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Forum Topic - [Q] on build a DLL from static shared objects:

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Hans-Peter Reichert

10/08/2009 3:51 AM

post39571

[Q] on build a DLL from static shared objects

we are trying to build a shared object out of static shared archives only,
but the resulting .SO does not have any exported symbols.
As the S.a archives are all compiled using -fPIC and the functions are global, we would expect that the resulting .SO 
will contain the symbols from S.a files - but this is not working.
We tried to use a version script to explicitly declare the functions that should be exported, but it's not working.
So is it possible at all, to generate a .SO out of S.a files only?
are we doing something wrong, or what has to be done that a function from S.a file gets exported from within the build .
SO file?

any suggestions?
TIA
/hp

Ryan Mansfield(deleted)

10/08/2009 8:35 AM

post39584

Re: [Q] on build a DLL from static shared objects

Hans-Peter Reichert wrote:
> we are trying to build a shared object out of static shared archives only,
> but the resulting .SO does not have any exported symbols.
> As the S.a archives are all compiled using -fPIC and the functions are global, we would expect that the resulting .SO 
will contain the symbols from S.a files - but this is not working.
> We tried to use a version script to explicitly declare the functions that should be exported, but it's not working.
> So is it possible at all, to generate a .SO out of S.a files only?
> are we doing something wrong, or what has to be done that a function from S.a file gets exported from within the build
 .SO file?
> 
> any suggestions?

You can use force the entire archive into the shared object using 
--whole-archive. Otherwise ld will only pull the required objects from 
the archive.

Regards,

Ryan Mansfield

Daniel Weber

10/09/2009 2:00 AM

post39655

Re: [Q] on build a DLL from static shared objects

> You can use force the entire archive into the shared object using 
> --whole-archive. Otherwise ld will only pull the required objects from 
> the archive.

I did not know that flag, thanks. I also had to add --no-whole-archive after our own libs to avoid pulling in everything
 else, too. It works on the command line if all archives are listed directly. But in our automated build, we use a 
linker script file to provide the list of libraries (to avoid running into command line limits). These scripts contain 
an INPUT command per archive.
==> 
This works fine:
   qcc ... -Wl,--whole-archive liboneS.a libtwoS.a -Wl,--no-whole-archive ...

This doesn't:
   qcc ... -Wl,--whole-archive all_my_libs.txt -Wl,--no-whole-archive ...
where all_my_libs.txt is something like
   INPUT(liboneS.a)
   INPUT(libtwoS.a)

Should --whole-archive also affect the archives listed in the linker script (i.e. "is this a bug?")? Or is there another
 command we could use in the script?

Regards,
Daniel

Ryan Mansfield(deleted)

10/13/2009 1:39 PM

post39801

Re: [Q] on build a DLL from static shared objects

Daniel Weber wrote:
>> You can use force the entire archive into the shared object using 
>> --whole-archive. Otherwise ld will only pull the required objects from 
>> the archive.
> 
> I did not know that flag, thanks. I also had to add --no-whole-archive after our own libs to avoid pulling in 
everything else, too. It works on the command line if all archives are listed directly. But in our automated build, we 
use a linker script file to provide the list of libraries (to avoid running into command line limits). These scripts 
contain an INPUT command per archive.
> ==> 
> This works fine:
>    qcc ... -Wl,--whole-archive liboneS.a libtwoS.a -Wl,--no-whole-archive ...
> 
> This doesn't:
>    qcc ... -Wl,--whole-archive all_my_libs.txt -Wl,--no-whole-archive ...
> where all_my_libs.txt is something like
>    INPUT(liboneS.a)
>    INPUT(libtwoS.a)
> 
> Should --whole-archive also affect the archives listed in the linker script (i.e. "is this a bug?")? Or is there 
another command we could use in the script?

It's a bug. I've filed a PR and I have a fix for it. If you want I can 
provide an experimental linker or you can submit a ticket and we can get 
an official one to you.

Regards,

Ryan Mansfield

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