[PATCH 5/6] gdb.base/skip.exp: Don't abuse gdb_test's question support (Re: [PATCH 5/5] Make gdb_test's question non-optional if specified)

[Pedro Alves <pedro@palves.net>]

On 2022-04-08 13:18, Pedro Alves wrote:
> On 2022-04-07 21:31, Bruno Larsen wrote:
>> On 3/30/22 16:29, Pedro Alves wrote:
>>> gdb_test supports handling scenarios where GDB asks a question before
>>> finishing handling some command.  The full prototype of gdb_test is:
>>>
>>>    # gdb_test COMMAND PATTERN MESSAGE QUESTION RESPONSE
>>>
>>> However, QUESTION is a question that GDB _may_ ask, not one that GDB
>>> _must_ ask:
>>>
>>>   # QUESTION is a question GDB may ask in response to COMMAND, like
>>>   #   "are you sure?"
>>>   # RESPONSE is the response to send if QUESTION appears.
>>>
>>> If GDB doesn't raise the question, the test still passes.
>>>
>>> I think that this is a misfeature.  If GDB regresses and stops asking
>>> a question, the testsuite won't notice.  So I think that if a QUESTION
>>> is specified, gdb_test should ensure it comes out of GDB.
>>
>> I just ran into a neat use of this, or possibly a mis-use, depending on how much you like it. gdb.base/skip.exp uses:
>>
>> gdb_test "step" "desired spot" "go to desired spot" "undesirable spot" "step"
>>
>> as a simple way to handle a gcc 9.2.0 bug (misfeature) where gdb could stop in an undesirable spot without actually causing a failure in the test. This feels like a neat way to deal with compiler problems, as it would introduce a simple way to deal with clang's lack of epilogue, for instance.
> 
> This is:
> 
>     # With gcc 9.2.0 we jump once back to main before entering foo here.
>     # If that happens try to step a second time.
>     gdb_test "step" "foo \\(\\) at.*" "step 3" \
> 	"main \\(\\) at .*\r\n$gdb_prompt " "step"
> 
> I think this is a misuse.  That case doesn't really handle a GDB confirmation question.
> What if you need to issue more steps, or the program may stop elsewhere for
> different ports, and thus you need more than one regexp?  For the latter you can
> use (REGEX1|REGEX1), but it isn't as nice as separate -re entries, IMHO.
> 
> IMHO, writing it with gdb_test_multiple in these cases is OK:
> 
> gdb_test_multiple "step" "step 3" {
>   -re -wrap "foo \\(\\) at.*" {
>      pass $gdb_test_multiple
>   }
>   -re -wrap "main \\(\\) at .*" {
>     # With gcc 9.2.0 we jump once back to main before entering foo.
>     # If that happens try another step.
>     send_gdb "step\n"
>     exp_continue
>   }
> }
> 
> It's a standard pattern we use in many places, I don't think it's bad enough that we need
> to hide it.
> 
>>
>> I'm not suggesting that this patch be scrapped, but maybe this could be implemented on purpose, something like gdb_test_optional. The code itself LGTM, but I am not able to approve patches.
>>
> 

I'm adding the patch below to the series, before old patch #5, to prevent
gdb.base/skip.exp from starting to fail with older GCCs.

I'm going to merge the whole series now.



From d7440bee9ffa6767e704f226ec28b9aa2fb748d6 Mon Sep 17 00:00:00 2001
From: Pedro Alves <pedro@palves.net>
Date: Tue, 17 May 2022 10:25:12 +0100
Subject: [PATCH] gdb.base/skip.exp: Don't abuse gdb_test's question support

gdb.base/skip.exp abuses gdb_test's support for answering a GDB
question to do this:

    # With gcc 9.2.0 we jump once back to main before entering foo here.
    # If that happens try to step a second time.
    gdb_test "step" "foo \\(\\) at.*" "step 3" \
	"main \\(\\) at .*\r\n$gdb_prompt " "step"

After a patch later in this series, gdb_test will FAIL if GDB does NOT
issue the question, so this test would start failing on older GCCs.

Switch to using gdb_test_multiple instead.  There are three spots in
the file that have the same pattern, and they're actually in a
sequence of commands that is repeated those 3 times.  Factor all that
out to a procedure.

I don't have gcc 9.2 handy, but I do have gcc 6.5, and that one is
affected as well, so update the comment.

