Re: [PATCH] coverage: filter out lib{fdt,elf}-temp.o

[Jan Beulich <jbeulich@xxxxxxxx>]

On 18.01.2024 15:40, Michal Orzel wrote:
> On 18/01/2024 14:12, Jan Beulich wrote:
>> On 18.01.2024 13:06, Michal Orzel wrote:
>>> At the moment, trying to run xencov read/reset (calling SYSCTL_coverage_op
>>> under the hood) results in a crash. This is due to an attempt to
>>> access code in the .init.* sections (libfdt for Arm and libelf for x86)
>>> that are stripped after boot. Normally, the build system compiles any
>>> *.init.o file without COV_FLAGS. However, these two libraries are
>>> handled differently as sections will be renamed to init after linking.
>>>
>>> This worked until e321576f4047 ("xen/build: start using if_changed")
>>> that added lib{fdt,elf}-temp.o to extra-y. Any file listed there without
>>> *.init.o suffix will be part of non-init-objects for which COV_FLAGS
>>> will be appended.
>>
>> While this is true, aiui COV_FLAGS would be empty for anything listed
>> in nocov-y and all of the prerequisites of those objects (iirc target-
>> specific variable settings propagate to prerequisites). Therefore ...
> I'm not sure about this propagation.
> 
>>
>>> In such case, the solution is to add a file to nocov-y.
>>
>> ... libelf.o / libfdt.o already being listed there ought to suffice.
>> Alternatively listing only libelf-temp.o / libfdt-temp.o ought to
>> suffice as well.
>>
>> Since you apparently observed things not working, I must be missing
>> something.
> As I wrote on Matrix, I'm not a build system expert so it might be that the 
> issue
> is due to something else. I managed to find a commit after which building the 
> libfdt/libelf
> with coverage enabled resulted in .gcno files being present. This commit 
> added libfdt-temp.o
> (same as libfdt.o but without sections renaming) to extra-y, hence my fix.

You should probably have Cc-ed Anthony on the submission. Doing so now,
so at least he's aware (and may then also look at the patch).

Jan