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SubjectRe: [PATCH v3 0/6] Static calls
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> On Jan 11, 2019, at 8:07 AM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>
> On Fri, Jan 11, 2019 at 03:48:59PM +0000, Nadav Amit wrote:
>>> I liked the idea, BUT, how would it work for callee-saved PV ops? In
>>> that case there's only one clobbered register to work with (rax).
>>
>> That’s would be more tricky. How about using a per-CPU trampoline code to
>> hold a direct call to the target and temporarily disable preemption (which
>> might be simpler by disabling IRQs):
>>

Allow me to simplify/correct:

>> Static-call modifier:
>>
>> 1. synchronize_sched() to ensure per-cpu trampoline is not used
No need for (1) (We are going to sync using IPI).

>> 2. Patches the jmp in a per-cpu trampoline (see below)
>> 3. Saves the call source RIP in [per-cpu scratchpad RIP] (below)
Both do not need to be per-cpu

>> 4. Configures the int3 handler to use static-call int3 handler
>> 5. Patches the call target (as it currently does).
Note that text_poke_bp() would do eventually:

on_each_cpu(do_sync_core, NULL, 1);

So you should know no cores run the trampoline after (5).

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