[RFC/PATCH v2] ARM: vDSO gettimeofday using generic timer architecture
Nathan_Lynch at mentor.com
Tue Feb 11 11:23:38 EST 2014
On 02/11/2014 04:45 AM, Will Deacon wrote:
> On Mon, Feb 10, 2014 at 11:57:19PM +0000, Nathan Lynch wrote:
>> Right, this stuff doesn't appear to be necessary. Removed the vmap,
>> get_page, and ClearPageReserved calls for v3.
> Can you make the corresponding change for arm64 too, please?
Yes, will do.
>>>> +static long clock_gettime_fallback(clockid_t _clkid, struct timespec *_ts)
>>>> + register struct timespec *ts asm("r1") = _ts;
>>>> + register clockid_t clkid asm("r0") = _clkid;
>>>> + register long ret asm ("r0");
>>>> + register long nr asm("r7") = __NR_clock_gettime;
>>>> + asm("swi #0" : "=r" (ret) : "r" (clkid), "r" (ts), "r" (nr) : "memory");
> Might be worth making this volatile, rather than depend on the use of ret.
> Also, placing both _clkid and ret into "r0" worries me slightly -- is GCC
> smart enough to realise that writing to ret kills _clkid?
I pretty much lifted this from an example in the GCC manual:
register int *p1 asm ("r0") = ...;
register int *p2 asm ("r1") = ...;
register int *result asm ("r0");
asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));
I guess it doesn't directly answer your concern, but it's an indication
that GCC developers have this use case in mind.
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