On Sun, 25 Aug 2019 18:28:32 +0100,
Masahiro Yamada [off-list ref] wrote:

Kbuild provides per-file compiler flag addition/removal:

  CFLAGS_<basetarget>.o
  CFLAGS_REMOVE_<basetarget>.o
  AFLAGS_<basetarget>.o
  AFLAGS_REMOVE_<basetarget>.o
  CPPFLAGS_<basetarget>
  HOSTCFLAGS_<basetarget>.o
  HOSTCXXFLAGS_<basetarget>.o

The <basetarget> is the filename of the target without its suffix.

This syntax comes into a trouble when two files with the same name
appear in one Makefile, for example:

  obj-y += foo.o
  obj-y += dir/foo.o
  CFLAGS_foo.o := <some-flags>

Here, the <some-flags> applies to both foo.o and dir/foo.o

The real world problem is:

  scripts/kconfig/util.c
  scripts/kconfig/lxdialog/util.c

Both files are compiled into scripts/kconfig/mconf, but only the
latter should be given with additional flags for ncurses.

It is more sensible to use the relative path to the Makefile, like this:

  obj-y += foo.o
  CFLAGS_foo.o := <some-flags>
  obj-y += dir/foo.o
  CFLAGS_dir/foo.o := <other-flags>

The $* variable is replaced with the stem ('%') part in a pattern rule.
In other words, this only works for pattern rules.

Signed-off-by: Masahiro Yamada <redacted>
---

 arch/arm/kvm/Makefile        |  5 +++--
 arch/x86/entry/vdso/Makefile |  3 ++-
 scripts/Makefile.host        | 30 +++++++++++++++---------------
 scripts/Makefile.lib         | 10 +++++-----
 scripts/kconfig/Makefile     |  8 ++++----
 5 files changed, 29 insertions(+), 27 deletions(-)

For the KVM/arm part:

Acked-by: Marc Zyngier <maz@kernel.org>

Thanks,

	M.

-- 
Jazz is not dead, it just smells funny.

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