Re: [PATCH v2 42/47] gdb_test_multiple: Anchor prompt match if -lbl

[Pedro Alves <pedro@palves.net>]

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Hi!

On 2025-05-21 16:19, Tom de Vries wrote:
> On 5/19/25 15:23, Pedro Alves wrote:
>> I wrote a test like this:
>>
>>      gdb_test_multiple "command" "" -lbl {
>>         -re "^\r\nprefix foo(?=\r\n)" {
>>             exp_continue
>>         }
>>         -re "^\r\nprefix bar(?=\r\n)" {
>>             exp_continue
>>         }
>>         -re "^\r\prefix (?=\r\n)" {
> 
> Hi Pedro,
> 
> Missing n in "\r\n".
> 
>>             exp_continue
>>         }
>>         -re "^\r\n$::gdb_prompt $" {
>>                pass $gdb_test_name
>>         }
>>      }
>>
>> Anchors are needed in my case to avoid too-eager matching due to the
>> common prefix. 
> I'm not saying you don't need anchors, maybe you do or maybe you don't, but I don't understand how a common prefix is a reason to need one.
> 
> Also, if you need anchors, you need to match the command as well, so you need a -re "^command(?=\r\n)" clause.

Without anchors, then if the fake GDB outputs this:

	echo "prefix "
	echo "prefix foo"
	echo "prefix bar"
	echo "prefix "

and the expect buffer happens to contain at least:
 
  "prefix \r\nprefix foo\r\n"

... then the "prefix foo" pattern consumes the first "prefix " line inadvertently.

E.g., the version of the test that I'm attaching fails exactly like that, with:

(gdb) command
prefix 
prefix foo
prefix bar
prefix 
meant-to-be-matched-by-lbl-1
(gdb) <COMMAND>
<PREFIX-FOO>
<PREFIX-BAR>
<PREFIX>
<PROMPT>
PASS: gdb.testsuite/gdb-test-multiple.exp: command
PASS: gdb.testsuite/gdb-test-multiple.exp: $saw_command == 1
PASS: gdb.testsuite/gdb-test-multiple.exp: $saw_prompt == 1
FAIL: gdb.testsuite/gdb-test-multiple.exp: $saw_prefix == 2
PASS: gdb.testsuite/gdb-test-multiple.exp: $saw_prefix_foo == 1
PASS: gdb.testsuite/gdb-test-multiple.exp: $saw_prefix_bar == 1
saw_prompt: 1
saw_prefix: 1
saw_prefix_foo: 1
saw_prefix_bar: 1

This version is counting the matches, which notices that we only
saw "prefix" once, while we should have seen it twice.

That is patch #1 in the series I've attached.

> 
>> The intent is for the prompt match above to override the built-in
>> prompt match.  However, it doesn't and the test fails with output like
>> this:
>>
>>    (gdb) command
>>    prefix foo
>>    prefix bar
>>    meant-to-be-matched-by-lbl
>>    (gdb)
>>
>> That's because the built-in match for the prompt matches before the
>> -lbl pattern for this expect buffer:
>>
>>    \r\nmeant-to-be-matched-by-lbl\r\n(gdb)
>>
> 
> You can fix that by dropping the anchor and using "\r\n$::gdb_prompt $" instead.  Even more simple, use -wrap "".

That doesn't work properly.  See the commit logs of the patches I've attached.  The series is meant to show the
incremental results as we get to the final fully-passing testcase.  One of the steps adds a prompt match like that,
and the slightly tweaked testcase in the same patch fails.  Take a look at the commit logs of the patches, in
sequence, please.  It is easier to see it incrementally like that, I think.

> 
>> This this by anchoring the built-in prompt match if -lbl was
>> requested.
>>
> 
> This might be a good idea indeed.
> 
> FWIW, the intent of -lbl was to handle except buffers overflows, so the -lbl pattern is meant to match lines in absence of a prompt.

FYI, I needed this for an earlier version of the testcase in patch #44 of this series:

 https://inbox.sourceware.org/gdb-patches/20250519132308.3553663-45-pedro@palves.net/T/#u

That is doing "info threads", and extracting the output of every thread.  If you search
for ${common_prefix} in there, you'll find it.

I can't trigger the original issue with that version anymore without the gdb_test_multiple fix,
though, I think because the patterns in the current version consume all lines, so there's
no "meant-to-be-matched-by-lbl" anymore.  I guess I don't really need -lbl there anymore at all.

Still, this new testcase based on what yours does need it.  I can try to combine all of
this in a single patch, including the new testcase and a better description.  WDYT?

