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Re: mips gas is horribly broken

To: hjl@lucon.org
Subject: Re: mips gas is horribly broken
From: Geoff Keating <geoffk@geoffk.org>
Date: Wed, 6 Jun 2001 12:32:15 -0700
Cc: binutils@sourceware.cygnus.com, linux-mips@oss.sgi.com
In-reply-to: <20010606091846.A21652@lucon.org> (hjl@lucon.org)
References: <20010606091846.A21652@lucon.org>
Reply-to: Geoff Keating <geoffk@redhat.com>
Sender: owner-linux-mips@oss.sgi.com
> Date: Wed, 6 Jun 2001 09:18:46 -0700
> From: "H . J . Lu" <hjl@lucon.org>
> Cc: linux-mips@oss.sgi.com
> Content-Disposition: inline
> User-Agent: Mutt/1.2.5i
> 
> Around line 9544 in gas/config/tc-mips.c, there are
> 
>         if (value != 0 && ! fixP->fx_pcrel)
>           {
>             /* In this case, the bfd_install_relocation routine will
>                incorrectly add the symbol value back in.  We just want
>                the addend to appear in the object file.
>                FIXME: If this makes VALUE zero, we're toast.  */
>             value -= S_GET_VALUE (fixP->fx_addsy);
>           }
> 
> I spent several days trying to figure out why libstdc++ was miscompiled
> on Linux/mipsel. That was because value was zero. That is totally
> unacceptable for gas to knowingly generate incorrect binaries. At
> least, we should do
> 
>             value -= S_GET_VALUE (fixP->fx_addsy);
>           assert (value != 0);
> 
> But I'd like to fix it once for all. Does anyone have any suggestions?

There is no easy fix.  This has been a longstanding problem, but any
change to bfd_install_relocation would require modifying every port in
a corresponding way, see for instance the FIXME at line 4816 or so in
tc-ppc.c.

-- 
- Geoffrey Keating <geoffk@geoffk.org>

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