[Xen-devel] compile flags overrides

["Jan Beulich" <JBeulich@xxxxxxxx>]

All,

looks like for the tools part of the tree, at least something has been
done to that effect (via APPEND_CFLAGS).

I don't see how one is supposed to override (e.g. optimization level,
or add to) CFLAGS for the hypervisor part of the build though.

Passing CFLAGS= as make option would suppress all += additions
throughout the makefiles, as they're not being done with "override".

Passing CFLAGS through the environment accumulates the
additions to the variable as the tree gets recursed through (i.e.
at the second recursion level you end up having all flags specified
three times). While that might not appear to be a problem, it really
is (besides being rather odd in the first place) for the EFI build:
The tool chain capability detection passes $(CFLAGS) with
$(CFLAGS-y) stripped off (in particular to suppress the use of
"-MMD -MF -$(@F).d", as $@ and $(@F) are not defined in this
context), thus leaving - from the upper recursion levels - .xen.d
and .built_in.d as stray input files on the command line.

I don't think passing CFLAGS itself through either means is really
to be supported (other than someone passing the _full_ set of
them, suppressing _everything_ the build scripts do, say for
build process debugging purposes). Instead, a separate variable
intended for just that purpose ought to be introduced and then
appended to CFLAGS. Question of course is whether that ought
to be uniform for all subtrees, or separate for each of them.

Opinions, ideas?

Jan


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