On Wednesday 06 October 2010 18:19:53, Oleg Nesterov wrote:
On 10/05, Pedro Alves wrote:
The stub must support @samp{vCont} if it reports support for
multiprocess extensions (@pxref{multiprocess extensions}).
Cough. Previously I was told here (on arc...@sourceware.org) that
Hc + s/c is enough and I shouldn't worry about vCont;s/c ;)
vCont was introduced because with only 'Hc', 's' and 'c', there's
no way to distinguish step a thread and resume all others vs step
a thread and leave others stopped (scheduler-locking, in gdb lingo).
This was added way before non-stop was added, back in 2002/2003,
I believe. vCont;t was added much later, when non-stop was
introduced.
The stub must also support vCont for non-stop, though I'll give you
that it doesn't appear to be mentioned in the manual,
Yes, the manual doesn't explain this. Quite contrary, the decsription
of 'vCont?' definitely looks as if the stub is not obliged to implement
all vCont commands.
And, if the stub must support vCont for non-stop, then why gdb
doesn't complain after 'vCont?' but falls back to '$s' ?
Because nobody took the trouble to made it complain. As I said,
I'll give you that gdb could be noisier about that...
Look at remote.c:remote_resume, and you'll see that gdb does not
wait for the OK after 'c'/'s'/'S'/'C' in non-stop mode.
Then gdbserver should be fixed? It does send OK in response to '$s',
that is why ugdb does this.
Think of it as undefined behavior. It could be made to
error out instead, if somebody cared. Not sure how you got gdb to
send gdbserver 's' or 'c' (well, unless you used
set remote verbose-resume-packet off, or started gdbserver
with --disable-packet=vCont).
Again, the documentation is very confusing. Looking at
remote_resume()-remote_vcont_resume()-getpkt() I think that
vCont;s needs OK. Looking at D.3 Stop Reply Packets in
gdb.info I do not see any difference between `s' and `vCont'.
Yeah. It's the problem that those that are very familiar with
the thing get to write docs for it, so may have missed spelling
out things that were obvious to them.
It goes without saying, but ... patches to improve the docs are
always welcome.
In any case ugdb should fully support vCont, hopefully I'll finish
this tomorrow. Could you answer a couple of questions?
1. Say, $vCont;s or $vCont;s:p-1.-1
I assume, this should ignore the running threads, correct?
IOW, iiuc this 's' applies to all threads which we already
reported as stopped.
Yes.
2. Say, $vCont;c:pPID.TID;s:p-1.-1
This would be effectively
$vCont;c:pPID.TID;s
Can I assume that gdb can never send this request as
$vCont;s:p-1.-1;c:pPID.TID ?
If yes, then the implementation will be much simpler, I can
add something like gencounters to ugdb_thread/process. Otherwise
this needs more complications to figure out what should be done
with each tracee.
All GDB currently sends is in gdb/remote.c:remote_vcont_resume.
All vCont packets GDB sends today have the actions ordered
from more specific to less specific --- the most complicated
is something like vCont;s:pPID.TID;c (step PID.TID, continue
all others). It will probably make sense to maintain that
ordering, if we ever make a single vCont contain more
actions.
--
Pedro Alves
