[perl] Portably linking to libstdc++

[perl] Portably linking to libstdc++

[Sisyphus]

Hi,

On linux, I can have my perl distro link to libstdc++ by simply specifying 
(in the Makefile.PL's %WriteMakefile) :

  LIBS => ['-lstdc++'],

And, for MinGW-built perls on Win32, the same construct works.
For Cygwin, it seems that is not sufficient (as the directory that houses 
libstdc++.a is apparently not searched by default). Instead, Cygwin needs 
something like:

  LIBS => ['-L/lib/gcc/i686-pc-cygwin/3.4.4 -lstdc++'],

But that doesn't look very portable across different Cygwin installations. 
(I'm looking mainly at the '3.4.4', and thinking that not every Cygwin 
installation will have such a directory.)

How do I write that LIBS assignment so that it would be portable across 
different *Cygwin* installations ?

Cheers,
Rob 


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Re: [perl] Portably linking to libstdc++

[Sisyphus]

----- Original Message ----- 
From: "Sisyphus" <sisyphus1@optusnet.com.au>
.
.
>
> How do I write that LIBS assignment so that it would be portable across 
> different *Cygwin* installations ?
>

I still don't know how to do that - though I did come to a better 
understanding of how the problem arises.

For both linux and cygwin, 'perl -V:libpth' returns 'libpth='/usr/local/lib 
/usr/lib /lib'.

On linux I can run 'perl Makefile.PL LIBS="-lstdc++"' and that runs fine 
because '-lstdc++' is found in $Config{libpth}, in the form of libstdc++.so.

But on cygwin, there is no '-lstdc++' to be found in $Config{libpth}, so 
MakeMaker decides to not pass the switch on (which has always been 
MakeMaker's policy in such cases, afaik). This is a pity - there would be no 
problem if it *did* the pass switch on, as both gcc and g++ on cygwin will 
resolve that link.

IMO, on my cygwin perl, $Config{libpth} should be set to '/usr/local/lib 
/usr/lib /lib /lib/gcc/i686-pc-cygwin/3.4.4', and I regard it as a bug that 
'/lib/gcc/i686-pc-cygwin/3.4.4' is not being included in $Config{libpth}. In 
fact, I've modified the libpth setting in Config.pm to '/usr/local/lib 
/usr/lib /lib /lib/gcc/i686-pc-cygwin/3.4.4'.

Is there somewhere I should lodge a bug report about this ?

Cheers,
Rob 


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Re: [perl] Portably linking to libstdc++

[Brian Dessent]

Sisyphus wrote:

> But on cygwin, there is no '-lstdc++' to be found in $Config{libpth}, so
> MakeMaker decides to not pass the switch on (which has always been
> MakeMaker's policy in such cases, afaik). This is a pity - there would be no
> problem if it *did* the pass switch on, as both gcc and g++ on cygwin will
> resolve that link.

MakeMaker should be fixed to allow the switch through.

Really the correct way to link C++ code is by using g++ which doesn't
require this manual -lstdc++ nonsense.  Can't you just do that, by
either fixing the makefile to link with $(CXX) or overriding the
appropriate variable?

Or, how about:

$ perl Makefile.PL LIBS="$(${CC:-gcc} -print-file-name=libstdc++.a)"

But this is still not optimal because it assumes static libstdc++, which
has been the only available choice until now but will not be in the
future, i.e. we want to move to shared libstdc++ eventually with gcc4. 
The optimal solution again is to link by calling $(CXX) and not have to
worry about any of this.

> IMO, on my cygwin perl, $Config{libpth} should be set to '/usr/local/lib
> /usr/lib /lib /lib/gcc/i686-pc-cygwin/3.4.4', and I regard it as a bug that
> '/lib/gcc/i686-pc-cygwin/3.4.4' is not being included in $Config{libpth}. In
> fact, I've modified the libpth setting in Config.pm to '/usr/local/lib
> /usr/lib /lib /lib/gcc/i686-pc-cygwin/3.4.4'.

