linux-kernel - Re: [PATCH v3 03/12] arm: vdso: inline assembler operations to compiler.h

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Message-ID: <20171030140755.clqmqnyyunodoors@lakrids.cambridge.arm.com>
Date:   Mon, 30 Oct 2017 14:07:55 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Mark Salyzyn <salyzyn@...roid.com>
Cc:     linux-kernel@...r.kernel.org, James Morse <james.morse@....com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Andy Lutomirski <luto@...capital.net>,
        Dmitry Safonov <dsafonov@...tuozzo.com>,
        John Stultz <john.stultz@...aro.org>,
        Laura Abbott <labbott@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Andy Gross <andy.gross@...aro.org>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Andrew Pinski <apinski@...ium.com>,
        linux-arm-kernel@...ts.infradead.org,
        Mark Salyzyn <salyzyn@...gle.com>
Subject: Re: [PATCH v3 03/12] arm: vdso: inline assembler operations to
 compiler.h

Hi,

On Fri, Oct 27, 2017 at 03:25:10PM -0700, Mark Salyzyn wrote:
> Move compiler-specific code to a local compiler.h file. CONFIG_AEABI
> dependency check. System call fallback functions standardized into
> a DEFINE_FALLBACK macro. Accept that __arch_counter_get_cntvct()
> is the API for aarch64. 

This reads like a stream-of-conciousness, and it's difficult to figure
out which bits are intent and which bits are simply a summary of the
diff.

It would be really helpful to have a sentence or two at the start
explaining the high level idea, and why things must change.

For instance, it's really not clear to me what you mean by:

  Accept that __arch_counter_get_cntvct() is the API for aarch64.

... and whether using a #define for this is the best approach.

>From a scan of v4.14-rc7, there is no __arch_counter_get_cntvct() in the
tree, so I'm very confused here.

[...]

> +#define __arch_counter_get_cntvct() arch_counter_get_cntvct()

> @@ -127,7 +105,7 @@ static notrace u64 get_ns(const struct vdso_data *vd)
>  	u64 cycle_now;
>  	u64 nsec;
>  
> -	cycle_now = arch_counter_get_cntvct();
> +	cycle_now = __arch_counter_get_cntvct();

... and it's difficult to see what the point of these changes is.

Thanks,
Mark.