Fix an issue with the gdb step-over aka. "n" command
Commit Message
On 12/20/19 7:13 AM, Simon Marchi wrote:
> Hi Bernd,
>
> On 2019-12-19 5:53 p.m., Bernd Edlinger wrote:
>> Does this explanation make sense?
>
> Yes. Well I think so, I have to admit this is a bit over my head,
> there are a lot of pieces to put together to have a good understanding
> of the problem. I just did a first read, I'll sleep on it and come
> back to it later.
>
> Thanks for the small reproducer, this is extremely valuable. I think it
> will be a good idea to integrate it as a test case in the test suite.
>
> In your patch to dwarf2read.c, I was a bit surprised to see:
>
> m_last_subfile != m_cu->get_builder ()->get_current_subfile ()
>
> So your fix only works if the inlined subroutine comes from another file? If
> I move the tree_check function in next-inline.cc, the fix no longer applies,
> and we get the broken behavior. From your previous email, I understand that
> this is expected. I guess that if both are in the same file, we can't detect
> this situation using the same technique.
>
> I also read about location views, since that's what Alexandre referred to. It
> sounds like it's a magic solution that will allow GDB to do the right thing in
> this kind of situation. If that's indeed the case, then it might be good to start
> exploring this path. I'd like to have a better understanding of how this will help
> GDB make a smarter "next", and what kind of effort is needed to make GDB use it. My
> understanding is that location views allow having an address mapped to multiple
> source locations. For example, here's the problematic address in the next-inline
> test case I've compiled:
>
> ./next-inline.h:[++]
> next-inline.h 28 0x1175 x
> next-inline.h 30 0x1175 1 x
>
> ./next-inline.cc:[++]
> next-inline.cc 22 0x1175 2
>
> Today, when I ask GDB "which source line does this address correspond to", it gives me
> one answer. Does this mean that GDB will now say that 0x1175 corresponds to
>
> - next-inline.h:28
> - next-inline.h:30
> - next-inline.cc:22
>
> all at the same time? Is one of these source locations more important than the others?
> If execution happens to stop exactly at this address, which location do we present to
> the user?
>
> And to come back the problem at hand, how does this help GDB make a smarter "next"?
>
> Btw, I stumbled on a bug with the TUI source display. It might be caused by this patch,
> or it might be that this patch uncovers it.
>
> When I do these actions:
>
> - Start GDB with the next-inline test file (from this patch)
> - Enable the TUI
> - Type "start"
> - Type "s"
> - Type "n" twice
>
> The TUI source display wrongfully jumps to the header file, line 24.
> When I type "frame", it says I'm stopped at next-line.cc:24. So it
> is showing the right line number of the wrong file.
>
I think meanwhile the display bug in the TUI window is fixed (by one of Tom Tromey's
recent patches), could you please check again?
I post both parts of the patch again for your reference here, and add a ChangeLog
which I forgot previously:
gdb:
2019-12-28 Bernd Edlinger <bernd.edlinger@hotmail.de>
* dwarf2read.c (lnp_state_machine): New member m_last_address.
(lnp_state_machine::record_line): After a file changes or
end sequence always assume a statement boundary.
gdb/testsuite:
2019-12-28 Bernd Edlinger <bernd.edlinger@hotmail.de>
* gdb.cp/next-inline.exp: New file.
* gdb.cp/next-inline.cc: New file.
* gdb.cp/next-inline.h: New file.
Thanks
Bernd.
From 95ba4780488b53104ea51cc0702f99a9a800984b Mon Sep 17 00:00:00 2001
From: Bernd Edlinger <bernd.edlinger@hotmail.de>
Date: Thu, 19 Dec 2019 23:41:37 +0100
Subject: [PATCH 2/2] Add a test case for step over inline functions
---
gdb/testsuite/gdb.cp/next-inline.cc | 34 +++++++++++++++++++++++++++++++
gdb/testsuite/gdb.cp/next-inline.exp | 39 ++++++++++++++++++++++++++++++++++++
gdb/testsuite/gdb.cp/next-inline.h | 34 +++++++++++++++++++++++++++++++
3 files changed, 107 insertions(+)
create mode 100644 gdb/testsuite/gdb.cp/next-inline.cc
create mode 100644 gdb/testsuite/gdb.cp/next-inline.exp
create mode 100644 gdb/testsuite/gdb.cp/next-inline.h
new file mode 100644
@@ -0,0 +1,34 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2019 Free Software Foundation, Inc.
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>. */
+
+#include "next-inline.h"
+
+int __attribute__((noinline, noclone))
+get_alias_set (tree *t)
+{ if (t != NULL
+ && TREE_TYPE (t).z != 1
+ && TREE_TYPE (t).z != 2
+ && TREE_TYPE (t).z != 3)
+ return 0;
+ return 1;
+}
+
+tree xx;
+int main()
+{ get_alias_set(&xx);
+ abort();
+}
new file mode 100644
@@ -0,0 +1,39 @@
+# Copyright 2019 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+standard_testfile
+
+if { [prepare_for_testing "failed to prepare" "next-inline" \
+ {next-inline.cc} \
+ {debug nowarnings optimize=-O2}] } {
+ return -1
+}
+
+if ![runto_main] {
+ fail "can't run to main"
+ return
+}
+
+gdb_test "bt" "\\s*\\#0\\s+main.*" "in main"
+gdb_test "step" ".*" "step into get_alias_set"
+gdb_test "bt" "\\s*\\#0\\s+\[^\r\]*next-inline\\.cc:.*" "not in inline"
+gdb_test "next" ".*" "next step 1"
+gdb_test "bt" "\\s*\\#0\\s+\[^\r\]*next-inline\\.cc:.*" "not in inline 1"
+gdb_test "next" ".*" "next step 2"
+gdb_test "bt" "\\s*\\#0\\s+\[^\r\]*next-inline\\.cc:.*" "not in inline 2"
+gdb_test "next" ".*" "next step 3"
+gdb_test "bt" "\\s*\\#0\\s+\[^\r\]*next-inline\\.cc:.*" "not in inline 3"
+gdb_test "next" ".*" "next step 4"
+gdb_test "bt" "\\s*\\#0\\s+\[^\r\]*next-inline\\.cc:.*" "not in inline 4"
new file mode 100644
@@ -0,0 +1,34 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2019 Free Software Foundation, Inc.
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>. */
+
+#include <stdlib.h>
+
+struct tree{
+ volatile int x;
+ volatile int z;
+};
+
+#define TREE_TYPE(NODE) (*tree_check (NODE, 0))
+
+inline tree *
+tree_check (tree *t, int i)
+{
+ if (t->x != i)
+ abort();
+ tree *x = t;
+ return x;
+}
--
1.9.1