Re: [Xen-devel] [XEN PATCH v2 02/12] xen/build: Use obj-y += subdir/ instead of subdir-y

[Jan Beulich <jbeulich@xxxxxxxx>]

On 17.01.2020 11:53, Anthony PERARD wrote:
> This is part of upgrading our build system and import more of Linux's
> one.
> 
> In Linux, subdir-y in Makefiles is only used to descend into
> subdirectory when there are no object to build, Xen doesn't have that
> and all subdir have object to be included in the final binary.
> 
> To allow the new syntax, the "obj-y" and "subdir-*" calculation in
> Rules.mk is changed and partially imported from Linux's Kbuild.
> 
> The command used to modify the Makefile was:
>     sed -i -r 's#^subdir-(.*)#obj-\1/#;' **/Makefile
> 
> Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
with two remarks:

> --- a/xen/Rules.mk
> +++ b/xen/Rules.mk
> @@ -105,17 +105,16 @@ define gendep
>  endef
>  $(foreach o,$(filter-out %/,$(obj-y) $(obj-bin-y) $(extra-y)),$(eval $(call 
> gendep,$(o))))
>  
> -# Ensure each subdirectory has exactly one trailing slash.
> -subdir-n := $(patsubst %,%/,$(patsubst %/,%,$(subdir-n) $(subdir-)))
> -subdir-y := $(patsubst %,%/,$(patsubst %/,%,$(subdir-y)))
> -
> -# Add explicitly declared subdirectories to the object lists.
> -obj-y += $(patsubst %/,%/built_in.o,$(subdir-y))
> -
> -# Add implicitly declared subdirectories (in the object lists) to the
> -# subdirectory list, and rewrite the object-list entry.
> -subdir-y += $(filter %/,$(obj-y))
> -obj-y    := $(patsubst %/,%/built-in.o,$(obj-y))
> +# Handle objects in subdirs
> +# ---------------------------------------------------------------------------
> +# o if we encounter foo/ in $(obj-y), replace it by foo/built_in.o
> +#   and add the directory to the list of dirs to descend into: $(subdir-y)
> +__subdir-y   := $(filter %/, $(obj-y))
> +subdir-y     += $(__subdir-y)

I realize I'll be called guilty of bike-shedding again, and I also
realize this is the way Linux does it, but what use is the
intermediate __subdir-y? Linux has no 2nd use, and hence I also
don't see why we would gain one. I further think according to our
style there should be no use of tabs here.

> +obj-y                := $(patsubst %/, %/built_in.o, $(obj-y))
> +
> +subdir-n := $(subdir-n) $(subdir-) \
> +             $(filter %/, $(obj-n) $(obj-))

This will easily fit on one line (and isn't anything cloned from
Linux).

Jan

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