From: Arnd Bergmann <arnd@arndb.de>
To: kvm-ia64@vger.kernel.org
Subject: Re: [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps
Date: Fri, 23 Apr 2010 13:12:55 +0000 [thread overview]
Message-ID: <201004231512.55240.arnd@arndb.de> (raw)
In-Reply-To: <20100420200353.2d2a6dec.yoshikawa.takuya@oss.ntt.co.jp>
On Friday 23 April 2010, Avi Kivity wrote:
> Ah so the 31st bit is optional as far as userspace is concerned? What
> does it mean? (just curious)
On data pointers it's ignored. When you branch to a function, this bit
determines whether the target function is run in 24 or 31 bit mode.
This allows linking to legacy code on older operating systems that
also support 24 bit libraries.
> What happens on the opposite conversion? is it restored?
>
> What about
>
> int compare_pointer(void *a, void *b)
> {
> unsigned long ai = (unsigned long)a;
> void *aia = (void *)ai;
>
> return a = b; /* true if a and b point to the same object */
> }
Some instructions set the bit, others clear it, so aia and a may not
be bitwise identical.
> Does gcc mask the big in pointer comparisons as well?
Yes. To stay in the above example:
a = aia; /* true */
(unsigned long)a = (unsigned long)aia; /* true */
*(unsigned long *)&a = *(unsigned long *)&aia; /* undefined on s390 */
Arnd
WARNING: multiple messages have this Message-ID (diff)
From: Arnd Bergmann <arnd@arndb.de>
To: Avi Kivity <avi-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: "Alexander Graf" <agraf-l3A5Bk7waGM@public.gmane.org>,
"Fernando Luis Vázquez Cao"
<fernando-gVGce1chcLdL9jVzuh4AOg@public.gmane.org>,
"Takuya Yoshikawa"
<yoshikawa.takuya-gVGce1chcLdL9jVzuh4AOg@public.gmane.org>,
mtosatti-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org,
kvm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
kvm-ia64-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
kvm-ppc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps
Date: Fri, 23 Apr 2010 13:12:55 +0000 [thread overview]
Message-ID: <201004231512.55240.arnd@arndb.de> (raw)
In-Reply-To: <4BD19831.5000405-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
On Friday 23 April 2010, Avi Kivity wrote:
> Ah so the 31st bit is optional as far as userspace is concerned? What
> does it mean? (just curious)
On data pointers it's ignored. When you branch to a function, this bit
determines whether the target function is run in 24 or 31 bit mode.
This allows linking to legacy code on older operating systems that
also support 24 bit libraries.
> What happens on the opposite conversion? is it restored?
>
> What about
>
> int compare_pointer(void *a, void *b)
> {
> unsigned long ai = (unsigned long)a;
> void *aia = (void *)ai;
>
> return a = b; /* true if a and b point to the same object */
> }
Some instructions set the bit, others clear it, so aia and a may not
be bitwise identical.
> Does gcc mask the big in pointer comparisons as well?
Yes. To stay in the above example:
a = aia; /* true */
(unsigned long)a = (unsigned long)aia; /* true */
*(unsigned long *)&a = *(unsigned long *)&aia; /* undefined on s390 */
Arnd
WARNING: multiple messages have this Message-ID (diff)
From: Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>
To: Avi Kivity <avi-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: "Alexander Graf" <agraf-l3A5Bk7waGM@public.gmane.org>,
"Fernando Luis Vázquez Cao"
<fernando-gVGce1chcLdL9jVzuh4AOg@public.gmane.org>,
"Takuya Yoshikawa"
<yoshikawa.takuya-gVGce1chcLdL9jVzuh4AOg@public.gmane.org>,
mtosatti-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org,
kvm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
kvm-ia64-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
kvm-ppc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps
Date: Fri, 23 Apr 2010 15:12:55 +0200 [thread overview]
Message-ID: <201004231512.55240.arnd@arndb.de> (raw)
In-Reply-To: <4BD19831.5000405-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
On Friday 23 April 2010, Avi Kivity wrote:
> Ah so the 31st bit is optional as far as userspace is concerned? What
> does it mean? (just curious)
On data pointers it's ignored. When you branch to a function, this bit
determines whether the target function is run in 24 or 31 bit mode.
This allows linking to legacy code on older operating systems that
also support 24 bit libraries.
> What happens on the opposite conversion? is it restored?
>
> What about
>
> int compare_pointer(void *a, void *b)
> {
> unsigned long ai = (unsigned long)a;
> void *aia = (void *)ai;
>
> return a == b; /* true if a and b point to the same object */
> }
Some instructions set the bit, others clear it, so aia and a may not
be bitwise identical.
> Does gcc mask the big in pointer comparisons as well?
