Re: [PATCH] efi/libstub: Cast away type warning in use of max()

[Lukas Wunner <lukas@wunner.de>]

On Thu, Mar 28, 2024 at 11:13:07AM +0200, Ard Biesheuvel wrote:
> On Thu, 28 Mar 2024 at 10:21, Lukas Wunner <lukas@wunner.de> wrote:
> > On Tue, Mar 26, 2024 at 11:18:51AM +0100, Ard Biesheuvel wrote:
> > > Add a missing (u64) cast to alloc_min, which is passed into
> > > efi_random_alloc() as unsigned long, while efi_physical_addr_t is u64.
> > [...]
> > > --- a/drivers/firmware/efi/libstub/randomalloc.c
> > > +++ b/drivers/firmware/efi/libstub/randomalloc.c
> > > @@ -120,7 +120,7 @@ efi_status_t efi_random_alloc(unsigned long size,
> > >                       continue;
> > >               }
> > >
> > > -             target = round_up(max(md->phys_addr, alloc_min), align) + target_slot * align;
> > > +             target = round_up(max(md->phys_addr, (u64)alloc_min), align) + target_slot * align;
> >
> > Why not
> >
> >     max_t(u64, md->phys_addr, alloc_min)
> 
> Why is that better?

It just seems to be the idiomatic way to handle these casts in the kernel.

It's also what checkpatch suggests, so by not using it you risk getting
"helpful" fixup patches from the usual suspects.

It's your call buddy. :)