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Re: x86-64 and large code model questions/bugs
On Tue, Jan 27, 2009 at 09:33:17AM -0800, Steve Ellcey wrote:
> On Tue, 2009-01-27 at 12:31 +0100, Andi Kleen wrote:
> > Steve Ellcey <sje@cup.hp.com> writes:
> >
> > > because the crt files can't handle the large code model if they aren't
> > > compiled with this option.
> >
> > My understanding is that this would likely break old linkers which
> > didn't do all large model relocations correctly. Right now they
> > work as long as you don't need the large model.
>
> Are these old GNU linkers or old system/non-GNU linkers? We often
(not that old actually) GNU linkers.
> require a certain minimum version of binutils for GCC to work.
That would be pretty extreme for something as obscure as large model.
>
> > BTW the standard way to work around large model issues if your
> > code isn't really that large but you just want to move it is to move
> > parts of the programs into a .so and compile -fPIC. large is only
> > really needed if you really have gigantic programs (but then gcc
> > tends to be also quite slow on them)
>
> It's not really a gigantic program, it is a program where he wants to
> put all his text in the upper address range (using the --section-start
> option of the GNU linker).
He'll get much better code by putting the program into a -fPIC .so,
loading it from a small stub and then unmap the stub.
large model generates really very bad code because all jumps
will be indirect.
-Andi
--
ak@linux.intel.com -- Speaking for myself only.