[reverse RFC] test for restored machine state

Michael Snyder
2008-09-16T23:57:56Z

[-- Attachment #1: Type: text/plain, Size: 1065 bytes --]

Here's a test for the question we've been discussing,
about the restored machine state after reverse execution
stops.

Although it probably would have been sufficient to test
two cases (register and memory), I went for completeness
and tested five cases:
* a register variable
* an auto variable
* a function static
* a module static, and
* a module global.

In each case, I let the program increment the variable.
Then I tested whether the pre-increment value was restored
under two conditions:
* continue backward to a breakpoint, and
* step backward.

I checked each value "before" and "after", and the
Teawater record/replay implementation passes 100 percent.

I would welcome any suggestions for improving or extending
the test. I've suggested a few possible extensions in the
comments. I did a little hoop-dancing to make it as likely
as possible that the compiler would emit a single instruction
in the register case, so we can see that the side effect of
the breakpoint instruction (incrementing the register variable)
is in fact reverted.

[-- Attachment #2: machinestate.txt --]
[-- Type: text/plain, Size: 10017 bytes --]

2008-09-16 Michael Snyder <msnyder@vmware.com>

* gdb.twreverse/machinestate.exp: New file.
* gdb.twreverse/machinestate.c: New file.
* gdb.twreverse/machinestate1.c: New file.
* gdb.twreverse/Makefile.in: Update for make clean.

