

#endif

typedef void *GoMap;

typedef void *GoChan;

typedef struct { void *t; void *v; } GoInterface;

typedef struct { void *data; GoInt len; GoInt cap; } GoSlice;

#endif

/* End of boilerplate cgo prologue.  */

#ifdef __cplusplus

extern "C" {

#endif

extern void RVExtensionVersion(char* p0, size_t p1);

extern void RVExtension(char* p0, size_t p1, char* p2);

#ifdef __cplusplus

}

#endif

понедельник, 24 июня 2019 г., 14:00:49 UTC+3 пользователь Alexander Kapshuk написал:

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[Alexander Kapshuk]

Ok. Thanks.
What's the output of dumpbin.exe /EXPORTS /path/to/slib.dll showing
the listing of your exported functions?

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[nicolas...@yahoo.fr]

Hello Alexander

you can find the dump at this place:

https://pastebin.com/cg33nktu

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[nicolas...@yahoo.fr]

i don't know why it so much verbose perhaps i don't use the good compilation flag .

Here another dump of a 32 bit dll extension with the same entry point but coded with c# (for comparaison purpose)

Microsoft (R) COFF/PE Dumper Version 14.21.27702.2
Copyright (C) Microsoft Corporation.  All rights reserved.


Dump of file inidbi2.dll

File Type: DLL

  Section contains the following exports for \inidbi2.dll

    00000000 characteristics
    5D0EB90A time date stamp Sun Jun 23 01:26:02 2019
        0.00 version
           0 ordinal base
           1 number of functions
           1 number of names

    ordinal hint RVA      name

          0    0 000038EE _RVExtension@12

  Summary

        2000 .reloc
        2000 .rsrc
        2000 .sdata
        2000 .text

[Alexander Kapshuk]

The part of interest is the functions you want exported from the Go program:

1 0 000813C0 RVExtension
2 1 00081360 RVExtensionArgs
3 2 00081310 RVExtensionVersion

This article, http://www.mingw.org/wiki/sampledll, in section
'Building and using a DLL without the dllexport/dllimport attibutes'
suggests the following approach:
If you pass the --no-undefined and --enable-runtime-pseudo-reloc
options to the linker, you don't have to add dllimport or dllexport
attributes to the source code that the DLL is made with ; all
functions are imported/exported automatically by default, just like in
unices.

Can you please try putting the following cgo directive for the linker
in your Go file:
// #cgo LDFLAGS: --no-undefined --enable-runtime-pseudo-reloc

If you then rebuild your dll and see if the definition of your
exported functions changes to _fn_name@arg_size in the output of
dumpbin.
You can use 'findstr' to filter the output of dumpbin based on a
search pattern like so:
dumpbin.exe /EXPORTS slib.dll | findstr "RVExtension"

On Mon, Jun 24, 2019 at 7:35 PM nicolas_boiteux via golang-nuts

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[nicolas...@yahoo.fr]

it seems that flags --no-undefined --enable-runtime-pseudo-reloc are invalid flags :(

/*
#cgo LDFLAGS: --no-undefined --enable-runtime-pseudo-reloc

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

*/
import "C"

[nicolas...@yahoo.fr]

it tried to also allow those flags by setting the env variablee ldflag allow but it seems to have no effect.

[Alexander Kapshuk]

Wander if specifying those linker flags via the '-ldflags' command
line option would make a difference:
go help build:
-ldflags '[pattern=]arg list'
arguments to pass on each go tool link invocation.

On Tue, Jun 25, 2019 at 9:16 AM nicolas_boiteux via golang-nuts

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[Alexander Kapshuk]

Tried that. Still no luck. Hm.

I'm not sure how you've been building your DLL, but if you're
including the _cgo_export.h in your .c file which is then
compiled/linked into a DLL, perhaps you could manually try changing
this line:
extern void RVExtension(char* p0, size_t p1, char* p2);

into what is suggested here, https://community.bistudio.com/wiki/Extensions:
extern __attribute__((dllexport)) void RVExtension(char *output, int
outputSize, const char *function);

And see if that does it.
Other than that, I'm afraid I don't have any more ideas for you to try. Sorry.

On Tue, Jun 25, 2019 at 10:07 AM Alexander Kapshuk

[nicolas...@yahoo.fr]

Conflicting declaration for RVExtension declaration :( and the -ldflags doesn't shown the same parameters.

[nicolas...@yahoo.fr]

If you want to test, you can retrieve the content of this git :

https://github.com/code34/armago_x64/tree/32bits

build the 32 bits dll in the same directory with the name : armago.dll

after this you only have to called : callextension.exe ./test_script.sqf

if the dll doesn't works as expected it will return a method unrecognized, if not return the string declared in the test_script.sqf

[Amnon Baron Cohen]

https://docs.microsoft.com/en-us/cpp/build/reference/decorated-names?view=vs-2019

[nicolas...@yahoo.fr]

i have some news.

