compiler.h: introduce TYPEOF_UNQUAL() macro

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.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Uros Bizjak <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Dennis Zhou <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Cc: Kent Overstreet <[email protected]>
Cc: Nadav Amit <[email protected]>
Cc: Paolo Abeni <[email protected]>
Cc: Waiman Long <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

include/linux/compiler-clang.h

@@ -128,3 +128,11 @@
  */
 #define ASM_INPUT_G "ir"
 #define ASM_INPUT_RM "r"
+
+/*
+ * Declare compiler support for __typeof_unqual__() operator.
+ *
+ * Bindgen uses LLVM even if our C compiler is GCC, so we cannot
+ * rely on the auto-detected CONFIG_CC_HAS_TYPEOF_UNQUAL.
+ */
+#define CC_HAS_TYPEOF_UNQUAL (__clang_major__ >= 19)

include/linux/compiler-gcc.h

@@ -137,3 +137,11 @@
 #if GCC_VERSION < 90100
 #undef __alloc_size__
 #endif
+
+/*
+ * Declare compiler support for __typeof_unqual__() operator.
+ *
+ * Bindgen uses LLVM even if our C compiler is GCC, so we cannot
+ * rely on the auto-detected CONFIG_CC_HAS_TYPEOF_UNQUAL.
+ */
+#define CC_HAS_TYPEOF_UNQUAL (__GNUC__ >= 14)

include/linux/compiler.h

@@ -210,6 +210,26 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 #define __must_be_cstr(p) \
 	__BUILD_BUG_ON_ZERO_MSG(__annotated(p, nonstring), "must be cstr (NUL-terminated)")
 
+/*
+ * Use __typeof_unqual__() when available.
+ *
+ * XXX: Remove test for __CHECKER__ once
+ * sparse learns about __typeof_unqual__().
+ */
+#if CC_HAS_TYPEOF_UNQUAL && !defined(__CHECKER__)
+# define USE_TYPEOF_UNQUAL 1
+#endif
+
+/*
+ * Define TYPEOF_UNQUAL() to use __typeof_unqual__() as typeof
+ * operator when available, to return an unqualified type of the exp.
+ */
+#if defined(USE_TYPEOF_UNQUAL)
+# define TYPEOF_UNQUAL(exp) __typeof_unqual__(exp)
+#else
+# define TYPEOF_UNQUAL(exp) __typeof__(exp)
+#endif
+
 #endif /* __KERNEL__ */
 
 /**