linux-kernel - Re: [patch 4/7] Immediate Values

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <46F14A58.60904@zytor.com>
Date:	Wed, 19 Sep 2007 09:12:08 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@....de>,
	Chuck Ebbert <cebbert@...hat.com>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [patch 4/7] Immediate Values - i386 Optimization

Mathieu Desnoyers wrote:
> 
> Ok, let's have a good look at what we want:
> 
> 1 - get a pointer to the beginning of the immediate value within the
>     instruction.
> 2 - make sure that the immediate value, within the instruction, is
>     written to atomically wrt all CPUs, even on older architectures
>     where non aligned writes are not atomic.
> 

I think you'll find that even on modern architectures cross-cacheline
writes aren't atomic.

Anyway, disregard the bit I mentioned about one byte longer; I've been
staring myself too blind at instruction variants lately (lots of
arguments about how to generate various instructions using NASM syntax).

> 
> * 4 bytes
> B8 + rd         MOV r32, imm32   (1 byte opcode)
> C7 /0           MOV r/m32, imm32 (2 bytes opcode)
> (the 2 bytes opcode can be a problem)
> 

If gas generates the C7 opcodes by default, then that's a bug, nothing less.

	-hpa
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/