This idea of replacing GDB with a script is super interesting.  Did you consider writing that script
in tcl/expect, though?  Seems like it would be a perfect fit.  Read input, match against pattern, print
output.  :-P  Another alternative would be to write a bit of GDB python to register a new command, and
run the real GDB with that.  But a script like you came up with mocking GDB completely is nice, it's
very light and more decoupled.

> 
> But AFAIU, your patch will make matching more predictable, so that's a good thing.
> 
> I created a mockup test-case to emulate the case you describe above. I've left the anchoring in place for the prefix lines, but for the gdb output printed by gdb.sh, it doesn't look necessary. [ The test-case has hardcoded paths in it. ]

[ The version I attached does not hardcode paths any more. ]

Thanks,
Pedro Alves

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From c422a58d258e1a9a14a911c31a492b84518e300c Mon Sep 17 00:00:00 2001
From: Pedro Alves <pedro@palves.net>
Date: Tue, 27 May 2025 20:01:36 +0100
Subject: [PATCH 1/4] With no anchors in testcase, patterns eat too much

Without anchors, then if the fake GDB outputs this:

	echo "prefix "
	echo "prefix foo"
	echo "prefix bar"
	echo "prefix "

and the expect buffer happens to contain at least:

  "prefix \r\nprefix foo\r\n"

... then the "prefix foo" pattern match may well consume the first "prefix " line.

Full relevant parts of the log:

(gdb) command
prefix
prefix foo
prefix bar
prefix
<COMMAND>
<PREFIX-FOO>
<PREFIX-BAR>
<PREFIX>
meant-to-be-matched-by-lbl-1
(gdb) <PROMPT>
PASS: gdb.testsuite/gdb-test-multiple.exp: command
PASS: gdb.testsuite/gdb-test-multiple.exp: $saw_command == 1
PASS: gdb.testsuite/gdb-test-multiple.exp: $saw_prompt == 1
FAIL: gdb.testsuite/gdb-test-multiple.exp: $saw_prefix == 3
PASS: gdb.testsuite/gdb-test-multiple.exp: $saw_prefix_foo == 1
PASS: gdb.testsuite/gdb-test-multiple.exp: $saw_prefix_bar == 1
saw_prompt: 1
saw_prefix: 1
saw_prefix_foo: 1
saw_prefix_bar: 1

Change-Id: Ib59084bad199f3fe945c14fbe1970e730104d3f4
---
 .../gdb.testsuite/gdb-test-multiple.exp       | 47 ++++++++++++++++++
 gdb/testsuite/gdb.testsuite/gdb.sh            | 49 +++++++++++++++++++
 2 files changed, 96 insertions(+)
 create mode 100644 gdb/testsuite/gdb.testsuite/gdb-test-multiple.exp
 create mode 100755 gdb/testsuite/gdb.testsuite/gdb.sh

