Re: [patch] Fix internal error on breaking at a multi-locations caller

[Jan Kratochvil <jan dot kratochvil at redhat dot com>]

On Fri, 01 May 2009 17:47:59 +0200, Joel Brobecker wrote:
> I think Tom must be pretty busy right now :),

I have no news on that issue. :-)


> Based on that, "break" in my opinion should be equivalent to "break *PC"
> where PC is the current frame's PC.  So, I think that the correct way
> to fix this is to set the "explicit_pc" flag in the sal.

Attached.  If you do not agree with the fix credit I am willing to fully
accept it as I agree with this change.


> I also understand the reason why you think a warning might help,
> especially since I had a different intuitive perception of what
> the argument-less command was doing.

As I was surprised of the change requested by Tom Tromey I share the feeling
there is no agreement on the intuitive expectation on side-effects of the
parameter-less `break' command.


> But I think that such a warning would quickly become more annoying than
> anything if the user knows precisely the meaning of his command.

Just my general opinion on this matter: In such cases there should be a GDB
variable to turn it off in the power user's `~/.gdbinit' file.  Reading the
GDB manual should not be a prerequisite for starting GDB.


> Nonetheless, I think we can treat the two issues separately. We can
> fix the problem first with a one-liner, and then we can discuss the
> idea of a warning if you think it might be useful.

As I found out in this discussion it is not clear what the side-effects should
be and as I do not think newbie GDB users are aware the parameter-less `break'
command feature exists at all I no longer have any objections.


Regression tested on x86_64-unknown-linux-gnu.


Thanks,
Jan


gdb/
2009-05-01  Joel Brobecker <brobecker@adacore.com>
	    Jan Kratochvil  <jan.kratochvil@redhat.com>

	Fix internal error on breaking at a multi-locations caller source line.
	* breakpoint.c (parse_breakpoint_sals): Set EXPLICIT_PC for the `break'
	command with no parameters.

gdb/testsuite/
2009-05-01  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.cp/expand-sals.exp, gdb.cp/expand-sals.cc: New.

--- gdb/breakpoint.c	29 Apr 2009 19:31:58 -0000	1.392
+++ gdb/breakpoint.c	1 May 2009 16:45:49 -0000
@@ -5488,6 +5475,13 @@ parse_breakpoint_sals (char **address,
 	  sal.line = default_breakpoint_line;
 	  sal.symtab = default_breakpoint_symtab;
 	  sal.section = find_pc_overlay (sal.pc);
+
+	  /* In the case of breaking at the caller line (right after the
+	     calling instruction) GDB should use neither the first instruction
+	     of the source line (before the calling instruction) nor any other
+	     existing locations (function instances) for that source line.  */
+	  sal.explicit_pc = 1;
+
 	  sals->sals[0] = sal;
 	  sals->nelts = 1;
 	}
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ gdb/testsuite/gdb.cp/expand-sals.cc	1 May 2009 16:45:50 -0000
@@ -0,0 +1,53 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright (C) 2009 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   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/>.  */
+
+int
+func ()
+{
+  return 42;	/* func-line */
+}
+
+volatile int global_x;
+
+class A
+{
+public:
+  A ()
+    {
+      global_x = func ();	/* caller-line */
+    }
+};
+
+/* class B is here just to make the `func' calling line above having multiple
+   instances - multiple locations.  Template cannot be used as its instances
+   would have different function names which get discarded by GDB
+   expand_line_sal_maybe.  */
+
+class B : public A
+{
+};
+
+int
+main (void)
+{
+  A a;
+  B b;
+
+  return 0;	/* exit-line */
+}
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ gdb/testsuite/gdb.cp/expand-sals.exp	1 May 2009 16:45:50 -0000
@@ -0,0 +1,83 @@
+# Copyright 2009 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/>.
+
+if { [skip_cplus_tests] } { continue }
+
+set srcfile expand-sals.cc
+if { [prepare_for_testing expand-sals.exp expand-sals $srcfile {debug c++}] } {
+    return -1
+}
+if ![runto_main] {
+    return -1
+}
+
+gdb_breakpoint [gdb_get_line_number "exit-line"]
+
+gdb_breakpoint [gdb_get_line_number "func-line"]
+gdb_continue_to_breakpoint "func" ".*func-line.*"
+
+gdb_test "up" "caller-line.*"
+
+# PC should not be at the boundary of source lines to make the original bug
+# exploitable.
+
+set test "p/x \$pc"
+set pc {}
+gdb_test_multiple $test $test {
+    -re "\\$\[0-9\]+ = (0x\[0-9a-f\]+)\r\n$gdb_prompt $" {
+	set pc $expect_out(1,string)
+	pass $test
+    }
+}
+
+set test "info line"
+set end {}
+gdb_test_multiple $test $test {
+    -re "Line \[0-9\]+ of .* starts at address 0x\[0-9a-f\]+.* and ends at (0x\[0-9a-f\]+).*\\.\r\n$gdb_prompt $" {
+	set end $expect_out(1,string)
+	pass $test
+    }
+}
+
+set test "caller line has trailing code"
+if {$pc != $end} {
+    pass $test
+} else {
+    fail $test
+}
+
+# Original problem was an internal error here.
+set test "break"
+gdb_test_multiple $test $test {
+    -re "Breakpoint \[0-9\]+ at .*, line \[0-9\]+\\. \\(\[2-9\] locations\\)\r\n$gdb_prompt $" {
+	fail $test
+    }
+    -re "Breakpoint \[0-9\]+ at .*, line \[0-9\]+\\.\r\n$gdb_prompt $" {
+	pass $test
+    }
+}
+
+gdb_continue_to_breakpoint "caller" ".*caller-line.*"
+
+# Test GDB caught this return call and not the next one through B::B()
+gdb_test "bt" \
+	 "#0 \[^\r\n\]* A \[^\r\n\]*\r\n#1 \[^\r\n\]* main \[^\r\n\]*" \
+	 "bt from A"
+
+gdb_continue_to_breakpoint "next caller func" ".*func-line.*"
+
+# Verify GDB really could not catch any other breakpoint location.
+
+gdb_continue_to_breakpoint "uncaught return" ".*exit-line.*"