Re: [GIT PULL] MM updates for 6.14-rc1

[Uros Bizjak <ubizjak@gmail.com>]

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On Sun, Jan 26, 2025 at 11:00 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Sun, 26 Jan 2025 at 11:47, Uros Bizjak <ubizjak@gmail.com> wrote:
> >
> > >   #if __clang_major__ >= 19
> > >   # define CC_HAS_TYPEOF_UNQUAL 1
> > >   #endif
> >
> > It is available in gcc-14.
>
> Ok, let's take that approach, instead of messing with CONFIG_CC_HAS_xyz.

Please find attached an incremental patch that implements the proposed approach.

The detection is put in include/linux/compiler.h where we can
consolidate checks for both compilers:

--cut here--
/*
 * 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.
 *
 * XXX: Remove test for __CHECKER__ once
 * sparse learns about __typeof_unqual__.
 */
#if ((defined(__GNUC__) && __GNUC__ >= 14) ||        \
     (defined(__clang__) && __clang_major__ >= 19)) &&    \
    !defined(__CHECKER__)
# define CC_HAS_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(CC_HAS_TYPEOF_UNQUAL)
# define TYPEOF_UNQUAL(exp) __typeof_unqual__(exp)
#else
# define TYPEOF_UNQUAL(exp) __typeof__(exp)
#endif
--cut here--

The above also consolidates checks for __CHECKER__, resulting in a
much simpler compile check in arch/x86/include/percpu.h.

I have tested the new patch series with a bunch of compilers, works as
expected, but it is getting a bit late here. I'll resend the series
tomorrow, after some more testing.

Uros.

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diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index 1ef08289e667..9f0831a5e712 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -95,12 +95,7 @@
 
 #endif /* CONFIG_SMP */
 
-/*
- * XXX: Remove test for __CHECKER__ once
- * sparse learns about __typeof_unqual__.
- */
-#if defined(CONFIG_USE_X86_SEG_SUPPORT) && \
-    defined(CONFIG_CC_HAS_TYPEOF_UNQUAL) && !defined(__CHECKER__)
+#if defined(CONFIG_USE_X86_SEG_SUPPORT) && defined(CC_HAS_TYPEOF_UNQUAL)
 # define __my_cpu_type(var)	typeof(var)
 # define __my_cpu_ptr(ptr)	(ptr)
 # define __my_cpu_var(var)	(var)
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index eac58025ecfc..7a52bea4ba76 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -314,13 +314,25 @@ static inline void *offset_to_ptr(const int *off)
 #define prevent_tail_call_optimization()	mb()
 
 /*
- * Define TYPEOF_UNQUAL() to use __typeof_unqual__() as typeof
- * operator when available, to return unqualified type of the exp.
+ * 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.
  *
  * XXX: Remove test for __CHECKER__ once
  * sparse learns about __typeof_unqual__.
  */
-#if defined(CONFIG_CC_HAS_TYPEOF_UNQUAL) && !defined(__CHECKER__)
+#if ((defined(__GNUC__) && __GNUC__ >= 14) ||		\
+     (defined(__clang__) && __clang_major__ >= 19)) &&	\
+    !defined(__CHECKER__)
+# define CC_HAS_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(CC_HAS_TYPEOF_UNQUAL)
 # define TYPEOF_UNQUAL(exp) __typeof_unqual__(exp)
 #else
 # define TYPEOF_UNQUAL(exp) __typeof__(exp)
diff --git a/init/Kconfig b/init/Kconfig
index a1507b8714e4..7fe82a46e88c 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -897,9 +897,6 @@ 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)