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

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

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.

Thanks, Roger.