linux-kernel - Re: [PATCH 2/2] parisc: fix module loading failure of large modules

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Message-Id: <20081229161446.C91EB4EDA@hiauly1.hia.nrc.ca>
Date:	Mon, 29 Dec 2008 11:14:46 -0500 (EST)
From:	"John David Anglin" <dave@...uly1.hia.nrc.ca>
To:	deller@....de (Helge Deller)
Cc:	linux-parisc@...r.kernel.org, linux-kernel@...r.kernel.org,
	kyle@...artin.ca, randolph@...sq.org, jmm@...til.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	deller@....de
Subject: Re: [PATCH 2/2] parisc: fix module loading failure of large modules

Hi Helge,

> With this patch we now instead append individual PLT stub entries
> directly at the end of the code sections where the stubs are actually
> called. This reduces the distance between the PCREL location and the
> stub entry so that the relocations can be fulfilled.

GCC for PA-RISC assumes that the stubs will be placed before the code
section.  This is what HP-UX does.  It's also not possible to compute
the distance to the end of a function in GCC due to the way branch
shortening is done.  If the distance to the start of the code section
is too large, GCC outputs a long call.

If you can insert them before the code section where the stubs are
called, this will minimize the chance that a pc-relative call will
not reach its stub.

It is possible to put the stubs after the code section if you can ensure
the distance for each call isn't too large.  I believe GNU ld does some
consolidation of stub blocks.

Great patch!

Dave
-- 
J. David Anglin                                  dave.anglin@...-cnrc.gc.ca
National Research Council of Canada              (613) 990-0752 (FAX: 952-6602)
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