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

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Mon, Jan 22, 2024 at 10:54:13AM +0000, Anthony PERARD wrote:
> On Mon, Jan 22, 2024 at 11:04:41AM +0100, Jan Beulich wrote:
> > On 19.01.2024 16:25, Anthony PERARD wrote:
> > > On Fri, Jan 19, 2024 at 09:43:30AM +0100, Michal Orzel wrote:
> > >> Is my understanding correct that by switching from extra-y to targets we 
> > >> are preventing these objects to
> > >> appear in non-init-objects (and thus having COV_FLAGS appended) while 
> > >> retaining the proper if_changed behavior?
> > >>
> > >> According to docs/misc/xen-makefiles/makefiles.rst:
> > >> Any target that utilises if_changed must be listed in $(targets),
> > >> otherwise the command line check will fail, and the target will
> > >> always be built.
> > > 
> > > Indeed, and $(extra-y) is added to $(targets) via
> > > $(targets-for-builtin).
> > > 
> > > While switching from $(extra-y) to $(targets) prevents the objects from
> > > been added to $(non-init-objets), it doesn't matter because "libelf.o"
> > > is in that variable, so $(COV_FLAGS) is added to $(_c_flags) and its
> > > value is used in all the prerequisites of "libelf.o" which includes
> > > "libelf-temp.o" and for example "libelf-dominfo.o". So the only thing
> > > preventing $(COV_FLAGS) from been added when building "libelf-tools.o"
> > > for example is that we set `COV_FLAGS:=` for "libelf.o".
> > 
> > Yet doesn't that (again) mean things should actually work as-is, [...]
> 
> No, because I've explain how it should work, in the hypothetical world
> where we have `targets += libelf-temp.o $(libelf-objs)`.

The problem is that there's currently two "paths" to build libelf-temp.o
(and even three I think for libelf-tools.o libelf-loader.o
libelf-dominfo.o):

Simplified makefile:

    obj-y := libelf.o
    extra-y := libelf-temp.o
    COV_FLAGS := -fcoverage

    __build: $(extra-y) built_in.o
    built_in.o: $(obj-y)
    libelf.o: COV_FLAGS :=
    libelf.o: libelf-temp.o

So, make can build "libelf-temp.o" as prerequisite of "__build" the
default target, or as prerequisite of "libelf.o".
In the first case, COV_FLAGS would have all the flags, and in the second
case, COV_FLAGS would be reset, but that second case is too late as make
is more likely to have already built libelf-temp.o with all the flags.

Cheers,

-- 
Anthony PERARD