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SubjectRe: [RFC 1/3] kbuild: add support for ensuring headers are self-contained
Hi Jani

> Sometimes it's useful to be able to explicitly ensure certain headers
> remain self-contained, i.e. that they are compilable as standalone
> units, by including and/or forward declaring everything they depend on.
>
> Add special target header-test-y where individual Makefiles can add
> headers to be tested if CONFIG_HEADER_TEST is enabled. This will
> generate a dummy C file per header that gets built as part of extra-y.

Very useful, thanks.
I have cooked up something ad-hoc a couple of times but having it as a
standard feature in the build system is much better.
The we can let some of our infrastructure pick up an issues
automatically.

>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
> Cc: Michal Marek <michal.lkml@markovi.net>
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> ---
> Documentation/kbuild/makefiles.txt | 7 +++++++
> init/Kconfig | 9 +++++++++
> scripts/Makefile.build | 10 ++++++++++
> scripts/Makefile.lib | 3 +++
> 4 files changed, 29 insertions(+)
>
> diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt
> index 03c065855eaf..73df58e5ea0c 100644
> --- a/Documentation/kbuild/makefiles.txt
> +++ b/Documentation/kbuild/makefiles.txt
> @@ -1036,6 +1036,13 @@ When kbuild executes, the following steps are followed (roughly):
> In this example, extra-y is used to list object files that
> shall be built, but shall not be linked as part of built-in.a.
>
> + header-test-y
> +
> + header-test-y specifies headers (*.h) in the current directory that
> + should be compile tested to ensure they are self-contained,
> + i.e. compilable as standalone units. If CONFIG_HEADER_TEST is enabled,
> + this autogenerates dummy sources to include the headers, and builds them
> + as part of extra-y.
Do we want to restrict this to current directory only?
Sometimes we could use this for headers in include/ but let it
trigger for the relevant subsystem.
So for example drivers/gpu/drm/Makefile will include the rules
for all headers in include/drm/*

The alternative would be Makefiles (of Kbuild files)
scattered in the directories with headers and then some
infrastructure to visit those.

Follow patch extend the header-test feature to work with
headers in include/

Example:
# Header files from this directory
header-test-y += drm_crtc_helper_internal.h
header-test-y += drm_crtc_internal.h
..
.
# Header files from include/drm
header-test-y += drm/amd_asic_type.h
header-test-y += drm/ati_pcigart.h
...


In the patch $* is used to get the "stem" from the pattern.
This is the filname of the header file without extension.


Sam


diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 4d4bf698467a..ca132ab3a551 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -295,11 +295,10 @@ $(obj)/%.lst: $(src)/%.c FORCE
# ---------------------------------------------------------------------------

quiet_cmd_header_test = HDRTEST $@
- cmd_header_test = echo "\#include \"$(<F)\"" > $@
+ cmd_header_test = echo "\#include <$(2).h>" > $@

-# FIXME: would be nice to be able to limit this implicit rule to header-test-y
-$(obj)/%.header_test.c: $(src)/%.h FORCE
- $(call if_changed,header_test)
+$(obj)/%.header_test.c:
+ $(call cmd,header_test,$*)

# Compile assembler sources (.S)
# ---------------------------------------------------------------------------
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