Re: [XEN PATCH 02/15] build: rework asm-offsets.* build step to use kbuild

[Jan Beulich <jbeulich@xxxxxxxx>]

On 23.05.2023 18:37, Anthony PERARD wrote:
> Use $(if_changed_dep, ) macro to generate "asm-offsets.s" and remove
> the use of $(move-if-changes,). That mean that "asm-offset.s" will be
> changed even when the output doesn't change.
> 
> But "asm-offsets.s" is only used to generated "asm-offsets.h". So
> instead of regenerating "asm-offsets.h" every time "asm-offsets.s"
> change, we will use "$(filechk, )" to only update the ".h" when the
> output change. Also, with "$(filechk, )", the file does get
> regenerated when the rule change in the makefile.
> 
> This changes also result in a cleaner build log.
> 
> Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
> ---
> 
> Instead of having a special $(cmd_asm-offsets.s) command, we could
> probably reuse $(cmd_cc_s_c) from Rules.mk, but that would mean that
> an hypothetical additional flags "-flto" in CFLAGS would not be
> removed anymore, not sure if that matter here.

There's no real code being generated there, and what we're after are
merely the special .ascii directives. So the presence of -flto should
have no effect there, and hence it would even look more consistent to
me if we didn't use different options (and even rules) for .c -> .s
transformations.

> But then we could write this:
> 
> targets += arch/$(TARGET_ARCH)/$(TARGET_SUBARCH)/asm-offsets.s
> arch/$(TARGET_ARCH)/$(TARGET_SUBARCH)/asm-offsets.s: CFLAGS-y += -g0
> arch/$(TARGET_ARCH)/include/asm/asm-offsets.h: 
> arch/$(TARGET_ARCH)/$(TARGET_SUBARCH)/asm-offsets.s FORCE
> 
> instead of having to write a rule for asm-offsets.s

Ftaod, I'd be happy to ack the patch as it is, but I would favor if
you could do the rework / simplification as outlined.

Jan