Re: [XEN PATCH v5 04/16] xen/build: have the root Makefile generates the CFLAGS

[Jan Beulich <jbeulich@xxxxxxxx>]

On 21.04.2020 18:11, Anthony PERARD wrote:
> Instead of generating the CFLAGS in Rules.mk everytime we enter a new
> subdirectory, we are going to generate most of them a single time, and
> export the result in the environment so that Rules.mk can use it.  The
> only flags left to be generated are the ones that depend on the
> targets, but the variable $(c_flags) takes care of that.
> 
> Arch specific CFLAGS are generated by a new file "arch/*/arch.mk"
> which is included by the root Makefile.
> 
> We export the *FLAGS via the environment variables XEN_*FLAGS because
> Rules.mk still includes Config.mk and would add duplicated flags to
> CFLAGS.
> 
> When running Rules.mk in the root directory (xen/), the variable
> `root-make-done' is set, so `need-config' will remain undef and so the
> root Makefile will not generate the cflags again.
> 
> We can't use CFLAGS in subdirectories to add flags to particular
> targets, instead start to use CFLAGS-y. Idem for AFLAGS.
> So there are two different CFLAGS-y, the one in xen/Makefile (and
> arch.mk), and the one in subdirs that Rules.mk is going to use.
> We can't add to XEN_CFLAGS because it is exported, so making change to
> it might be propagated to subdirectory which isn't intended.
> 
> Some style change are introduced in this patch:
>     when LDFLAGS_DIRECT is included in LDFLAGS
>     use of CFLAGS-$(CONFIG_INDIRECT_THUNK) instead of ifeq().
> 
> The LTO change hasn't been tested properly, as LTO is marked as
> broken.
> 
> Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>

While committing this, in my pre-push build test I noticed that
presumably an earlier change of yours has caused

Makefile:103: include/config/auto.conf: No such file or directory
Makefile:106: include/config/auto.conf.cmd: No such file or directory

for a build in a completely fresh tree.

Jan