With this kind of declaration

extern void __fastcall RVExtension(char *output, int outputSize, const char *function){
    goRVExtension(output, outputSize, function);
};

// export goRVExtension
func goRVExtension(output *C.char, outputsize C.size_t, input *C.char) {
    temp := fmt.Sprintf("Hello %s!", C.GoString(input))
    // Return a result to Arma
    result := C.CString(temp)
    defer C.free(unsafe.Pointer(result))
    var size = C.strlen(result) + 1
    if size > outputsize {
        size = outputsize
    }
    C.memmove(unsafe.Pointer(output), unsafe.Pointer(result), size)
}

i have this error message during the build

go : # command-line-arguments
Au caractère Ligne:1 : 1
+ go build -o armago.dll -buildmode=c-shared armago.go 2> result.txt
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (# command-line-arguments:String) [], RemoteException
    + FullyQualifiedErrorId : NativeCommandError
 
C:\Users\code34\AppData\Local\Temp\go-build126339458\b001\_x002.o: In function `@RVExtension@12':
C:/Users/code34/go/src/github.com/code34/armago_x64/armago.go:8: multiple definition of `@RVExtension@12'
C:\Users\code34\AppData\Local\Temp\go-build126339458\b001\_x001.o:/tmp/go-build/armago.go:8: first defined here
C:\Users\code34\AppData\Local\Temp\go-build126339458\b001\_x001.o: In function `@RVExtension@12':
/tmp/go-build/armago.go:9: undefined reference to `goRVExtension'
C:\Users\code34\AppData\Local\Temp\go-build126339458\b001\_x002.o: In function `@RVExtension@12':
C:/Users/code34/go/src/github.com/code34/armago_x64/armago.go:9: undefined reference to `goRVExtension'
collect2.exe: error: ld returned 1 exit status

# command-line-arguments
In file included from _cgo_export.c:4:0:
armago.go: In function 'RVExtension':
armago.go:9:2: warning: implicit declaration of function 'goRVExtension' [-Wimplicit-function-declaration]
# command-line-arguments
.\armago.go: In function 'RVExtension':
.\armago.go:9:2: warning: implicit declaration of function 'goRVExtension' [-Wimplicit-function-declaration]
  goRVExtension(output, outputSize, function);
  ^

as you can see in error message this time the entry point is correctly identified as @RVExtension@12 (but without underscore) , but i don't succeed to resolv the bug :(

[Marvin Renich]

* nicolas_boiteux via golang-nuts <golan...@googlegroups.com> [190626 12:15]:

> i have some news.
>
> With this kind of declaration
> extern void __fastcall RVExtension(char *output, int outputSize, const char
> *function){
> goRVExtension(output, outputSize, function);
> };

> as you can see in error message this time the entry point is correctly

> identified as* @RVExtension@12* (but without underscore) , but i don't

> succeed to resolv the bug :(

My original message (and the link I included) identified leading
underscore and trailing @ and number as being __stdcall, not __fastcall.
Try using __stdcall instead of __fastcall.

Note that the @RVExtension@12 above has a leading @ instead of _.

...Marvin

[nicolas...@yahoo.fr]

/*

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

extern void __stdcall RVExtension(char *output, int outputSize, const char *function);
*/

//export RVExtensionVersion
func RVExtensionVersion(output *C.char, outputsize C.size_t) {
    result := C.CString("Version 1.0")

    defer C.free(unsafe.Pointer(result))
    var size = C.strlen(result) + 1
    if size > outputsize {
        size = outputsize
    }
    C.memmove(unsafe.Pointer(output), unsafe.Pointer(result), size)
}

with this code ? it compiled but the entry point is not visible via dumpbin

[Marvin Renich]

* nicolas_boiteux via golang-nuts <golan...@googlegroups.com> [190626 13:19]:

> /*
> #include <stdlib.h>
> #include <stdio.h>
> #include <string.h>
> extern void __stdcall RVExtension(char *output, int outputSize, const char
> *function);
> */
>
> //export RVExtensionVersion
> func RVExtensionVersion(output *C.char, outputsize C.size_t) {
> result := C.CString("Version 1.0")
> defer C.free(unsafe.Pointer(result))
> var size = C.strlen(result) + 1
> if size > outputsize {
> size = outputsize
> }
> C.memmove(unsafe.Pointer(output), unsafe.Pointer(result), size)
> }
>
>
> with this code ? it compiled but the entry point is not visible via dumpbin

Does the declaration of RVExtension in the .c file match the cgo
declaration above (i.e. with extern and __stdcall)?

...Marvin

[nicolas...@yahoo.fr]

Marvin, i just publish the last version of my files on git:

can you please check them, and say me if the declaration/definition are ok ? I m not familiar with this cross langage compilation context/

https://github.com/code34/armago_x64/tree/32bits

[nicolas...@yahoo.fr]

hi

don't success to solve this subject. Here an example with the simple code shown in those slides:

http://akrennmair.github.io/golang-cgo-slides/#10

This code doesn't works anymore, or perhaps there is some special command line to build it ?

I thought it was possible to create a C function wich export the mangle name wich call the go code. When i put my c code in a c file in the directory, the c file is not compiled.

Le dimanche 23 juin 2019 13:49:33 UTC+2, nobody nobodye a écrit :

Hello,

I need some assistance to export a GO dll function to a C program.

The C program (wich i m not the author) required to call a function with this name: _RVExtension@12

so, i simply declare my go function like this:

//export _RVExtension@12
func _RVExtension@12(output *C.char, outputsize C.size_t, input *C.char) {Saisissez le code ici...

but when i try to compile it, it returns an illegal character U+0040 '@' error.

Do you know if there is a workaround about this ? I m not familiar with C code and i don't understand why there is @12 in the function name.

note: for the 64 bits the entry point is simple : RVExtension and it works perfectly well.


[nicolas...@yahoo.fr]

Hello

Finaly, Isegal helps me to solve this problem. You can have a complete description on how to proceed here:

https://github.com/golang/go/issues/32851