Change-Id: If0a7e3cdf5191b4eec95ce0c8845c3a4d801c39e
---
 gdb/testsuite/gdb.base/skip.exp | 55 +++++++++++++++++++--------------
 1 file changed, 31 insertions(+), 24 deletions(-)

diff --git a/gdb/testsuite/gdb.base/skip.exp b/gdb/testsuite/gdb.base/skip.exp
index 7c71bb07a84..e6b660004d9 100644
--- a/gdb/testsuite/gdb.base/skip.exp
+++ b/gdb/testsuite/gdb.base/skip.exp
@@ -122,6 +122,32 @@ with_test_prefix "step after deleting 1" {
     gdb_test "step" "main \\(\\) at.*" "step 3"
 }
 
+# Test that we step into foo(), then into bar(), but not into baz().
+proc step_bar_foo_skip_baz {} {
+    gdb_test "step" "bar \\(\\) at.*" "step 1"
+    gdb_test "step" ".*" "step 2"; # Return from bar()
+
+    # With at least gcc 6.5.0 and 9.2.0, we jump once back to main
+    # before entering foo here.  If that happens try to step a second
+    # time.
+    set stepped_again 0
+    gdb_test_multiple "step" "step 3" {
+	-re -wrap "foo \\(\\) at.*" {
+	    pass $gdb_test_name
+	}
+	-re -wrap "main \\(\\) at .*" {
+	    if {!$stepped_again} {
+		set stepped_again 1
+		send_gdb "step\n"
+	    }
+	    exp_continue
+	}
+    }
+
+    gdb_test "step" ".*" "step 4"; # Return from foo()
+    gdb_test "step" "main \\(\\) at.*" "step 5"
+}
+
 # Now disable the skiplist entry for  skip1.c.  We should now
 # step into foo(), then into bar(), but not into baz().
 
@@ -136,14 +162,7 @@ with_test_prefix "step after disabling 3" {
 	return
     }
 
-    gdb_test "step" "bar \\(\\) at.*" "step 1"
-    gdb_test "step" ".*" "step 2"; # Return from bar()
-    # With gcc 9.2.0 we jump once back to main before entering foo here.
-    # If that happens try to step a second time.
-    gdb_test "step" "foo \\(\\) at.*" "step 3" \
-	"main \\(\\) at .*\r\n$gdb_prompt " "step"
-    gdb_test "step" ".*" "step 4"; # Return from foo()
-    gdb_test "step" "main \\(\\) at.*" "step 5"
+    step_bar_foo_skip_baz
 }
 
 # Enable skiplist entry 3 and make sure we step over it like before.
@@ -254,14 +273,8 @@ with_test_prefix "step using -fu for baz" {
 
     gdb_test_no_output "skip disable"
     gdb_test_no_output "skip enable 7"
-    gdb_test "step" "bar \\(\\) at.*" "step 1"
-    gdb_test "step" ".*" "step 2"; # Return from bar()
-    # With gcc 9.2.0 we jump once back to main before entering foo here.
-    # If that happens try to step a second time.
-    gdb_test "step" "foo \\(\\) at.*" "step 3" \
-	"main \\(\\) at .*\r\n$gdb_prompt " "step"
-    gdb_test "step" ".*" "step 4"; # Return from foo()
-    gdb_test "step" "main \\(\\) at.*" "step 5"
+
+    step_bar_foo_skip_baz
 }
 
 with_test_prefix "step using -rfu for baz" {
@@ -271,14 +284,8 @@ with_test_prefix "step using -rfu for baz" {
 
     gdb_test_no_output "skip disable"
     gdb_test_no_output "skip enable 8"
-    gdb_test "step" "bar \\(\\) at.*" "step 1"
-    gdb_test "step" ".*" "step 2"; # Return from bar()
-    # With gcc 9.2.0 we jump once back to main before entering foo here.
-    # If that happens try to step a second time.
-    gdb_test "step" "foo \\(\\) at.*" "step 3" \
-	"main \\(\\) at .*\r\n$gdb_prompt " "step"
-    gdb_test "step" ".*" "step 4"; # Return from foo()
-    gdb_test "step" "main \\(\\) at.*" "step 5"
+
+    step_bar_foo_skip_baz
 }
 
 # Test -fi + -fu.

-- 
2.36.0