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

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Message-ID: <738a941ba2ff4e2db8f2268b281d9bd5@AcuMS.aculab.com>
Date:   Tue, 17 May 2022 08:26:42 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Peter Zijlstra' <peterz@...radead.org>,
        Mikulas Patocka <mpatocka@...hat.com>
CC:     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

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.

Immediates can be 64bit (but not if the addressing mode
includes an offset).

	David

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