linux-kernel - Re: [PATCH] objtool: fix objtool regression on x32 systems

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Date:   Tue, 17 May 2022 11:42:12 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Laight <David.Laight@...lab.com>
Cc:     Mikulas Patocka <mpatocka@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] objtool: fix objtool regression on x32 systems

On Tue, May 17, 2022 at 08:26:42AM +0000, David Laight wrote:
> From: Peter Zijlstra
> > Sent: 16 May 2022 22:25
> ...
> > A quick look seems to suggest at least all the 'offset' fields should be
> > u64 or something. The only reason that works is because -mcmodel=kernel
> > keeps everything in the 2G range to make s32 immediates work. But it
> > isn't right.
> 
> Offsets in instructions are only 8bit or 32bit.
> The mod/reg/rm and SiB encodings don't support anything else.
> If offsets might be large then they have to be loaded into
> registers - which will slow things down.

Not relevant; these are Elf64_Addr fields, objtool currently uses
'unsigned long' for them, but that goes sideways if ILP32.