Re: [PATCH-for-5.2 v2] trace: use STAP_SDT_V2 to work around symbol visibility

[Stefan Hajnoczi]

On Thu, Nov 19, 2020 at 2:38 PM Frank Ch. Eigler <fche@redhat.com> wrote:
>
> Hi -
>
> > > Maybe add a comment? (no need to repost if you agree):
> > >
> > >        # Workaround to avoid dtrace(1) produces file with 'hidden'
> > >        # symbol visibility, define STAP_SDT_V2 to produce 'default'
> > >        # symbol visibility instead.
> > >
> > > > +    QEMU_CFLAGS="$QEMU_CFLAGS -DSTAP_SDT_V2"
>
> Please note that we don't know how long this behavior will persist.
> You are relying on an accident. :-)
>
> Much of the systemtap code doesn't support real STAP_SDT_V2 format,
> and /usr/include/sys/sdt.h cannot generate it at all.  That macro
> tricks only the dtrace-header-generator to suppress the "hidden"
> visibility attribute, but doesn't change probe metadata format to the
> old V2 (in .probes sections rather than .note.* ELF notes).
>
> We'll try not to break it, but please move toward the more proper
> per-solib or per-executable hidden copies of the semaphore objects.

Yes, thanks. Gerd Hoffmann has started working on per-solib semaphore
linking and this workaround will be replaced by it.

Stefan