Hi Jan, > On 23 Nov 2020, at 15:20, Jan Beulich <jbeul...@suse.com> wrote: > > This case can occur when combining empty lists > > obj-y := > ... > obj-y += $(empty) > > or > > obj-y := $(empty) $(empty) > > where (only) blanks would accumulate. This was only a latent issue until > now, but would become an active issue for Arm once lib/ gets populated > with all respective objects going into the to be introduced lib.a. > > Also address a related issue at this occasion: When an empty built_in.o > gets created, .built_in.o.d will have its dependencies recorded. If, on > a subsequent incremental build, an actual constituent of built_in.o > appeared, the $(filter-out ) would leave these recorded dependencies in > place. But of course the linker won't know what to do with C header > files. (The apparent alternative of avoiding to pass $(c_flags) or > $(a_flags) would not be reliable afaict, as among these flags there may > be some affecting information conveyed via the object file to the > linker. The linker, finding inconsistent flags across object files, may > then error out.) Using just $(obj-y) won't work either: It breaks when > the same object file is listed more than once. > > Reported-by: Julien Grall <jul...@xen.org> > Signed-off-by: Jan Beulich <jbeul...@suse.com> Reviewed-by: Bertrand Marquis <bertrand.marq...@arm.com>
Cheers Bertrand > --- > xen/Rules.mk | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > diff --git a/xen/Rules.mk b/xen/Rules.mk > index 333e19bec343..d5e5eb33de39 100644 > --- a/xen/Rules.mk > +++ b/xen/Rules.mk > @@ -130,13 +130,13 @@ c_flags += $(CFLAGS-y) > a_flags += $(CFLAGS-y) $(AFLAGS-y) > > built_in.o: $(obj-y) $(extra-y) > -ifeq ($(obj-y),) > +ifeq ($(strip $(obj-y)),) > $(CC) $(c_flags) -c -x c /dev/null -o $@ > else > ifeq ($(CONFIG_LTO),y) > - $(LD_LTO) -r -o $@ $(filter-out $(extra-y),$^) > + $(LD_LTO) -r -o $@ $(filter $(obj-y),$^) > else > - $(LD) $(XEN_LDFLAGS) -r -o $@ $(filter-out $(extra-y),$^) > + $(LD) $(XEN_LDFLAGS) -r -o $@ $(filter $(obj-y),$^) > endif > endif > > @@ -145,10 +145,10 @@ targets += $(filter-out $(subdir-obj-y), $(obj-y)) > $(extra-y) > targets += $(MAKECMDGOALS) > > built_in_bin.o: $(obj-bin-y) $(extra-y) > -ifeq ($(obj-bin-y),) > +ifeq ($(strip $(obj-bin-y)),) > $(CC) $(a_flags) -c -x assembler /dev/null -o $@ > else > - $(LD) $(XEN_LDFLAGS) -r -o $@ $(filter-out $(extra-y),$^) > + $(LD) $(XEN_LDFLAGS) -r -o $@ $(filter $(obj-bin-y),$^) > endif > > # Force execution of pattern rules (for which PHONY cannot be directly used). > -- > 2.22.0 > > >
