[PATCH 2/6] compiler.h: Introduce TYPEOF_UNQUAL() macro

[Uros Bizjak]

Define TYPEOF_UNQUAL() to use __typeof_unqual__() as typeof operator
when available, to return unqualified type of the expression.

Current version of sparse doesn't know anything about __typeof_unqual__()
operator. Avoid the usage of __typeof_unqual__() when sparse checking
is active to prevent sparse errors with unknowing keyword.

Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Cc: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Dennis Zhou <dennis@xxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Nadav Amit <nadav.amit@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx
---
 include/linux/compiler.h | 13 +++++++++++++
 init/Kconfig             |  3 +++
 2 files changed, 16 insertions(+)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 469a64dd6495..bb0bde335129 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -321,6 +321,19 @@ static inline void *offset_to_ptr(const int *off)
  */
 #define prevent_tail_call_optimization()	mb()
 
+/*
+ * Define unqual_typeof() to use __typeof_unqual__() as typeof
+ * operator when available, to return unqualified type of the exp.
+ *
+ * XXX: Remove test for __CHECKER__ once
+ * sparse learns about __typeof_unqual__.
+ */
+#if defined(CONFIG_CC_HAS_TYPEOF_UNQUAL) && !defined(__CHECKER__)
+# define TYPEOF_UNQUAL(exp) __typeof_unqual__(exp)
+#else
+# define TYPEOF_UNQUAL(exp) __typeof__(exp)
+#endif
+
 #include <asm/rwonce.h>
 
 #endif /* __LINUX_COMPILER_H */
diff --git a/init/Kconfig b/init/Kconfig
index a20e6efd3f0f..c1f9eb3d5f2e 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -894,6 +894,9 @@ config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
 config CC_HAS_INT128
 	def_bool !$(cc-option,$(m64-flag) -D__SIZEOF_INT128__=0) && 64BIT
 
+config CC_HAS_TYPEOF_UNQUAL
+	def_bool $(success,echo 'int foo (int a) { __typeof_unqual__(a) b = a; return b; }' | $(CC) -x c - -S -o /dev/null)
+
 config CC_IMPLICIT_FALLTHROUGH
 	string
 	default "-Wimplicit-fallthrough=5" if CC_IS_GCC && $(cc-option,-Wimplicit-fallthrough=5)
-- 
2.42.0