Index: machinestate.c
===================================================================
RCS file: machinestate.c
diff -N machinestate.c
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ machinestate.c 16 Sep 2008 23:43:04 -0000
@@ -0,0 +1,101 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2008 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/>. */
+
+/*
+ * Test restoration of machine state
+ */
+
+extern void hide (int);
+
+/* Test register variable
+ Requires -- compiler honors 'register'. */
+
+void
+register_state (void)
+{
+ register int a = 0;
+
+ hide (a); /* External function to defeat optimization. */
+ a++; /* register_state: set breakpoint here */
+ hide (a); /* register post-change */
+}
+
+/* Test auto variable (whatever that means). */
+
+void
+auto_state (void)
+{
+ auto int a = 0;
+
+ hide (a); /* External function to defeat optimization. */
+ a++; /* auto_state: set breakpoint here */
+ hide (a); /* auto post-change */
+}
+
+/* Test function-static variable. */
+
+void
+function_static_state (void)
+{
+ static int a = 0;
+
+ hide (a); /* External function to defeat optimization. */
+ a++; /* function_static_state: set breakpoint here */
+ hide (a); /* function static post-change */
+}
+
+/* Test module-static variable. */
+
+static int astatic;
+
+void
+module_static_state (void)
+{
+ astatic = 0;
+
+ hide (astatic); /* External function to defeat optimization. */
+ astatic++; /* module_static_state: set breakpoint here */
+ hide (astatic); /* module static post-change */
+}
+
+/* Test module-global variable. */
+
+int aglobal;
+
+void
+module_global_state (void)
+{
+ aglobal = 0;
+
+ hide (aglobal); /* External function to defeat optimization. */
+ aglobal++; /* module_global_state: set breakpoint here */
+ hide (aglobal); /* module global post-change */
+}
+
+/* main test driver */
+
+int
+main (int argc, char **argv)
+{
+ register_state (); /* begin main */
+ auto_state ();
+ function_static_state ();
+ module_static_state ();
+ module_global_state ();
+
+ return 0; /* end main */
+}
Index: machinestate.exp
===================================================================
RCS file: machinestate.exp
diff -N machinestate.exp
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ machinestate.exp 16 Sep 2008 23:43:04 -0000
@@ -0,0 +1,142 @@
+# Copyright 2008 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/>.
+
+# Please email any bugs, comments, and/or additions to this file to:
+# bug-gdb@prep.ai.mit.edu
+
+#
+# This test tests the restoration of various kinds of machine state
+# to their original values by reverse execution. We will execute
+# the program forward while it changes various types of data, and
+# then execute it backward to see if their values get restored.
+#
+# The types of machine state (data) that are tested are:
+# register variable
+# auto variable
+# function static variable
+# module static variable
+# module global variable
+#
+# TODO:
+# various, possibly including...
+# .bss variable, .data variable, ...
+# shared library variable
+# heap variable (pointer)...
+# overlay variables...
+#
+
+
+set testfile "machinestate"
+set srcfile ${testfile}.c
+set srcfile1 ${testfile}1.c
+
+if { [prepare_for_testing machinestate.exp $testfile {machinestate.c machinestate1.c} ] } {
+ return -1
+}
+
+set newline "\[\r\n\]+"
+
+set beginmain [gdb_get_line_number " begin main " $srcfile]
+set endmain [gdb_get_line_number " end main " $srcfile]
+
+# Test begins
+
+runto main
+
+# FIXME 'record' command should say something so we know it's working.
+gdb_test "record" "" "start recording"
+
+# Proceed to end of main
+
+gdb_test "break $endmain" \
+ "Breakpoint.* file .*/$srcfile, line $endmain.*" ""
+gdb_continue_to_breakpoint "end of main" ".*/$srcfile:$endmain.*"
+
+###
+###
+###
+
+# Now run backward to each of several points where data is changed.
+#
+
+# Module global variable
+
+set breakloc [gdb_get_line_number \
+ "module_global_state: set breakpoint here" $srcfile]
+
+gdb_test "tbreak $breakloc" ".*/$srcfile, line $breakloc.*" ""
+gdb_test "reverse-continue" ".*/$srcfile:$breakloc.*" "reverse to $breakloc"
+
+gdb_test "print aglobal" ".* = 0$newline" "module global reverse"
+gdb_test "step" ".* module global post-change .*" ""
+gdb_test "print aglobal" ".* = 1$newline" "module global forward"
+
+
+# Module static variable
+
+set breakloc [gdb_get_line_number \
+ "module_static_state: set breakpoint here" $srcfile]
+
+gdb_test "tbreak $breakloc" ".*/$srcfile, line $breakloc.*" ""
+gdb_test "reverse-continue" ".*/$srcfile:$breakloc.*" "reverse to $breakloc"
+
+gdb_test "print astatic" ".* = 0$newline" "module static reverse-breakpoint"
+gdb_test "step" ".* module static post-change .*" ""
+gdb_test "print astatic" ".* = 1$newline" "module static forward"
+gdb_test "reverse-step" ".*$newline$breakloc.*" ""
+gdb_test "print astatic" ".* = 0$newline" "module static reverse-step"
+
+# Function static variable
+
+set breakloc [gdb_get_line_number \
+ "function_static_state: set breakpoint here" $srcfile]
+
+gdb_test "tbreak $breakloc" ".*/$srcfile, line $breakloc.*" ""
+gdb_test "reverse-continue" ".*/$srcfile:$breakloc.*" "reverse to $breakloc"
+
+gdb_test "print a" ".* = 0$newline" "function static reverse-breakpoint"
+gdb_test "step" ".* function static post-change .*" ""
+gdb_test "print a" ".* = 1$newline" "function static forward"
+gdb_test "reverse-step" ".*$newline$breakloc.*" ""
+gdb_test "print a" ".* = 0$newline" "function static reverse-step"
+
+# Auto variable
+
+set breakloc [gdb_get_line_number \
+ "auto_state: set breakpoint here" $srcfile]
+
+gdb_test "tbreak $breakloc" ".*/$srcfile, line $breakloc.*" ""
+gdb_test "reverse-continue" ".*/$srcfile:$breakloc.*" "reverse to $breakloc"
+
+gdb_test "print a" ".* = 0$newline" "auto var reverse-breakpoint"
+gdb_test "step" ".* auto post-change .*" ""
+gdb_test "print a" ".* = 1$newline" "auto var forward"
+gdb_test "reverse-step" ".*$newline$breakloc.*" ""
+gdb_test "print a" ".* = 0$newline" "auto var reverse-step"
+
+# Register variable
+
+set breakloc [gdb_get_line_number \
+ "register_state: set breakpoint here" $srcfile]
+
+gdb_test "tbreak $breakloc" ".*/$srcfile, line $breakloc.*" ""
+gdb_test "reverse-continue" ".*/$srcfile:$breakloc.*" "reverse to $breakloc"
+
+gdb_test "print a" ".* = 0$newline" "register var reverse-breakpoint"
+gdb_test "step" ".* register post-change .*" ""
+gdb_test "print a" ".* = 1$newline" "register var forward"
+gdb_test "reverse-step" ".*$newline$breakloc.*" ""
+gdb_test "print a" ".* = 0$newline" "register var reverse-step"
+
Index: machinestate1.c
===================================================================
RCS file: machinestate1.c
diff -N machinestate1.c
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ machinestate1.c 16 Sep 2008 23:43:04 -0000
@@ -0,0 +1,25 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2008 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/>. */
+
+/*
+ * Aux function for machine state test.
+ */
+
+void
+hide (int x)
+{
+}
Index: Makefile.in
===================================================================
RCS file: /cvs/src/src/gdb/testsuite/gdb.twreverse/Attic/Makefile.in,v
retrieving revision 1.1.2.5
diff -u -p -r1.1.2.5 Makefile.in
--- Makefile.in 9 Sep 2008 19:05:17 -0000 1.1.2.5
+++ Makefile.in 16 Sep 2008 23:43:04 -0000
@@ -1,7 +1,9 @@
VPATH = @srcdir@
srcdir = @srcdir@

-EXECUTABLES = break-reverse step-reverse return2-reverse watch-reverse
+EXECUTABLES = break-reverse step-reverse finish-reverse \
+ until-reverse watch-reverse consecutive-reverse machinestate
+
MISCELLANEOUS =

all info install-info dvi install uninstall installcheck check: