diff mbox series

[04/10] linux/bits.h: simplify GENMASK_INPUT_CHECK() by using is_const_true()

Message ID 20241203-is_constexpr-refactor-v1-4-4e4cbaecc216@wanadoo.fr (mailing list archive)
State New, archived
Headers show
Series compiler.h: refactor __is_constexpr() into is_const{,_true,_false}() | expand

Commit Message

Vincent Mailhol via B4 Relay Dec. 2, 2024, 5:33 p.m. UTC 
From: Vincent Mailhol <mailhol.vincent@wanadoo.fr>

In GENMASK_INPUT_CHECK(),

  __builtin_choose_expr(__is_constexpr((l) > (h)), (l) > (h), 0)

is equivalent to:

  is_const_true((l) > (h))

Apply is_const_true() to simplify GENMASK_INPUT_CHECK().

Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
---
This change passes the unit tests from CONFIG_BITS_TEST, including the
extra negative tests provided under #ifdef TEST_GENMASK_FAILURES [1].

[1] commit 6d511020e13d ("lib/test_bits.c: add tests of GENMASK")
Link: https://git.kernel.org/torvalds/c/6d511020e13d
---
 include/linux/bits.h | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

Comments

Vincent Mailhol Dec. 5, 2024, 3:49 p.m. UTC | #1 
On Thu. 5 Dec 2024 at 03:52, David Laight <David.Laight@aculab.com> wrote:
> From: Vincent Mailhol
> > Sent: 02 December 2024 17:33
> >
> >   __builtin_choose_expr(__is_constexpr((l) > (h)), (l) > (h), 0)
> >
> > is equivalent to:
> >
> >   is_const_true((l) > (h))
>
> Change it to BUILD_BUG_ON_MSG(statically_true((l) < (h)), "error message")
>
> and then fix all the fallout :-)

BUILD_BUG_ON_MSG() is not suitable for GENMASK_INPUT_CHECK. We need
one of the variants that returns zero here.

But I agree that it is good to have a more meaningful error message
here. I will use __BUILD_BUG_ON_ZERO_MSG() in v2.


Yours sincerely,
Vincent Mailhol
diff mbox series

Patch

diff --git a/include/linux/bits.h b/include/linux/bits.h
index 60044b6088172b3f26aa3f17cdaede9786863dae..ef0119e6179e1ca95345a3d4d3327ba19633028e 100644
--- a/include/linux/bits.h
+++ b/include/linux/bits.h
@@ -20,9 +20,8 @@ 
  */
 #if !defined(__ASSEMBLY__)
 #include <linux/build_bug.h>
-#define GENMASK_INPUT_CHECK(h, l) \
-	(BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
-		__is_constexpr((l) > (h)), (l) > (h), 0)))
+#include <linux/compiler.h>
+#define GENMASK_INPUT_CHECK(h, l) BUILD_BUG_ON_ZERO(is_const_true((l) > (h)))
 #else
 /*
  * BUILD_BUG_ON_ZERO is not available in h files included from asm files,