Re: [PATCH] xen/Kconfig: livepatch-build-tools requires debug information

[Jan Beulich <jbeulich@xxxxxxxx>]

On 07.11.2024 12:30, Andrew Cooper wrote:
> On 07/11/2024 9:48 am, Jan Beulich wrote:
>> On 07.11.2024 10:40, Roger Pau Monné wrote:
>>> On Thu, Nov 07, 2024 at 09:21:26AM +0000, Andrew Cooper wrote:
>>>> On 07/11/2024 8:49 am, Roger Pau Monne wrote:
>>>>> The tools infrastructure used to build livepatches for Xen
>>>>> (livepatch-build-tools) consumes some DWARF debug information present in
>>>>> xen-syms to generate a livepatch (see livepatch-build script usage of 
>>>>> readelf
>>>>> -wi).
>>>>>
>>>>> The current Kconfig defaults however will enable LIVEPATCH without 
>>>>> DEBUG_INFO
>>>>> on release builds, thus providing a default Kconfig selection that's not
>>>>> suitable for livepatch-build-tools even when LIVEPATCH support is enabled,
>>>>> because it's missing the DWARF debug section.
>>>>>
>>>>> Fix by forcing the selection of DEBUG_INFO from LIVEPATCH.
>>>>>
>>>>> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>>>> Oops, yes.
>>>>
>>>> Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>>>
>>>> Fixes tag ?
>>> Was borderline on adding one, but wasn't sure since it's strictly
>>> livepatch-build-tools that requires the DWARF data, but custom made
>>> livepatches (like the examples in tests) do not require such
>>> information.
> 
> Ok.  I guess it doesn't matter too much.
> 
>> At which point: Is "select" really appropriate then? Wouldn't it be more
>> logical then to change DEBUG_INFO's default to take LIVEPATCH into account
>> (still permitting people to turn debug info off if they know they won't
>> need it)?
> 
> I am very disinterested in letting people who think they can do
> livepatching without debug symbols shoot themselves in the foot like that.
> 
> It's only debugging symbols.   If people *really* think they know
> better, they can strip them themselves.

Besides my abstract concern, let me also add a concrete practical one. I'm
sure you've noticed that xen.efi is _much_ slower to link with debug info
than without, or than xen-syms. That's a consequence of how GNU ld (really:
libbfd) works internally. By not allowing DEBUG_INFO to stay off you're
forcing me to either wait longer for every single one of my post-commit
pre-push build tests, or to turn off LIVEPATCH there. The latter not really
being a good idea.

Nevertheless, as said in reply to Roger: Go ahead if you absolutely think
that's the only sensible way.

Jan