Re: updating ebuilds for alpha, incude -fPIC.

Okay, here's the deal with -fPIC:

PIC stands for "Position Independent Code". This means that the code can 
be loaded into any address in memory and still work okay. All the 
pointers are stored as addresses relative to their block of code, rather 
than absolute addresses in memory. This requires a little compiler 
overhead to convert the fixed addresses to relative ones, and then a 
little runtime overhead to resolve these relative addresses to actual 
memory locations. It also makes the objects a little bigger, as it has 
to keep extra information to help the loader fill in unresolved 
addresses at runtime.

Here's the important bit: All code in shared librares must be PIC.

On certain architectures (like, I believe, i386), because of the way 
memory stuff is laid out, all code is automatically position 
independent. This is why people in x86-land sometimes forget to force 
shared library code to be compiled with -fPIC. Thins like libtool 
handles this automatically, so it usually isn't a problem, but there are 
other cases where it is. Such as xfree.

Sigurd Stordal wrote:	[Wed Jun 25 2003, 07:24:16AM EDT]

 >I've seen for ebuilds like xfree 4.3, that there is no -fPIC in the
 >allowed cflags, this makes sense for x86, but if I have understood
 >right, it's nearly a requirement for the alpha architecture.

It's a requirement for *shared libraries* on alpha. We don't want to 
compile everything with -fPIC, because that would make everything bigger 
and slower. Only the parts that are going into shared libraries need 
-fPIC. The problem with xfree 4.3 was that a new module (shared object) 
was including parts of libz.a (static library, not normally compiled 
with -fPIC). Compiling libz.a with -fPIC fixes the problem, and that's 
the fix we chose to use.

If you merged xfree-4.3.0-r3 with -fPIC in CFLAGS, you may want to 
re-merge now that there's a bugfix.

Hope this clears things up a bit.

-will

(for more info:)
http://www.llnl.gov/casc/components/docs/users_guide/node56.html
http://sources.redhat.com/autobook/autobook/autobook_71.html


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