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

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

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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
> >
>

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From e7cd0475141921282d5c9044b2450ae8e196efc4 Mon Sep 17 00:00:00 2001
From: Christophe Lyon <christophe.lyon@linaro.org>
Date: Thu, 25 Jan 2024 15:43:56 +0000
Subject: [PATCH v2] [testsuite] Fix pretty printers regexp for GDB output

GDB emits end of lines as \r\n, we currently match any >0 number of
either \n or \r, possibly leading to mismatches under racy conditions.

I noticed this while running the GCC testsuite using the equivalent of
GDB's READ1 feature [1] which helps detecting bufferization issues.

We try to match
\n$1 = empty std::tuple\r

against {^(type|\$([0-9]+)) = ([^\n\r]*)[\n\r]+} which fails because
of the leading \n (which was left in the buffer after the previous
"skipping" pattern matched the preceding \r).

This patch accepts any number of leading \n and/or \r in the "got" clause.

Also take this opportunity to quote \r and \r in the logs, to make
debugging such issues easier.

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 regexp.  Quote
	newlines in logs.
---
 libstdc++-v3/testsuite/lib/gdb-test.exp | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/libstdc++-v3/testsuite/lib/gdb-test.exp b/libstdc++-v3/testsuite/lib/gdb-test.exp
index 31206f2fc32..2ec5596983d 100644
--- a/libstdc++-v3/testsuite/lib/gdb-test.exp
+++ b/libstdc++-v3/testsuite/lib/gdb-test.exp
@@ -194,8 +194,11 @@ 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]+} {
-	    send_log "got: $expect_out(buffer)"
+	-re {^[\n\r]*(type|\$([0-9]+)) = ([^\n\r]*)[\n\r]+} {
+	    # Escape newlines so that we can print them.
+	    set escaped [string map {"\n" "\\n"} $expect_out(buffer)]
+	    set escaped2 [string map {"\r" "\\r"} $escaped]
+	    send_log "got: $escaped2"
 
 	    incr test_counter
 	    set first $expect_out(3,string)
@@ -251,7 +254,10 @@ proc gdb-test { marker {selector {}} {load_xmethods 0} } {
 	}
 
 	-re {^[^$][^\n\r]*[\n\r]+} {
-	    send_log "skipping: $expect_out(buffer)"
+	    # Escape newlines so that we can print them.
+	    set escaped [string map {"\n" "\\n"} $expect_out(buffer)]
+	    set escaped2 [string map {"\r" "\\r"} $escaped]
+	    send_log "skipping: $escaped2"
 	    exp_continue
 	}
 
-- 
2.34.1