On Fri, Jul 17, 2015 at 12:46 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> On Fri, Jul 17, 2015 at 11:47:28AM -0500, Josh Poimboeuf wrote:
>> stackvalidate reports the following warnings for __schedule():
>>
>> stackvalidate: kernel/sched/core.o: __schedule()+0x3e7: duplicate frame pointer save
>> stackvalidate: kernel/sched/core.o: __schedule()+0x424: sibling call from callable instruction with changed frame pointer
>> stackvalidate: kernel/sched/core.o: __schedule()+0x431: call without frame pointer save/setup
>> stackvalidate: kernel/sched/core.o: __schedule()+0x8b8: frame pointer state mismatch
>> stackvalidate: kernel/sched/core.o: __schedule()+0x447: frame pointer state mismatch
>>
>> __schedule() is obviously a special case which is allowed to do unusual
>> things with the frame pointer.
>
> Yes, but is the code actually correct? We can't dismiss the warnings
> just on that basis alone.
It's really only __switch_to that does weird things, right? I kinda
want to rework that thing anyway to have a well-defined saved state
format anyway, which would have the nice benefit of letting us get rid
of all the ret_from_fork crap.
That is, we'd context switch like:
static inline void __switch_to(...) {
switch extra stuff;
switch everything except gpregs;
asm volatile ("call __switch_stack_and_ip" : [__sp thing goes here]
: "S" (&prev->bottom_of_stack), "D" (&next->bottom_of_stack) :
"basically all regs and flags");
}
Then the low level bit would be:
__switch_stack_and_ip:
pushq %rbp
mov %rsp, (%rsi)
mov (%rdi), %rsp
popq %rbp
ret
Now, when we create a new task, we can set up its stack directly
rather than setting some TI flag, because we actually know the layout.
Hmm?
--Andy
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