From: Andy Lutomirski <luto@amacapital.net>
To: "H. Peter Anvin" <hpa@zytor.com>,
behanw@converseincode.com, tglx@linutronix.de, mingo@redhat.com,
x86@kernel.org, peterz@infradead.org, ak@linux.intel.com,
oleg@redhat.com
Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86: LLVMLinux: Reimplement current_stack_pointer without register usage.
Date: Tue, 25 Feb 2014 19:00:29 -0800 [thread overview]
Message-ID: <530D58CD.4080202@mit.edu> (raw)
In-Reply-To: <5306DC49.4060603@zytor.com>
On 02/20/2014 08:55 PM, H. Peter Anvin wrote:
> This seems like really deep magic when looking at it... at the very
> least, this needs to be very carefully commented, including why it works
> on the various platforms.
>
> How much does this actually affect the output? I only see three uses of
> current_stack_pointer:
>
> /* how to get the thread information struct from C */
> static inline struct thread_info *current_thread_info(void)
> {
> return (struct thread_info *)
> (current_stack_pointer & ~(THREAD_SIZE - 1));
> }
>
> ... here we need the mov anyway, because we have to then AND it with a
> mask, which we obviously can't do inside the stack pointer.
No clue what code is actually generated, but the new code could generate:
mov $MASK, %rax;
and %esp, %rax;
Admittedly, I can't see any reason why this would be an improvement.
--Andy
next prev parent reply other threads:[~2014-02-26 3:00 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-21 4:44 [PATCH] x86: LLVMLinux: Reimplement current_stack_pointer without register usage behanw
2014-02-21 4:55 ` H. Peter Anvin
2014-02-26 3:00 ` Andy Lutomirski [this message]
2014-02-26 3:03 ` H. Peter Anvin
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=530D58CD.4080202@mit.edu \
--to=luto@amacapital.net \
--cc=ak@linux.intel.com \
--cc=akpm@linux-foundation.org \
--cc=behanw@converseincode.com \
--cc=hpa@zytor.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=oleg@redhat.com \
--cc=peterz@infradead.org \
--cc=tglx@linutronix.de \
--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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox