Re: [PATCH] IB/core: Fix different types mix in ib_device_cap_flags structure values

[Jason Gunthorpe <jgunthorpe@obsidianresearch.com>]

On Tue, May 31, 2016 at 08:35:10AM -0700, Bart Van Assche wrote:
> On 05/30/16 03:09, Max Gurtovoy wrote:
> >ib_device_cap_flags 64-bit expansion caused a possible caps overlapping
> >(depending on machine endianness) and made consumers read wrong device
> >capabilities. For example IB_DEVICE_SG_GAPS_REG was falsely read by the
> >iser driver causing it to use a non-existing capability. Fix this by
> >casting ib_device_cap_flags enumerations to ULL.
> >
> > [ ... ]
> >diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
> >[ ... ]
> > enum ib_device_cap_flags {
> >       [ ... ]
> > 	IB_DEVICE_SG_GAPS_REG			= (1ULL << 32),
> >      [ ... ]
> > };
> 
> How can this patch make a difference? The presence of any constant
> in an enum that does not fit in a 32-bit integer makes an enum 64
> bits wide. In other words, all the changes from "1" into "1ULL" in
> this patch do not have

The expressions are evaluated before the enum type is decided, the
enum type has no impact on the type of the expressions.

(1<<32) is always undefined behavior because '1' is only a 32 bit type.

I'm confused why we didn't get any static checker hits on the shift
overflow - modern compilers warn on that??

Jason