AIX & shared libstdc++

AIX & shared libstdc++

[Andrey Slepuhin]

Hi,

I tried to build egcs-970929 on AIX 4.2.1 configured with
--enable-shared
option. The resulting shared libstdc++ was only ~600K instead of ~3M
static one.
This is because AIX linker does not know what symbols must be exported.
Passing option -bexpall to linker did not solve the problem, so I tried
to build export file manually by hacking makeC++SharedLib script. After
removing some symbols causing linker warnings from resulting export
file,
I obtain shared libstdc++ with size ~2.3M and I can successfully link my
programs with this library.
I'm not sure that all my operation were correct and I can't check if all
necessary symbols are included into the export file. But it seems to me,
that the only way to receive correct shared version of libstdc++ on AIX
is to use explicit export file. Any help will be appreciated.

Regards,

Andrey Slepuhin,
Moscow State University

PS: Passing option -unix to linker is incorrect on AIX, because AIX
linker
    recognize it as option -u with a parameter "nix". As a result there
are
    many linker warnings.

Re: AIX & shared libstdc++

[David Edelsohn]

>>>>> Andrey Slepuhin writes:

Andrey> I tried to build egcs-970929 on AIX 4.2.1 configured with
Andrey> --enable-shared
Andrey> option. The resulting shared libstdc++ was only ~600K instead of ~3M
Andrey> static one.
Andrey> This is because AIX linker does not know what symbols must be exported.
Andrey> Passing option -bexpall to linker did not solve the problem, so I tried
Andrey> to build export file manually by hacking makeC++SharedLib script. After
Andrey> removing some symbols causing linker warnings from resulting export
Andrey> file,
Andrey> I obtain shared libstdc++ with size ~2.3M and I can successfully link my
Andrey> programs with this library.
Andrey> I'm not sure that all my operation were correct and I can't check if all
Andrey> necessary symbols are included into the export file. But it seems to me,
Andrey> that the only way to receive correct shared version of libstdc++ on AIX
Andrey> is to use explicit export file. Any help will be appreciated.

	I am somewhat surprised that -bexpall does not export all
necessary symbols.  That is not the default because it can cause
significant bloat and is not the way that XLC operates.  AIX linker
performs garbage collection on symbols and removes any symbols which are
not referenced or exported.  If -bexpall does not trivially work around
the problem, one must use something like makeC++SharedLib.  Note: IBM's
C++ compiler and G++ use different name mangling schemes, so assumptions
about the internal structure of C++ symbols is incorrect.

Andrey> PS: Passing option -unix to linker is incorrect on AIX, because AIX
Andrey> linker
Andrey> recognize it as option -u with a parameter "nix". As a result there
Andrey> are
Andrey> many linker warnings.

	Who is passing -unix option to linker?  That is not in the GCC
specs.  Does libstdc++ assume that?

David

Re: AIX & shared libstdc++

[David Edelsohn]

>>>>> Andrey Slepuhin writes:

Andrey> 1) I obtain many warnings about undefined symbols which are really class names
Andrey> themselves (for example, range_error), so I remove these symbols from export
Andrey> file.

	This may depend on the type of symbol.  I do not know how class
names appear as symbols and how this would appear in an exports list.  A
class name is not an actual method or member.

Andrey> 2) When linking programs with shared libstdc++, I obtain warnings about
Andrey> multiple defined symbols like __eh<something>. After removing these symbols
Andrey> all my test programs linked and worked fine.

	As mentioned in the README.RS6000 file, AIX 4.1 linker became much
more pedantic about warning of duplicate symbols.  These always have been
there and should not affect correctness of the resulting executable.

Andrey> 3) I am worried about shared libstdc++ size (2.3M instead of 3M static). This
Andrey> can be caused differences in library structure (for example a large number of
Andrey> separate modules in ar file), but I cannot check this.

	*Shrug*

David

Re: AIX & shared libstdc++

[Andrey Slepuhin]

David Edelsohn wrote:
>         I am somewhat surprised that -bexpall does not export all
> necessary symbols.  That is not the default because it can cause
> significant bloat and is not the way that XLC operates.  AIX linker
> performs garbage collection on symbols and removes any symbols which are
> not referenced or exported.  If -bexpall does not trivially work around
> the problem, one must use something like makeC++SharedLib.  Note: IBM's
> C++ compiler and G++ use different name mangling schemes, so assumptions
> about the internal structure of C++ symbols is incorrect.
Some times ago I experimented on building shared libs with GCC 2.7.2
and I had to hack makeC++SharedLib to do this. So, I was surprised that
I obtain export list without any problems. The only things I cannot
understand are the following:
1) I obtain many warnings about undefined symbols which are really class names
themselves (for example, range_error), so I remove these symbols from export
file.
2) When linking programs with shared libstdc++, I obtain warnings about
multiple defined symbols like __eh<something>. After removing these symbols
all my test programs linked and worked fine.
3) I am worried about shared libstdc++ size (2.3M instead of 3M static). This
can be caused differences in library structure (for example a large number of
separate modules in ar file), but I cannot check this.

> Andrey> PS: Passing option -unix to linker is incorrect on AIX, because AIX
> Andrey> linker
> Andrey> recognize it as option -u with a parameter "nix". As a result there
> Andrey> are
> Andrey> many linker warnings.
> 
>         Who is passing -unix option to linker?  That is not in the GCC
> specs.  Does libstdc++ assume that?