$libexec/gcc/$target/$version is a private directory of the compiler. 
The compiler knows how to find it, and other external apps should not
need to know what it is or even that it exists.  Exposing this internal
detail of the compiler to any other build system is just plain wrong for
many reasons.

Brian

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Re: [perl] Portably linking to libstdc++

[Sisyphus]

----- Original Message ----- 
From: "Brian Dessent" <brian@dessent.net>
>> But on cygwin, there is no '-lstdc++' to be found in $Config{libpth}, so
>> MakeMaker decides to not pass the switch on (which has always been
>> MakeMaker's policy in such cases, afaik). This is a pity - there would be 
>> no
>> problem if it *did* the pass switch on, as both gcc and g++ on cygwin 
>> will
>> resolve that link.
>
> MakeMaker should be fixed to allow the switch through.
>

This has been a long standing feature of MakeMaker, and I expect that a 
significant number of modules would be broken if that behaviour was changed. 
It allows module authors the convenience of being able to specify all libs 
that might be needed, without having to worry about the fact that some of 
those libs will be both unneeded and absent on some systems. At least, I 
*guess* that's the idea behind it.
It would be better, however, if there was some way to override that 
behaviour and force MakeMaker to pass the switch on. (I don't think such a 
facility exists ... but I couldn't say for sure ...)

>
> Really the correct way to link C++ code is by using g++ which doesn't
> require this manual -lstdc++ nonsense.  Can't you just do that, by
> either fixing the makefile to link with $(CXX) or overriding the
> appropriate variable?
>

Aaah ... good point. I had missed something.

I had changed $Config{cc} from 'gcc' to 'g++' thinking that should do the 
trick. And it works fine for MinGW-built perls .... but (as it turns out) 
only because $Config{ld} is already set to 'g++'.
On both linux and cygwin, I've just realised that $Config{ld} is still set 
to 'gcc' - which is what necessitates linking explicitly to libstdc++.
Of course, the other option on both linux and cygwin is to set *both* 
$Config{cc} and $Config{ld} to 'g++', and that works fine on linux, but 
doesn't quite work on cygwin where I still get an undefined reference to 
`_WinMain@16':

/usr/lib/gcc/i686-pc-cygwin/3.4.4/../../../libcygwin.a(libcmain.o):(.text+0xab): 
undefined reference to `_WinMain@16'
collect2: ld returned 1 exit status

Why does that happen ?

Btw, overriding $Config{cc} and $Config{ld} is trivial. In the Makefile.PL's 
%WriteMakefile() it's just a matter of:

  CC => 'g++',
  LD => 'g++',

Or they can be overridden from the command line when the Makefile.PL is run:

  perl Makefile.PL CC="g++" LD="g++"

And I think that's all I need do on any perl build where g++ is the name of 
the c++ compiler .... except for Cygwin (where it doesn't work because of 
that undefined reference to `_WinMain@16').

Thanks for the reply, Brian.

Cheers,
Rob


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Re: [perl] Portably linking to libstdc++

[Reini Urban]

2008/10/20 Sisyphus:
>> Really the correct way to link C++ code is by using g++ which doesn't
>> require this manual -lstdc++ nonsense.  Can't you just do that, by
>> either fixing the makefile to link with $(CXX) or overriding the
>> appropriate variable?

> Aaah ... good point. I had missed something.
>
> I had changed $Config{cc} from 'gcc' to 'g++' thinking that should do the
> trick. And it works fine for MinGW-built perls .... but (as it turns out)
> only because $Config{ld} is already set to 'g++'.

LD is already g++. And if you need to compile C++ you have to use g++
anyway as CC.
No need to change anything in current cygwin perl IMO.

