[xen stable-4.17] include/compat: produce stubs for headers not otherwise generated

[patchbot@xxxxxxx]

commit c871e05e138aae2ac75e9b4ccebe6cf3fd1a775b
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Feb 7 16:57:52 2023 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Feb 7 16:57:52 2023 +0100

    include/compat: produce stubs for headers not otherwise generated
    
    Public headers can include other public headers. Such interdependencies
    are retained in their compat counterparts. Since some compat headers are
    generated only in certain configurations, the referenced headers still
    need to exist. The lack thereof was observed with hvm/hvm_op.h needing
    trace.h, where generation of the latter depends on TRACEBUFFER=y. Make
    empty stubs in such cases (as generating the extra headers is relatively
    slow and hence better to avoid). Changes to .config and incrementally
    (re-)building is covered by the respective .*.cmd then no longer
    matching the command to be used, resulting in the necessary re-creation
    of the (possibly stub) header.
    
    Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
    master commit: 6bec713f871f21c6254a5783c1e39867ea828256
    master date: 2023-01-12 16:17:54 +0100
---
 xen/include/Makefile | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/xen/include/Makefile b/xen/include/Makefile
index 65be310eca..cfd7851614 100644
--- a/xen/include/Makefile
+++ b/xen/include/Makefile
@@ -34,6 +34,8 @@ headers-$(CONFIG_TRACEBUFFER) += compat/trace.h
 headers-$(CONFIG_XENOPROF) += compat/xenoprof.h
 headers-$(CONFIG_XSM_FLASK) += compat/xsm/flask_op.h
 
+headers-n := $(filter-out $(headers-y),$(headers-n) $(headers-))
+
 cppflags-y                := -include public/xen-compat.h 
-DXEN_GENERATING_COMPAT_HEADERS
 cppflags-$(CONFIG_X86)    += -m32
 
@@ -43,13 +45,16 @@ public-$(CONFIG_X86) := $(wildcard 
$(srcdir)/public/arch-x86/*.h $(srcdir)/publi
 public-$(CONFIG_ARM) := $(wildcard $(srcdir)/public/arch-arm/*.h 
$(srcdir)/public/arch-arm/*/*.h)
 
 .PHONY: all
-all: $(addprefix $(obj)/,$(headers-y))
+all: $(addprefix $(obj)/,$(headers-y) $(headers-n))
 
 quiet_cmd_compat_h = GEN     $@
 cmd_compat_h = \
     $(PYTHON) $(srctree)/tools/compat-build-header.py <$< $(patsubst 
$(obj)/%,%,$@) >>$@.new; \
     mv -f $@.new $@
 
+quiet_cmd_stub_h = GEN     $@
+cmd_stub_h = echo '/* empty */' >$@
+
 quiet_cmd_compat_i = CPP     $@
 cmd_compat_i = $(CPP) $(filter-out -Wa$(comma)% -include 
%/include/xen/config.h,$(XEN_CFLAGS)) $(cppflags-y) -o $@ $<
 
@@ -69,6 +74,13 @@ targets += $(headers-y)
 $(obj)/compat/%.h: $(obj)/compat/%.i $(srctree)/tools/compat-build-header.py 
FORCE
        $(call if_changed,compat_h)
 
+# Placeholders may be needed in case files in $(headers-y) include files we
+# don't otherwise generate.  Real dependencies would need spelling out 
explicitly,
+# for them to appear in $(headers-y) instead.
+targets += $(headers-n)
+$(addprefix $(obj)/,$(headers-n)): FORCE
+       $(call if_changed,stub_h)
+
 .PRECIOUS: $(obj)/compat/%.i
 targets += $(patsubst %.h, %.i, $(headers-y))
 $(obj)/compat/%.i: $(obj)/compat/%.c FORCE
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.17