[PATCH V2] mkimage: fit: Do not tail-pad fitImage with external data

[Tom Rini <trini@konsulko.com>]

On Fri, May 08, 2020 at 03:37:01AM +0200, Marek Vasut wrote:
> On 5/7/20 10:46 PM, Samuel Holland wrote:
> > On 5/6/20 12:02 PM, trini at konsulko.com (Tom Rini) wrote:
> >>>>>> I'm not sure that it is.  Can we easily/safely memmove the data to be
> >>>>>> aligned?  Is that really a better option in this case than ensuring
> >>>>>> alignment within the file?
> >>>>>
> >>>>> Can't we use the new mkimage -B option to enforce the alignment IFF and
> >>>>> only IFF it is required ? 
> >>>>
> >>>> Perhaps.  But..
> >>>>
> >>>>> Then we can enforce it separately for 32bit
> >>>>> and 64bit platforms to 4 and 8 bytes respectively even.
> >>>>
> >>>> It's 8 bytes for both.  It's possible that Linux doesn't hard fail if
> >>>> you only do 4 byte alignment but the documented requirement is 8, for
> >>>> arm32.
> >>>
> >>> With Linux you usually need to move the kernel anyway, no ? It's 2 MiB
> >>> for arm64 for example.
> >>
> >> For arm64 you have to move it to where text_offset says it needs to be.
> >> For arm32 the common (always, practically?) case is you're firing off
> >> the zImage which does what's needed.  But..
> >>
> >>> And what you usually parse in-place would be the DT then.
> >>
> >> Yes, the practical case is that it's a DT and that needs 8 byte
> >> alignment.  And we should just get back to aligning that correctly.
> >> Going back to the v1 thread, it turns out the answer to "why do we even
> >> have this padding?" is "we need the DT to be aligned".
> > 
> > This change broke SPL booting for me on MACH_SUN50I as well. One thing that I
> > haven't seen brought up yet is that SPL FIT code assumes exactly a 4-byte
> > alignment of external data after the FIT. In spl_load_simple_fit():
> > 
> >  /*
> >   * For FIT with external data, figure out where the external images
> >   * start. This is the base for the data-offset properties in each
> >   * image.
> >   */
> >  size = fdt_totalsize(fit);
> >  size = (size + 3) & ~3;
> >  size = board_spl_fit_size_align(size);
> >  base_offset = (size + 3) & ~3;
> 
> Somehow this doesn't match the 8-byte alignment Tom was suggesting.
> And that only leads me to believe that we can either make assumptions
> about alignment, which would very likely fail one way or the other OR we
> can say that for SPL as a special case, we enforce some alignment.

It's likely the case that on arm32 as there's no natural alignment
problem, even tho the kernel says 8 byte, 4 byte doesn't lead to failure
and is rarely if ever given 4-but-not-8-byte-aligned addresses of the
DTB.  Which is why we should probably move the alignment here to 8 bytes
instead of 4.

> But that in turn fails for fitImage with embedded data, where the
> embedded data are always aligned to 4 bytes, because that's how DTC
> aligns properties.

I think the answer is that the use-case you're talking about is simply
going to require data to be relocated.

-- 
Tom
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