Yes. To stay in the above example:
a == aia; /* true */
(unsigned long)a == (unsigned long)aia; /* true */
*(unsigned long *)&a == *(unsigned long *)&aia; /* undefined on s390 */
Arnd
next prev parent reply other threads:[~2010-04-23 13:12 UTC|newest]
Thread overview: 141+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-04-20 11:03 [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty Takuya Yoshikawa
2010-04-20 11:03 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps Takuya Yoshikawa
2010-04-20 11:03 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty Takuya Yoshikawa
2010-04-20 11:15 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps Alexander Graf
2010-04-20 11:15 ` Alexander Graf
2010-04-20 11:15 ` Alexander Graf
2010-04-20 11:33 ` Alexander Graf
2010-04-20 11:33 ` Alexander Graf
2010-04-20 11:33 ` Alexander Graf
2010-04-20 11:33 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty Takuya Yoshikawa
2010-04-20 11:33 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps Takuya Yoshikawa
2010-04-20 11:33 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty Takuya Yoshikawa
2010-04-20 11:44 ` Takuya Yoshikawa
2010-04-20 11:44 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps Takuya Yoshikawa
2010-04-20 11:44 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty Takuya Yoshikawa
2010-04-21 8:29 `
2010-04-21 8:29 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps Fernando Luis Vázquez Cao
2010-04-21 8:29 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty
2010-04-21 9:41 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps Alexander Graf
2010-04-21 9:41 ` Alexander Graf
2010-04-21 9:41 ` Alexander Graf
2010-04-21 11:46 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty Avi Kivity
2010-04-21 11:46 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps Avi Kivity
2010-04-21 11:46 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty Avi Kivity
2010-04-22 2:45 `
2010-04-22 2:45 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps Fernando Luis Vázquez Cao
2010-04-22 2:45 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty
2010-04-22 6:09 `
2010-04-22 6:09 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps Fernando Luis Vázquez Cao
2010-04-22 6:09 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty
2010-04-22 9:34 ` Takuya Yoshikawa
2010-04-22 9:34 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps Takuya Yoshikawa
2010-04-22 9:34 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty Takuya Yoshikawa
2010-04-22 23:29 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps Alexander Graf
2010-04-22 23:29 ` Alexander Graf
2010-04-22 23:29 ` Alexander Graf
2010-04-23 10:17 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty
2010-04-23 10:17 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps Fernando Luis Vázquez Cao
2010-04-23 10:17 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty
2010-04-23 10:20 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps Alexander Graf
2010-04-23 10:20 ` Alexander Graf
2010-04-23 10:20 ` Alexander Graf
2010-04-23 11:57 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty Avi Kivity
2010-04-23 11:57 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps Avi Kivity
2010-04-23 11:57 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty Avi Kivity
2010-04-23 11:58 ` Avi Kivity
2010-04-23 11:58 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps Avi Kivity
2010-04-23 11:58 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty Avi Kivity
2010-04-23 12:26 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps Alexander Graf
2010-04-23 12:26 ` Alexander Graf
2010-04-23 12:26 ` Alexander Graf
2010-04-23 12:27 ` Arnd Bergmann
2010-04-23 12:27 ` Arnd Bergmann
2010-04-23 12:27 ` Arnd Bergmann
2010-04-23 12:42 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty Avi Kivity
2010-04-23 12:42 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps Avi Kivity
2010-04-23 12:42 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty Avi Kivity
2010-04-23 12:46 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps Arnd Bergmann
2010-04-23 12:46 ` Arnd Bergmann
2010-04-23 12:46 ` Arnd Bergmann
2010-04-23 12:53 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty Avi Kivity
2010-04-23 12:53 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps Avi Kivity
2010-04-23 12:53 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty Avi Kivity
2010-04-23 12:59 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps Alexander Graf
2010-04-23 12:59 ` Alexander Graf
2010-04-23 12:59 ` Alexander Graf
2010-04-23 13:12 ` Arnd Bergmann [this message]