> On both linux and cygwin, I've just realised that $Config{ld} is still set
> to 'gcc' - which is what necessitates linking explicitly to libstdc++.
> Of course, the other option on both linux and cygwin is to set *both*
> $Config{cc} and $Config{ld} to 'g++', and that works fine on linux, but
> doesn't quite work on cygwin where I still get an undefined reference to
> `_WinMain@16':

Current cygwin perl already has g++ as LD for some releases.

> /usr/lib/gcc/i686-pc-cygwin/3.4.4/../../../libcygwin.a(libcmain.o):(.text+0xab):
> undefined reference to `_WinMain@16'
> collect2: ld returned 1 exit status
>
> Why does that happen ?

Maybe because the linker believes you have a -mwindows GUI app?
Which distro are you talking about?
InlineX::CPP2XS I assume.

> Btw, overriding $Config{cc} and $Config{ld} is trivial. In the Makefile.PL's
> %WriteMakefile() it's just a matter of:
>
>  CC => 'g++',
>  LD => 'g++',
>
> Or they can be overridden from the command line when the Makefile.PL is run:
>
>  perl Makefile.PL CC="g++" LD="g++"

  perl Makefile.PL CC="g++"
should be enough.

> And I think that's all I need do on any perl build where g++ is the name of
> the c++ compiler .... except for Cygwin (where it doesn't work because of
> that undefined reference to `_WinMain@16').
-- 
Reini Urban
http://phpwiki.org/              http://murbreak.at/

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Re: [perl] Portably linking to libstdc++

[Sisyphus]

[-- Attachment #1: Type: text/plain, Size: 1922 bytes --]


----- Original Message ----- 
From: "Reini Urban" <rurban@x-ray.at>
.
.
>
> Current cygwin perl already has g++ as LD for some releases.

Good - I think that's a step in the right direction. (I wonder how we can
get linux builds to start doing the same.)
On my 5.8.8, LD is set to ld2 which, I think, is an alias for 'gcc:

----------------------------
Rob@desktop2 ~
$ perl -V:ld
ld='ld2';

Rob@desktop2 ~
$ ld2 -v
gcc -v
Reading specs from /usr/lib/gcc/i686-pc-cygwin/3.4.4/specs
............
----------------------------

>> /usr/lib/gcc/i686-pc-cygwin/3.4.4/../../../libcygwin.a(libcmain.o):(.text+0xab):
>> undefined reference to `_WinMain@16'
>> collect2: ld returned 1 exit status
>>
>> Why does that happen ?
>
> Maybe because the linker believes you have a -mwindows GUI app?

There is some Microsoft-specific stuff in the XS file ... so such a 
confusion is not out of the question.
Is it strange that it believes that only when LD is set to g++ ?
If I leave LD set to gcc and explicitly link to libstdc++.a, then there's no 
problem.

> Which distro are you talking about?
> InlineX::CPP2XS I assume.

No problems with InlineX::CPP2XS.

I was doing some testing of someone else's upcoming release of Devel::Size 
(0.72), which
has been significantly rewritten and is quite different to the current CPAN
version (0.71).

It's only small, so I'll attach it and you can take a look if you like.
Sounds like it should build ok for you, without the need to make any
amendment.

In the Makefile.PL you'll see that I've commented out the line:

  LIBS => '-lstdc++',

If I'm to successfully build that module on my cygwin perl, I need to
include that line. And even then, that works only because I've added the 
location of
libstdc++.a to my $Config{libpth}.

If it does build for more recent cygwin perls, then I guess the matter has 
already been dealt with - and one can't ask for more than that :-)

Cheers,
Rob 

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Re: [perl] Portably linking to libstdc++

[Brian Dessent]

Sisyphus wrote:

> Of course, the other option on both linux and cygwin is to set *both*
> $Config{cc} and $Config{ld} to 'g++', and that works fine on linux, but
> doesn't quite work on cygwin where I still get an undefined reference to
> `_WinMain@16':
> 
> /usr/lib/gcc/i686-pc-cygwin/3.4.4/../../../libcygwin.a(libcmain.o):(.text+0xab):
> undefined reference to `_WinMain@16'
> collect2: ld returned 1 exit status
> 
> Why does that happen ?

