Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752020AbdGFJGT (ORCPT ); Thu, 6 Jul 2017 05:06:19 -0400 Received: from mailapp01.imgtec.com ([195.59.15.196]:34424 "EHLO imgpgp01.kl.imgtec.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751009AbdGFJGG (ORCPT ); Thu, 6 Jul 2017 05:06:06 -0400 X-PGP-Universal: processed; by imgpgp01.kl.imgtec.org on Thu, 06 Jul 2017 11:16:18 +0100 Date: Thu, 6 Jul 2017 10:05:53 +0100 From: James Hogan To: "Maciej W. Rozycki" CC: Aleksandar Markovic , , Goran Ferenc , Miodrag Dinic , Aleksandar Markovic , Douglas Leung , , Paul Burton , Petar Jovanovic , Raghu Gandham , Ralf Baechle Subject: Re: [PATCH v2 2/4] MIPS: VDSO: Add implementation of clock_gettime() fallback Message-ID: <20170706090553.GO31455@jhogan-linux.le.imgtec.org> References: <1498665337-28845-1-git-send-email-aleksandar.markovic@rt-rk.com> <1498665337-28845-3-git-send-email-aleksandar.markovic@rt-rk.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="aTCJOP0qgkSGqHWA" Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.7.2 (2016-11-26) X-Originating-IP: [192.168.154.110] X-ESG-ENCRYPT-TAG: 1b7d744b Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3302 Lines: 93 --aTCJOP0qgkSGqHWA Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Jul 06, 2017 at 01:00:34AM +0100, Maciej W. Rozycki wrote: > On Wed, 28 Jun 2017, Aleksandar Markovic wrote: >=20 > > diff --git a/arch/mips/vdso/gettimeofday.c b/arch/mips/vdso/gettimeofda= y.c > > index fd7d433..5f63375 100644 > > --- a/arch/mips/vdso/gettimeofday.c > > +++ b/arch/mips/vdso/gettimeofday.c > > @@ -20,6 +20,24 @@ > > #include > > #include > > =20 > > +static __always_inline long clock_gettime_fallback(clockid_t _clkid, > > + struct timespec *_ts) > > +{ > > + register struct timespec *ts asm("a1") =3D _ts; > > + register clockid_t clkid asm("a0") =3D _clkid; > > + register long ret asm("v0"); > > + register long nr asm("v0") =3D __NR_clock_gettime; > > + register long error asm("a3"); > > + > > + asm volatile( > > + " syscall\n" > > + : "=3Dr" (ret), "=3Dr" (error) > > + : "r" (clkid), "r" (ts), "r" (nr) > > + : "memory"); > > + > > + return error ? -ret : ret; > > +} >=20 > Hmm, are you sure it is safe nowadays WRT the syscall restart convention= =20 > to leave out the instruction explicitly loading the syscall number that= =20 > would normally immediately precede SYSCALL It should be fine. syscall restart only rewinds one (32-bit) instruction, and it preserves the syscall number in pt_regs::regs[0] (see handle_signal() / do_signal() and this code in e.g. scall32-o32.S:) sw t1, PT_R0(sp) # save it for syscall restarting > (and would have to forcibly use the 32-bit encoding in the microMIPS > case)? I don't believe there is a 16-bit SYSCALL encoding in microMIPS, at least I can't see one in the 5.04 manual. However, the clobber list is incomplete. The following registers are written as outputs: $2 (v0), $7 (a3) The following registers are used as arguments and should be preserved: $4-$6 (a0-a2), [$8-$9 (a4-a5)] (n32 / n64 only) And the following other registers are preserved: $16-$23, $28-$31 So assuming you already have $2 and $7 as outputs, the clobber list should be: "$1", "$3", ["$8", "$9",] "$10", "$11", "$12", "$13", "$14", "$15", "$24", "$25", "hi", "lo", "memory" (only o32 needs to mark $8-$9 clobbered, but no harm doing so on n32/n64 too) Cheers James --aTCJOP0qgkSGqHWA Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEd80NauSabkiESfLYbAtpk944dnoFAlld/WkACgkQbAtpk944 dnoitRAAjseL+PlvbC+PH3gr5tmbba2vLaBhETrgiq4sXEG8VTvKTWqaxBI5WKc8 5wX+tGmvFhjI4CUv5INF/KnrUMPoHEplGYjRxUVfGjkwL00w4wvbtLISykhAsI6t D4jan35chJrQ59lOzwxkJ7a+equk8WUbVWsovFKJW8o6odq5TLXcmWyqM2/sMMvY BLsxYFX96jFSbkuvw3l3WwMDHxSGIro7qNFX0uKAtrjI7H1BOxu7DvFc+Jbu9em6 5P8kn97xITaQvNNPGut/NTymykQ7ZLfnVBFMmH0lwDqEr7pTWUmMyp8zpGYgLv6T RfmfiSz4RMu8lfbzJBxaMGjkzy4TXEHahsJgemHH0RC10ZC0K2ytBTOHLnhO6SdF gJMG1IfcDx52+V4oxT9Xn41TwiKFELSq5br1bL/VEs3sC6z6d/ACXF215bbE9MEC tauA/qgripHRZmBQCBHDvA0BJWH2v6XTbfTu0neeJD7YFnxBv5B7N0fguljFLSxH cMx6u478XdTwkb1FLwNT5sPpY9S3FRidEjFsehc2thjUSZZw/ItYztdnnHJQe/nS pJidlyGgyObPjMXzxNPbTVdANJLsFcZlo8jESiFlZDUSLfU3vCzB2vcFK8c0eV9V NoxcIGT3rxyCcjYqQxHucs94D1i3iz7+Byj/+h5GAJqkWUhcstA= =FDa7 -----END PGP SIGNATURE----- --aTCJOP0qgkSGqHWA--