Re: [PATCH] x86/mce: Compile do_mca() for CONFIG_PV only

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 19/11/2024 2:34 pm, Jan Beulich wrote:
> On 19.11.2024 13:59, Andrew Cooper wrote:
>> Eclair reports a Misra Rule 8.4 violation; that do_mca() can't see it's
>> declaration.  It turns out that this is a consequence of do_mca() being
>> PV-only, and the declaration being compiled out in !PV builds.
>>
>> Therefore, arrange for do_mca() to be compiled out in !PV builds.  This in
>> turn requires a number of static functions to become static inline.
> Which generally we advocate against.

It's `static inline` or `static __maybe_unused`, but I refer you to to
the Matrix conversation on June 24th on the matter.


>  The #ifdef variant you pointed at on
> Matrix wasn't all that bad.

It worked as a test, but ifdefary like that is a maintenance nightmare.

>  Plus ...
>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> ---
>> CC: Jan Beulich <JBeulich@xxxxxxxx>
>> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
>> CC: consulting@xxxxxxxxxxx <consulting@xxxxxxxxxxx>
>>
>> Bloat-o-meter on a !PV build reports:
>>
>>   add/remove: 0/6 grow/shrink: 0/0 up/down: 0/-3717 (-3717)
>>   Function                                     old     new   delta
>>   x86_mc_mceinject                              31       -     -31
>>   do_mca.cold                                  117       -    -117
>>   x86_mc_msrinject                             147       -    -147
>>   x86_mc_msrinject.cold                        230       -    -230
>>   do_mc_get_cpu_info                           500       -    -500
>>   do_mca                                      2692       -   -2692
> ... what's the effect of the addition of "inline" on a PV=y build? By
> using the keyword, we may end up talking the compiler into inlining of
> code that better wouldn't be inlined.

xen.git/xen$ ../scripts/bloat-o-meter xen-syms-{before,after}
add/remove: 0/0 grow/shrink: 0/0 up/down: 0/0 (0)
Function                                     old     new   delta
Total: Before=3901801, After=3901801, chg +0.00%
xen.git/xen$ diff -u dis-{before,after}
--- dis-before    2024-11-19 18:08:02.284091931 +0000
+++ dis-after    2024-11-19 18:08:24.491035756 +0000
@@ -1,5 +1,5 @@
 
-xen-syms-before:     file format elf64-x86-64
+xen-syms-after:     file format elf64-x86-64
 
 
 Disassembly of section .text:

xen.git/xen$


Which is not surprising because at -O2, the keyword is effectively
ignored because of the various -finline-*

~Andrew