Position Independent Code usage on x86-64

[Alexey Skidanov]

Ok. Thanks.
I don't really understand ALL technical details in a found link. Could
you explain this briefly (or refer me to other sources).

Thank you,
Alexey  

-----Original Message-----
From: Andrew Haley [mailto:aph@redhat.com] 
Sent: Wednesday, December 16, 2009 4:58 PM
To: Alexey Skidanov
Cc: gcc-help@gcc.gnu.org
Subject: Re: Position Independent Code usage on x86-64

Alexey Skidanov wrote:

> We ported our code to 64 bit (CentOS 5.2 64 bit). We have some static
> library that linked with some shared library. In 32 bit version, the
> shared library was successfully created. Trying to create it in with
64
> bit version compiler, we get the error: 
> 
> /usr/bin/ld: .//libstatic.a(static.o): relocation R_X86_64_32 against
> `__gxx_personality_v0' can not be used when making a shared object;
> recompile with -fPIC
> .//libstatic.a: could not read symbols: Bad value
> collect2: ld returned 1 exit status
> 
> We also found that if static library is linked with shared library
then
> it should be compiled with -fPIC option. But if the static library is
> linked with ELF executable it shouldn't.

It can be, but it's not absolutely nmecessary.

> The questions are:
> 1. Does it make sense that we need to know about static library exact
> usage? 
> 2. Is there an option of gcc that "generate" backward compatible (with
> 32 bit version) compilation/linking process? 

No.  You best option is always to link with the -fPIC option all code
that
may go into shared libraries.  It won't hurt 32-bit libraries, and it
may
save memory.

> We found some explanation here
> http://www.technovelty.org/code/c/amd64-pic.html

That seems right.  What more do you need?

Andrew.