Re: [PATCH 2/2] xen: update CONFIG_DEBUG_INFO help text

[Jan Beulich <jbeulich@xxxxxxxx>]

On 07.03.2023 15:23, Juergen Gross wrote:
> On 07.03.23 15:18, Jan Beulich wrote:
>> On 07.03.2023 15:04, Juergen Gross wrote:
>>> On 07.03.23 11:41, Jan Beulich wrote:
>>>> On 07.03.2023 07:32, Juergen Gross wrote:
>>>>> --- a/xen/Kconfig.debug
>>>>> +++ b/xen/Kconfig.debug
>>>>> @@ -15,8 +15,11 @@ config DEBUG_INFO
>>>>>           bool "Compile Xen with debug info"
>>>>>           default DEBUG
>>>>>           ---help---
>>>>> -   If you say Y here the resulting Xen will include debugging info
>>>>> -   resulting in a larger binary image.
>>>>> +   Say Y here if you want to build Xen with debug information. This
>>>>> +   information is needed e.g. for doing crash dump analysis of the
>>>>> +   hypervisor via the "crash" tool.
>>>>> +   Saying Y will increase the size of xen-syms and the built EFI
>>>>> +   binary.
>>>>
>>>> Largely fine with me, just one question: Why do you mention xen-syms by
>>>> name, but then verbally describe xen.efi? And since, unlike for xen-syms,
>>>
>>> For xen-syms I couldn't find an easily understandable wording. I'd be fine
>>> with just saying "xen.efi".
>>>
>>>> this affects the installed binary actually used for booting (which may
>>>> be placed on a space constrained partition), it may be prudent to
>>>> mention INSTALL_EFI_STRIP here (as a way to reduce the binary size of
>>>> what ends up on the EFI partition, even if that wouldn't affect the
>>>> "normal" way of putting the binary on the EFI partition - people would
>>>> still need to take care of that in their distros).
>>>
>>> What about adding a related Kconfig option instead?
>>
>> How would a Kconfig option possibly affect this? You want debug info
>> in the xen.efi in its standard install location (outside of the EFI
>> partition); or else if you don't want it there why would you want it
>> in xen-syms? It is the step of populating the EFI partition from the
>> standard install location where some equivalent of INSTALL_EFI_STRIP
>> would come into play. That step is done outside of Xen's build
>> system and hence outside of any Kconfig control.
> 
> We have 2 binaries for the non-EFI hypervisor (xen-syms and xen[.gz]).
> Why can't we have the same for EFI? E.g. xen-syms.efi and xen.efi.
> The former would have the debug-info, the latter could be installed
> into the EFI partition.

I view the two-binaries model of the non-EFI case as merely an
implementation detail; it just so happens that there's little point
in mkelf32 retaining debug info. I therefore don't view it as very
reasonable to artificially introduce yet another binary. Another
thing would be if there was a way to produce a binary without
debug info accompanied by a separate file holding just the debug
info. Yet I'm unaware of such being possible with PE/COFF binaries.

But yes - technically this might be an option (although, just to
mention it, I'm having a vague recollection of there being an issue
with this, but I can't say what this might be, plus it is easily
possible that I'm misremembering or mixing up things).

Jan