The error means you tried to link an executable that didn't contain a
main() function.  The fact that it refers to a missing WinMain() is
incidental, a byproduct of some compatibility code in Cygwin that
provides a backup main() which calls WinMain(), allowing the
Windows-style tradition where the user provides a WinMain() instead of
main().  Regardless of how it's spelled, you can't link an executable
without a proper entrypoint which is all the error means.

Please post the entire link command and not just the error.  It's
impossible to say what the true nature of the problem is otherwise.  For
example, if you're trying to link a library and not an executable then
the above error would be due to missing the "-shared" flag.

Brian

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Re: [perl] Portably linking to libstdc++

[Sisyphus]

----- Original Message ----- 
From: "Brian Dessent" <brian@dessent.net>
.
.
>
> Please post the entire link command and not just the error.  It's
> impossible to say what the true nature of the problem is otherwise.  For
> example, if you're trying to link a library and not an executable then
> the above error would be due to missing the "-shared" flag.

For the failure in question (ie the WinMain error), I start by running 'perl 
Makefile.PL LD="g++"'.
This means that both CC and LD have been set to g++. The failing link 
command is:

###################################
g++  -s -L/usr/local/lib Size.o  -o blib/arch/auto/Devel/Size/Size.dll  \
   /usr/lib/perl5/5.8/cygwin/CORE/libperl.dll.a    \

/usr/lib/gcc/i686-pc-cygwin/3.4.4/../../../libcygwin.a(libcmain.o):(.text+0xab): 
undefined reference to `_WinMain@16'
collect2: ld returned 1 exit status
make: *** [blib/arch/auto/Devel/Size/Size.dll] Error 1
###################################

If I start by running simply 'perl Makefile.PL', then CC is set to g++, but 
LD is set to ld2 (gcc).
The error is:

###################################
ld2  -s -L/usr/local/lib Size.o  -o blib/arch/auto/Devel/Size/Size.dll  \
   /usr/lib/perl5/5.8/cygwin/CORE/libperl.dll.a    \

gcc -shared -o 
 Size.dll -Wl,--out-implib=libSize.dll.a -Wl,--export-all-symbols -Wl,--enable-auto-import 
 -Wl,--stack,8388608 -Wl,--enable-auto-image-base -s -L/usr/local/lib Size.o 
/usr/lib/perl5/5.8/cygwin/CORE/libperl.dll.a
Size.o:Size.c:(.text+0x122): undefined reference to `___gxx_personality_sj0'
Size.o:Size.c:(.text+0x21b): undefined reference to `___cxa_begin_catch'
Size.o:Size.c:(.text+0x24b): undefined reference to `___cxa_end_catch'
[followed by more undefined references to the same symbols]
###################################

If I start by running 'perl Makefile.PL LIBS="-lstdc++"', then everything 
proceeds fine - but only because I've hacked $Config{libpth} to include the 
location of libstdc++.a. The same section of the build output is:

###################################
ld2  -s -L/usr/local/lib Size.o  -o blib/arch/auto/Devel/Size/Size.dll  \
   /usr/lib/perl5/5.8/cygwin/CORE/libperl.dll.a -lstdc++   \

gcc -shared -o 
 Size.dll -Wl,--out-implib=libSize.dll.a -Wl,--export-all-symbols -Wl,--enable-auto-import 
 -Wl,--stack,8388608 -Wl,--enable-auto-image-base \
-s -L/usr/local/lib Size.o 
 /usr/lib/perl5/5.8/cygwin/CORE/libperl.dll.a -lstdc++
Creating library file: libSize.dll.a
mv Size.dll libSize.dll.a blib/arch/auto/Devel/Size/
chmod 755 blib/arch/auto/Devel/Size/Size.dll
cp Size.bs blib/arch/auto/Devel/Size/Size.bs
chmod 644 blib/arch/auto/Devel/Size/Size.bs
/usr/bin/perl.exe "-MExtUtils::Command::MM" "-e" "test_harness(0, 
'blib/lib', 'blib/arch')" t/*.t
t/basic......ok
t/pod........ok
t/pod_cov....ok
t/recurse....ok
All tests successful.
Files=4, Tests=69,  2 wallclock secs ( 0.93 cusr +  0.73 csys =  1.66 CPU)
###################################

