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Re: SHN_MIPS_SCOMMON

To: "H . J . Lu" <hjl@lucon.org>
Subject: Re: SHN_MIPS_SCOMMON
From: Ralf Baechle <ralf@oss.sgi.com>
Date: Sun, 22 Jul 2001 01:20:16 +0200
Cc: Greg Satz <satz@ayrnetworks.com>, linux-mips@oss.sgi.com
In-reply-to: <20010721120302.A10173@lucon.org>; from hjl@lucon.org on Sat, Jul 21, 2001 at 12:03:02PM -0700
References: <20010721104144.A17894@lucon.org> <B77F222C.888C%satz@ayrnetworks.com> <20010721111315.A9479@lucon.org> <20010721205659.B25928@bacchus.dhis.org> <20010721120302.A10173@lucon.org>
Sender: owner-linux-mips@oss.sgi.com
User-agent: Mutt/1.2.5i
On Sat, Jul 21, 2001 at 12:03:02PM -0700, H . J . Lu wrote:

> > Actually for all code; we don't support GP optimization in any of our code
> > models.
> 
> Even for the user space code?

Yes.  GP optimization isn't comparible with SVR4 PIC code.  I don't see a
fundamental problem to get that to work but gcc refuses the use of -G with
PIC code.

What would limit the value of the GP optimization is that for alot of code
a single 64kb GP data segment is not large enough; the IRIX compiler and
Alpha binutils afaik support a multi-gp code model already.

> Do you have a testcase to show what should be the desired behavior? As I
> understand, the SHN_MIPS_SCOMMON section only appears in the relocatable
> files. You won't see it in
> executables nor DSOs. Are there any problems with SHN_MIPS_SCOMMON
> in .o files? Can we always pass `-G 0' to the assemebler for Linux.

It's already guanteed that we never use GP optimization.  The particular
case which was reported by the user was caused ld directly which defaults to
-G 8.  That's not an issue for userspace.

  Ralf

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