Re: [Qemu-devel] [PATCH v2] osdep: Fix ROUND_UP(64-bit, 32-bit)

[Richard Henderson]

On 09/14/2017 06:49 AM, 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 a ternary to force proper arithmetic promotion).
> Unpatched, ROUND_UP(2ULL*1024*1024*1024*1024, 512U) produces 0,
> instead of the intended 2TiB, because negation of an unsigned
> 32-bit quantity followed by widening to 64-bits does not
> sign-extend the mask.
> 
> Broken since its introduction in commit 292c8e50 (v1.5.0).
> Callers that passed the same width type to both macro parameters,
> or that had other code to ensure the first parameter's maximum
> runtime value did not exceed the second parameter's width, are
> unaffected, but I did not audit to see which (if any) existing
> clients of the macro could trigger incorrect behavior (I found
> the bug while adding a new use of the macro).
> 
> While preparing the patch, checkpatch complained about poor
> spacing, so I also fixed that here and in the nearby DIV_ROUND_UP.
> 
> CC: address@hidden
> CC: address@hidden
> Signed-off-by: Eric Blake <address@hidden>
> 
> ---
> v2: use ternary instead of addition of 0 [Laszlo], improve commit message
> ---
>  include/qemu/osdep.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)

Reviewed-by: Richard Henderson <address@hidden>

r~