Re: [PATCH v3 1/8] xen: fix build when $(obj-y) consists of just blanks

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

Hi Jan,

> On 23 Nov 2020, at 15:20, Jan Beulich <jbeulich@xxxxxxxx> 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 <julien@xxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>

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
> 
> 
>