2010-04-23 13:12 ` Arnd Bergmann
2010-04-23 13:12 ` Arnd Bergmann
2010-04-23 13:20 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty Avi Kivity
2010-04-23 13:20 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty bitmaps Avi Kivity
2010-04-23 13:20 ` [PATCH RFC v2 6/6] KVM: introduce a new API for getting dirty Avi Kivity
-- strict thread matches above, loose matches on Subject: below --
2010-04-20 10:59 [PATCH RFC v2 3/6] KVM: introduce a wrapper function to copy dirty Takuya Yoshikawa
2010-04-20 10:59 ` [PATCH RFC v2 3/6] KVM: introduce a wrapper function to copy dirty bitmaps to user space Takuya Yoshikawa
2010-04-20 10:59 ` [PATCH RFC v2 3/6] KVM: introduce a wrapper function to copy dirty Takuya Yoshikawa
2010-04-21 11:12 ` [PATCH RFC v2 3/6] KVM: introduce a wrapper function to copy Avi Kivity
2010-04-21 11:12 ` [PATCH RFC v2 3/6] KVM: introduce a wrapper function to copy dirty bitmaps to user space Avi Kivity
2010-04-21 11:12 ` [PATCH RFC v2 3/6] KVM: introduce a wrapper function to copy Avi Kivity
2010-04-22 8:57 ` Takuya Yoshikawa
2010-04-22 8:57 ` [PATCH RFC v2 3/6] KVM: introduce a wrapper function to copy dirty bitmaps to user space Takuya Yoshikawa
2010-04-22 8:57 ` [PATCH RFC v2 3/6] KVM: introduce a wrapper function to copy Takuya Yoshikawa
2010-04-23 10:26 ` Avi Kivity
2010-04-23 10:26 ` [PATCH RFC v2 3/6] KVM: introduce a wrapper function to copy dirty bitmaps to user space Avi Kivity
2010-04-23 10:26 ` [PATCH RFC v2 3/6] KVM: introduce a wrapper function to copy Avi Kivity
2010-04-20 10:58 [PATCH RFC v2 5/6] KVM: moving dirty bitmaps to user space Takuya Yoshikawa
2010-04-20 11:02 ` Takuya Yoshikawa
2010-04-20 10:58 ` Takuya Yoshikawa
2010-04-20 11:10 ` Alexander Graf
2010-04-20 11:10 ` Alexander Graf
2010-04-20 11:10 ` Alexander Graf
2010-04-20 11:26 ` Takuya Yoshikawa
2010-04-20 11:26 ` Takuya Yoshikawa
2010-04-20 11:26 ` Takuya Yoshikawa
2010-04-21 11:26 ` Avi Kivity
2010-04-21 11:26 ` Avi Kivity
2010-04-21 11:26 ` Avi Kivity
2010-04-22 9:07 ` Takuya Yoshikawa
2010-04-22 9:07 ` Takuya Yoshikawa
2010-04-22 9:07 ` Takuya Yoshikawa
2010-04-23 10:28 ` Avi Kivity
2010-04-23 10:28 ` Avi Kivity
2010-04-23 10:28 ` Avi Kivity
2010-04-23 11:14 ` Takuya Yoshikawa
2010-04-23 11:14 ` Takuya Yoshikawa
2010-04-23 11:14 ` Takuya Yoshikawa
2010-04-23 11:29 ` Yoshiaki Tamura
2010-04-23 11:29 ` Yoshiaki Tamura
2010-04-23 11:29 ` Yoshiaki Tamura
2010-04-23 11:45 ` Avi Kivity
2010-04-23 11:45 ` Avi Kivity
2010-04-23 11:45 ` Avi Kivity
2010-04-20 10:57 [PATCH RFC v2 2/6] KVM: introduce wrapper functions to create and Takuya Yoshikawa
2010-04-20 10:57 ` [PATCH RFC v2 2/6] KVM: introduce wrapper functions to create and destroy dirty bitmaps Takuya Yoshikawa
2010-04-20 10:57 ` [PATCH RFC v2 2/6] KVM: introduce wrapper functions to create and Takuya Yoshikawa
2010-04-20 10:57 [PATCH RFC v2 4/6] KVM: change mark_page_dirty() to handle endian Takuya Yoshikawa
2010-04-20 11:00 ` [PATCH RFC v2 4/6] KVM: change mark_page_dirty() to handle endian issues explicitly Takuya Yoshikawa
2010-04-20 10:57 ` [PATCH RFC v2 4/6] KVM: change mark_page_dirty() to handle endian Takuya Yoshikawa
2010-04-20 11:00 ` [PATCH RFC v2 4/6] KVM: change mark_page_dirty() to handle endian issues explicitly Alexander Graf
2010-04-20 11:00 ` Alexander Graf
2010-04-20 11:00 ` Alexander Graf
2010-04-20 11:20 ` [PATCH RFC v2 4/6] KVM: change mark_page_dirty() to handle endian Takuya Yoshikawa
2010-04-20 11:20 ` [PATCH RFC v2 4/6] KVM: change mark_page_dirty() to handle endian issues explicitly Takuya Yoshikawa
2010-04-20 11:20 ` [PATCH RFC v2 4/6] KVM: change mark_page_dirty() to handle endian Takuya Yoshikawa
2010-04-21 11:15 ` Avi Kivity
2010-04-21 11:15 ` [PATCH RFC v2 4/6] KVM: change mark_page_dirty() to handle endian issues explicitly Avi Kivity
2010-04-21 11:15 ` [PATCH RFC v2 4/6] KVM: change mark_page_dirty() to handle endian Avi Kivity
2010-04-20 10:56 [PATCH RFC v2 1/6] KVM: introduce slot level dirty state management Takuya Yoshikawa
2010-04-20 10:56 ` Takuya Yoshikawa
2010-04-20 10:56 ` Takuya Yoshikawa
2010-04-20 10:53 [PATCH RFC v2 0/6] KVM: moving dirty gitmaps to user space! Takuya Yoshikawa
2010-04-20 10:53 ` Takuya Yoshikawa
2010-04-20 10:53 ` Takuya Yoshikawa
2010-04-20 10:54 ` Alexander Graf
2010-04-20 10:54 ` Alexander Graf
2010-04-20 10:54 ` Alexander Graf
2010-04-20 11:13 ` Takuya Yoshikawa
2010-04-20 11:13 ` Takuya Yoshikawa
2010-04-20 11:13 ` Takuya Yoshikawa
2010-04-20 12:05 ` Takuya Yoshikawa
2010-04-20 12:05 ` Takuya Yoshikawa
2010-04-20 12:05 ` Takuya Yoshikawa
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