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Re: [PATCH v2 3/4] xen: arm: enable stack protector feature
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Date: Mon, 9 Dec 2024 12:45:44 +0000
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- Cc: Julien Grall <julien.grall.oss@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Delivery-date: Mon, 09 Dec 2024 12:45:57 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHbQsSdZeSazgkTckCfCx9gDu8jUA==
- Thread-topic: [PATCH v2 3/4] xen: arm: enable stack protector feature
Hi Jan,
Jan Beulich <jbeulich@xxxxxxxx> writes:
[...]
>
>> #else
>> const unsigned long a = 2862933555777941757;
>> #endif
>> const unsigned c = 1;
>
> I'm having a hard time seeing why this need to be a static variable. Its
> sole use is ...
It's a constant in a hope that compiler is smart enough to optimize it out.
>> unsigned long cycles = get_cycles();
>>
>> if ( !cycles )
>> return;
>>
>> __stack_chk_guard = cycles * a + c;
>
> ... here, where you can as well write a literal 1.
For readability. Formula for LCG is X_n+1 = (X_n * a + c) mod m.
--
WBR, Volodymyr
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