Re: [PATCH] PowerPC, fix gdb.reverse/finish-reverse-bkpt.exp and gdb.reverse/next-reverse-bkpt-over-sr.exp

[Carl Love <cel@us.ibm.com>]

Bruno, GDB maintainers:

Version 3, per the comments from Ulrich, I created new source files for
the two tests based on their original source files.  The expect files
were then updated to use the new source files.  The updated patch has
been re-tested on PowerPC and x86-64 with no new regression test
failures.

The first attempt to fix test next-reverse-bkpt-over-sr.exp basically
breaks the test per the comments from Bruno in the thread with the
subject [PATCH] Fix test next-reverse-bkpt-over-sr.exp.

The following is a second, new approach to fixing the issue.

PowerPC uses a Global Entry Point (GEP) and a Local Entry Point (LEP). 
The GEP is located on the first instruction of the function.  It sets
up register r2 before the LEP.

  <callee>:
   lis     r2,4098        <- GEP
   addi    r2,r2,32512
   mflr    r0             <- LEP
   std     r0,16(r1)
   ...

The issue is the gdb command break *callee sets the breakpoint on the
first instruction in the function.  The call to function callee enters
the function at the LEP.  Thus gdb never "sees" the breakpoint at the
GEP resulting in the test failing on PowerPC.  If the function is
called using a function pointer, then the linker will setup the call to
use the GEP rather instead of the LEP and the test then works as
expected on PowerPC.  

A new function pointer call to callee afollowed by a normal call to
callee is added for test next-reverse-bkpt-over-sr.exp at the end of
the main so as to not change the test behavior of step-reverse.exp. 
Note, the source file step-reverse.c is used by both test next-reverse-
bkpt-over-sr.exp and test step-reverse.exp.  Test next-reverse-bkpt-
over-sr.exp starts at the new call to callee at the end of the main
program. The rest of the test runs without changes.  By entering via
the GEP on PowerPC, the breakpoint is seen and the test passes as
expected.  

Note, on non PowerPC systems the GEP and LEP are the same.  Calling
function callee normally or with a function pointer has the same
behavior on non-PowerPC systems.  This was specifically verified on
Intel X86-64.

Test gdb.reverse/finish-reverse-bkpt.exp also fails on PowerPC for the
same reasons as discussed above.  Again, this test is modified by
adding a function pointer call to void_func at the end of main.  The
source code is used for both test finish-reverse-bkpt.exp and finish-
reverse.exp so the a breakpoint is added to finish-reverse-bkpt.exp to
stop before the function pointer call to void_func where the test then
starts.

The addition of the function pointer declarations in the two source
files require an additional next statement to tests step-precsave.exp
and step-reverse.exp to keep the keep things lined up.

Hopefully, this approach to fixing the failing tests on PowerPC is
acceptable without changing the behavior on non-PowerPC platforms.

The patch has been tested on both PowerPC and X86-64 with no
regressions.

Please let me know if this patch is acceptable.  Thanks.

                          Carl Love

--------------------------------

PowerPC, version 3, fix gdb.reverse/finish-reverse-bkpt.exp and gdb.reverse/next-reverse-bkpt-over-sr.exp

The tests set a break point with the command break *func.  This sets a
breakpoint on the first instruction of the function.  PowerPC uses
Global Entry Points (GEP) and Local Entry Points (LEP).  The first
instruction in the function is the GEP.  The GEP sets up register
r2 before reaching the LEP.  When the function is called with func() the
function is entered via the LEP and the test fails because GDB does not
see the breakpoint on the GEP.  However, if the function is called via a
function pointer, execution begins at the GEP as the test expects.

Currently finish-reverse-bkpt.exp uses source file finish-reverse.c and
next-reverse-bpkt-over-sr.exp uses source file step-reverse.c  A new
source file was created for tests finish-reverse-bkpt.exp and
next-reverse-bkpt-over-sr.exp.  The new files use the new function
pointer method to call the functions so the tests will work correctly on
both PowerPC with a GEP and LEP as well as on other systems.  The GEP is
the same as the LEP on non PowerPC systems.

The expect files were changed to use the new source files and to set the
initial break point for the rest of the test on the function pointer call
for the function.

This patch fixes two PowerPC test failures in each of the tests
gdb.reverse/finish-reverse-bkpt.exp and
gdb.reverse/next-reverse-bkpt-over-sr.exp.

