RE: [PATCH 13/17] btrace: non-stop

["Metzger, Markus T" <markus.t.metzger@intel.com>]

> -----Original Message-----
> From: Pedro Alves [mailto:palves@redhat.com]
> Sent: Wednesday, September 9, 2015 3:47 PM
> To: Metzger, Markus T
> Cc: gdb-patches@sourceware.org
> Subject: Re: [PATCH 13/17] btrace: non-stop
> 
> On 09/09/2015 01:20 PM, Metzger, Markus T wrote:
> >> -----Original Message-----
> >> From: Pedro Alves [mailto:palves@redhat.com]
> >> Sent: Wednesday, September 9, 2015 1:54 PM
> >> To: Metzger, Markus T
> >> Cc: gdb-patches@sourceware.org
> >> Subject: Re: [PATCH 13/17] btrace: non-stop
> >>
> >> On 09/09/2015 11:35 AM, Markus Metzger wrote:
> >>
> >>> +# make sure $line matches the full expected output per thread.
> >>> +# and let's hope that GDB never mixes the output from different
> threads.
> >>> +#
> >>> +# this is quite fragile, mostly because the prompt appears somewhere
> in
> >>> +# the middle of the output.
> >>> +proc gdb_cont_to { threads cmd line nthreads } {
> >>> +    global gdb_prompt
> >>> +    set full_cmd "thread apply $threads $cmd"
> >>> +    set prompt_seen 0
> >>> +
> >>> +    send_gdb "$full_cmd\n"
> >>> +
> >>> +    for {set i 0} {$i < $nthreads} {incr i} {
> >>> +        set test "$full_cmd: thread $i"
> >>> +
> >>> +        # check for the prompt.  it may be in front of one of the lines we
> >>> +        # try to match.
> >>> +        gdb_test_multiple "" "$test: check prompt" {
> >>> +            -notransfer -re "$gdb_prompt " {
> >>> +                set prompt_seen 1
> >>> +            }
> >>> +        }
> >>> +
> >>
> >> Hmmm.  I'm not sure I'm missing some subtlety, but it seems to me
> >> that if you used -notransfer, then the prompt will still be in the buffer,
> >> and ...
> >>
> >>> +        # check for the line.  and for a typical error.
> >>> +        gdb_test_multiple "" $test {
> >>> +            -re "Cannot execute this command \[^\\\r\\\n\]* is running\." {
> >>> +                fail $test
> >>> +            }
> >>> +            -re "$line\[^\\\r\\\n\]*\r\n" {
> >>> +                pass $test
> >>> +            }
> >>> +        }
> >>
> >> ... thus this gdb_test_multiple can trip on it and issue a fail.
> >
> > As far as I understand expect, the above gdb_test_multiple would
> > simply skip the $gdb_prompt at the beginning of the line.
> 
> Only if the buffer already holds enough data for the regex to match.
> Expect reads data in chunks and puts it in the buffer, and then tries
> a match.  If nothing matches, it fetches more data, and retries matching.
> On an on, until a timeout.  So say $line is
> 
> [multi_line \
>              "No more reverse-execution history\." \
>              "\[^\\\r\\\n\]*" \
>              "\[^\\\r\\\n\]*" \
>             ]
> 
> It sometimes will happen that the expect buffer has:
> 
>  "$gdb_prompt\r\n...No more reverse-exe"
> 
> Because that doesn't match any of the regexs you have, gdb_test_multiple's
> internal regex for the prompt matches, and issues a FAIL.
> Try "make check-read1".  It may well be it catches this.

It doesn't; "make check-read1" runs without fails.  With my version as well
as with your version.  Both also catch errors if I revert one of the patches.

Btw, the output is not "$gdb_prompt\r\n...No more reverse-exe"
but "$gdb_prompt No more reverse-exe".  The $gdb_prompt simply
precedes some other output.


> > That's why I'm trying to detect it with a separate gdb_test_multiple
> > above.  I use -notransfer so I can still analyse the line for the expected
> > output.
> >
> >
> >> Wouldn't this instead work?
> >>
> >>         gdb_test_multiple "" $test {
> >>             -re "Cannot execute this command \[^\\\r\\\n\]* is running\." {
> >>                 fail $test
> >>             }
> >>             -re "$line\[^\\\r\\\n\]*\r\n" {
> >>                 pass $test
> >>             }
> >>             -re "$gdb_prompt " {
> >>                 set prompt_seen 1
> >>                 exp_continue
> >>             }
> >>        }
> >
> > Wouldn't the 1st or 2nd pattern skip any $gdb_prompt before the pattern?
> 
> Yes.  Is that a problem?  Don't we always get another prompt after that
> error?

No, we don't.  We have a single prompt that appears somewhere in the output.

	(gdb) thread apply all continue
	
	Thread 1 (Thread 0x7ffff7fcc740 (LWP 22139)):
	Continuing.
	[New Thread 0x7ffff74fb700 (LWP 22143)]
	
	Breakpoint 2, test (arg=0x0) at gdb.btrace/non-stop.c:27
	27        i = 0; /* bp.1 */
	PASS: gdb.btrace/non-stop.exp: thread apply all continue: thread 0
	(gdb) 
	Breakpoint 2, test (arg=0x0) at gdb.btrace/non-stop.c:27
	27        i = 0; /* bp.1 */
	PASS: gdb.btrace/non-stop.exp: thread apply all continue: thread 1
	record btrace

Sometimes, the prompt appears on the same line as some other output.
So far, I have only seen it at the beginning of a line.

That's what makes it so difficult.  The test needs to read past the prompt.


> > For the "Cannot execute..." pattern, I could add "^" but this will be difficult
> > for the $line pattern.
> >
> > Does the 3rd pattern consume just the $gdb_prompt or the entire line?
> 
> Consumes everything up to the prompt.  Whatever follows is left in the
> buffer.

Then putting the 3rd line first should work.


> > This non-stop testing is quite difficult.  I also have not found too many
> > examples when I searched for "non-stop".
> 
> Could you push the series to a branch somewhere?  The easiest would be
> a users/ branch in the master repo.

OK.  This is temporary.  I have not followed the discussion.  Can I force-push
and remove such a user branch?

Thanks,
Markus.
Intel Deutschland GmbH
Registered Address: Am Campeon 10-12, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de
Managing Directors: Christin Eisenschmid, Prof. Dr. Hermann Eul
Chairperson of the Supervisory Board: Tiffany Doon Silva
Registered Office: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928