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Re: [Xen-devel] [PATCH v6 1/4] xen: introduce SYMBOL

On Thu, 10 Jan 2019, Jan Beulich wrote:
> >>> On 10.01.19 at 03:40, <julien.grall@xxxxxxxxx> wrote:
> > On Wed, 9 Jan 2019, 18:43 Stefano Stabellini, <sstabellini@xxxxxxxxxx>
> > wrote:
> > 
> >> Introduce a macro, SYMBOL, which is similar to RELOC_HIDE, but it is
> >> meant to be used everywhere symbols such as _stext and _etext are used
> >> in the code. It can take an array type as a parameter, and it returns
> >> the same type.
> >>
> >> SYMBOL is needed when accessing symbols such as _stext and _etext
> >> because the C standard forbids for both comparisons and substraction
> >> (see C Standard, 6.5.6 [ISO/IEC 9899:2011] and [1]) between pointers
> >> pointing to different objects. _stext, _etext, etc. are all pointers to
> >> different objects from ANCI C point of view.
> >>
> > 
> > This does not make sense because you still return a pointer and therefore
> > the undefined behavior is still present.
> > 
> > I really don't believe this patch is going to make the MISRA tool happy.
> Well, till now I've been assuming that no version of this series was
> posted without being certain the changes achieve the goal (of
> making that tool happy).

No, Jan: unfortunately we cannot re-run the scanning tool against any
version of Xen we wish to :-(

We cannot know in advance if a set of changes will make the tool happy
or not.

If I knew that SYMBOL returning the native point type as in v6 is
sufficient to make the tool happy, I wouldn't be here arguing. We cannot
know for sure until we commit the changes, then we ask PRQA to re-scan
against a more recent version of Xen. It is an heavy process and for
this reason I preferred the safer of the two approaches.

Anyway, I would rather get something in, even if insufficient, than
nothing. So I'll address all your comments based on returning the
pointer type, and submit a new version. The bothersome changes are the
ones to the call sites, and I would like to get those in no matter the
implementation of SYMBOL.

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