linux-kernel - Re: replace "memset(...,0,PAGE_SIZE)" calls with "clear

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: <Pine.LNX.4.64.0612301750550.16519@localhost.localdomain>
Date:	Sat, 30 Dec 2006 18:04:14 -0500 (EST)
From:	"Robert P. J. Day" <rpjday@...dspring.com>
To:	Arjan van de Ven <arjan@...radead.org>
cc:	Denis Vlasenko <vda.linux@...glemail.com>,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: replace "memset(...,0,PAGE_SIZE)" calls with "clear_page()"?

On Sat, 30 Dec 2006, Arjan van de Ven wrote:

> rday wrote:

> > ... most of the definitions of the clear_page() macro are simply
> > invocations of memset().  see for yourself:

> *MOST*. Not all.

i did notice that.  while the majority of the architectures simply
define clear_page() as a macro calling memset(ptr, 0, PAGE_SIZE), the
rest will implement it in assembler code for whatever reason.  (i'm
assuming that *every* architecture *must* define clear_page() one way
or the other, is that correct?  that would seem fairly obvious, but
i just want to make sure i'm not missing anything obvious.)

> clear_page() is supposed to be for full real pages only... for
> example it allows the architecture to optimize for alignment, cache
> aliasing etc etc.

fair enough.  *technically*, not every call of the form
"memset(ptr,0,PAGE_SIZE)" necessarily represents an address that's on
a page boundary.  but, *realistically*, i'm guessing most of them do.
just grabbing a random example from some grep output:

arch/sh/mm/init.c:
  ...
  /* clear the zero-page */
  memset(empty_zero_page, 0, PAGE_SIZE);
  ...

my only point here is that, given that every architecture needs to
supply some kind of definition of a "clear_page()" routine, one would
think that *lots* of those memset() calls could reasonably be
rewritten as a clear_page() call for improved readibility, no?

and there are a *lot* of memset() calls like that.

rday
-
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/