linux-kernel - Re: [PATCH 00/28] nios2 Linux kernel port

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Message-ID: <20140424152819.GI8521@arm.com>
Date:	Thu, 24 Apr 2014 16:28:19 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Chung-Lin Tang <cltang@...esourcery.com>
Cc:	"Pinski, Andrew" <Andrew.Pinski@...iumnetworks.com>,
	Ley Foon Tan <lftan@...era.com>,
	Arnd Bergmann <arnd@...db.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linux-Arch <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Andrew Pinski <apinski@...ium.com>,
	"Tang, Chung-Lin" <ChungLin_Tang@...tor.com>
Subject: Re: [PATCH 00/28] nios2 Linux kernel port

On Thu, Apr 24, 2014 at 09:55:25AM +0100, Chung-Lin Tang wrote:
> On 2014/4/24 02:26 PM, Chung-Lin Tang wrote:
> > On 2014/4/24 上午 02:15, Pinski, Andrew wrote:
> >>
> >>>> On Apr 23, 2014, at 10:59 AM, "Chung-Lin Tang" <cltang@...esourcery.com> wrote:
> >>>>
> >>>>>> On 2014/4/22 07:20 PM, Ley Foon Tan wrote:
> >>>>>> On Tue, Apr 22, 2014 at 6:56 PM, Arnd Bergmann <arnd@...db.de> wrote:
> >>>>>>>>>> On Tuesday 22 April 2014 18:37:11 Ley Foon Tan wrote:
> >>>>>>>>>>>>>> Hi Arnd and Peter Anvin,
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> Other than 64-bit time_t, clock_t and suseconds_t, can you confirm
> >>>>>>>>>>>>>> that we don't need to have 64 bit off_t? See detail in link below.
> >>>>>>>>>>>>>> I can submit the patches for 64-bit time changes
> >>>>>>>>>>>>>> (include/asm-generic/posix_types.h and other archs) if everyone is
> >>>>>>>>>>>>>> agreed on this.
> >>>>>>>>>>
> >>>>>>>>>> Yes.
> >>>>>> Okay, will doing that.
> >>>>
> >>>> I believe that arm64 ILP32 will also be affected. What is the status of
> >>>> this configuration? Has the glibc/kernel ABI been finalized?
> >> Not yet.  I am still working out the signal handling part. But we
> >> already agreed on 64bit time_t, clock_t, and suseconds_t.  And we
> >> agreed to a 64bit offset_t too. 
> >>
> >> On a related note suseconds in the timespec in posix is defined to
> >> be long. So it would nice if the kernel ignores the upper 32bits so
> >> we (glibc developers) can fix this for new targets including x32
> >> and arm64/ilp32. 
> > 
> > Hmm, but that means for purely 32-bit architectures like nios2, which
> > unlike x86_64 or arm64, never has a 64-bit mode, suseconds_t as a 64-bit
> > type in the kernel is simply wasted.
> 
> The more I think of this, the more I feel that suseconds_t should jsut
> be 'long', not strictly 64-bitified. An ILP32 sub-mode in a 64-bit
> kernel should be using compat_* code paths, something like a
> COMPAT_USE_32BIT_SUSECONDS case.

ILP32 mode should use LP64 syscalls as much as possible and that's the
aim with arm64 as well (of course, we still have a few that wouldn't be
possible and we route them via compat).

But here if time_t is 64-bit while susecconds_t is 32-bit, the compat
code wouldn't help.

-- 
Catalin
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