From: David Laight <David.Laight@ACULAB.COM>
To: 'Alexander Potapenko' <glider@google.com>,
"paulmck@linux.ibm.com" <paulmck@linux.ibm.com>,
"hpa@zytor.com" <hpa@zytor.com>,
"peterz@infradead.org" <peterz@infradead.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"dvyukov@google.com" <dvyukov@google.com>,
"jyknight@google.com" <jyknight@google.com>,
"x86@kernel.org" <x86@kernel.org>,
"mingo@redhat.com" <mingo@redhat.com>
Subject: RE: [PATCH v2] x86/asm: fix assembly constraints in bitops
Date: Tue, 2 Apr 2019 11:45:20 +0000 [thread overview]
Message-ID: <4c6a1e592fd345618ef7b7d5bee592da@AcuMS.aculab.com> (raw)
In-Reply-To: <20190402112813.193378-1-glider@google.com>
From: Alexander Potapenko
> Sent: 02 April 2019 12:28
>
> 1. Use memory clobber in bitops that touch arbitrary memory
>
> Certain bit operations that read/write bits take a base pointer and an
> arbitrarily large offset to address the bit relative to that base.
Although x86_64 can use a signed 64bit bit number, looking at arm and arm64
they use 'int nr' throughout as do the generic functions.
Maybe x86 ought to be consistent here.
I doubt negative bit numbers are expected to work?
Did you try telling gcc that a big buffer (250MB is the limit for 32bit)
from the pointer might be changed?
That ought to be softer than a full 'memory' clobber as it should
only affect memory that could be accessed through the pointer.
....
> -#define BITOP_ADDR(x) "+m" (*(volatile long *) (x))
> +#define RLONG_ADDR(x) "m" (*(volatile long *) (x))
> +#define WBYTE_ADDR(x) "+m" (*(volatile char *) (x))
>
> -#define ADDR BITOP_ADDR(addr)
> +#define ADDR RLONG_ADDR(addr)
Is it worth just killing ADDR ?
(as a different patch)
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2019-04-02 11:44 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-02 11:28 [PATCH v2] x86/asm: fix assembly constraints in bitops Alexander Potapenko
2019-04-02 11:33 ` Alexander Potapenko
2019-04-02 11:45 ` David Laight [this message]
2019-04-02 12:35 ` Alexander Potapenko
2019-04-02 12:37 ` Alexander Potapenko
2019-04-05 9:39 ` Ingo Molnar
2019-04-05 11:12 ` David Laight
2019-04-05 11:53 ` Alexander Potapenko
2019-04-06 8:20 ` Ingo Molnar
2019-04-06 8:46 ` [tip:x86/urgent] x86/asm: Use stricter " tip-bot for Alexander Potapenko
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=4c6a1e592fd345618ef7b7d5bee592da@AcuMS.aculab.com \
--to=david.laight@aculab.com \
--cc=dvyukov@google.com \
--cc=glider@google.com \
--cc=hpa@zytor.com \
--cc=jyknight@google.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=paulmck@linux.ibm.com \
--cc=peterz@infradead.org \
--cc=x86@kernel.org \
/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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.