Hi Catalin,

On 3/19/20 6:10 PM, Catalin Marinas wrote:

Hi Vincenzo,

On Thu, Mar 19, 2020 at 12:38:42PM +0000, Vincenzo Frascino wrote:

quoted

On 3/18/20 6:36 PM, Catalin Marinas wrote:

quoted

On Wed, Mar 18, 2020 at 04:14:26PM +0000, Vincenzo Frascino wrote:

quoted

On 3/17/20 5:48 PM, Catalin Marinas wrote:

quoted

So clock_gettime() on arm32 always falls back to the syscall?

This seems not what you asked, and I think I answered accordingly. Anyway, in
the case of arm32 the error code path is handled via syscall fallback.

Look at the code below as an example (I am using getres because I know this
email will be already too long, and I do not want to add pointless code, but the
concept is the same for gettime and the others):

static __maybe_unused
int __cvdso_clock_getres(clockid_t clock, struct __kernel_timespec *res)
{
	int ret = __cvdso_clock_getres_common(clock, res);

	if (unlikely(ret))
		return clock_getres_fallback(clock, res);
	return 0;
}

When the return code of the "vdso" internal function returns an error the system
call is triggered.

But when __cvdso_clock_getres_common() does *not* return an error, it
means that it handled the clock_getres() call without a fallback to the
syscall. I assume this is possible on arm32. When the clock_getres() is
handled directly (not as a syscall), why doesn't arm32 need the same
(res >= TASK_SIZE) check?

Ok, I see what you mean.

I'm not sure.

Thank you for the long chat this morning. As we agreed I am going to repost the
patches removing the checks discussed in this thread and we will address the
syscall ABI difference subsequently with a different series.

-- 
Regards,
Vincenzo

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