[Linux-ia64] Re: PROPOSED: 32/64 bit coexistance

[David Mosberger <davidm@hpl.hp.com>]

>>>>> On Tue, 18 Sep 2001 10:34:50 +0200, Andreas Jaeger <aj@suse.de> said:

  Andreas> George, you forgot to add the appended part.  Especially
  Andreas> the paragraph is important that this will not imply a
  Andreas> binary incompatible change for ia64, ia64 has an emulation
  Andreas> for 32-bit binaries but is not a real 32/64-bit platform
  Andreas> like Sparc64, x86-64, PPC64 and S390.

  Andreas> David, does this satisfy your ia64 concerns?

To be honest, I think the description is confusing and incomplete.
This is because it doesn't clearly distinguish between code model and
data model.  On ia64, there are presently two code models (x86 and
ia64) and two data models (ILP32 and LP64).  It turns out that three
of the four resulting possibilities make sense:

  (1) ia64/ilp32
  (2) ia64/lp64
  (3) x86/ilp32

In the future, there could be others.  For example, I'm pretty sure
that Alpha->ia64 binary translators are in the process of being
written and on a Compaq system, it could make sense to have
"alpha/lp64", for example.

I think LSB is correct in suggesting /libXX for the native code model
and "something" else for emulated code models.  /opt/emu32 is clearly
a silly name though: it mixes up the data model and the code model
again.  For the IA-64 Linux project, we're currently using
/emul/ia32-linux for the IA-32 subsystem.  (If there is strong
objection and good reasons to reject the "/emul" prefix, I suppose we
could use /opt/emu/ia32-linux/ instead.)

A related question is whether /emul/ is reserved for "same OS"
emulation.  E.g., where would a Windows emulator go?  If /emul/ only
ever contains Linux emulators, then we could change the prefix to
/emul/ia32/ but, from a user perspective, I think it would be
preferable if /emul/ were allowed to contain foreign OS emulators as
well.

Now, as far as /libXX is concerned: in my opinion, /lib should contain
the "native" or "preferred" library format (primarily for source
compatibility and user convenience reasons).  LSB is in denial if it
claims /lib is used for 32-bit libraries only.  Both IA-64 and Alpha
use it for 64-bit libraries and if, god forbid, someone ever added
ILP32 support to IA-64 Linux, those libraries would certainly go into
/lib32 or something of that sort.  LSB should consider and accommodate
this case.

Thanks,

	--david