[U-Boot] [PATCH] disk:efi: avoid unaligned access on efi partition

Albert ARIBAUD
2013-10-14T14:22:34Z

Hi Piotr,

On Mon, 14 Oct 2013 15:49:43 +0200, Piotr Wilczek
<p.wilczek@samsung.com> wrote:

> Dear Albert and M?ns,
>
> > -----Original Message-----
> > From: M?ns Rullg?rd [mailto:mans at mansr.com]
> > Sent: Monday, October 14, 2013 3:05 PM
> > To: Albert ARIBAUD
> > Cc: Piotr Wilczek; 'Tom Rini'; u-boot at lists.denx.de; 'Kyungmin Park'
> > Subject: Re: [U-Boot] [PATCH] disk:efi: avoid unaligned access on efi
> > partition
> >
> > Albert ARIBAUD <albert.u.boot@aribaud.net> writes:
> >
> > >> > Please do not advise using native unaligned accesses on code that
> > >> > is not strictly used by ARMv6+ architectures: the present code,
> > for
> > >> > instance, might be run on pre-ARMv6 or non-ARM platforms, and
> > thus,
> > >> > should never assume ability to perform unaligned accesses
> > natively.
> > >>
> > >> I'm advising no such thing. I said two things:
> > >>
> > >> 1. Declaring a struct with the 'packed' attribute makes gcc
> > >> automatically generate correct code for all targets. _IF_ the
> > >> selected target supports unaligned ldr/str, these might get
> > used.
> > >>
> > >> 2. If your target is ARMv6 or later _AND_ you enable strict
> > alignment
> > >> checking in the system control register, you _MUST_ build with
> > the
> > >> -mno-unaligned-access flag.
> > >
> > > Then I apologize; I had read "Note that on ARMv6 and later ldr/str
> > > support unaligned addresses unless this is explicitly disabled in the
> > > system control register" as a suggestion to use that capability.
> >
> > If building for ARMv6 or later, I do suggest allowing unaligned
> > accesses. The moment you add -march=armv6 (or equivalent), you allow
> > for a number of things not supported by older versions, so why not
> > unaligned memory accesses?
> >
>
> Thank you for your comments, I will follow your advice.

I will NAK building part_efi.c with options to allow native unaligned
access.

I will, OTOH, be ok with explicit unaligned reads/writes.

> Best regards
> Piotr Wilczek

Amicalement,
--
Albert.