Building an XIP application on arm-elf

[Jeff Johnston]

Shaun Jackman wrote:
> Hello,
> 
> I'd like to try my hand at building an XIP application with newlib for
> an arm-elf target. The application will be statically linked, so I'm
> not worried about shared libraries yet. To build the XIP application
> though, all the code has to be compiled as PIC. This includes libc, of
> course. Well, now I say of course. That fine point slipped my mind
> this morning.
> 
> Can newlib be coerced to build both a PIC and non-PIC libc.a in the
> same build tree? I suspect the answer is no. In which case I'll build
> the PIC libc.a in a separate build tree. I see newlib/configure has a
> --with-pic option. Should I use this? Or should I simply pass -fPIC on
> to the target's CFLAGS somehow?
> 

Newlib can only be coerced to build two or more versions of libc.a in 
the same build tree through a multilib option.  A multilib solution also 
automatically takes care of libgcc.a and any other target libraries for you.

The --with-pic option is for libtool's usage.  Using libtool requires 
you build on a native platform because it performs execution tests which 
won't run if you are doing a cross-build.  You have to specify libtool 
usage in the newlib configure.host file.  By default, libtool usage in 
newlib builds a shared library unless overridden by --disable-shared on 
the configure.  I am assuming you are building cross-platform in this case.

You can pass -fPIC on a newlib build by specifying TARGET_CFLAGS=-fPIC 
on the make call.

> Off-topic, will I likely have to do the same thing for libgcc.a?
>

Yes, the arm-linux configuration knows to add -fPIC, but not arm-elf, if 
I read the gcc/config/arm files correctly.  I'm not sure how you 
override the target flags in this case.

-- Jeff J.