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Date: Fri, 12 Jun 2020 09:57:20 +0200
From: Mikhail Morfikov <mmorfikov@...il.com>
To: lkrg-users@...ts.openwall.com
Subject: Re: RE: ISRA optimized functions
On 12/06/2020 00:19, Adam Zabrocki wrote:
>
> I would need to do manual investigation how your build process looks and works.
> However, I don't think it makes any sense.
Actually it's not just my build process, only the kernel's bindeb-pkg target
which I think all people using Debian call when they're building their custom
kernels. It produces simple deb packages that can be installed via
apt-get/aptitude to make the system clean when you don't need them anymore. So
this is quite common technique to build the kernel, at least on Debian/Ubuntu.
> However, which function would be affected by such optimization purely
> depends on the kernel configuration.
I have a question. There's "Compiler optimization level" in the kernel config
with the following options to choose:
CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE:
This is the default optimization level for the kernel, building
with the "-O2" compiler flag for best performance and most
helpful compile-time warnings.
CONFIG_CC_OPTIMIZE_FOR_SIZE:
Choosing this option will pass "-Os" to your compiler resulting
in a smaller kernel.
So either one is used with the default to CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE.
Maybe this is the problem with "-O2"? If so, it's default and I don't think this
"-O2" flag can be removed without changing kernel distro config, which I don't
think is likely to happen. The following is from the Debian default kernel
config:
$ grep CONFIG_CC_OPTIMIZE /boot/config-5.6.0-2-amd64
CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE=y
# CONFIG_CC_OPTIMIZE_FOR_SIZE is not set
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