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Re: What does --with-pic really mean?

From: Ralf Wildenhues
Subject: Re: What does --with-pic really mean?
Date: Mon, 29 Oct 2007 07:17:17 +0100
User-agent: Mutt/1.5.16 (2007-10-15)

Hello Kent,

* Kent Boortz wrote on Sun, Oct 28, 2007 at 11:34:13PM CET:
> I use --with-pic for builds created with autoconf/automake assuming
> that everything in the build will be compiled with the PIC flag. But
> examining the logs some compile lines lacks the PIC flag. The configure
> flag seems not to mean what it says when you do "./configure --help"
>   --with-pic  try to use only PIC/non-PIC objects [default=use both]
> >From reading the generated configure script, it seems to me that the
> flag --with-pic only affects libraries under "libtool control",

Yes, that is true.  This switch is provided by Libtool.

> i.e.  the help text is a bit misleading.

Can you suggest a better text that is less misleading and not too long,

BTW, --with-pic is regarded as rather useless, as libtool will choose
the right objects when creating shared libraries anyway.  Why do you
want all objects to be PIC?  Just in case: if you're out for PIE
executables, then really with GCC you should specify -pie in CFLAGS.

> The flag is in fact originating
> from "libtool.m4". So unless your libraries are "libtool convenience
> libraries", the compile lines will not have any PIC flags at all.

Yes.  And real shared libraries created by libtool will have PIC

> Reading the generated make files the reason seems to be that "normal"
> libraries are built from "*.o" files where the "*.o" files are the
> intermediate targets, not using libtool at all. But libtool
> convenience libraries are built from ".libs/*.o" files created where
> "*.lo" are the intermediate targets, and libtool was used. And no
> libtool usage, no reaction on the --with-pic.


If I knew more about why you want PIC objects, then I could say which of
the two (convert all libraries to libtool-controlled ones, or just put
the pic flag in CFLAGS) would be more appropriate.  Note that libtool
convenience archives are not intended to be installed, for consistency

Hope that helps.


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