diff --git a/gdb/testsuite/gdb.testsuite/gdb-test-multiple.exp b/gdb/testsuite/gdb.testsuite/gdb-test-multiple.exp
new file mode 100644
index 00000000000..a1c9d95a71c
--- /dev/null
+++ b/gdb/testsuite/gdb.testsuite/gdb-test-multiple.exp
@@ -0,0 +1,47 @@
+set GDB $srcdir/$subdir/gdb.sh
+clean_restart
+
+set saw_prompt 0
+set saw_prefix 0
+set saw_command 0
+set saw_prefix_foo 0
+set saw_prefix_bar 0
+
+gdb_test_multiple "command" "" -lbl {
+    -re "command(?=\r\n)" {
+	verbose -log <COMMAND>
+	incr saw_command
+	exp_continue
+    }
+    -re "\r\nprefix foo(?=\r\n)" {
+	verbose -log <PREFIX-FOO>
+	incr saw_prefix_foo
+	exp_continue
+    }
+    -re "\r\nprefix bar(?=\r\n)" {
+	verbose -log <PREFIX-BAR>
+	incr saw_prefix_bar
+	exp_continue
+    }
+    -re "\r\nprefix (?=\r\n)" {
+	verbose -log <PREFIX>
+	incr saw_prefix
+	exp_continue
+    }
+    -re -wrap "" {
+	verbose -log "<PROMPT>"
+	incr saw_prompt
+	pass $gdb_test_name
+    }
+}
+
+gdb_assert {$saw_command == 1}
+gdb_assert {$saw_prompt == 1}
+gdb_assert {$saw_prefix == 3}
+gdb_assert {$saw_prefix_foo == 1}
+gdb_assert {$saw_prefix_bar == 1}
+
+verbose -log "saw_prompt: $saw_prompt"
+verbose -log "saw_prefix: $saw_prefix"
+verbose -log "saw_prefix_foo: $saw_prefix_foo"
+verbose -log "saw_prefix_bar: $saw_prefix_bar"
diff --git a/gdb/testsuite/gdb.testsuite/gdb.sh b/gdb/testsuite/gdb.testsuite/gdb.sh
new file mode 100755
index 00000000000..1e9ceee8e23
--- /dev/null
+++ b/gdb/testsuite/gdb.testsuite/gdb.sh
@@ -0,0 +1,49 @@
+#!/bin/sh
+
+while [ $# -gt 0 ]; do
+    case $1 in
+	--version)
+	    echo "gdb.sh"
+	    exit 0
+	    ;;
+	*)
+	    ;;
+    esac
+
+    shift
+done
+
+while true; do
+    echo -n "(gdb) "
+    read line
+
+    if [ "$line" = "set height 0" ]; then
+	continue
+    fi
+
+    if [ "$line" = "set width 0" ]; then
+	continue
+    fi
+
+    if [ "$line" = "dir" ]; then
+	echo -n "Reinitialize source path to empty? (y or n) "
+	read response
+	echo 'Source directories searched: $cdir:$cwd'
+	continue
+    fi
+    case "$line" in
+	dir\ */gdb/testsuite/gdb.testsuite)
+            echo "Source directories searched: ${line#dir }:\$cdir:\$cwd"
+            continue
+            ;;
+    esac
+    if [ "$line" = "command" ]; then
+	echo "prefix "
+	echo "prefix foo"
+	echo "prefix bar"
+	echo "prefix "
+	for n in $(seq 1 1); do
+            echo "meant-to-be-matched-by-lbl-$n"
+	done
+    fi
+done

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prerequisite-patch-id: 4b0e0479048fa69b9236726c31d4d3a1c4eb8d25
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prerequisite-patch-id: 54baec47a1e16993889d013307fa76712e1c70fd
prerequisite-patch-id: cb790ccd633dcd7c802038eddf8ee41aa45b91a3
prerequisite-patch-id: 49703c9edd4a081dc8287e87ac0c6badb762e147
prerequisite-patch-id: 72d1db10cd1fa53fe070141bcfbe084d201b96e3
prerequisite-patch-id: 2245f4e6ca9330f3eb216d32e413d7079f3ae1c2
prerequisite-patch-id: 9e823607f8c00be8d064a1206f6f5d3fa996322a
-- 
2.49.0


[-- Attachment #3: 0002-Testcase-showing-need-for-prompt-anchor-too.patch --]
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From c6a0aacd51a4f5d72b46a313eba1789aedfc883e Mon Sep 17 00:00:00 2001
From: Pedro Alves <pedro@palves.net>
Date: Tue, 27 May 2025 20:01:36 +0100
Subject: [PATCH 2/4] Testcase showing need for prompt anchor too

Let's add some interspersed lines meant to be consumed by -lbl, an
<LBL> tag for when the built-in -lbl match triggers, and add anchors
to the testcase's "prefix" matches.

With that, the prefix matches no longer each too much, but the
testcase now fails like so:

(gdb) command
prefix
meant-to-be-matched-by-lbl-1
prefix foo
prefix bar
meant-to-be-matched-by-lbl-2
prefix
prefix
meant-to-be-matched-by-lbl-3
(gdb) <COMMAND>
<PREFIX>
<PROMPT>
PASS: gdb.testsuite/gdb-test-multiple.exp: command
PASS: gdb.testsuite/gdb-test-multiple.exp: $saw_command == 1
PASS: gdb.testsuite/gdb-test-multiple.exp: $saw_prompt == 1
FAIL: gdb.testsuite/gdb-test-multiple.exp: $saw_prefix == 3
FAIL: gdb.testsuite/gdb-test-multiple.exp: $saw_prefix_foo == 1
FAIL: gdb.testsuite/gdb-test-multiple.exp: $saw_prefix_bar == 1
saw_prompt: 1
saw_prefix: 1
saw_prefix_foo: 0
saw_prefix_bar: 0

What happened was that expect managed to put all the output up to and
including the prompt in the expect buffer, and since the testcase's
prompt match does not have an ^\r\n anchor, the built-in prompt match
consumed all the output in the expected buffer (since the previous
<PREFIX> match).

