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Re: [PATCH] x86/ACPI: Fix build error when tboot is disabled


  • To: Jan Beulich <jbeulich@xxxxxxxx>, Costin Lupu <costin.lupu@xxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Thu, 29 Apr 2021 14:51:48 +0100
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  • Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
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On 29/04/2021 14:42, Jan Beulich wrote:
> On 29.04.2021 15:22, Costin Lupu wrote:
>> On 4/29/21 3:40 PM, Jan Beulich wrote:
>>> If there is a specific case where the compiler fails to DCE the
>>> offending code, then you need to describe this in sufficient
>>> detail.
>> Yes, indeed. My bad, it is for a debug build with -O0, so without DCE.
> Iirc there's a series pending to switch to -Og; I don't think we
> build with -O0 under any circumstances (for this very reason).

-Og is roughly about -O0.9.  There is certainly some trivial DCE
involved, but no optimisations which radically rearrange the code
structure.  The -Og series did survive some randconfig testing, but I
can't guarantee that it was comprehensive.

As for -O0, I think causality is the other way around there.  Wei
elected to rely on DCE for conditional compilation because we didn't
seem to care about compiling at -O0.


Part of me thinks that we ought to cope compiling at any optimisation
level, including -O0, but I doubt I'd like the extra ifdef-ary required
to make that work.

I think we absolutely should have Kconfig to select between -Og/1/2/3,
as well as binutils new microarch levels

~Andrew




 


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