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Date: Fri, 12 Jun 2020 20:38:35 +0200
From: Adam Zabrocki <>
Subject: Re: RE: ISRA optimized functions

On Fri, Jun 12, 2020 at 07:03:06PM +0200, Mikhail Morfikov wrote:
> On 12/06/2020 16:07, Adam Zabrocki wrote:
> > As you can see, even CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE is configured, so this 
> > is "lowlatency" kernel, and CONSTPROP optimization is enforced in various 
> > places (590 funtions was optimized using this method), function "lookup_fast" 
> > is not touched. This is Ubuntu 20.xx kernel package.
> > The main reason why you have that problem is unusual and specific kernel 
> > configuration which allows for such optimization.
> But the kernel config I have is the same I had with gcc9 -- nothing has changed 
> here, and in the case of gcc9 I also have lookup_fast without the constprop, 
> which I already mentioned. So something has changed in gcc10 itself, and I don't 
> know what that would be. Maybe you could try building a kernel with gcc10 and
> check whether you also have this issue? In this way we could confirm that 
> there's a problem with gcc10.

Using GCC version 10.0.1, exactly:

gcc version 10.0.1 20200411 (experimental) [master revision bb87d5cc77d:75961caccb7:f883c46b4877f637e0fa5025b4d6b5c9040ec566] (Ubuntu 10-20200411-0ubuntu1)

$ cat /proc/version
Linux version 5.7.0-g4 (root@oi3) (gcc version 10.0.1 20200411 (experimental) [master revision bb87d5cc77d:75961caccb7:f883c46b4877f637e0fa5025b4d6b5c9040ec566] (Ubuntu 10-20200411-0ubuntu1), GNU ld (GNU Binutils for Ubuntu) 2.34) #28 SMP PREEMPT Fri Jun 12 18:09:14 UTC 2020

$ cat /proc/kallsyms |grep lookup_fast|head -1
0000000000000000 t lookup_fast

However, as I mentioned in my previous emails, I need to discuss and research 
more in details if adding such non-standard kernel configuration / compilation 
support makes sense from LKRG perspective. Maybe it does, maybe not.


pi3 (pi3ki31ny) - pi3 (at) itsec pl

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