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

[Michal Orzel <michal.orzel@xxxxxxx>]

Hi Jan,

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.

~Michal