Re: [PATCH v5 02/23] kernel: Define gettimeofday vdso common code

[Thomas Gleixner <tglx@linutronix.de>]

On Fri, 22 Feb 2019, Vincenzo Frascino wrote:
> +static notrace int __cvdso_clock_getres(clockid_t clock,
> +					struct __vdso_timespec *res)
> +{
> +	u64 sec, ns;
> +	u32 msk;
> +
> +	/* Check for negative values or invalid clocks */
> +	if (unlikely((u32) clock >= MAX_CLOCKS))
> +		goto fallback;
> +
> +	/*
> +	 * Convert the clockid to a bitmask and use it to check which
> +	 * clocks are handled in the VDSO directly.
> +	 */
> +	msk = 1U << clock;
> +	if (msk & VDSO_HRES) {
> +		/*
> +		 * Preserves the behaviour of posix_get_hrtimer_res().
> +		 */

So much for the theory.

> +		sec = 0;
> +		ns = MONOTONIC_RES_NSEC;

posix_get_hrtimer_res() does:

	sec = 0;
	ns = hrtimer_resolution;

and hrtimer_resolution depends on the enablement of high resolution timers
either compile or run time.

So you need to have a copy of hrtimer_resolution in the vdso data and use
that.

> +	} else if (msk & VDSO_COARSE) {
> +		/*
> +		 * Preserves the behaviour of posix_get_coarse_res().
> +		 */
> +		ns = LOW_RES_NSEC;
> +		sec = __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);

Do we allow CONFIG_HZ = 1?

Thanks,

	tglx

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