But you're right, of course, about the missing "-shared" being a (the?) 
problem. If I start with 'perl Makefile.PL LD="g++ -shared"' then everything 
works fine:

###################################
g++ -shared  -s -L/usr/local/lib Size.o  -o 
blib/arch/auto/Devel/Size/Size.dll  \
   /usr/lib/perl5/5.8/cygwin/CORE/libperl.dll.a    \

chmod 755 blib/arch/auto/Devel/Size/Size.dll
cp Size.bs blib/arch/auto/Devel/Size/Size.bs
chmod 644 blib/arch/auto/Devel/Size/Size.bs
/usr/bin/perl.exe "-MExtUtils::Command::MM" "-e" "test_harness(0, 
'blib/lib', 'blib/arch')" t/*.t
t/basic......ok
t/pod........ok
t/pod_cov....ok
t/recurse....ok
All tests successful.
Files=4, Tests=69,  3 wallclock secs ( 0.93 cusr +  0.79 csys =  1.72 CPU)
###################################

Apparently g++ needs a "-shared" but ld2 doesn't. (I don't understand that.)

And I don't understand what is achieved by:

gcc -shared -o 
 Size.dll -Wl,--out-implib=libSize.dll.a -Wl,--export-all-symbols -Wl,--enable-auto-import 
 -Wl,--stack,8388608 -Wl,--enable-auto-image-base \
-s -L/usr/local/lib Size.o  /usr/lib/perl5/5.8/cygwin/CORE/libperl.dll.a

That command gets run only if LD is ld2 - there doesn't seem to be a 
comparable command if LD is set to either "g++" or "g++ -shared".

Cheers,
Rob



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Re: [perl] Portably linking to libstdc++

[Brian Dessent]

Sisyphus wrote:

> Apparently g++ needs a "-shared" but ld2 doesn't. (I don't understand that.)
> 
> And I don't understand what is achieved by:
> 
> gcc -shared -o
>  Size.dll -Wl,--out-implib=libSize.dll.a -Wl,--export-all-symbols -Wl,--enable-auto-import
>  -Wl,--stack,8388608 -Wl,--enable-auto-image-base \
> -s -L/usr/local/lib Size.o  /usr/lib/perl5/5.8/cygwin/CORE/libperl.dll.a
> 
> That command gets run only if LD is ld2 - there doesn't seem to be a
> comparable command if LD is set to either "g++" or "g++ -shared".

/usr/bin/ld2 is a wrapper script that calls /usr/bin/perlld which is
another wrapper script that adds all those extra parameters if it
detects that a library is being linked.  So yet another workaround would
be to edit perlld and change "my $CC = 'gcc'" to g++.

Maybe you should try the current perl 5.10 where all these crufty
wrapper scripts are gone and it should work without any hacks.

Brian

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Re: [perl] Portably linking to libstdc++

[Reini Urban]

> I was doing some testing of someone else's upcoming release of Devel::Size
> (0.72), which
> has been significantly rewritten and is quite different to the current CPAN
> version (0.71).

I believe I was the one who rewrote it recently.

> If it does build for more recent cygwin perls, then I guess the matter has
> already been dealt with - and one can't ask for more than that :-)

The new Devel::Size works for sure with latest cygwin perl, because I
rewrote it :)
-- 
Reini Urban
http://phpwiki.org/              http://murbreak.at/

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