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From: Andrew Morton <akpm@linux-foundation.org>
To: akpm@linux-foundation.org, andy.shevchenko@gmail.com,
	ardb@kernel.org, arnd@arndb.de, linux-mm@kvack.org,
	mm-commits@vger.kernel.org, penguin-kernel@I-love.SAKURA.ne.jp,
	peterz@infradead.org, rikard.falkeborn@gmail.com,
	torvalds@linux-foundation.org, yury.norov@gmail.com
Subject: [patch 07/10] linux/bits.h: fix compilation error with GENMASK
Date: Sat, 22 May 2021 17:42:02 -0700	[thread overview]
Message-ID: <20210523004202.MOjiaAIxA%akpm@linux-foundation.org> (raw)
In-Reply-To: <20210522174113.47fd4c853c0a1470c57deefa@linux-foundation.org>

From: Rikard Falkeborn <rikard.falkeborn@gmail.com>
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@rasmusvillemoes.dk
[1]: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=19449
[2]: 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>
---

 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@med.uni-goettingen.de>
+ */
+#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@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))
 
--- 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@med.uni-goettingen.de>
+ */
+#define __is_constexpr(x) \
+	(sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
+
 #endif /* _LINUX_CONST_H */
_

  parent reply	other threads:[~2021-05-23  0:42 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-23  0:41 incoming Andrew Morton
2021-05-23  0:41 ` [patch 01/10] mm/shuffle: fix section mismatch warning Andrew Morton
2021-05-23  0:41 ` [patch 02/10] Revert "mm/gup: check page posion status for coredump." Andrew Morton
2021-05-23  0:41 ` [patch 03/10] ipc/mqueue, msg, sem: avoid relying on a stack reference past its expiry Andrew Morton
2021-05-23  0:41 ` [patch 04/10] tools/testing/selftests/exec: fix link error Andrew Morton
2021-05-23  0:41 ` [patch 05/10] kasan: slab: always reset the tag in get_freepointer_safe() Andrew Morton
2021-05-23  0:41 ` [patch 06/10] watchdog: reliable handling of timestamps Andrew Morton
2021-05-23  0:42 ` Andrew Morton [this message]
2021-05-23  0:42 ` [patch 08/10] proc: remove Alexey from MAINTAINERS Andrew Morton
2021-05-23  0:42 ` [patch 09/10] lib: kunit: suppress a compilation warning of frame size Andrew Morton
2021-05-23  0:42 ` [patch 10/10] userfaultfd: hugetlbfs: fix new flag usage in error path Andrew Morton

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