From: James Bottomley <James.Bottomley@SteelEye.com> To: Stephen Rothwell <firstname.lastname@example.org> Cc: Davide Libenzi <email@example.com>, Andrew Morton <firstname.lastname@example.org>, David Woodhouse <email@example.com>, Linux Kernel Mailing List <firstname.lastname@example.org>, email@example.com Subject: Re: [patch] (2nd try) add epoll compat code to kernel/compat.c ... Date: Tue, 13 Feb 2007 08:43:05 -0600 [thread overview] Message-ID: <firstname.lastname@example.org> (raw) In-Reply-To: <email@example.com> On Tue, 2007-02-13 at 15:35 +1100, Stephen Rothwell wrote: > OK, I have thought about this some more and I *think* the only > architecture that needs compat_sys_epoll_ctl or compat_sys_epoll_wait is > ia64 where the 64 bit version of struct epoll_event is different from the > 32 bit version. On x86_64, the struct is explictly packed (so it is the > same as the 32 bit version) and on all the other 64 bit architectures the > alignment of the u64 is the same as the equivalent 32 bit version. > > Since ia64 already has its own version of these two, we only have to > worry about epoll_pwait and then the struct epoll_event is only a problem > for ia64. > > Am I right? (I have cc'd linux-arch for guidance.) Not for parisc at the instruction level. In narrow mode (32 bit mode), a u64 load has to be done by two 32 bit loads which gives it a 4 byte alignment requirement. In wide mode (64 bit mode) the 64 bit load instruction explicitly requires 8 byte alignment, so our u64 alignment requirements are different. However, this is from the machine code point of view. I can't say that gcc doesn't enforce an artificial 8 byte alignment of u64 in narrow mode, so I'll defer to the gcc experts on that one. James
next prev parent reply other threads:[~2007-02-13 14:43 UTC|newest] Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top 2007-02-12 0:24 Davide Libenzi 2007-02-13 4:35 ` Stephen Rothwell 2007-02-13 7:26 ` Davide Libenzi 2007-02-13 10:11 ` Stephen Rothwell 2007-02-13 14:43 ` James Bottomley [this message] 2007-02-13 23:17 ` Stephen Rothwell
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