g++ linker problem with libcygwin.a

g++ linker problem with libcygwin.a

[Philipp Kraus]

Hello,

I use Cygwin with g++ for compiling my source codes and on some codes I 
get the error:

/usr/lib/gcc/i686-pc-cygwin/4.5.3/../../../libcygwin.a(libcmain.o):(.text+0xa9): 
undefined reference to `_WinMain@16'

I link my sources to libraries like Boost, Atlas, LAPack...

All codes can be compiled under OSX and Linux without any warning / 
error. I've found the information that the
error is thrown, if the main method is not found, but all programs have 
the main methode like int main(int argc, char* argv[])
I try to solve the problem with a full reinstall of Cygwin but it does 
not run. The linker command
shows like:

g++ -o build/test.exe -enable-stdcall-fixup examples/test.o 
-L/usr/local/bin -L/usr/bin -L/cygdrive/c/Windows/system32 
-L/cygdrive/c/Windows -L/cygdrive/c/Windows/system32/Wbem
-L/cygdrive/c/Windows/system32/WindowsPowerShell/v1.0 
"-L/cygdrive/c/Program Files/TortoiseSVN/bin" "-L/cygdrive/c/Program 
Files/Java/jdk1.6.0_29/bin" -L/usr/bin 
-L/cygdrive/c/opt/library/atlas/3.9.51/lib 
-L/cygdrive/c/opt/library/hdf/1.8.7/lib 
-L/cygdrive/c/opt/library/xml2/2.7.8/bin 
-L/cygdrive/c/opt/library/boost/1.47.0/bin -L/cygdrive/c/opt/library/boo
st/1.47.0/lib -L/cygdrive/c/opt/library/jsoncpp/0.5.0/lib 
-L/cygdrive/c/opt/scons/bin
-lcygboost_system -lcygboost_thread -lcygboost_iostreams 
-lcygboost_regex -lcygboost_program_options -lboost_exception 
-lcygboost_filesystem -llapack -lcblas -lf77blas -latlas -lgfortran 
-lhdf5_cpp -lhdf5

All depend libraries are build with Cygwin Gcc / G++ / GFortran also. 
I've found a lot of posting with the similar / equal problem, but no 
solution. Does anybody know a solution for the linker problem?

Thanks

Phil



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Re: g++ linker problem with libcygwin.a

[René Berber]

On 10/22/2011 2:18 PM, Philipp Kraus wrote:

> I use Cygwin with g++ for compiling my source codes and on some codes I
> get the error:
> 
> /usr/lib/gcc/i686-pc-cygwin/4.5.3/../../../libcygwin.a(libcmain.o):(.text+0xa9):
> undefined reference to `_WinMain@16'
[snip]

That means the linking is being done for a GUI application.  I guess you
wanted to build a console application, so you should learn what these
options for the linker mean:

-Wl,-subsystem,console
-Wl,-subsystem,windows

There are equivalent options used with the compiler g++, I think they are:

-mconsole
-mwindows

In general there are many options that apply only to Windows builds, for
instance building Qt GUI applications I use these for the linker:

-Wl,-enable-stdcall-fixup -Wl,-enable-auto-import
-Wl,-enable-runtime-pseudo-reloc -Wl,-as-needed

but they are not for solving linking errors, just to quiet the warnings,
and try to optimize the result.
-- 
René Berber



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Re: g++ linker problem with libcygwin.a

[Philipp Kraus]

Thanks for your great answer.

On 2011-10-22 22:17:06 +0200, René Berber said:

> On 10/22/2011 2:18 PM, Philipp Kraus wrote:
> 
>> I use Cygwin with g++ for compiling my source codes and on some codes I
>> get the error:
>> 
>> /usr/lib/gcc/i686-pc-cygwin/4.5.3/../../../libcygwin.a(libcmain.o):(.text+0xa9): 
>> 
>> undefined reference to `_WinMain@16'
> [snip]
> 
> That means the linking is being done for a GUI application.  I guess you
> wanted to build a console application, so you should learn what these
> options for the linker mean:
> 
> -Wl,-subsystem,console
> -Wl,-subsystem,windows
> 
> There are equivalent options used with the compiler g++, I think they are:
> 
> -mconsole
> -mwindows

Yes I would build a console application (or a shared library, I can 
build the library).

I have tried both commands -mconsole and -Wl,-subsystem,console but the error
is created again. Should I rebuild my libraries with the -mconsole 
option, at the time
I have build them only with configure, make, make install?

Thanks

Phil



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Re: g++ linker problem with libcygwin.a

[René Berber]

On 10/22/2011 3:37 PM, Philipp Kraus wrote:

[snip]
> error
> is created again. Should I rebuild my libraries with the -mconsole
> option, at the time
> I have build them only with configure, make, make install?

You can check which libraries have a reference to _WinMain@16 by using nm.

$ nm /usr/local/bin/<your_library>.dll | grep WinMain

then rebuild only those.
-- 
René Berber



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Re: g++ linker problem with libcygwin.a

[Philipp Kraus]

On 2011-10-22 23:43:32 +0200, René Berber said:

> On 10/22/2011 3:37 PM, Philipp Kraus wrote:
> 
> [snip]
>> error
>> is created again. Should I rebuild my libraries with the -mconsole
>> option, at the time
>> I have build them only with configure, make, make install?
> 
> You can check which libraries have a reference to _WinMain@16 by using nm.
> 
> $ nm /usr/local/bin/<your_library>.dll | grep WinMain
> 
> then rebuild only those.

