From: Randy Dunlap <rdunlap@infradead.org>
To: Matthias Goergens <matthias.goergens@gmail.com>,
linux-arch@vger.kernel.org, linux-mm@kvack.org
Cc: Andrew Morton <akpm@linux-foundation.org>,
Mike Kravetz <mike.kravetz@oracle.com>,
songmuchun@bytedance.com
Subject: Re: [PATCH] tools/headers: Fix undefined behaviour (34 << 26)
Date: Mon, 5 Sep 2022 13:30:45 -0700 [thread overview]
Message-ID: <feb2ad2f-c3ed-54e4-6c06-9787f20ce8f2@infradead.org> (raw)
In-Reply-To: <20220905031904.150925-1-matthias.goergens@gmail.com>
Hi,
On 9/4/22 20:19, Matthias Goergens wrote:
> Left-shifting past the size of your datatype is undefined behaviour in
> C. The literal 34 gets the type `int`, and that one is not big enough
> to be left shifted by 26 bits.
>
> An `unsigned` is long enough (on any machine that has at least 32 bits
> for their ints.)
>
> For uniformity, we mark all the literals as unsigned. But it's only
> really needed for HUGETLB_FLAG_ENCODE_16GB.
>
> Thanks to Randy Dunlap for an initial review and suggestion.
>
> Signed-off-by: Matthias Goergens <matthias.goergens@gmail.com>
a. Since the header file in tools/ is just a synced-up copy of the
include/uapi/asm-generic/ header file, I think that the subject would be
better if "tools/" were omitted.
b. Adding Andrew Morton and the HUGETLB maintainers to Cc: list.
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Thanks.
> ---
> include/uapi/asm-generic/hugetlb_encode.h | 26 +++++++++++-----------
> tools/include/asm-generic/hugetlb_encode.h | 26 +++++++++++-----------
> 2 files changed, 26 insertions(+), 26 deletions(-)
>
> diff --git a/include/uapi/asm-generic/hugetlb_encode.h b/include/uapi/asm-generic/hugetlb_encode.h
> index 4f3d5aaa11f5..de687009bfe5 100644
> --- a/include/uapi/asm-generic/hugetlb_encode.h
> +++ b/include/uapi/asm-generic/hugetlb_encode.h
> @@ -20,18 +20,18 @@
> #define HUGETLB_FLAG_ENCODE_SHIFT 26
> #define HUGETLB_FLAG_ENCODE_MASK 0x3f
>
> -#define HUGETLB_FLAG_ENCODE_16KB (14 << HUGETLB_FLAG_ENCODE_SHIFT)
> -#define HUGETLB_FLAG_ENCODE_64KB (16 << HUGETLB_FLAG_ENCODE_SHIFT)
> -#define HUGETLB_FLAG_ENCODE_512KB (19 << HUGETLB_FLAG_ENCODE_SHIFT)
> -#define HUGETLB_FLAG_ENCODE_1MB (20 << HUGETLB_FLAG_ENCODE_SHIFT)
> -#define HUGETLB_FLAG_ENCODE_2MB (21 << HUGETLB_FLAG_ENCODE_SHIFT)
> -#define HUGETLB_FLAG_ENCODE_8MB (23 << HUGETLB_FLAG_ENCODE_SHIFT)
> -#define HUGETLB_FLAG_ENCODE_16MB (24 << HUGETLB_FLAG_ENCODE_SHIFT)
> -#define HUGETLB_FLAG_ENCODE_32MB (25 << HUGETLB_FLAG_ENCODE_SHIFT)
> -#define HUGETLB_FLAG_ENCODE_256MB (28 << HUGETLB_FLAG_ENCODE_SHIFT)
> -#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_16KB (14U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_64KB (16U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_512KB (19U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_1MB (20U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_2MB (21U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_8MB (23U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_16MB (24U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_32MB (25U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_256MB (28U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_512MB (29U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_1GB (30U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_2GB (31U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_16GB (34U << HUGETLB_FLAG_ENCODE_SHIFT)
>
> #endif /* _ASM_GENERIC_HUGETLB_ENCODE_H_ */
> diff --git a/tools/include/asm-generic/hugetlb_encode.h b/tools/include/asm-generic/hugetlb_encode.h
> index 4f3d5aaa11f5..de687009bfe5 100644
> --- a/tools/include/asm-generic/hugetlb_encode.h
> +++ b/tools/include/asm-generic/hugetlb_encode.h
> @@ -20,18 +20,18 @@
> #define HUGETLB_FLAG_ENCODE_SHIFT 26
> #define HUGETLB_FLAG_ENCODE_MASK 0x3f
>
> -#define HUGETLB_FLAG_ENCODE_16KB (14 << HUGETLB_FLAG_ENCODE_SHIFT)
> -#define HUGETLB_FLAG_ENCODE_64KB (16 << HUGETLB_FLAG_ENCODE_SHIFT)
> -#define HUGETLB_FLAG_ENCODE_512KB (19 << HUGETLB_FLAG_ENCODE_SHIFT)
> -#define HUGETLB_FLAG_ENCODE_1MB (20 << HUGETLB_FLAG_ENCODE_SHIFT)
> -#define HUGETLB_FLAG_ENCODE_2MB (21 << HUGETLB_FLAG_ENCODE_SHIFT)
> -#define HUGETLB_FLAG_ENCODE_8MB (23 << HUGETLB_FLAG_ENCODE_SHIFT)
> -#define HUGETLB_FLAG_ENCODE_16MB (24 << HUGETLB_FLAG_ENCODE_SHIFT)
> -#define HUGETLB_FLAG_ENCODE_32MB (25 << HUGETLB_FLAG_ENCODE_SHIFT)
> -#define HUGETLB_FLAG_ENCODE_256MB (28 << HUGETLB_FLAG_ENCODE_SHIFT)
> -#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_16KB (14U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_64KB (16U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_512KB (19U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_1MB (20U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_2MB (21U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_8MB (23U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_16MB (24U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_32MB (25U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_256MB (28U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_512MB (29U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_1GB (30U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_2GB (31U << HUGETLB_FLAG_ENCODE_SHIFT)
> +#define HUGETLB_FLAG_ENCODE_16GB (34U << HUGETLB_FLAG_ENCODE_SHIFT)
>
> #endif /* _ASM_GENERIC_HUGETLB_ENCODE_H_ */
--
~Randy
prev parent reply other threads:[~2022-09-05 20:30 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CA+X7ob9QaUxiusEBC2eW8Wk+2FnGVATeC8pmb9pdU0Tg7-XfyA@mail.gmail.com>
[not found] ` <CA+X7ob-XeKwM0r=6e+O=Se=pGQFjKVGZVihHC-Mc6YoRFf=6SQ@mail.gmail.com>
2022-09-03 22:03 ` Fwd: " Randy Dunlap
2022-09-05 3:19 ` Matthias Goergens
2022-09-05 20:30 ` Randy Dunlap [this message]
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