lkml.org 
[lkml]   [2019]   [Dec]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] mm/hugetlb: ensure signedness of large numbers
From
Date
On Sat, 2019-12-28 at 13:33 +0300, isidentical wrote:
> This change introduces a sanitity helper for
> numbers that are larger than 2^5.

What's the rationale for this ... i.e. what problem are you trying to
solve? left to its own devices, gcc will assume int size for all
literals, so 34<<26 doesn't appear to have a problem, except that it
will be sign extended as a negative number into a 64 bit variable.
However, it's designed use is for an int flags in mmap, so its current
definition seems to be fine.

> Signed-off-by: isidentical <batuhanosmantaskaya@gmail.com>
> ---
> include/uapi/asm-generic/hugetlb_encode.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/uapi/asm-generic/hugetlb_encode.h
> b/include/uapi/asm-generic/hugetlb_encode.h
> index b0f8e87235bd..42c06c62ae17 100644
> --- a/include/uapi/asm-generic/hugetlb_encode.h
> +++ b/include/uapi/asm-generic/hugetlb_encode.h
> @@ -31,6 +31,6 @@
> #define HUGETLB_FLAG_ENCODE_512MB (29 <<
> HUGETLB_FLAG_ENCODE_SHIFT)
> #define HUGETLB_FLAG_ENCODE_1GB (30 <<
> HUGETLB_FLAG_ENCODE_SHIFT)
> #define HUGETLB_FLAG_ENCODE_2GB (31 <<
> HUGETLB_FLAG_ENCODE_SHIFT)
> -#define HUGETLB_FLAG_ENCODE_16GB (34 <<
> HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_16GB (UINT32_C(34) <<
> HUGETLB_FLAG_ENCODE_SHIFT)

And if there is a literal problem here, it can't be solved like this:
UINT32_C is a Cism which has no analogue in the kernel because we don't
pull in the /usr/include headers where it is defined. Usually in the
kernel we solve this by making the literal type explicit, like 34U, but
as I said above, I don't see a problem that this would solve.

James

\
 
 \ /
  Last update: 2019-12-29 02:33    [W:0.022 / U:5.760 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site