From: "H. Peter Anvin" <hpa@zytor.com>
To: Harvey Harrison <harvey.harrison@gmail.com>
Cc: Olaf Hering <olaf@aepfle.de>,
Andrew Morton <akpm@linux-foundation.org>,
Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: Fw: asm-x86/byteorder.h, CONFIG_X86_BSWAP leaks to userland
Date: Sat, 26 Jul 2008 12:48:31 -0400 [thread overview]
Message-ID: <488B555F.4090709@zytor.com> (raw)
In-Reply-To: <1217090446.5971.57.camel@brick>
Harvey Harrison wrote:
>>
>> An undefined CONFIG_foo defaults to 0 (I think), so bswap is never used.
>> Is this done on purpose, or can the CONFIG_ foo be moved inside
>> __KERNEL__ somehow?
>
> I believe it's there to prevent the bswap instruction from being used on
> early x86_32 models (i386/i486). As this will be 0 in userspace it is
> effectively never using the bswap instruction for these routines.
>
i386, specifically.
However, you shouldn't leak these symbols to userspace; there is a
warning option in gcc for undefined macros, and it's a *good thing* to
use it. Causing warnings in user space is not nice.
> I'm not sure if it's time yet to make the bswap ones be exported, as they
> would no longer be usable for those early machines. X86 guys CC:d.
On i386 we still default to i386-compatible binaries; I *think* gcc has
macros telling you if the user has used -march=i486 etc.
-hpa
next prev parent reply other threads:[~2008-07-26 16:50 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20080726013931.bcc4682d.akpm@linux-foundation.org>
2008-07-26 16:40 ` Fw: asm-x86/byteorder.h, CONFIG_X86_BSWAP leaks to userland Harvey Harrison
2008-07-26 16:48 ` H. Peter Anvin [this message]
2008-07-26 16:59 ` Arjan van de Ven
2008-07-26 18:18 ` H. Peter Anvin
2008-07-26 17:00 ` Fw: " Harvey Harrison
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=488B555F.4090709@zytor.com \
--to=hpa@zytor.com \
--cc=akpm@linux-foundation.org \
--cc=harvey.harrison@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@elte.hu \
--cc=olaf@aepfle.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox