[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20240322153738.GC5634@willie-the-truck>
Date: Fri, 22 Mar 2024 15:37:38 +0000
From: Will Deacon <will@...nel.org>
To: Petr Tesarik <petrtesarik@...weicloud.com>
Cc: Christoph Hellwig <hch@....de>,
Marek Szyprowski <m.szyprowski@...sung.com>,
Robin Murphy <robin.murphy@....com>,
Petr Tesarik <petr.tesarik1@...wei-partners.com>,
Michael Kelley <mhklinux@...look.com>,
open list <linux-kernel@...r.kernel.org>,
"open list:DMA MAPPING HELPERS" <iommu@...ts.linux.dev>,
Roberto Sassu <roberto.sassu@...weicloud.com>,
Petr Tesarik <petr@...arici.cz>
Subject: Re: [PATCH v3 2/2] bug: introduce ASSERT_VAR_CAN_HOLD()
On Thu, Mar 21, 2024 at 06:19:02PM +0100, Petr Tesarik wrote:
> From: Petr Tesarik <petr.tesarik1@...wei-partners.com>
>
> Introduce an ASSERT_VAR_CAN_HOLD() macro to check at build time that a
> variable can hold the given value.
>
> Use this macro in swiotlb to make sure that the list and pad_slots fields
> of struct io_tlb_slot are big enough to hold the maximum possible value of
> IO_TLB_SEGSIZE.
>
> Signed-off-by: Petr Tesarik <petr.tesarik1@...wei-partners.com>
> ---
> include/linux/build_bug.h | 10 ++++++++++
> kernel/dma/swiotlb.c | 2 ++
> 2 files changed, 12 insertions(+)
>
> diff --git a/include/linux/build_bug.h b/include/linux/build_bug.h
> index 3aa3640f8c18..6e2486508af0 100644
> --- a/include/linux/build_bug.h
> +++ b/include/linux/build_bug.h
> @@ -86,4 +86,14 @@
> "Offset of " #field " in " #type " has changed.")
>
>
> +/*
> + * Compile time check that a variable can hold the given value
> + */
> +#define ASSERT_VAR_CAN_HOLD(var, value) ({ \
> + typeof(value) __val = (value); \
> + typeof(var) __tmp = __val; \
> + BUILD_BUG_ON_MSG(__tmp != __val, \
> + #var " cannot hold " #value "."); \
> +})
nit, but I think this prevents putting negative values into unsigned
types. Not sure whether we care? Arguably it's even correct to complain.
e.g.
u16 s;
ASSERT_VAR_CAN_HOLD(s, -1);
explodes for me.
Will
Powered by blists - more mailing lists