[U-Boot] arm: wrong Relocation and not cleared BSS

From: Heiko Schocher <hs@denx.de>
To: u-boot@lists.denx.de
Subject: [U-Boot] arm: wrong Relocation and not cleared BSS
Date: Sun, 31 Oct 2010 08:43:44 +0100	[thread overview]
Message-ID: <4CCD1E30.6060800@denx.de> (raw)
In-Reply-To: <4CCC18E7.8080708@ahsoftware.de>

Hello Alexander,

Alexander Holler wrote:
> to give the topic a better meaning and to summarize what I think is
> currently happening along with some "pictures" for a better understanding:
> 
> We are starting with code (c) and data (d) somewhere in the memory:
> 
> ----------
> |cd      |
> ----------
> 
> The relocation in start.S should achieve this:
> 
> ----------
> |      cd|
> ----------

Yep, and this works fine on boards, I have access(
arm1136 qong, arm926ejs tx25, suen3 arm926ejs kirkwood,
mx25 magnesium, armv7 omap3_beagle)

> That means code and data should be moved upwards. What
> currently is happening is the following:
> 
> ----------
> | d    c |
> ----------

really?

I posted you on 27.10.2010 in u-boot%irc.freenode.org (couldn;t
find this in the history :-(  )  a log on the tx25, where this works
fine, and we came to the opinion, that you maybe have problems
with your toolchain! IIRC you use gcc-4.5x ... Alexander, did
you tried (as you thought to do) ELDK-4.2 with gcc-4.2.x ?

Are you sure your toolchain works correct with -pie?

> The code is moved upwards, but that code still uses the data at d.
> This results another problem: Some parts in the code are assuming that d
> is cleared (set to zero in start.S). But what start.S does it to clear
> the new location (z in the picture below).
> 
> ----------
> | d    cz|
> ----------

which is OK.

> Because the code (c) still uses the data (bss) in d and not in z, some
> hard to find errors might occur because the used data isn't set to zero
> as required.

Yep, an that is, what you(we?) have to find out, why this not works
with your toolchain!

> I have almost no knowledge about how gcc and the binutils are handling
> relocation, therfore I can't help much further here. What I think is
> part of the problem, is that -fPIC was removed. Using -pie in LDFLAGS
> might be used to get relocatable code, but the data will not be
> relocated. And I would wonder if that is possible without instructing
> the compiler to build stuff for relocation (-fPIC).

Try to find out, why -pie not works with your tollchain!

bye,
Heiko
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