I have checked each library (*.dll, *.a, *.dll.a) but no library file 
as got a reference to the _WinMain
and I use the -mconsole linker flag. I don't understand why the linker 
creates the error on some
codes and on other code there is no error. Linker options are the same

Thx

Phil



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Re: g++ linker problem with libcygwin.a

[René Berber]

On 10/22/2011 5:48 PM, Philipp Kraus wrote:

> I have checked each library (*.dll, *.a, *.dll.a) but no library file as
> got a reference to the _WinMain
> and I use the -mconsole linker flag. I don't understand why the linker
> creates the error on some
> codes and on other code there is no error. Linker options are the same

Sorry I missed the obvious, from your first message the library in
question is libcygwin.a :

$ nm /usr/lib/libcygwin.a | grep WinMain
         U _WinMain@16

I'm not sure why this static library is pulled.  I also don't know what
it is, cygwin1.dll doesn't have the reference.
-- 
René Berber



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Re: g++ linker problem with libcygwin.a

[René Berber]

On 10/22/2011 6:28 PM, René Berber wrote:

> I also don't know what it is [libcygwin.a]

Looking at where it came from, libg.a is a symlink to this one, and libg
is known as "special debugging-enabled C library".

Still don't know what its doing in your program.
-- 
René Berber



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Re: g++ linker problem with libcygwin.a

[Philipp Kraus]

On 2011-10-23 01:37:19 +0200, René Berber said:

> On 10/22/2011 6:28 PM, René Berber wrote:
> 
>> I also don't know what it is [libcygwin.a]
> 
> Looking at where it came from, libg.a is a symlink to this one, and libg
> is known as "special debugging-enabled C library".
> 
> Still don't know what its doing in your program.

If I add  #include <windows.h> to the program compiling and linking works fine,
but I don't understand it....

Phil



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Re: g++ linker problem with libcygwin.a

[Philipp Kraus]

On 2011-10-23 01:28:37 +0200, René Berber said:

> I'm not sure why this static library is pulled.

yes *g* that my problem also. My cygwin g++ / ld
links it automatically

Phil



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Re: g++ linker problem with libcygwin.a

[René Berber]

On 10/23/2011 5:07 AM, Philipp Kraus wrote:

> On 2011-10-23 01:28:37 +0200, René Berber said:
> 
>> I'm not sure why this static library is pulled.
> 
> yes *g* that my problem also. My cygwin g++ / ld
> links it automatically

Where it comes from? The compiler specs:

$ g++ -dumpspecs
...
*lib:
  %{pg:-lgmon}   %{!mno-cygwin:-lcygwin}  ...

Its always linked and needed, and it doesn't cause the "undefined
reference to _WinMain" problem in other compilations.

There must be something else that uses something that pulls _WinMain.

Perhaps looking at the link map will clarify what is going on:

	g++ -Wl,-M ... > link-map.txt
-- 
René Berber



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Re: g++ linker problem with libcygwin.a

[René Berber]

On 10/23/2011 12:52 PM, René Berber wrote:

> Perhaps looking at the link map will clarify what is going on:
> 
> 	g++ -Wl,-M ... > link-map.txt

Or better, use the linker trace symbol functionality:

	g++ -Wl,-trace-symbol=_WinMain ...
-- 
René Berber



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Re: g++ linker problem with libcygwin.a

[zosrothko]

Hi

Here the definition of the cmain.c program, part of libcygwin.a. This code
has a "main" entry point which is  calling the WinMain by the end.... So the
question remains: Why g++/ld links with this "main" entry instead of the one
of the user's main program?

zos

/* libcmain.c

   Copyright 1996, 1997, 1998, 2000, 2001, 2006, 2009 Red Hat, Inc.

This file is part of Cygwin.

This software is a copyrighted work licensed under the terms of the
Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
details. */

#include <windows.h>

#define SP " \t\n"

/* Allow apps which don't have a main to work, as long as they define
WinMain */
int
main ()
{
  HMODULE x = GetModuleHandle (0);
  char *s = GetCommandLine ();
  STARTUPINFO si;
  char *nexts;

  s += strspn (s, SP);

  if (*s != '"')
    nexts = strpbrk (s, SP);
  else
    while ((nexts = strchr (s + 1, '"')) != NULL && nexts[-1] == '\\')
      s = nexts;

  if (!nexts)
    nexts = strchr (s, '\0');
  else
    nexts += strspn (nexts + 1, SP);

  GetStartupInfo (&si);

  return WinMain (x, 0, nexts,
		  ((si.dwFlags & STARTF_USESHOWWINDOW) != 0
		   ? si.wShowWindow
		   : SW_SHOWNORMAL));
}




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Re: g++ linker problem with libcygwin.a

[Marco Atzeri]

On 16/03/2014 18:03, zosrothko wrote:
> Hi

Dear,
re-opening a thread dead 3 years ago, is NOT a good way to have
any answer here.

If you have any problem, please follow

> Problem reports:       http://cygwin.com/problems.html

start a new thread and clarify your need or doubts

Regards
Marco


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Re: g++ linker problem with libcygwin.a

[Csaba Raduly]

On Sat, Oct 22, 2011 at 9:18 PM, Philipp Kraus  wrote:
> Hello,
>
> I use Cygwin with g++ for compiling my source codes and on some codes I get
> the error:
>
> /usr/lib/gcc/i686-pc-cygwin/4.5.3/../../../libcygwin.a(libcmain.o):(.text+0xa9):
> undefined reference to `_WinMain@16'

If there is no main(), libcygwin.a gives you a last chance: maybe
there is a WinMain function defined in your code, which will be called
by libc to start the program.

(or something like that)

Csaba
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