[XEN PATCH v2 1/4] build,include: rework shell script for headers++.chk

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

The command line generated for headers++.chk by make is quite long,
and in some environment it is too long. This issue have been seen in
Yocto build environment.

Error messages:
    make[9]: execvp: /bin/sh: Argument list too long
    make[9]: *** [include/Makefile:181: include/headers++.chk] Error 127

Rework so that we do the foreach loop in shell rather that make to
reduce the command line size by a lot. We also need a way to get
headers prerequisite for some public headers so we use a switch "case"
in shell to be able to do some simple pattern matching. Variables
alone in POSIX shell don't allow to work with associative array or
variables with "/".

Reported-by: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>
Fixes: 28e13c7f43 ("build: xen/include: use if_changed")
Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
---

Notes:
    v2:
    - fix typo in commit message
    - fix out-of-tree build
    
    v1:
    - was sent as a reply to v1 of the series

 xen/include/Makefile | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/xen/include/Makefile b/xen/include/Makefile
index 6d9bcc19b0..49c75a78f9 100644
--- a/xen/include/Makefile
+++ b/xen/include/Makefile
@@ -158,13 +158,22 @@ define cmd_headerscxx_chk
            touch $@.new;                                                     \
            exit 0;                                                           \
        fi;                                                                   \
-       $(foreach i, $(filter %.h,$^),                                        \
-           echo "#include "\"$(i)\"                                          \
+       get_prereq() {                                                        \
+           case $$1 in                                                       \
+           $(foreach i, $(filter %.h,$^),                                    \
+           $(if $($(patsubst $(srctree)/%,%,$(i))-prereq),                   \
+               $(i)$(close)                                                  \
+               echo "$(foreach j, $($(patsubst $(srctree)/%,%,$(i))-prereq), \
+                       -include c$(j))";;))                                  \
+           esac;                                                             \
+       };                                                                    \
+       for i in $(filter %.h,$^); do                                         \
+           echo "#include "\"$$i\"                                           \
            | $(CXX) -x c++ -std=gnu++98 -Wall -Werror -D__XEN_TOOLS__        \
              -include stdint.h -include $(srcdir)/public/xen.h               \
-             $(foreach j, $($(patsubst $(srctree)/%,%,$i)-prereq), -include 
c$(j)) \
+             `get_prereq $$i`                                                \
              -S -o /dev/null -                                               \
-           || exit $$?; echo $(i) >> $@.new;) \
+           || exit $$?; echo $$i >> $@.new; done;                            \
        mv $@.new $@
 endef
 
-- 
Anthony PERARD