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Re: [Qemu-block] [PATCH] osdep: Fix ROUND_UP(64-bit, 32-bit)
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-block] [PATCH] osdep: Fix ROUND_UP(64-bit, 32-bit) |
Date: |
Wed, 13 Sep 2017 23:28:53 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 |
On 13/09/2017 23:03, Eric Blake wrote:
> When using bit-wise operations that exploit the power-of-two
> nature of the second argument of ROUND_UP(), we still need to
> ensure that the mask is as wide as the first argument (done
> by using addition of 0 to force proper arithmetic promotion).
> Unpatched, ROUND_UP(2ULL*1024*1024*1024*1024, 512) produces 0,
> instead of the intended 2TiB.
>
> Broken since its introduction in commit 292c8e50 (v1.5.0).
>
> CC: address@hidden
> Signed-off-by: Eric Blake <address@hidden>
>
> ---
> I did not audit to see how many potential users of ROUND_UP
> are actually passing in different sized types where the first
> argument can be larger than UINT32_MAX; I stumbled across the
> problem when iotests 190 started failing on a patch where I
> added a new use. We can either be conservative and put this
> on qemu-stable no matter what, or go through the effort of an
> audit to see what might be broken (many callers in the block
> layer, but not just there).
> ---
> include/qemu/osdep.h | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index 6855b94bbf..7a3000efc5 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -189,13 +189,13 @@ extern int daemon(int, int);
>
> /* Round number up to multiple. Requires that d be a power of 2 (see
> * QEMU_ALIGN_UP for a safer but slower version on arbitrary
> - * numbers) */
> + * numbers); works even if d is a smaller type than n. */
> #ifndef ROUND_UP
> -#define ROUND_UP(n,d) (((n) + (d) - 1) & -(d))
> +#define ROUND_UP(n, d) (((n) + (d) - 1) & -((n) - (n) + (d)))
> #endif
>
> #ifndef DIV_ROUND_UP
> -#define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d))
> +#define DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d))
> #endif
>
> /*
>
Cc: address@hidden
Paolo