linux-kernel - Re: [PATCH v6 16/19] arm: Add support for generic vDSO

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Date:   Fri, 31 May 2019 10:32:22 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
Cc:     linux-arch <linux-arch@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mips@...r.kernel.org,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Russell King <linux@...linux.org.uk>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mark Salyzyn <salyzyn@...roid.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Shuah Khan <shuah@...nel.org>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Huw Davies <huw@...eweavers.com>
Subject: Re: [PATCH v6 16/19] arm: Add support for generic vDSO

On Thu, May 30, 2019 at 4:16 PM Vincenzo Frascino
<vincenzo.frascino@....com> wrote:
> diff --git a/arch/arm/include/asm/vdso/gettimeofday.h b/arch/arm/include/asm/vdso/gettimeofday.h
> new file mode 100644
> index 000000000000..eeeb319840ba
> --- /dev/null
> +++ b/arch/arm/include/asm/vdso/gettimeofday.h
> @@ -0,0 +1,96 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2018 ARM Limited
> + */
> +#ifndef __ASM_VDSO_GETTIMEOFDAY_H
> +#define __ASM_VDSO_GETTIMEOFDAY_H
> +
> +#ifndef __ASSEMBLY__
> +
> +#include <asm/barrier.h>
> +#include <asm/cp15.h>
> +#include <asm/unistd.h>
> +#include <uapi/linux/time.h>
> +
> +#ifndef CONFIG_AEABI
> +#error This code depends on AEABI system call conventions
> +#endif

Instead of an #error here, I would use a Kconfig conditional and make it

'select HAVE_GENERIC_VDSO if AEABI'

> diff --git a/arch/arm/vdso/vdso.lds.S b/arch/arm/vdso/vdso.lds.S
> index 89ca89f12d23..05581140fd12 100644
> --- a/arch/arm/vdso/vdso.lds.S
> +++ b/arch/arm/vdso/vdso.lds.S
> @@ -82,6 +82,8 @@ VERSION
>         global:
>                 __vdso_clock_gettime;
>                 __vdso_gettimeofday;
> +               __vdso_clock_getres;
> +               __vdso_clock_gettime64;
>         local: *;
>         };

Why are you adding __vdso_clock_getres here? I would probably
leave the addition of the new entry point(s) for a separate patch
at the end, adding __vdso_clock_gettime64 to all 32-bit ABIs
at once, since while that part is a trivial change, it's also user
visible and deserves its own changelog text.

     Arnd