From: Arnd Bergmann <arnd@arndb•de>
To: linuxppc-embedded@ozlabs•org, benh@kernel•crashing.org
Cc: "Sadashiiv, Halesh" <halesh.sadashiv@ap•sony.com>
Subject: Re: Regarding select() on PPC
Date: Wed, 24 Sep 2008 08:45:51 +0200 [thread overview]
Message-ID: <200809240845.52262.arnd@arndb.de> (raw)
In-Reply-To: <1222237739.8277.62.camel@pasglop>
On Wednesday 24 September 2008, Benjamin Herrenschmidt wrote:
> Why do we want it ?
>
> It's an int, it's zero extended, but that should still be a valid signed
> 32 bits int in compat_sys_select() or do I miss something ?
IIRC, the calling conventions on 64 bit ppc assume that a signed int
argument is sign-extended into a 64 bit register. The compat syscall
entry point does not know which registers are signed or unsigned, so
it will always to zero-extend, making the register contain an undefined
bit pattern (e.g. 0x00000000fffffffe), which may be interpreted as being
a positive number. An explicit cast as it is done in ppc32_select turns
this into a well-defined 32-bit number stored in a 64-bit register (e.g.
0xfffffffffffffffe).
Arnd <><
next prev parent reply other threads:[~2008-09-24 6:46 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-09-23 7:16 Regarding select() on PPC Sadashiiv, Halesh
2008-09-23 9:07 ` Benjamin Herrenschmidt
2008-09-24 6:23 ` Arnd Bergmann
2008-09-24 6:28 ` Benjamin Herrenschmidt
2008-09-24 6:45 ` Arnd Bergmann [this message]
2008-09-24 7:08 ` Benjamin Herrenschmidt
2008-09-24 21:46 ` Benjamin Herrenschmidt
2008-09-24 6:39 ` [PATCH] remove bogus ppc_select syscall Arnd Bergmann
2008-09-24 16:29 ` Paul Mackerras
2008-09-24 17:03 ` Arnd Bergmann
2008-10-10 7:40 ` Paul Mackerras
2008-10-10 8:44 ` Arnd Bergmann
2008-10-10 4:29 ` Benjamin Herrenschmidt
2008-10-10 7:43 ` Paul Mackerras
2008-10-10 8:45 ` Arnd Bergmann
2008-10-10 23:17 ` Benjamin Herrenschmidt
2008-10-12 8:58 ` Arnd Bergmann
2008-10-13 2:42 ` i2o driver work with AMCC 460EX? Ayman El-Khashab
-- strict thread matches above, loose matches on Subject: below --
2008-09-23 9:31 Regarding select() on PPC Sadashiiv, Halesh
2008-09-23 5:27 Sadashiiv, Halesh
2008-09-23 5:01 Sadashiiv, Halesh
2008-09-23 5:11 ` Benjamin Herrenschmidt
2008-09-23 5:46 ` Arnd Bergmann
2008-09-23 5:56 ` Benjamin Herrenschmidt
2008-09-23 6:01 ` Arnd Bergmann
2008-09-23 6:29 ` Benjamin Herrenschmidt
2008-09-23 4:50 Sadashiiv, Halesh
2008-09-23 4:55 ` Benjamin Herrenschmidt
2008-09-22 15:30 Sadashiiv, Halesh
2008-09-22 15:15 Sadashiiv, Halesh
2008-09-22 15:24 ` Josh Boyer
2008-09-23 4:42 ` Benjamin Herrenschmidt
2008-09-19 14:28 Sadashiiv, Halesh
2008-09-19 13:30 Sadashiiv, Halesh
2008-09-19 14:19 ` Josh Boyer
2008-09-19 11:50 Sadashiiv, Halesh
2008-09-19 14:53 ` Dale Farnsworth
2008-09-19 16:53 ` Dale Farnsworth
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=200809240845.52262.arnd@arndb.de \
--to=arnd@arndb$(echo .)de \
--cc=benh@kernel$(echo .)crashing.org \
--cc=halesh.sadashiv@ap$(echo .)sony.com \
--cc=linuxppc-embedded@ozlabs$(echo .)org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
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