From: David Laight <David.Laight@ACULAB.COM>
To: 'Peter Zijlstra' <peterz@infradead.org>,
Mikulas Patocka <mpatocka@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Josh Poimboeuf <jpoimboe@redhat.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] objtool: fix objtool regression on x32 systems
Date: Tue, 17 May 2022 08:26:42 +0000 [thread overview]
Message-ID: <738a941ba2ff4e2db8f2268b281d9bd5@AcuMS.aculab.com> (raw)
In-Reply-To: <20220516212517.GP76023@worktop.programming.kicks-ass.net>
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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Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2022-05-17 8:27 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-16 15:06 [PATCH] objtool: fix objtool regression on x32 systems Mikulas Patocka
2022-05-16 15:41 ` Peter Zijlstra
2022-05-16 15:56 ` Mikulas Patocka
2022-05-16 21:25 ` Peter Zijlstra
2022-05-17 8:26 ` David Laight [this message]
2022-05-17 9:42 ` Peter Zijlstra
2022-05-18 13:28 ` [PATCH v2] " Mikulas Patocka
2022-05-18 18:08 ` Josh Poimboeuf
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