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* [reverse RFC] test for restored machine state
@ 2008-09-16 23:57 Michael Snyder
  2008-09-17 16:14 ` teawater
  0 siblings, 1 reply; 2+ messages in thread
From: Michael Snyder @ 2008-09-16 23:57 UTC (permalink / raw)
  To: gdb-patches; +Cc: teawater

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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.


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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:

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2008-09-16 23:57 [reverse RFC] test for restored machine state Michael Snyder
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