Re: [PATCH 1/4] catch syscall -- try 4 -- Architecture-independent part

[Daniel Jacobowitz <drow at false dot org>]

On Wed, Feb 25, 2009 at 08:26:29AM -0300, Sérgio Durigan Júnior wrote:
> I'm not sure I understood what you said, so please correct me if I'm
> wrong. IIUC, you want me to create another field in 'struct
> thread_info', and this field would be a 'struct target_waitstatus',
> right? This is because you think I could copy the whole 'struct
> target_waitstatus' in 'deal_with_syscall_event', and use it someplace
> else. Is it right? If it is, I have a question: would I have access to
> the current 'struct thread_info' inside breakpoint.c?

The copy in to the thread is not syscall-specific, so that's not where
it should go.  Maybe in infrun.c below this?

  /* Cache the last pid/waitstatus. */
  target_last_wait_ptid = ecs->ptid;
  target_last_waitstatus = ecs->ws;
...
  ecs->event_thread = find_thread_pid (ecs->ptid);

> > > +  get_last_target_status (&ptid, &last);
> > > +
> > > +  annotate_catchpoint (b->number);
> > > +
> > > +  if (s.name == NULL)
> > > +    syscall_id = xstrprintf ("%d", b->syscall_number);
> > > +  else
> > > +    syscall_id = xstrprintf ("'%s'", s.name);
> > 
> > For instance, here we've got the waitstatus in addition to the breakpoint.
> 
> That's what confused me. I didn't get if you want me to use 'struct
> thread_info' or 'struct target_waitstatus' to hold the syscall_number
> info :-).

It doesn't matter - as long as you don't put it in the breakpoint, and
it comes from somewhere thread-specific.

> > > +/* Implement the "print_one" breakpoint_ops method for syscall
> > > +   catchpoints.  */
> > > +
> > > +static void
> > > +print_one_catch_syscall (struct breakpoint *b, CORE_ADDR *last_addr)
> > > +{
> > 
> > Have you tried hitting a syscall catchpoint in MI mode, and is the
> > output anything useful?
> 
> No, unfortunately I haven't. Actually, I must first learn how to use the
> MI interface, but that should not be hard :-).

I'd suggest doing that as part of this submission so that we know
you're on the right track.  It isn't too hard; you can start by
looking at the test logs from gdb.mi tests, if that helps.

> > > +# Fills the struct syscall (passed as argument) with the corresponding
> > > +# system call represented by syscall_number.
> > > +M:void:get_syscall_by_number:int syscall_number, struct syscall *s:syscall_number, s
> > > +
> > > +# Fills the struct syscall (passed as argument) with the corresponding
> > > +# system call represented by syscall_name.
> > > +M:void:get_syscall_by_name:const char *syscall_name, struct syscall *s:syscall_name, s
> > > +
> > > +# Returns the array containing the syscall names for the architecture.
> > > +M:const char **:get_syscall_names:void:
> > 
> > If every target is going to use XML for this, these three do not need
> > to be gdbarch methods and the support code can move from linux-tdep.c
> > to xml-syscall.c.
> 
> As far as I understood (from our discussion a few months ago), not every
> target is supposed to use the XML for syscalls. That's specially true
> for embedded systems and/or architectures for which the XML file is
> missing (for some obscure reason, don't know). That's why I thought it
> would be better not to generalize.

I don't think this is a big deal.  If it is, we can handle it the same
way as for target-descriptions: pre-compile them into GDB.

> > > +  if (target_passed_by_entrypoint () > 0
> > > +      && catch_syscall_enabled () > 0)
> > > +    request = PT_SYSCALL;
> > > +  else
> > > +    request = PT_CONTINUE;
> > 
> > Why is target_passed_by_entrypoint still necessary?  If we understand
> > why, I think there'll be some other more appropriate flag.  Is it to
> > avoid using PTRACE_SYSCALL when the shell is running, before the
> > application starts?
> 
> It's been a long time since I added this check, but as far as I
> remember, that's exactly the reason. I tried to remove this, and the
> testcase simply freezes. Do you have another idea? :-)

Not sure that the flag exists any more, but you're trying to avoid it
when called by startup_inferior.  I suppose you could use the
inferior_created observer (not new_inferior!  The distinction is not
too clear in the manual but that one is too early).  The problem is,
again, that this flag needs to be per-inferior.

Pedro, any thoughts?

> 
> > > diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
> > > index 9a7e39c..1d0f66f 100644
> > > --- a/gdb/linux-nat.c
> > > +++ b/gdb/linux-nat.c
> > > @@ -676,6 +676,7 @@ linux_child_post_attach (int pid)
> > >  {
> > >    linux_enable_event_reporting (pid_to_ptid (pid));
> > >    check_for_thread_db ();
> > > +  linux_enable_tracesysgood (pid_to_ptid (pid));
> > >  }
> > >  
> > >  static void
> > > @@ -683,6 +684,7 @@ linux_child_post_startup_inferior (ptid_t ptid)
> > >  {
> > >    linux_enable_event_reporting (ptid);
> > >    check_for_thread_db ();
> > > +  linux_enable_tracesysgood (ptid);
> > >  }
> > >  
> > >  static int
> > > @@ -4160,6 +4162,7 @@ linux_target_install_ops (struct target_ops *t)
> > >    t->to_follow_fork = linux_child_follow_fork;
> > >    t->to_find_memory_regions = linux_nat_find_memory_regions;
> > >    t->to_make_corefile_notes = linux_nat_make_corefile_notes;
> > > +  t->to_passed_by_entrypoint = linux_passed_by_entrypoint;
> > >  
> > >    super_xfer_partial = t->to_xfer_partial;
> > >    t->to_xfer_partial = linux_xfer_partial;
> > 
> > These bits must be for another patch in the series :-)
> 
> I'm sorry, I didn't understand what you meant by that :-(. These
> modifications are all architecture-independent, so this is the right
> place for them right?

No - since they're specific to Linux.  Also, I don't think they'll
compile at this point, you haven't added the function yet.

-- 
Daniel Jacobowitz
CodeSourcery