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
> >
>