Re: [PATCH] [testsuite] Fix pretty printers regexps for GDB output

[Christophe Lyon <christophe.lyon@linaro.org>]

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On Thu, 25 Jan 2024 at 16:54, Christophe Lyon
<christophe.lyon@linaro.org> wrote:
>
> On Wed, 24 Jan 2024 at 12:02, Jonathan Wakely <jwakely@redhat.com> wrote:
> >
> > On Wed, 24 Jan 2024 at 10:48, Christophe Lyon wrote:
> > >
> > > GDB emits end of lines as \r\n, we currently match the reverse \n\r,
> >
> > We currently match [\n\r]+ which should match any of \n, \r, \n\r or \r\n
> >
>
> Hmm, right, sorry I had this patch in my tree for quite some time, but
> wrote the description just now, so I read a bit too quickly.
>
> >
> > > possibly leading to mismatches under racy conditions.
> >
> > What do we incorrectly match? Is the problem that a \r\n sequence
> > might be incompletely printed, due to buffering, and so the regex only
> > sees (and matches) the \r which then leaves an unwanted \n in the
> > stream, which then interferes with the next match? I don't understand
> > why that problem wouldn't just result in a failed match with your new
> > regex though.
> >
> Exactly: READ1 forces read() to return 1 byte at a time, so we leave
> an unwanted \r in front of a string that should otherwise match the
> "got" case.
>
> >
> > >
> > > I noticed this while running the GCC testsuite using the equivalent of
> > > GDB's READ1 feature [1] which helps detecting bufferization issues.
> > >
> > > Adjusting the first regexp to match the right order implied fixing the
> > > second one, to skip the empty lines.
> >
> > At the very least, this part of the description is misleading. The
> > existing regex matches "the right order" already. The change is to
> > match *exactly* \r\n instead of any mix of CR and LF characters.
> > That's not about matching "the right order", it's being more precise
> > in what we match.
> >
> > But I'm still confused about what the failure scenario is and how the
> > change fixes it.
> >
>
> I followed what the GDB testsuite does (it matches \r\n at the end of
> many regexps), but in fact it seems it's not needed:
> it works if I update the "got" regexp like this (ie. accept any number
> of leading \r or \n):
> -       -re {^(type|\$([0-9]+)) = ([^\n\r]*)[\n\r]+} {
> +       -re {^[\n\r]*(type|\$([0-9]+)) = ([^\n\r]*)[\n\r]+} {
> and leave the "skipping" regexp as it is currently.
>
> Is the new attached version OK?
>
> Thanks,
>
> Christophe
>
> > >
> > > Tested on aarch64-linux-gnu.
> > >
> > > [1] https//github.com/bminor/binutils-gdb/blob/master/gdb/testsuite/README#L269
> > >
> > > 2024-01-24  Christophe Lyon  <christophe.lyon@linaro.org>
> > >
> > >         libstdc++-v3/
> > >         * testsuite/lib/gdb-test.exp (gdb-test): Fix regexps.
> > > ---
> > >  libstdc++-v3/testsuite/lib/gdb-test.exp | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/libstdc++-v3/testsuite/lib/gdb-test.exp b/libstdc++-v3/testsuite/lib/gdb-test.exp
> > > index 31206f2fc32..0de8d9ee153 100644
> > > --- a/libstdc++-v3/testsuite/lib/gdb-test.exp
> > > +++ b/libstdc++-v3/testsuite/lib/gdb-test.exp
> > > @@ -194,7 +194,7 @@ proc gdb-test { marker {selector {}} {load_xmethods 0} } {
> > >
> > >      set test_counter 0
> > >      remote_expect target [timeout_value] {
> > > -       -re {^(type|\$([0-9]+)) = ([^\n\r]*)[\n\r]+} {
> > > +       -re {^(type|\$([0-9]+)) = ([^\n\r]*)\r\n} {
> > >             send_log "got: $expect_out(buffer)"
> > >
> > >             incr test_counter
> > > @@ -250,7 +250,7 @@ proc gdb-test { marker {selector {}} {load_xmethods 0} } {
> > >             return
> > >         }
> > >
> > > -       -re {^[^$][^\n\r]*[\n\r]+} {
> > > +       -re {^[\r\n]*[^$][^\n\r]*\r\n} {
> > >             send_log "skipping: $expect_out(buffer)"
> > >             exp_continue
> > >         }
> > > --
> > > 2.34.1
> > >
> >