Change-Id: Ib59084bad199f3fe945c14fbe1970e730104d3f4
---
 gdb/testsuite/gdb.testsuite/gdb-test-multiple.exp | 8 ++++----
 gdb/testsuite/gdb.testsuite/gdb.sh                | 7 ++++---
 gdb/testsuite/lib/gdb.exp                         | 1 +
 3 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/gdb/testsuite/gdb.testsuite/gdb-test-multiple.exp b/gdb/testsuite/gdb.testsuite/gdb-test-multiple.exp
index a1c9d95a71c..d593d5dc81a 100644
--- a/gdb/testsuite/gdb.testsuite/gdb-test-multiple.exp
+++ b/gdb/testsuite/gdb.testsuite/gdb-test-multiple.exp
@@ -8,22 +8,22 @@ set saw_prefix_foo 0
 set saw_prefix_bar 0
 
 gdb_test_multiple "command" "" -lbl {
-    -re "command(?=\r\n)" {
+    -re "^command(?=\r\n)" {
 	verbose -log <COMMAND>
 	incr saw_command
 	exp_continue
     }
-    -re "\r\nprefix foo(?=\r\n)" {
+    -re "^\r\nprefix foo(?=\r\n)" {
 	verbose -log <PREFIX-FOO>
 	incr saw_prefix_foo
 	exp_continue
     }
-    -re "\r\nprefix bar(?=\r\n)" {
+    -re "^\r\nprefix bar(?=\r\n)" {
 	verbose -log <PREFIX-BAR>
 	incr saw_prefix_bar
 	exp_continue
     }
-    -re "\r\nprefix (?=\r\n)" {
+    -re "^\r\nprefix (?=\r\n)" {
 	verbose -log <PREFIX>
 	incr saw_prefix
 	exp_continue
diff --git a/gdb/testsuite/gdb.testsuite/gdb.sh b/gdb/testsuite/gdb.testsuite/gdb.sh
index 1e9ceee8e23..55bd6473bf8 100755
--- a/gdb/testsuite/gdb.testsuite/gdb.sh
+++ b/gdb/testsuite/gdb.testsuite/gdb.sh
@@ -39,11 +39,12 @@ while true; do
     esac
     if [ "$line" = "command" ]; then
 	echo "prefix "
+	echo "meant-to-be-matched-by-lbl-1"
 	echo "prefix foo"
 	echo "prefix bar"
+	echo "meant-to-be-matched-by-lbl-2"
 	echo "prefix "
-	for n in $(seq 1 1); do
-            echo "meant-to-be-matched-by-lbl-$n"
-	done
+	echo "prefix "
+	echo "meant-to-be-matched-by-lbl-3"
     fi
 done
diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index c51cea86a9d..3515d88bae5 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -1431,6 +1431,7 @@ proc gdb_test_multiple { command message args } {
     if {$line_by_line} {
        append code {
            -re "\r\n\[^\r\n\]*(?=\r\n)" {
+	       verbose -log "<LBL>"
                exp_continue
            }
        }
-- 
2.49.0


[-- Attachment #4: 0003-Anchor-prompt-in-testcase.patch --]
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From 7579b5e08a4d1a0370a5551353e782da15dd936c Mon Sep 17 00:00:00 2001
From: Pedro Alves <pedro@palves.net>
Date: Tue, 27 May 2025 22:46:40 +0100
Subject: [PATCH 3/4] Anchor prompt in testcase

If we anchor the prompt in the testcase, so that it doesn't consume
too much, we now see:

(gdb) command
prefix
meant-to-be-matched-by-lbl-1
prefix foo
prefix bar
meant-to-be-matched-by-lbl-2
prefix
prefix
meant-to-be-matched-by-lbl-3
(gdb) <COMMAND>
<PREFIX>
<BUILT-IN PROMPT>
FAIL: gdb.testsuite/gdb-test-multiple.exp: command
PASS: gdb.testsuite/gdb-test-multiple.exp: $saw_command == 1
FAIL: gdb.testsuite/gdb-test-multiple.exp: $saw_prompt == 1
FAIL: gdb.testsuite/gdb-test-multiple.exp: $saw_prefix == 3
FAIL: gdb.testsuite/gdb-test-multiple.exp: $saw_prefix_foo == 1
FAIL: gdb.testsuite/gdb-test-multiple.exp: $saw_prefix_bar == 1
saw_prompt: 0
saw_prefix: 1
saw_prefix_foo: 0
saw_prefix_bar: 0

I.e., the built-in prompt match was not overriden, and that one
consumed too much output, like in the previous patch our prompt match
did.

