Re: Revamp sniffer; Was: [obish?sym;rfa:doc] Wire up vsyscall

[Roland McGrath <roland@redhat.com>]

> > If I understood your description correctly, the source of the current
> > problem scenario is that glibc supplies CFI for the trampoline code
> > (__restore_rt), but that CFI is not written to match how the peculiar frame
> > will look.  So, glibc could change its CFI to use the same hack that the
> > x86 kernel CFI uses for the analogous code, or it could omit that CFI
> > entirely and expect gdb to recognize the name and/or instruction sequence.
> > 
> > My inclination is to omit the CFI because that's how it is on x86 in the
> > analogous case.  (If in future x86-64 has kernel-supplied trampoline code,
> > we expect it will be in the form of a vsyscall DSO that supplies CFI via
> > existing glibc support, as on x86.  In that case, the CFI will use the same
> > sort of hack as the x86 CFI does.)  Would that make things better?
> 
> Ah!  I guess it would help.  GDB will still need to do something more 
> immediate though.

I guess it can do the magic name-matching first and ignore CFI if it matches,
but I don't really have anything to add to the gdb part of the discussion.

Which change would gdb people prefer in glibc?  No CFI, or CFI that is
fixed with the kludge to match one byte before the entry point?


Thanks,
Roland