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From: Arnd Bergmann <arnd@arndb.de>
To: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: linux-arch <linux-arch@vger.kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	Will Deacon <will.deacon@arm.com>,
	Russell King - ARM Linux <linux@armlinux.org.uk>,
	Ralf Baechle <ralf@linux-mips.org>,
	Mark Salyzyn <salyzyn@android.com>,
	Paul Burton <paul.burton@mips.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Peter Collingbourne <pcc@google.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2 06/28] kernel: Define gettimeofday vdso common code
Date: Tue, 11 Dec 2018 22:41:01 +0100
Message-ID: <CAK8P3a0LgFuv_s4xiC_rD0X7-GxHRWfzmdDcxJ7vvHrEETApRw@mail.gmail.com> (raw)
In-Reply-To: <64ff3b50-ce55-ff69-ac3a-61f221299895@arm.com>

On Tue, Dec 11, 2018 at 2:39 PM Vincenzo Frascino
<vincenzo.frascino@arm.com> wrote:
> On 29/11/2018 20:42, Arnd Bergmann wrote:
> > On Thu, Nov 29, 2018 at 6:06 PM Vincenzo Frascino
> > <vincenzo.frascino@arm.com> wrote:
> >
> >> +/*
> >> + * The definitions below are required to overcome the limitations
> >> + * of time_t on 32 bit architectures, which overflows in 2038.
> >> + * The new code should use the replacements based on time64_t and
> >> + * timespec64.
> >> + *
> >> + * The abstraction below will be updated once the migration to
> >> + * time64_t is complete.
> >> + */
> >> +#ifdef CONFIG_GENERIC_VDSO_32
> >> +#define __vdso_timespec                old_timespec32
> >> +#define __vdso_timeval         old_timeval32
> >> +#else
> >> +#ifdef ENABLE_COMPAT_VDSO
> >> +#define __vdso_timespec                old_timespec32
> >> +#define __vdso_timeval         old_timeval32
> >> +#else
> >> +#define __vdso_timespec                __kernel_timespec
> >> +#define __vdso_timeval         __kernel_old_timeval
> >> +#endif /* CONFIG_COMPAT_VDSO */
> >> +#endif /* CONFIG_GENERIC_VDSO_32 */
> >>
> >
> > Have you considered doing this in the reverse way, by including
> > the common parts from multiple implementations (32 and 64
> > bit), instead of compiling the same source file multiple
> > times with different macros set? I think that would make it
> > easier to understand.
> >
>
> The common code is never compiled as standalone. It includes arch specific code
> (for the fallbacks) and it is included in the arch specific vdso library (for
> both 32 and 64 bit where it makes sense). Hence it is built once or twice.
>
> If I understand correctly your question, seems inline with what I am doing.

The result is very similar, it's just a question of which file includes which
other file. If I understand your current method right, you use Makefile
logic to build multiple object files from a single source file, and setting
ENABLE_COMPAT_VDSO on one of them, right?

My preference would be to keep that Makefile simpler and have one
source file per object file, but have each one define a set of macros
before including the common source file, similarly to how we deal
with fs/compat_binfmt_elf.c. If that turns out to be worse than what
you have here, I'm not overly attached to that solution since including
C files is still ugly, but I think it's worth trying if that lets you end
up with more easily understandable source code.

       Arnd

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  reply index

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-29 17:05 [PATCH v2 00/28] Unify vDSOs across more architectures Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 01/28] kernel: Standardize vdso_datapage Vincenzo Frascino
2018-11-29 22:39   ` Thomas Gleixner
2018-12-11 13:22     ` Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 02/28] kernel: Add Monotonic boot time support Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 03/28] kernel: Add International Atomic Time support Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 04/28] kernel: Add masks support for Raw and NTP time Vincenzo Frascino
2018-11-29 22:41   ` Thomas Gleixner
2018-12-11 13:24     ` Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 05/28] kernel: Add clock_mode support Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 06/28] kernel: Define gettimeofday vdso common code Vincenzo Frascino
2018-11-29 20:42   ` Arnd Bergmann
2018-12-11 13:39     ` Vincenzo Frascino
2018-12-11 21:41       ` Arnd Bergmann [this message]
2018-12-13  9:46         ` Vincenzo Frascino
2018-11-29 22:11   ` Thomas Gleixner
2018-11-30 14:29     ` Arnd Bergmann
2018-12-11 14:02       ` Vincenzo Frascino
2018-12-07 17:53     ` Will Deacon
2019-02-08 17:35       ` Will Deacon
2019-02-08 19:28         ` Thomas Gleixner
2019-02-08 19:30           ` Thomas Gleixner
2019-02-13 17:04             ` Will Deacon
2019-02-13 19:35               ` Thomas Gleixner
2019-02-13 17:05           ` Will Deacon
2018-12-11 13:54     ` Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 07/28] arm64: Build vDSO with -ffixed-x18 Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 08/28] arm64: Substitute gettimeofday with C implementation Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 09/28] arm64: compat: Alloc separate pages for vectors and sigpage Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 10/28] arm64: compat: Split kuser32 Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 11/28] arm64: compat: Refactor aarch32_alloc_vdso_pages() Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 12/28] arm64: compat: Add KUSER_HELPERS config option Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 13/28] arm64: compat: Add missing syscall numbers Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 14/28] arm64: compat: Expose signal related structures Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 15/28] arm64: compat: Generate asm offsets for signals Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 16/28] lib: vdso: Add compat support Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 17/28] arm64: compat: Add vDSO Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 18/28] arm64: Refactor vDSO code Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 19/28] arm64: compat: vDSO setup for compat layer Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 20/28] arm64: elf: vDSO code page discovery Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 21/28] arm64: compat: Get sigreturn trampolines from vDSO Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 22/28] arm64: Add vDSO compat support Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 23/28] arm64: Enable compat vDSO support Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 24/28] arm: Add support for generic vDSO Vincenzo Frascino
2018-12-10 22:13   ` Mark Salyzyn
2018-12-11 14:15     ` Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 25/28] mips: Introduce vdso_direct Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 26/28] clock: csrc-4k: Add support for vdso_direct Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 27/28] clock: gic-timer: " Vincenzo Frascino
2018-11-29 17:05 ` [PATCH v2 28/28] mips: Add support for generic vDSO Vincenzo Frascino

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