From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Wed, 21 Jan 2004 15:22:53 +0000 (GMT) Received: from nevyn.them.org ([IPv6:::ffff:66.93.172.17]:9111 "EHLO nevyn.them.org") by linux-mips.org with ESMTP id ; Wed, 21 Jan 2004 15:22:53 +0000 Received: from drow by nevyn.them.org with local (Exim 4.30 #1 (Debian)) id 1AjKBr-0000Ll-BV; Wed, 21 Jan 2004 10:22:47 -0500 Date: Wed, 21 Jan 2004 10:22:47 -0500 From: Daniel Jacobowitz To: "Maciej W. Rozycki" Cc: Ralf Baechle , Pavel Kiryukhin , linux-mips@linux-mips.org Subject: Re: __MIPSEL__ in sys32_rt_sigtimedwait Message-ID: <20040121152247.GA1308@nevyn.them.org> References: <400D6877.1000105@dev.rtsoft.ru> <20040120183157.GB5495@linux-mips.org> <20040120193918.GA2108@nevyn.them.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.1i Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 4080 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: dan@debian.org Precedence: bulk X-list: linux-mips On Wed, Jan 21, 2004 at 02:47:17PM +0100, Maciej W. Rozycki wrote: > On Tue, 20 Jan 2004, Daniel Jacobowitz wrote: > > > No, I'm pretty sure Pavel's right. > > > > -#ifdef __MIPSEB__ > > case 1: these.sig[0] = these32.sig[0] | (((long)these32.sig[1]) << 32); > > -#endif > > -#ifdef __MIPSEL__ > > - case 1: these.sig[0] = these32.sig[1] | (((long)these32.sig[0]) << 32); > > -#endif > > > > Consider a 64-bit sigset. 32-bit userland, 64-bit kernel. Here's a > > userland sigset with signal 33 set, only, on a little endian target. > > Word 1, least significant bit, right? > > Right, but... > > > byte address in memory > > 1 2 3 4 5 6 7 8 > > val 0 0 0 0 0 0 0 1 > > ... this is incorrect -- it would be right for big-endian; word #1, bit #1 > for little-endian is: > > byte address in memory > 1 2 3 4 5 6 7 8 > val 0 0 0 0 1 0 0 0 > > > > Obviously, as a 64-bit integer the sigset looks different. There it's > > supposed to be 1 << (33 - 1). > > val 0 0 0 1 0 0 0 0 > > Again, for little-endian it should actually be: > > val 0 0 0 0 1 0 0 0 > > i.e. the whole operation is actually a no-op, except that the 64-bit > vector is assured to be properly aligned for doubleword accesses. Re-reading what I wrote, the above was actually supposed to be a big-endian example. D'oh! If you pretend I wrote "big endian" up at the top, then it makes sense. > As a side note -- that's the reason certain C code portability problems > related to the width of the machine word only get actually discovered when > problematic software is run on a big-endian processor. I've been hit by > this property once -- I was porting a 16-bit program and it appeared to > run just fine on both a 32-bit (i386) and a 64-bit (Alpha) little-endian > CPU, but when run on a 32-bit big-endian one (SPARC) I discovered a few > more bits to be cleaned up. > > > So the correct algorithm to convert a userspace sigset to a kernel > > sigset is to shift the second word left 32 bits, and leave the first > > word right aligned, and or them together. Which is what using the > > __MIPSEB__ case does. > > But this conclusion is of course right. > > Maciej > > -- > + Maciej W. Rozycki, Technical University of Gdansk, Poland + > +--------------------------------------------------------------+ > + e-mail: macro@ds2.pg.gda.pl, PGP key available + > -- Daniel Jacobowitz MontaVista Software Debian GNU/Linux Developer