Re: [XEN PATCH] automation/eclair: add a deviation for MISRA C:2012 Rule 8.6

[Federico Serafini <federico.serafini@xxxxxxxxxxx>]

On 10/11/23 13:41, Jan Beulich wrote:
> On 10.11.2023 12:23, Federico Serafini wrote:
> > --- a/automation/eclair_analysis/ECLAIR/deviations.ecl
> > +++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
> > @@ -214,6 +214,15 @@ definition is compiled-out or optimized-out by the 
> > compiler)"
> >   -config=MC3R1.R8.6,reports+={deliberate, "first_area(^.*has no definition$)"}
> >   -doc_end
> >   
> > +-doc_begin="For functions memcpy(), memmove() and memset(), if there are
> > +multiple definitions, those belong to different archives and the behavior of
> > +linking is well defined by the toolchain: only one of the definitions will be
> > +linked in (the first that is encountered searching the archives in the order
> > +they appear on the command line)."
> > +-config=MC3R1.R8.6,declarations+={deliberate, "name(memcpy||memmove||memset)"}
> > +-doc_end
> Why would this be limited to mem*()? Anything put into lib.a is going to
> be treated like that.
If one day another arch-specific definition for a function will be
introduced, a violation will appear but that is not necessarily a bad
thing because it will lead to another check of the compilation scripts
to ensure objects and archives are linked in the right order.
However, if in your opinion this will be a waste of time,
I can propose another deviation based on "xen/lib/*".


> The description also isn't quite accurate: Per-arch mem*() won't be put
> in archives, but in .o files. Those are always linked in. Anything not
> otherwise resolved may then be resolved by picking objects from
> archives (appearing later on the command line, unless specially grouped).
What do you think of the following as justification:

The search procedure for Unix linkers is well defined, see ld(1) manual:
"The linker will search an archive only once, at the location where it
is specified on the command line. If the archive defines a symbol which
was undefined in some object which appeared before the archive on the
command line, the linker will include the appropriate file(s) from the
archive."
In Xen, thanks to the order in which file names appear in the build
commands, if arch-specific definitions are present, they get always 
linked in before searching in the lib.a archive resulting from
"xen/lib".

--
Federico Serafini, M.Sc.

Software Engineer, BUGSENG (http://bugseng.com)