Re: [Xen-devel] [PATCH v2] multiboot2: clarify usage of the address tag

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Fri, Jun 08, 2018 at 12:39:28PM +0200, Daniel Kiper wrote:
> On Fri, Jun 08, 2018 at 12:08:22PM +0200, Roger Pau Monné wrote:
> > On Fri, Jun 08, 2018 at 11:35:52AM +0200, Daniel Kiper wrote:
> > > On Thu, Jun 07, 2018 at 05:59:06PM +0200, Roger Pau Monne wrote:
> > > > Add a note to spell out that if the address tag is not present the
> > > > file should be loaded using the elf header.
> > > >
> > > > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > > > ---
> > > > Cc: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
> > > > Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
> > > > ---
> > > > Changes since v1:
> > > >  - s/elf/@sc{elf}/
> > > >  - s/Multiboot/Multiboot2/
> > > > ---
> > > >  doc/multiboot.texi | 6 ++++++
> > > >  1 file changed, 6 insertions(+)
> > > >
> > > > diff --git a/doc/multiboot.texi b/doc/multiboot.texi
> > > > index 2e2d7e74a..3c797787c 100644
> > > > --- a/doc/multiboot.texi
> > > > +++ b/doc/multiboot.texi
> > > > @@ -509,6 +509,12 @@ assumes that no bss segment is present.
> > > >
> > > >  @end table
> > > >
> > > > +Note: This information does not need to be provided if the kernel image
> > > > +is in @sc{elf} format, but it must be provided if the image is in a.out
> > > > +format or in some other format. Compliant boot loaders must be able to
> > > > +load images that are either in @sc{elf} format or contain the address
> > > > +tag embedded in the Multiboot2 header.
> > > > +
> > >
> > > Now it is better. However, there is a lack of information that this tag
> > > should be preferred over the relevant data provided in the ELF header if
> > > both are available in the image. This have to be clear like it is in
> > > Multiboot spec.
> >
> > Would you be OK with adding the following sentence at the end:
> >
> > "When the address tag is present it must be used in order to load the
> > image, regardless of whether an @sc{elf} header is also present."
> 
> I would put this as a second sentence in note, just after "... some
> other format." However, then probably last sentence should be rephrased
> a bit.

I think the following is clear enough:

"Note: This information does not need to be provided if the kernel image is in
@sc{elf} format, but it must be provided if the image is in a.out format or in
some other format. When the address tag is present it must be used in order to
load the image, regardless of whether an @sc{elf} header is also present.
Compliant boot loaders must be able to load images that are either in @sc{elf}
format or contain the address tag embedded in the Multiboot2 header."

Roger.

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