Change-Id: Id0080b6b04450d6eb5043d682efdbbd67b4139b4
---
 gdb/testsuite/gdb.testsuite/gdb-test-multiple.exp | 2 +-
 gdb/testsuite/lib/gdb.exp                         | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/gdb/testsuite/gdb.testsuite/gdb-test-multiple.exp b/gdb/testsuite/gdb.testsuite/gdb-test-multiple.exp
index d593d5dc81a..f6f254ddf8f 100644
--- a/gdb/testsuite/gdb.testsuite/gdb-test-multiple.exp
+++ b/gdb/testsuite/gdb.testsuite/gdb-test-multiple.exp
@@ -28,7 +28,7 @@ gdb_test_multiple "command" "" -lbl {
 	incr saw_prefix
 	exp_continue
     }
-    -re -wrap "" {
+    -re "^\r\n$gdb_prompt $" {
 	verbose -log "<PROMPT>"
 	incr saw_prompt
 	pass $gdb_test_name
diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index 3515d88bae5..cd920d2624c 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -1392,6 +1392,7 @@ proc gdb_test_multiple { command message args } {
 	    set result -1
 	}
 	-re "\r\n$prompt_regexp" {
+	    verbose -log "<BUILT-IN PROMPT>"
 	    if {![string match "" $message]} {
 		fail "$message"
 	    }
-- 
2.49.0


[-- Attachment #5: 0004-gdb_test_multiple-Anchor-prompt-match-if-lbl.patch --]
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From 05f32b5c30d52bd46dc671e923c38becdf7227b5 Mon Sep 17 00:00:00 2001
From: Pedro Alves <pedro@palves.net>
Date: Thu, 17 Apr 2025 22:55:25 +0100
Subject: [PATCH 4/4] gdb_test_multiple: Anchor prompt match if -lbl

This is the original patch (rebased on the <BUILT-IN PROMPT> thingy).

If we make the built-in prompt have an anchor as well, then it won't
match prematurely, and our own prompt match overrides it.  So now we
get a clean pass:

(gdb) command
prefix
meant-to-be-matched-by-lbl-1
prefix foo
prefix bar
meant-to-be-matched-by-lbl-2
prefix
prefix
meant-to-be-matched-by-lbl-3
(gdb) <COMMAND>
<PREFIX>
<LBL>
<PREFIX-FOO>
<PREFIX-BAR>
<LBL>
<PREFIX>
<PREFIX>
<LBL>
<PROMPT>
PASS: gdb.testsuite/gdb-test-multiple.exp: command
PASS: gdb.testsuite/gdb-test-multiple.exp: $saw_command == 1
PASS: gdb.testsuite/gdb-test-multiple.exp: $saw_prompt == 1
PASS: gdb.testsuite/gdb-test-multiple.exp: $saw_prefix == 3
PASS: gdb.testsuite/gdb-test-multiple.exp: $saw_prefix_foo == 1
PASS: gdb.testsuite/gdb-test-multiple.exp: $saw_prefix_bar == 1
saw_prompt: 1
saw_prefix: 3
saw_prefix_foo: 1
saw_prefix_bar: 1

Change-Id: Ic2571ec793d856a89ee0d533ec363e2ac6036ea2
---
 gdb/testsuite/lib/gdb.exp | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index cd920d2624c..6e97d7a35d9 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -1124,6 +1124,7 @@ proc gdb_test_multiple { command message args } {
     global any_spawn_id
 
     set line_by_line 0
+    set lbl_anchor_re ""
     set prompt_regexp ""
     set prompt_anchor 1
     for {set i 0} {$i < [llength $args]} {incr i} {
@@ -1133,6 +1134,7 @@ proc gdb_test_multiple { command message args } {
 	    set prompt_regexp [lindex $args $i]
 	} elseif { $arg == "-lbl" } {
 	    set line_by_line 1
+	    set lbl_anchor_re "^"
 	} elseif { $arg == "-no-prompt-anchor" } {
 	    set prompt_anchor 0
 	} else {
@@ -1391,7 +1393,7 @@ proc gdb_test_multiple { command message args } {
 	    fail "$errmsg"
 	    set result -1
 	}
-	-re "\r\n$prompt_regexp" {
+	-re "${lbl_anchor_re}\r\n$prompt_regexp" {
 	    verbose -log "<BUILT-IN PROMPT>"
 	    if {![string match "" $message]} {
 		fail "$message"
-- 
2.49.0