On 27 Jun 2017, David Miller stated:
> From: Nagarathnam Muthusamy <nagarathnam.muthusamy@xxxxxxxxxx>
> Date: Mon, 26 Jun 2017 12:39:27 -0400
>
>> +static notrace inline u64
>> +vgetsns(struct vvar_data *vvar)
>> +{
>> + u64 v;
>> + u64 cycles;
>> +
>> + switch (vvar->vclock_mode) {
>> + case VCLOCK_TICK:
>> + cycles = vread_tick();
>> + break;
>> + case VCLOCK_STICK:
>> + cycles = vread_stick();
>> + break;
>> + default:
>> + return 0;
>> + }
>> + v = (cycles - vvar->clock.cycle_last) & vvar->clock.mask;
>> + return v * vvar->clock.mult;
>> +}
>
> If you're going to go through all of this trouble to make a vdso,
> it should be assembler code patched at boot time for the tick
> access etc.
Oh wait I see what you're getting at: it just needs to be a single jump,
doesn't it, with the target patched, and an asm label pointing at the
jump instruction? I was assuming something much more complex, analyzing
the compiler-generated instruction stream for vgetsns(), but you can
of course call something one instruction long that just jumps, and then
there's no analysis at all...
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