The patch titled
Subject: linux/bits.h: fix compilation error with GENMASK
has been added to the -mm tree. Its filename is
linux-bitsh-fix-compilation-error-with-genmask.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/linux-bitsh-fix-compilation-error-with-genmask.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/linux-bitsh-fix-compilation-error-with-genmask.patch
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------------------------------------------------------
From: Rikard Falkeborn <rikard.falkeborn@xxxxxxxxx>
Subject: 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.
[0]: https://lore.kernel.org/lkml/42b4342b-aefc-a16a-0d43-9f9c0d63ba7a@xxxxxxxxxxxxxxxxxx
[1]: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=19449
[2]: https://lore.kernel.org/lkml/1ac7bbc2-45d9-26ed-0b33-bf382b8d858b@xxxxxxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20210511203716.117010-1-rikard.falkeborn@xxxxxxxxx
Signed-off-by: Rikard Falkeborn <rikard.falkeborn@xxxxxxxxx>
Reported-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Acked-by: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Cc: Yury Norov <yury.norov@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/bits.h | 2 +-
include/linux/const.h | 8 ++++++++
include/linux/minmax.h | 10 ++--------
tools/include/linux/bits.h | 2 +-
tools/include/linux/const.h | 8 ++++++++
5 files changed, 20 insertions(+), 10 deletions(-)
--- a/include/linux/bits.h~linux-bitsh-fix-compilation-error-with-genmask
+++ a/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,
--- a/include/linux/const.h~linux-bitsh-fix-compilation-error-with-genmask
+++ a/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@xxxxxxxxxxxxxxxxxxxxx>
+ */
+#define __is_constexpr(x) \
+ (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
+
#endif /* _LINUX_CONST_H */
--- a/include/linux/minmax.h~linux-bitsh-fix-compilation-error-with-genmask
+++ a/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@xxxxxxxxxxxxxxxxxxxxx>
- */
-#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))
--- a/tools/include/linux/bits.h~linux-bitsh-fix-compilation-error-with-genmask
+++ a/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,
--- a/tools/include/linux/const.h~linux-bitsh-fix-compilation-error-with-genmask
+++ a/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@xxxxxxxxxxxxxxxxxxxxx>
+ */
+#define __is_constexpr(x) \
+ (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
+
#endif /* _LINUX_CONST_H */
_
Patches currently in -mm which might be from rikard.falkeborn@xxxxxxxxx are
linux-bitsh-fix-compilation-error-with-genmask.patch
