Re: [Xen-devel] [XEN PATCH v3 15/23] xen/build: have the root Makefile generates the CFLAGS

From: Jan Beulich <jbeulich@suse.com>
To: Anthony PERARD <anthony.perard@citrix.com>
Cc: "Stefano Stabellini" <sstabellini@kernel.org>,
	"Julien Grall" <julien@xen.org>, "Wei Liu" <wl@xen.org>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
	"George Dunlap" <George.Dunlap@eu.citrix.com>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Ian Jackson" <ian.jackson@eu.citrix.com>,
	xen-devel@lists.xenproject.org,
	"Daniel De Graaf" <dgdegra@tycho.nsa.gov>,
	"Volodymyr Babchuk" <Volodymyr_Babchuk@epam.com>,
	"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [XEN PATCH v3 15/23] xen/build: have the root Makefile generates the CFLAGS
Date: Wed, 4 Mar 2020 16:00:52 +0100	[thread overview]
Message-ID: <dd7bf903-6f51-7610-3963-2b572a6bde49@suse.com> (raw)
In-Reply-To: <20200226113355.2532224-16-anthony.perard@citrix.com>

On 26.02.2020 12:33, Anthony PERARD wrote:
> @@ -113,6 +115,64 @@ $(KCONFIG_CONFIG):
>  include/config/%.conf include/config/%.conf.cmd: $(KCONFIG_CONFIG)
>  	$(MAKE) -f $(BASEDIR)/tools/kconfig/Makefile.kconfig ARCH=$(ARCH) SRCARCH=$(SRCARCH) HOSTCC="$(HOSTCC)" HOSTCXX="$(HOSTCXX)" syncconfig
>  
> +ifeq ($(CONFIG_DEBUG),y)
> +CFLAGS += -O1
> +else
> +CFLAGS += -O2
> +endif
> +
> +ifeq ($(CONFIG_FRAME_POINTER),y)
> +CFLAGS += -fno-omit-frame-pointer
> +else
> +CFLAGS += -fomit-frame-pointer
> +endif
> +
> +CFLAGS += -nostdinc -fno-builtin -fno-common
> +CFLAGS += -Werror -Wredundant-decls -Wno-pointer-arith
> +$(call cc-option-add,CFLAGS,CC,-Wvla)
> +CFLAGS += -pipe -D__XEN__ -include $(BASEDIR)/include/xen/config.h
> +CFLAGS-$(CONFIG_DEBUG_INFO) += -g
> +
> +ifneq ($(CONFIG_CC_IS_CLANG),y)
> +# Clang doesn't understand this command line argument, and doesn't appear to
> +# have an suitable alternative.  The resulting compiled binary does function,
> +# but has an excessively large symbol table.
> +CFLAGS += -Wa,--strip-local-absolute
> +endif
> +
> +AFLAGS += -D__ASSEMBLY__
> +
> +CFLAGS += $(CFLAGS-y)

I can't seem to be able to spot a similar line for AFLAGS.

> @@ -107,7 +65,7 @@ $(foreach o,$(filter-out %/,$(obj-y) $(obj-bin-y) $(extra-y)),$(eval $(call gend
>  subdir-y := $(subdir-y) $(filter %/, $(obj-y))
>  obj-y    := $(patsubst %/, %/built_in.o, $(obj-y))
>  
> -$(filter %.init.o,$(obj-y) $(obj-bin-y) $(extra-y)): CFLAGS += -DINIT_SECTIONS_ONLY
> +$(filter %.init.o,$(obj-y) $(obj-bin-y) $(extra-y)): CFLAGS-y += -DINIT_SECTIONS_ONLY

While in the description you say "We can't use CFLAGS in
subdirectories to add flags to particular targets, ...", it
remains unclear there why that is, and hence why changes like
this one are necessary. If this is a restriction that's going to
remain, this also needs writing down in a prominent place. After
all if (for example) special compiler options are needed, CFLAGS
would be the natural thing one would want to alter. (Even better
if wrong playing with CFLAGS could be detected and at least
warned about, but I'm completely unclear on how feasible this
would be.)

> diff --git a/xen/arch/arm/Rules.mk b/xen/arch/arm/Rules.mk
> index 022a3a6f82ba..e69de29bb2d1 100644
> --- a/xen/arch/arm/Rules.mk
> +++ b/xen/arch/arm/Rules.mk
> @@ -1,93 +0,0 @@

As per the header here you're using git. Can you please arrange for
this file movement (to arch.mk, and also for x86) to actually be
expressed here as a rename, i.e. such that one can see what - if
anything - changes?

Jan

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