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Subject: Re: [perl] Portably linking to libstdc++
Date: Mon, 20 Oct 2008 23:48:10 +1100
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----- Original Message ----- 
From: "Brian Dessent" <brian AT dessent DOT 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 AT 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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