Re: [PATCH v2 3/3] gdb: introduce scoped debug prints

[Simon Marchi via Gdb-patches <gdb-patches@sourceware.org>]

On 2021-01-05 4:54 p.m., Simon Marchi wrote:
> On 2021-01-05 4:26 p.m., tdevries wrote:
>> Yeah, that's not a bad idea.
>>
>> The only bit that concerns me is that there's already a -prompt switch for gdb_test_multiple, which does not add on the terminating '$', while this version does.
>>
>> It's probably a good idea to have the -prompt switch to behave the same in both cases.
> 
> Hmm I see.  Intuitively, I'd try to make gdb_test_multiple add
> the terminating $.  Do you foresee some problems with that?
> 
> The prompt passed to gdb_test_multiple only appears to be used
> for the various failing cases, so I don't expect that to change
> any passing test (I'll give it a try).

Well, now that I think of it a bit more, it would be much easier and safer
to just make my gdb_test_sequence's -prompt work like gdb_test_multiple's -prompt,
and have the caller add the $ itself.

Updated patch below.

From 23d207b6f391312f82fcaeae9936c97470461415 Mon Sep 17 00:00:00 2001
From: Simon Marchi <simon.marchi@polymtl.ca>
Date: Tue, 05 Jan 2021 11:02:07 -0500
Subject: [PATCH] gdb/testsuite: fix race in gdb.threads/signal-while-stepping-over-bp-other-thread.exp

Commit 3ec3145c5dd6 ("gdb: introduce scoped debug prints") updated some
tests using "set debug infrun" to handle the fact that a debug print is
now shown after the prompt, after an inferior stop.  The same issue
happens in gdb.threads/signal-while-stepping-over-bp-other-thread.exp.
If I run it in a loop, it eventually fails like these other tests.

The problem is that the testsuite expects to see $gdb_prompt followed by
the end of the buffer.  It happens that expect reads $gdb_prompt and the
debug print at the same time, in which case the regexp never matches and
we get a timeout.

The fix is the same as was done in 3ec3145c5dd6, make the testsuite
believe that the prompt is the standard GDB prompt followed by that
debug print.

Since that test uses gdb_test_sequence, and the expected prompt is in
gdb_test_sequence, add a -prompt switch to gdb_test_sequence to override
the prompt used for that call.

gdb/testsuite/ChangeLog:

	* lib/gdb.exp (gdb_test_sequence): Accept -prompt switch.
	* gdb.threads/signal-while-stepping-over-bp-other-thread.exp:
	Pass prompt containing debug print to gdb_test_sequence.

Change-Id: I33161c53ddab45cdfeadfd50b964f8dc3caa9729
---

diff --git a/gdb/testsuite/gdb.threads/signal-while-stepping-over-bp-other-thread.exp b/gdb/testsuite/gdb.threads/signal-while-stepping-over-bp-other-thread.exp
index fe84253..2807485 100644
--- a/gdb/testsuite/gdb.threads/signal-while-stepping-over-bp-other-thread.exp
+++ b/gdb/testsuite/gdb.threads/signal-while-stepping-over-bp-other-thread.exp
@@ -102,7 +102,7 @@
 gdb_test "set debug infrun 1"
 
 set test "step"
-gdb_test_sequence $test $test {
+gdb_test_sequence $test $test -prompt "$gdb_prompt \\\[infrun\\\] fetch_inferior_event: exit\r\n$"  {
     "need to step-over"
     "resume_1: step=1,"
     "signal arrived while stepping over breakpoint"
diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index 3f61da8..140e396 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -1401,6 +1401,9 @@
 # EXPECTED_OUTPUT_LIST is a list of regexps of expected output, which are
 # processed in order, and all must be present in the output.
 #
+# The -prompt switch can be used to override the prompt expected at the end of
+# the output sequence.
+#
 # It is unnecessary to specify ".*" at the beginning or end of any regexp,
 # there is an implicit ".*" between each element of EXPECTED_OUTPUT_LIST.
 # There is also an implicit ".*" between the last regexp and the gdb prompt.
@@ -1413,16 +1416,32 @@
 #    0 if the test passes,
 #   -1 if there was an internal error.
 
-proc gdb_test_sequence { command test_name expected_output_list } {
+proc gdb_test_sequence { args } {
     global gdb_prompt
+
+    parse_args {{prompt ""}}
+
+    if { $prompt == "" } {
+	set prompt "$gdb_prompt $"
+    }
+
+    if { [llength $args] != 3 } {
+	error "Unexpected # of arguments, expecting: COMMAND TEST_NAME EXPECTED_OUTPUT_LIST"
+    }
+
+    lassign $args command test_name expected_output_list
+
     if { $test_name == "" } {
 	set test_name $command
     }
+
     lappend expected_output_list ""; # implicit ".*" before gdb prompt
+
     if { $command != "" } {
 	send_gdb "$command\n"
     }
-    return [gdb_expect_list $test_name "$gdb_prompt $" $expected_output_list]
+
+    return [gdb_expect_list $test_name $prompt $expected_output_list]
 }
 
 \f