Re: [XEN][PATCH] common/libfdt: optimize usage

[Jan Beulich <jbeulich@suse.com>]

On 21.11.2025 11:59, Grygorii Strashko wrote:
> 
> 
> On 17.11.25 11:34, Jan Beulich wrote:
>> On 17.11.2025 10:31, Jan Beulich wrote:
>>> On 14.11.2025 19:01, Grygorii Strashko wrote:
>>>> From: Grygorii Strashko <grygorii_strashko@epam.com>
>>>>
>>>> Now all libfdt features are built-it unconditionally, but...
>>>>
>>>> X86: The libfdt is used on x86 only to parse Hyperlaunch/dom0less Xen
>>>> nodes, so full libfdt is not needed in this case and minimal, RO
>>>> configuration can be used.
>>>>
>>>> ARM - situation is more complicated:
>>>> 1) ARM reads Host DT (fdt.c RO)
>>>> 2) ARM reads passthrough DT (RO)
>>>> 3) ARM generates dom0/hwdom DT from Host DT (there is a mix of WIP and SW APIs)
>>>> 4) ARM generates domU DT (there is a mix of WIP and SW APIs)
>>>> 4) With EFI enabled - ARM needs RW API and fdt_empty_tree
>>>> 5) With CONFIG_OVERLAY_DTB - ARM needs RW and fdt_overlay API
>>>
>>> This goes too far, imo.
>>
>> The more that, unless OVERLAY_DTB=y, all code and data moves to .init.*. Is
>> coverage in in .init.* really of as much concern as runtime code/data?
> 
> It is less priority, but still is. Any way it is unnecessary build units (build time) and
> increased binary size.
> 
> 
> Actually, I see interesting behavior - when build with CONFIG_CC_SPLIT_SECTIONS=y (CONFIG_LIVEPATCH=y)
> the libfdt code is not moved in ".init"
> 
> 0xa000027aa10 T fdt_ro_probe_
> 
> 0xa00002c0000 T __init_begin

Hmm, that's a bug, resulting from libfdt/ not using the usual machinery to do the
conversion.

Jan