[PATCH] Use -qualified flag when setting temporary breakpoint in start command
Simon Marchi
simon.marchi@efficios.com
Tue Apr 9 16:19:00 GMT 2019
On 2019-04-09 11:27 a.m., Pedro Alves wrote:
> On 4/9/19 3:55 AM, Simon Marchi wrote:
>> From: Simon Marchi <simon.marchi@efficios.com>
>>
>> When using the "start" command, GDB puts a temporary breakpoint on the
>> "main" symbol (we literally invoke the tbreak command). However, since
>> it does wild matching by default, it also puts a breakpoint on any C++
>> method or "main" function in a namespace. For example, when debugging
>> GDB, it creates a total of 24 locations:
>>
>> (gdb) start
>> Temporary breakpoint 1 at 0x198c1e9: main. (24 locations)
>>
>> as there are a bunch of methods called main in the selftests, such as
>>
>> selftests::string_view::capacity_1::main()
>>
>> If such method was called in the constructor of a global object, or a
>> function marked with the attribute "constructor", then we would stop at
>> the wrong place. Also, this causes a few extra symtabs (those that
>> contain the "wrong" mains) to be expanded for nothing.
>>
>> The dummiest, most straightforward solution is to add -qualified when
>> invoking tbreak. With this patch, "start" creates a single-location
>> breakpoint, as expected.
>>
>
> That seems fine.
>
>> I changed the start.exp test to use a C++ test file, which contains two
>> main functions. The test now verifies that the output of "start" is the
>> output we get when we set a single-location breakpoint.
>
> I'm mildly concerned that this drops testing with C, though. Given
> that "start" is a basic command, and that C++ symbol/name matching
> differs from C, and considering that some targets don't even
> support C++ (considering extended-remote too), I'd think it to
> be prudent to test both C and C++. I wouldn't say it's a big
> deal, but, the .exp file is small, so it shouldn't be much of
> a maintenance burden to copy & adjust it as a separate .exp
> file, IMHO.
I had initially changed start.exp to test both C and C++, then decided to just
keep C++ for simplicity. But your point about coverage is good, so I've done
as you suggested.
>>
>> gdb/ChangeLog:
>>
>> * infcmd.c (run_command_1): Pass -qualified to tbreak when usind
>> the "start" command.
>>
>> gdb/testsuite/ChangeLog:
>>
>> * gdb.base/start.exp: Change test file to start.cpp. Enhance
>> regexp to match output of single-location breakpoint.
>> * gdb.base/start.cpp: New file.
>
> Nit: all other C++ source files in the testsuite use .cc extension.
Fixed.
>> +namespace foo
>> +{
>> +
>> +int main ()
>> +{
>> + return 1;
>> +}
>> +
>> +} /* namespace foo */
>> +
>> +int main()
>
> Watch out for GNU formatting.
Woops. The blame is shared between the original start.c file and me not
doing enough GDB these days.
Here is the updated patch.
>From 232b274adfc6904d33bde3baa52e40836af6221b Mon Sep 17 00:00:00 2001
From: Simon Marchi <simon.marchi@efficios.com>
Date: Mon, 8 Apr 2019 22:55:57 -0400
Subject: [PATCH] Use -qualified flag when setting temporary breakpoint in
start command
When using the "start" command, GDB puts a temporary breakpoint on the
"main" symbol (we literally invoke the tbreak command). However, since
it does wild matching by default, it also puts a breakpoint on any C++
method or "main" function in a namespace. For example, when debugging
GDB, it creates a total of 24 locations:
(gdb) start
Temporary breakpoint 1 at 0x198c1e9: main. (24 locations)
as there are a bunch of methods called main in the selftests, such as
selftests::string_view::capacity_1::main()
If such method was called in the constructor of a global object, or a
function marked with the attribute "constructor", then we would stop at
the wrong place. Also, this causes a few extra symtabs (those that
contain the "wrong" mains) to be expanded for nothing.
The dummiest, most straightforward solution is to add -qualified when
invoking tbreak. With this patch, "start" creates a single-location
breakpoint, as expected.
I copied the start.exp test to start-cpp.exp and made it use a C++ test
file, which contains two main functions. The new test verifies that the
output of "start" is the output we get when we set a single-location
breakpoint.
gdb/ChangeLog:
* infcmd.c (run_command_1): Pass -qualified to tbreak when usind
the "start" command.
gdb/testsuite/ChangeLog:
* gdb.base/start-cpp.exp: New file.
* gdb.base/start-cpp.cc: New file.
---
gdb/infcmd.c | 5 +++-
gdb/testsuite/gdb.base/start-cpp.exp | 37 ++++++++++++++++++++++++++++
2 files changed, 41 insertions(+), 1 deletion(-)
create mode 100644 gdb/testsuite/gdb.base/start-cpp.exp
diff --git a/gdb/infcmd.c b/gdb/infcmd.c
index 3b26fd4a4671..178f89e95207 100644
--- a/gdb/infcmd.c
+++ b/gdb/infcmd.c
@@ -604,7 +604,10 @@ run_command_1 (const char *args, int from_tty, enum run_how run_how)
/* Insert temporary breakpoint in main function if requested. */
if (run_how == RUN_STOP_AT_MAIN)
- tbreak_command (main_name (), 0);
+ {
+ std::string arg = string_printf ("-qualified %s", main_name ());
+ tbreak_command (arg.c_str (), 0);
+ }
exec_file = get_exec_file (0);
diff --git a/gdb/testsuite/gdb.base/start-cpp.exp b/gdb/testsuite/gdb.base/start-cpp.exp
new file mode 100644
index 000000000000..5f98b92ffa41
--- /dev/null
+++ b/gdb/testsuite/gdb.base/start-cpp.exp
@@ -0,0 +1,37 @@
+# Copyright 2005-2019 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 .cc
+
+if {[prepare_for_testing "failed to prepare" $testfile $srcfile debug]} {
+ return -1
+}
+
+# This is a testcase specifically for the `start' GDB command. For regular
+# stop-in-main goal in the testcases consider using `runto_main' instead.
+
+# In this C++ version of the test (as opposed to start.exp), we specifically
+# test that the temporary breakpoint created by the start command has a single
+# location, even if we have a function named "main" in a non-root namespace.
+
+# For C++ programs, "start" should stop in main().
+if { [gdb_start_cmd] < 0 } {
+ untested start
+ return -1
+}
+
+gdb_test "" \
+ "Temporary breakpoint $decimal at $hex: file.*main \\(\\) at .*start-cpp.cc:.*" \
+ "start"
--
2.21.0
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