Re: [PATCH 5/5 V2] kvm tools: Initialize and use VESA and VNC

Ingo Molnar
2011-05-25T10:17:57Z

* Paolo Bonzini <pbonzini@redhat.com> wrote:

> > so what's your point?
>
> Using this kind of trick makes it harder to share code with other
> libraries that may require a higher standard of portability (not
> "better" or "worse", just "higher"). [...]

That's an complication but should be fixable, should it ever happen.

As things stand today we:

- Are *already* using an ELF linker script, see tools/kvm/bios/rom.ld.S

- Have multiple valid reasons not to use ((constructor))

- Want to use sections to implement other useful features as well

If the *only* linker script use would be the init facility then you'd
probably have a valid point - although the possible code flow
fragility with ((constructor)) is still a problem: we still would
want to know when no constructors were executed.

Also it's not clear why ((constructor)) was written in the way it
was: why apparently no access is given to the array of init functions
and why it's not possible to turn the auto-execution off but still
have the array generated, for legitimate cases that want to use data
driven constructor execution.

> >>>>>> I know portability is not relevant to tools/kvm/, but using
> >>>>>> unportable tricks for the sake of using them is a direct way
> >>>>>> to NIH. But oh well all of tools/kvm/ is NIH after all. :)
> >
> > Btw., that NIH claim was rather unfair and uncalled for as well.
>
> Hey hey I put a smiley for a reason!

Well after two insults in a single paragraph you need to put in at
least two smileys! Or not write the insults in a technical discssion
to begin with, especially if you are criticising a patch rather
forcefully. It will be easily misunderstood as a real insult, despite
the smiley ;-)

> Anyway I think we both agree that this debate is pointless. I
> learnt something (I wasn't aware of interaction between
> ((constructor)) and static libraries), you learnt something (it's
> the same with ((section)), and it's intrinsic in how static
> libraries work).

While i did not know whether static libraries would work with a
linker script (never tried it - and your experiment suggests that
they wont), the ((section)) approach we could create a clear runtime
BUG_ON() assert for a zero-sized array of init function pointers,
while ((constructor)) will silently not execute initialization
functions.

Thanks,

Ingo