Re: [PATCH] Handle SIGSEGV in gdb selftests

[Simon Marchi <simark@simark.ca>]

On 1/13/23 20:11, Simon Marchi via Gdb-patches wrote:
> 
> 
> On 12/26/22 03:02, tdevries via Gdb-patches wrote:
>> On 2022-12-16 16:11, Tom Tromey via Gdb-patches wrote:
>>>>>>>> "Tom" == Tom de Vries <tdevries@suse.de> writes:
>>>
>>> Tom> On 12/15/22 22:14, Tom Tromey via Gdb-patches wrote:
>>>>> The gdb.gdb self-tests were timing out for me.  Looking into it, the
>>>>> problem is that the version of the Boehm GC that is used by Guile on
>>>>> my machine causes a SEGV during stack probing.  This unexpected stop
>>>>> confuses the tests and causes repeated timeouts.
>>>>>
>>>
>>> Tom> FWIW, that's https://sourceware.org/bugzilla/show_bug.cgi?id=29325 .
>>>
>>> Thanks, I updated the commit message.
>>
>> I ran into this again, tried out the patch and checked that it fixes the problem.
>>
>> LGTM.
>>
>> Thanks,
>> - Tom
> 
> Hi both Toms,
> 
> I still see the issue on Ubuntu 22.04, when testing with the
> native-extended-gdbserver board:
> 
> ...
> Thread 1 "xgdb" received signal SIGSEGV, Segmentation fault.
> 0x00007ffff6d828f2 in GC_find_limit_with_bound () from /usr/lib/x86_64-linux-gnu/libgc.so.1
> (gdb) FAIL: gdb.gdb/selftest.exp: xgdb is at prompt
> 
> The modified code looks like this:
> 
> 
>         set test "xgdb is at prompt"
>         gdb_test_multiple "continue" $test {
>             -i "$inferior_spawn_id"
>             -re "received signal SIGSEGV.* in GC_.*$gdb_prompt" {
>                 # Some versions of the GC used by Guile cause a SEGV
>                 # during stack probing.  Ignore this and carry on.
>                 send_gdb "continue\n"
>                 exp_continue
>             }
>             -re "$banner" {
>                 pass $test
>             }
>         }
> 
> Shouldn't the SIGSEGV -re be before the `-i $inferior_spawn_id`?
> Otherwise we expect the "received signal SIGSEGV" message to come from
> the debugged GDB, when it's the top GDB that will print it (like when
> debugging any other test program).
> 
> I think we don't see the problem when testing with native because
> the top and bottom GDBs share the same spawn id.
> 
> Simon


Here's a patch to fix it, with a commit message.


From f2d47cdd63ea9abddabdccd8097b2a6e7d1e64b1 Mon Sep 17 00:00:00 2001
From: Simon Marchi <simon.marchi@efficios.com>
Date: Fri, 13 Jan 2023 20:08:41 -0500
Subject: [PATCH] gdb/testsuite: expect SIGSEGV from top GDB spawn id

When testing with the native-extended-gdbserver, I get:

    Thread 1 "xgdb" received signal SIGSEGV, Segmentation fault.
    0x00007ffff6d828f2 in GC_find_limit_with_bound () from /usr/lib/x86_64-linux-gnu/libgc.so.1
    (gdb) FAIL: gdb.gdb/selftest.exp: xgdb is at prompt

This is because the -re that is supposed to match this SIGSEGV is after
`-i $inferior_spawn_id`.  On native, the top and bottom GDB are on the
same spawn id, so it ends up working.  But with a gdbserver board,
that's not the case.  Move the SIGSEGV -re before the `-i
$inferior_spawn_id` line, such that it matches what the top GDB outputs.

Do the same fix in gdb.gdb/python-helper.exp.

Change-Id: I3291630e218a5a3a6a47805b999ddbc9b968c927
---
 gdb/testsuite/gdb.gdb/python-helper.exp | 2 +-
 gdb/testsuite/gdb.gdb/selftest.exp      | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/gdb/testsuite/gdb.gdb/python-helper.exp b/gdb/testsuite/gdb.gdb/python-helper.exp
index c147c6bcbb03..98f03ef456f3 100644
--- a/gdb/testsuite/gdb.gdb/python-helper.exp
+++ b/gdb/testsuite/gdb.gdb/python-helper.exp
@@ -86,13 +86,13 @@ proc test_python_helper {} {
     # stop is being detected from the inner GDB, hence the use of -i
     # here.
     gdb_test_multiple "continue" "start inner gdb" {
-	-i "$inferior_spawn_id"
 	-re "received signal SIGSEGV.* in GC_.*$outer_prompt_re" {
 	    # Some versions of the GC used by Guile cause a SEGV
 	    # during stack probing.  Ignore this and carry on.
 	    send_gdb "continue\n"
 	    exp_continue
 	}
+	-i "$inferior_spawn_id"
 	-re "\r\n$gdb_prompt $" {
 	    pass $gdb_test_name
 	}
diff --git a/gdb/testsuite/gdb.gdb/selftest.exp b/gdb/testsuite/gdb.gdb/selftest.exp
index 177c29fb224d..df12602b64bb 100644
--- a/gdb/testsuite/gdb.gdb/selftest.exp
+++ b/gdb/testsuite/gdb.gdb/selftest.exp
@@ -74,13 +74,13 @@ proc test_with_self { } {
 			"$gdb_prompt $"]
 	set test "xgdb is at prompt"
 	gdb_test_multiple "continue" $test {
-	    -i "$inferior_spawn_id"
 	    -re "received signal SIGSEGV.* in GC_.*$gdb_prompt" {
 		# Some versions of the GC used by Guile cause a SEGV
 		# during stack probing.  Ignore this and carry on.
 		send_gdb "continue\n"
 		exp_continue
 	    }
+	    -i "$inferior_spawn_id"
 	    -re "$banner" {
 		pass $test
 	    }

base-commit: 325ab797da3b71e03eba184930f08ee3179a30d6
-- 
2.39.0