Yes. Jason Merrill said that this option is needed for gnu ld. Did you try
to build egcs configured with --with-gnu-ld option?

Andrey.

Re: AIX & shared libstdc++

[Andrey Slepuhin]

Ian Lance Taylor wrote:
> 
>    Date: Thu, 09 Oct 1997 20:01:20 +0400
>    From: Andrey Slepuhin <pooh@msu.ru>
> 
>    3) Even the simple test program failed to run with message about exec
>    format error due to bad text alignment.
>    It seems to me that problem is not with egcs but with gnu ld which
>    generates
>    invalid executables. Any help is appreciated.
> 
> You're right; the GNU linker doesn't work on AIX 4.2.  It's possible
> that the appended patch to ld/emultempl/aix.em will fix the immediate
> problem.  There may be other problems.

Thanks for the help - it seems that your patch works fine. At least I
just
successfully build omniORB2 with egcs-971008 configured with
--enable-shared
--with-gnu-ld. The only problem was with multiple defined symbol
_mutex_global_np
in pthread.h (native linker ignores multiple defined symbols; this
symbol is not
defined as extern - this looks like IBM bug).

Andrey.

Re: AIX & shared libstdc++

[Ian Lance Taylor]

   Date: Thu, 09 Oct 1997 20:01:20 +0400
   From: Andrey Slepuhin <pooh@msu.ru>

   3) Even the simple test program failed to run with message about exec
   format error due to bad text alignment.
   It seems to me that problem is not with egcs but with gnu ld which
   generates
   invalid executables. Any help is appreciated.

You're right; the GNU linker doesn't work on AIX 4.2.  It's possible
that the appended patch to ld/emultempl/aix.em will fix the immediate
problem.  There may be other problems.

Ian

Index: aix.em
===================================================================
RCS file: /cvs/cvsfiles/devo/ld/emultempl/aix.em,v
retrieving revision 1.20
retrieving revision 1.21
diff -u -r1.20 -r1.21
--- aix.em	1997/06/16 16:56:24	1.20
+++ aix.em	1997/09/04 16:43:35	1.21
@@ -361,8 +361,8 @@
 				    exp_nameop (NAME, "."),
 				    exp_intop (0xfff)));
 	  t = exp_binop ('&',
-			 exp_binop ('+', t, exp_intop (7)),
-			 exp_intop (~ (bfd_vma) 7));
+			 exp_binop ('+', t, exp_intop (31)),
+			 exp_intop (~ (bfd_vma) 31));
 	  lang_section_start (".data", t);
 	}
       break;
@@ -382,8 +382,8 @@
 			 exp_intop (val),
 			 exp_nameop (SIZEOF_HEADERS, NULL));
 	  t = exp_binop ('&',
-			 exp_binop ('+', t, exp_intop (7)),
-			 exp_intop (~ (bfd_vma) 7));
+			 exp_binop ('+', t, exp_intop (31)),
+			 exp_intop (~ (bfd_vma) 31));
 	  lang_section_start (".text", t);
 	}
       break;

Re: AIX & shared libstdc++

[Andrey Slepuhin]

Hi,
I tried to compile egcs-971008 on AIX 4.2.1 configured with option
--with-gnu-ld.
1) I had problems when installing binutils 2.8.1 because function
finfo()
already defined in unistd.h with parameters different from finfo() that
comes
with binutils distribution (solved by renaming this function and all
calls to it).
2) Compilation was successful except the attempt of making unexistent
target
"libs" in libraries/soft-float/powerpc/libstdc++/Makefile (why???).
Shared libstdc++ was created successfully with a size ~2.5M
3) Even the simple test program failed to run with message about exec
format error due to bad text alignment.
It seems to me that problem is not with egcs but with gnu ld which
generates
invalid executables. Any help is appreciated.

Andrey.

PS: egcs-970929, with manually built shared libstdc++ (with native ld)
still
    works without errors. I just successfully compiled and tested
omniORB2,
    and it seems that combination of shared libstdc++, multithreading
and
    exceptions works fine.

Re: AIX & shared libstdc++

[Andrey Slepuhin]

Jason Merrill wrote:
> GCC support for shared libraries on AIX requires GNU ld, which supports the
> -unix flag.

The following line:
  * configure.in: Don't configure --with-gnu-ld on AIX
in file ChangeLog is not overrided yet (though it is dated Apr 25 1996
:-)).
Does anybody checked whether current snapshot can be configured with
this option? Can this be done with current version of binutils?
And the last: is shared libraries support with native ld possible in
principle?

Andrey

Re: AIX & shared libstdc++

[Jason Merrill]

>>>>> Andrey Slepuhin <pooh@msu.ru> writes:

> I tried to build egcs-970929 on AIX 4.2.1 configured with
> --enable-shared
> option. The resulting shared libstdc++ was only ~600K instead of ~3M
> static one.
> This is because AIX linker does not know what symbols must be exported.

> PS: Passing option -unix to linker is incorrect on AIX, because AIX
> linker recognize it as option -u with a parameter "nix". As a result
> there are many linker warnings.

GCC support for shared libraries on AIX requires GNU ld, which supports the
-unix flag.

Jason