Re: [Tarantool-patches] [PATCH luajit 1/2] Fix register mask for stack check in head of side trace.

[Maxim Kokryashkin via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

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Hi, Sergey!
Thanks for the explanation!
LGTM
--
Best regards,
Maxim Kokryashkin
 
  
>Понедельник, 23 октября 2023, 12:32 +03:00 от Sergey Kaplun <skaplun@tarantool.org>:
> 
>Hi, Maxim!
>Thanks for the review!
>Please, consider my answers below.
>
>On 13.10.23, Maxim Kokryashkin wrote:
>> Hi, Sergey!
>> Thanks for the patch!
>> LGTM, except for a few nits below.
>> On Wed, Oct 11, 2023 at 06:04:09PM +0300, Sergey Kaplun wrote:
>> > From: Mike Pall <mike>
>> >
>> > Analyzed by Sergey Kaplun.
>> >
>> > (cherry-picked from commit b7a8c7c184257858699454408420dd5f0b6c8a75)
>> >
>> > Assume we have parent and child traces with the following IRs from the
>> > IR dump:
>> >
>> > Parent:
>> > | 0009 rax > tab TNEW 0 0
>> > | 0010 p32 FLOAD 0008 tab.node
>> > | 0011 p32 HREFK 0010 "Name" @1
>> > | 0012 {0008} tab HSTORE 0011 0009
>> > | .... SNAP 2 [ ---- 0001 0002 0008 ---- ]
>> > | 0013 {sink} tab TNEW 0 0
>> > | 0014 {0008} fal HSTORE 0011 false
>> > | .... SNAP 3 [ ---- 0001 0002 0008 ---- ]
>> >
>> > Child:
>> > | 0001 r15 tab SLOAD 1 PI
>> > | 0002 rbp tab SLOAD 2 PI
>> > | 0003 tab PVAL 9
>> >
>> > As we can see from the trace dump above, the `rax` register is missing
>> > in the `0003 PVAL` IR for the side trace -- so it is assumed to be
>> > available in the allow RegSet inside `asm_stack_check()` and its value
>> > is spoiled during this check, so if we are restoring from the 3rd
>> Typo: s/spoiled/spilled/
>
>I mean spoiled (damaged) (with incorrect value) here -- there is no spill, but
>incorrect value as `ir->r`.
>
>> > snapshot by stack overflow -- we are in trouble.
>> >
>> > The moment when IR is spoiled is when we set a hint on the register
>> Typo: s/spoiled/spilled/
>
>Ditto.
>
>> > inherited from the parent trace (see `asm_setup_regsp()` for details).
>
><snipped>
>
>> >
>
>--
>Best regards,
>Sergey Kaplun
 

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