Re: [XEN PATCH v9 23/30] build,x86: remove the need for build32.mk

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Thu, Mar 03, 2022 at 11:29:36AM +0100, Jan Beulich wrote:
> On 25.01.2022 12:00, Anthony PERARD wrote:
> > Rework "arch/x86/boot/Makefile" to allow it to build both file
> > "cmdline.S" and "reloc.S" without "build32.mk".
> > 
> > These will now use the main rules for "%.o: %.c", and thus generate a
> > dependency file. (We will not need to track the dependency manually
> > anymore.)
> > 
> > But for that, we need to override the main CFLAGS to do a 32bit build.
> > We introduce XEN_TREEWIDE_CFLAGS which can be reused in boot/Makefile,
> > and avoid the need to reparse Config.mk with a different value for
> > XEN_TARGET_ARCH. From this new $(XEN_TREEWIDE_CFLAGS), we only need to
> > change -m64 to have the 32bit flags. Then those are applied only to
> > "cmdline.o" and "reloc.o".
> > 
> > Specifically apply the rule "%.S: %.bin" to both cmdline.S and reloc.S
> > to avoid make trying to regenerate other %.S files with it.
> > 
> > There is no change expected to the resulting "cmdline.S" and
> > "reloc.S", only the *.o file changes as their symbol for FILE goes
> > from "cmdline.c" to "arch/x86//cmdline.c". (No idea why "boot" is
> > missing from the string.) (I've only check with GCC, not clang.)
> > 
> > Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
> 
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> with one question, just to be sure I understand things right:
> 
> > --- a/xen/arch/x86/boot/Makefile
> > +++ b/xen/arch/x86/boot/Makefile
> > @@ -1,25 +1,42 @@
> >  obj-bin-y += head.o
> > +head-srcs := cmdline.S reloc.S
> >  
> > -DEFS_H_DEPS = $(abs_srctree)/$(src)/defs.h 
> > $(abs_srctree)/include/xen/stdbool.h
> > +nocov-y += $(head-srcs:.S=.o)
> > +noubsan-y += $(head-srcs:.S=.o)
> > +targets += $(head-srcs:.S=.o)
> >  
> > -CMDLINE_DEPS = $(DEFS_H_DEPS) $(abs_srctree)/$(src)/video.h \
> > -          $(BASEDIR)/include/xen/kconfig.h \
> > -          $(BASEDIR)/include/generated/autoconf.h
> > +head-srcs := $(addprefix $(obj)/, $(head-srcs))
> >  
> > -RELOC_DEPS = $(DEFS_H_DEPS) \
> > -        $(BASEDIR)/include/generated/autoconf.h \
> > -        $(BASEDIR)/include/xen/kconfig.h \
> > -        $(BASEDIR)/include/xen/multiboot.h \
> > -        $(BASEDIR)/include/xen/multiboot2.h \
> > -        $(BASEDIR)/include/xen/const.h \
> > -        $(BASEDIR)/include/public/arch-x86/hvm/start_info.h
> > +$(obj)/head.o: $(head-srcs)
> >  
> > -$(obj)/head.o: $(obj)/cmdline.S $(obj)/reloc.S
> > +CFLAGS_x86_32 := $(subst -m64,-m32 -march=i686,$(XEN_TREEWIDE_CFLAGS))
> > +$(call cc-options-add,CFLAGS_x86_32,CC,$(EMBEDDED_EXTRA_CFLAGS))
> > +CFLAGS_x86_32 += -Werror -fno-builtin -g0 -msoft-float
> > +CFLAGS_x86_32 += -I$(srctree)/include
> >  
> > -$(obj)/cmdline.S: $(src)/cmdline.c $(CMDLINE_DEPS) $(src)/build32.lds
> > -   $(MAKE) -f $(abs_srctree)/$(src)/build32.mk -C $(obj) $(@F) 
> > CMDLINE_DEPS="$(CMDLINE_DEPS)"
> > +# override for 32bit binaries
> > +$(head-srcs:.S=.o): CFLAGS_stack_boundary :=
> 
> You overriding CFLAGS_stack_boundary but not object_label_flags is
> merely because the latter has no (unwanted) effect on the compilation?

Yes.

Thanks,

-- 
Anthony PERARD