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

[Jan Beulich <jbeulich@xxxxxxxx>]

On 07.11.2024 12:25, Roger Pau Monné wrote:
> On Thu, Nov 07, 2024 at 10:48:21AM +0100, 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.
>>
>> 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)?
> 
> At least right now the only way to build useful livepatches for Xen
> (not dummy tests) is using livepatch-build-tools (that requires DWARF
> sections).  My concern with using the Fixes tag was that I don't know
> whether initially the DWARF info was needed or not, or maybe whether
> people used a different tool rather than livepatch-build-tools.
> 
> I don't mind changing, but I also don't think an hypervisor built with
> LIVEPATCH but without DEBUG_INFO is going to be useful to anyone given
> the requirements of the tools we provide to build livepatches.

Well, okay, especially Andrew looks to be pretty strong about this. I
don't want to stand in the way ...

Jan