2020-06-23 17:09:12

by Jonathan Lemon

Subject: [PATCH] linux/log2.h: enclose macro arg in parens

From: Jonathan Lemon <[email protected]>

roundup_pow_of_two uses its arg without enclosing it in parens.

A call of the form:

roundup_pow_of_two(boolval ? PAGE_SIZE : frag_size)

resulted in an compile warning:

warning: ?: using integer constants in boolean context [-Wint-in-bool-context]
PAGE_SIZE :
../include/linux/log2.h:176:4: note: in definition of macro ‘roundup_pow_of_two’
(n == 1) ? 1 : \
^
And the resulting code used '1' as the result of the operation.

Fixes: 312a0c170945 ("[PATCH] LOG2: Alter roundup_pow_of_two() so that it can use a ilog2() on a constant")

Signed-off-by: Jonathan Lemon <[email protected]>
---
include/linux/log2.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/log2.h b/include/linux/log2.h
index 83a4a3ca3e8a..c619ec6eff4a 100644
--- a/include/linux/log2.h
+++ b/include/linux/log2.h
@@ -173,7 +173,7 @@ unsigned long __rounddown_pow_of_two(unsigned long n)
#define roundup_pow_of_two(n) \
( \
__builtin_constant_p(n) ? ( \
- (n == 1) ? 1 : \
+ ((n) == 1) ? 1 : \
(1UL << (ilog2((n) - 1) + 1)) \
) : \
__roundup_pow_of_two(n) \
--
2.24.1

2020-06-23 21:01:52

by Jakub Kicinski

Subject: Re: [PATCH] linux/log2.h: enclose macro arg in parens

On Tue, 23 Jun 2020 10:07:39 -0700 Jonathan Lemon wrote:
> From: Jonathan Lemon <[email protected]>
>
> roundup_pow_of_two uses its arg without enclosing it in parens.
>
> A call of the form:
>
> roundup_pow_of_two(boolval ? PAGE_SIZE : frag_size)
>
> resulted in an compile warning:
>
> warning: ?: using integer constants in boolean context [-Wint-in-bool-context]
> PAGE_SIZE :
> ../include/linux/log2.h:176:4: note: in definition of macro ‘roundup_pow_of_two’
> (n == 1) ? 1 : \
> ^
> And the resulting code used '1' as the result of the operation.

I'd have thought that this warning is harmless, since the expression
clearly is not a constant, interesting.

> Fixes: 312a0c170945 ("[PATCH] LOG2: Alter roundup_pow_of_two() so that it can use a ilog2() on a constant")
>

Please no empty line between fixes and other tags.

> Signed-off-by: Jonathan Lemon <[email protected]>
> ---
> include/linux/log2.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/log2.h b/include/linux/log2.h
> index 83a4a3ca3e8a..c619ec6eff4a 100644
> --- a/include/linux/log2.h
> +++ b/include/linux/log2.h
> @@ -173,7 +173,7 @@ unsigned long __rounddown_pow_of_two(unsigned long n)
> #define roundup_pow_of_two(n) \
> ( \
> __builtin_constant_p(n) ? ( \
> - (n == 1) ? 1 : \
> + ((n) == 1) ? 1 : \
> (1UL << (ilog2((n) - 1) + 1)) \
> ) : \
> __roundup_pow_of_two(n) \