linux/bits.h: fix compilation error with GENMASK

GENMASK() has an input check which uses __builtin_choose_expr() to
enable a compile time sanity check of its inputs if they are known at
compile time.

However, it turns out that __builtin_constant_p() does not always return
a compile time constant [0].  It was thought this problem was fixed with
gcc 4.9 [1], but apparently this is not the case [2].

Switch to use __is_constexpr() instead which always returns a compile time
constant, regardless of its inputs.

Link: https://lore.kernel.org/lkml/42b4342b-aefc-a16a-0d43-9f9c0d63ba7a@rasmusvillemoes.dk
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=19449
Link: https://lore.kernel.org/lkml/1ac7bbc2-45d9-26ed-0b33-bf382b8d858b@I-love.SAKURA.ne.jp
Link: https://lkml.kernel.org/r/20210511203716.117010-1-rikard.falkeborn@gmail.com
Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Yury Norov <yury.norov@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/bits.h b/include/linux/bits.h
index 7f475d59a0974f17d7a9765c643b798a1dc6ee83..87d112650dfbb0ec9ac6825ae2746c61b2659960 100644 (file)
--- a/include/linux/bits.h
+++ b/include/linux/bits.h
@@ -22,7 +22,7 @@
 #include <linux/build_bug.h>
 #define GENMASK_INPUT_CHECK(h, l) \
        (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
-               __builtin_constant_p((l) > (h)), (l) > (h), 0)))
+               __is_constexpr((l) > (h)), (l) > (h), 0)))
 #else
 /*
  * BUILD_BUG_ON_ZERO is not available in h files included from asm files,

diff --git a/include/linux/const.h b/include/linux/const.h
index 81b8aae5a8559c9fabf0665c48d8e8659db4f239..435ddd72d2c464fdedd33889190009dde0a3bda9 100644 (file)
--- a/include/linux/const.h
+++ b/include/linux/const.h
@@ -3,4 +3,12 @@
 
 #include <vdso/const.h>
 
+/*
+ * This returns a constant expression while determining if an argument is
+ * a constant expression, most importantly without evaluating the argument.
+ * Glory to Martin Uecker <Martin.Uecker@med.uni-goettingen.de>
+ */
+#define __is_constexpr(x) \
+       (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
+
 #endif /* _LINUX_CONST_H */

diff --git a/include/linux/minmax.h b/include/linux/minmax.h
index c0f57b0c64d908b0ee298981031d14d6d3cb0de7..5433c08fcc685856798e833202c74b44330ce479 100644 (file)
--- a/include/linux/minmax.h
+++ b/include/linux/minmax.h
@@ -2,6 +2,8 @@
 #ifndef _LINUX_MINMAX_H
 #define _LINUX_MINMAX_H
 
+#include <linux/const.h>
+
 /*
  * min()/max()/clamp() macros must accomplish three things:
  *
@@ -17,14 +19,6 @@
 #define __typecheck(x, y) \
        (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
 
-/*
- * This returns a constant expression while determining if an argument is
- * a constant expression, most importantly without evaluating the argument.
- * Glory to Martin Uecker <Martin.Uecker@med.uni-goettingen.de>
- */
-#define __is_constexpr(x) \
-       (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
-
 #define __no_side_effects(x, y) \
                (__is_constexpr(x) && __is_constexpr(y))
 

diff --git a/tools/include/linux/bits.h b/tools/include/linux/bits.h
index 7f475d59a0974f17d7a9765c643b798a1dc6ee83..87d112650dfbb0ec9ac6825ae2746c61b2659960 100644 (file)
--- a/tools/include/linux/bits.h
+++ b/tools/include/linux/bits.h
@@ -22,7 +22,7 @@
 #include <linux/build_bug.h>
 #define GENMASK_INPUT_CHECK(h, l) \
        (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
-               __builtin_constant_p((l) > (h)), (l) > (h), 0)))
+               __is_constexpr((l) > (h)), (l) > (h), 0)))
 #else
 /*
  * BUILD_BUG_ON_ZERO is not available in h files included from asm files,

diff --git a/tools/include/linux/const.h b/tools/include/linux/const.h
index 81b8aae5a8559c9fabf0665c48d8e8659db4f239..435ddd72d2c464fdedd33889190009dde0a3bda9 100644 (file)
--- a/tools/include/linux/const.h
+++ b/tools/include/linux/const.h
@@ -3,4 +3,12 @@
 
 #include <vdso/const.h>
 
+/*
+ * This returns a constant expression while determining if an argument is
+ * a constant expression, most importantly without evaluating the argument.
+ * Glory to Martin Uecker <Martin.Uecker@med.uni-goettingen.de>
+ */
+#define __is_constexpr(x) \
+       (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
+
 #endif /* _LINUX_CONST_H */