linux-kernel - Re: [PATCH] ext4: improve str2hashbuf by processing 4-byte chunks

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] [day] [month] [year] [list]

Message-ID: <20251121115931.411ab538@pumpkin>
Date: Fri, 21 Nov 2025 11:59:31 +0000
From: David Laight <david.laight.linux@...il.com>
To: Andreas Schwab <schwab@...ux-m68k.org>
Cc: "Theodore Tso" <tytso@....edu>, Guan-Chun Wu <409411716@....tku.edu.tw>,
 Andreas Dilger <adilger.kernel@...ger.ca>, linux-ext4@...r.kernel.org,
 linux-kernel@...r.kernel.org, visitorckw@...il.com
Subject: Re: [PATCH] ext4: improve str2hashbuf by processing 4-byte chunks

On Fri, 21 Nov 2025 11:55:26 +0100
Andreas Schwab <schwab@...ux-m68k.org> wrote:

> On Nov 20 2025, Theodore Tso wrote:
> 
> > Secondly, it's not that a promotion happens before "any" arithmetic.
> > If we add two 8-bit values together, promotion doesn't happen.  
> 
> That is not true.  Integer promotion is applied individually to each
> operand independent of context.

True.

You can think of the promotion happening every time a 'variable' is
read into a cpu register for any operation (including an assignment).

Similarly every write to a variable discards the high bits.

	David