Re: [PATCH v6 01/24] erofs: add on-disk layout

Pavel Machek
2019-09-03T11:27:14Z

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Hi!

> > No. gdb tells you what the actual offsets _are_.
>
> Ok, reading your reply twice, I think we have different perspectives. I
> don't trust the comments.
>
> The tool I had in mind is pahole that parses dwarf information about the
> structures, the same as gdb does. The actual value of the struct members
> is the thing that needs to be investigated in memory dumps or disk image
> dumps.
>
> > > > The expected offset is somewhat valuable, but
> > > > perhaps the form is a bit off given the visual
> > > > run-in to the field types.
> > > >
> > > > The extra work with this form is manipulating all
> > > > the offsets whenever a structure change occurs.
> > >
> > > ... while this is error prone.
> >
> > While the comment tells you what they _should be_.
>
> That's exactly the source of confusion and bugs. For me an acceptable
> way of asserting that a value has certain offset is a build check, eg.
> like
>
> BUILD_BUG_ON(strct my_superblock, magic, 16);

Yes, that would work, too. As would documentation file with the disk
structures.

Best regards,
Pavel
--
DENX Software Engineering GmbH, Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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