[tip:sched/core] kbuild: Add option to turn incompatible pointer check into error

[tip-bot for Daniel Wagner]

Commit-ID:  ef50c046338948df9f23fb5ef853efda0274c7b3
Gitweb:     http://git.kernel.org/tip/ef50c046338948df9f23fb5ef853efda0274c7b3
Author:     Daniel Wagner <daniel.wagner@xxxxxxxxxxxx>
AuthorDate: Fri, 19 Feb 2016 09:46:38 +0100
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Thu, 25 Feb 2016 11:27:16 +0100

kbuild: Add option to turn incompatible pointer check into error

With the introduction of the simple wait API we have two very
similar APIs in the kernel. For example wake_up() and swake_up()
is only one character away. Although the compiler will warn
happily the wrong usage it keeps on going an even links the kernel.
Thomas and Peter would rather like to see early missuses reported
as error early on.

In a first attempt we tried to wrap all swait and wait calls
into a macro which has an compile time type assertion. The result
was pretty ugly and wasn't able to catch all wrong usages.
woken_wake_function(), autoremove_wake_function() and wake_bit_function()
are assigned as function pointers. Wrapping them with a macro around is
not possible. Prefixing them with '_' was also not a real option
because there some users in the kernel which do use them as well.
All in all this attempt looked to intrusive and too ugly.

An alternative is to turn the pointer type check into an error which
catches wrong type uses. Obviously not only the swait/wait ones. That
isn't a bad thing either.

Signed-off-by: Daniel Wagner <daniel.wagner@xxxxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: linux-rt-users@xxxxxxxxxxxxxxx
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1455871601-27484-3-git-send-email-wagi@xxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 Makefile | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Makefile b/Makefile
index 6c1a3c2..4513509 100644
--- a/Makefile
+++ b/Makefile
@@ -773,6 +773,9 @@ KBUILD_CFLAGS   += $(call cc-option,-Werror=strict-prototypes)
 # Prohibit date/time macros, which would make the build non-deterministic
 KBUILD_CFLAGS   += $(call cc-option,-Werror=date-time)
 
+# enforce correct pointer usage
+KBUILD_CFLAGS   += $(call cc-option,-Werror=incompatible-pointer-types)
+
 # use the deterministic mode of AR if available
 KBUILD_ARFLAGS := $(call ar-option,D)