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RE: [PATCH 13/17] btrace: non-stop
- From: "Metzger, Markus T" <markus dot t dot metzger at intel dot com>
- To: Pedro Alves <palves at redhat dot com>
- Cc: "gdb-patches at sourceware dot org" <gdb-patches at sourceware dot org>
- Date: Wed, 9 Sep 2015 14:08:30 +0000
- Subject: RE: [PATCH 13/17] btrace: non-stop
- Authentication-results: sourceware.org; auth=none
- References: <1441794909-32718-1-git-send-email-markus dot t dot metzger at intel dot com> <1441794909-32718-14-git-send-email-markus dot t dot metzger at intel dot com> <55F01DEC dot 4030209 at redhat dot com> <A78C989F6D9628469189715575E55B23331AB7A1 at IRSMSX104 dot ger dot corp dot intel dot com> <55F03852 dot 7030200 at redhat dot 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.
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