Patch tested on PowerPC and Intel X86-64 with no regressions.
---
 .../gdb.reverse/finish-reverse-bkpt.c         | 37 ++++++++++++++++
 .../gdb.reverse/finish-reverse-bkpt.exp       | 32 +++++++++++++-
 .../gdb.reverse/next-reverse-bkpt-over-sr.c   | 44 +++++++++++++++++++
 .../gdb.reverse/next-reverse-bkpt-over-sr.exp | 33 +++++++++++---
 4 files changed, 139 insertions(+), 7 deletions(-)
 create mode 100644 gdb/testsuite/gdb.reverse/finish-reverse-bkpt.c
 create mode 100644 gdb/testsuite/gdb.reverse/next-reverse-bkpt-over-sr.c

diff --git a/gdb/testsuite/gdb.reverse/finish-reverse-bkpt.c b/gdb/testsuite/gdb.reverse/finish-reverse-bkpt.c
new file mode 100644
index 00000000000..771793c389f
--- /dev/null
+++ b/gdb/testsuite/gdb.reverse/finish-reverse-bkpt.c
@@ -0,0 +1,37 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2008-2022 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 gdb's "return" command in reverse.  The code for this test is based
+   on the code in test finish-reverse.c.  The code was modified to call the
+   function via a function pointer so the test will behave the same on all
+   platforms.  See comments in finish-reverse-bkpt.exp.  */
+
+int void_test = 0;
+
+void void_func ()
+{
+  void_test = 1;		/* VOID FUNC */
+}
+
+int main (int argc, char **argv)
+{
+  int i;
+  void (*funp) (void) = void_func;
+
+  funp ();                              /* FUNCTION PTR call to void_func */
+  return 0;
+} /* end of main */
diff --git a/gdb/testsuite/gdb.reverse/finish-reverse-bkpt.exp b/gdb/testsuite/gdb.reverse/finish-reverse-bkpt.exp
index 2a204748d98..f9682b2962d 100644
--- a/gdb/testsuite/gdb.reverse/finish-reverse-bkpt.exp
+++ b/gdb/testsuite/gdb.reverse/finish-reverse-bkpt.exp
@@ -19,11 +19,32 @@
 # the functions entry would be ignored.  Make sure the bug doesn't
 # reappear.
 
+# The test sets a breakpoint with the command break *void_func to set a
+# breakpoint on the first instruction of the function.  The issue is on
+# PowerPC it uses Global Entry Points (GEP) and Local Entry Points (LEP).
+# The GEP is the first instruction in the function.  It sets up register
+# r2 and then reaches the LEP.
+#
+#   <void_func>:
+#  	lis     r2,4098        <- GEP
+#   	addi    r2,r2,32512
+#   	mflr    r0             <- LEP
+#   	std     r0,16(r1)
+#        ....
+
+#
+# The command break *void_func sets the breakpoint on the GEP.  Calling
+# the function with void_func() will enter the function via the LEP.  So,
+# this test needs to use a function pointer to call void_func() so the
+# function will be entered via the GEP to work as designed on PowerPC in
+# addition to non-PowerPC systems.  On non-PowerPC systems, the GEP and LEP
+# are the same.
+
 if ![supports_reverse] {
     return
 }
 
-standard_testfile finish-reverse.c
+standard_testfile
 
 if { [prepare_for_testing "failed to prepare" "$testfile" $srcfile] } {
     return -1
@@ -38,6 +59,15 @@ if [supports_process_record] {
     gdb_test_no_output "record" "turn on process record"
 }
 
+# Move to the function pointer call to void_func so we will use the GEP
+# to enter void_func and break.
+set breakloc [gdb_get_line_number "FUNCTION PTR" "$srcfile"]
+gdb_test "break $breakloc" \
+    "Breakpoint $decimal at .*$srcfile, line $breakloc\." \
+    "set breakpoint on funp"
+gdb_continue_to_breakpoint "funp call" ".*$srcfile:$breakloc.*"
+
+# Start the test
 set breakloc [gdb_get_line_number "VOID FUNC" "$srcfile"]
 gdb_test "tbreak void_func" \
     "Temporary breakpoint $decimal at .*$srcfile, line $breakloc\." \
diff --git a/gdb/testsuite/gdb.reverse/next-reverse-bkpt-over-sr.c b/gdb/testsuite/gdb.reverse/next-reverse-bkpt-over-sr.c
new file mode 100644
index 00000000000..ad771e05ca1
--- /dev/null
+++ b/gdb/testsuite/gdb.reverse/next-reverse-bkpt-over-sr.c
@@ -0,0 +1,44 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2008-2022 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>
+#include <string.h>
+
+/* Test reverse finish command.  The code for this test is based on the code
+   in test step-reverse.c.  The code was modified to call the function via
+   a function pointer so the test will behave the same on all platforms.
+   See comments in next-reverse-bkpt-over-sr.exp.  */
+
+int myglob = 0;
+
+int callee() {		/* ENTER CALLEE */
+  return myglob++;	/* ARRIVED IN CALLEE */
+}			/* RETURN FROM CALLEE */
+
+int main () {
+   int (*funp) (void) = callee;
+
+   /* Test next-reverse-bkpt-over-sr.exp needs to call function callee using
+      a function pointer to work correctly on PowerPC.  See comments in
+      next-reverse-bkpt-over-sr.exp.  */
+   funp ();       /* FUNCTION PTR CALL TO CALLEE */
+
+   /* Test that "step" doesn't */
+   callee ();	/* STEP INTO CALL AFTER FUNP CALL */
+
+   exit (0); /* end of main */
+}
diff --git a/gdb/testsuite/gdb.reverse/next-reverse-bkpt-over-sr.exp b/gdb/testsuite/gdb.reverse/next-reverse-bkpt-over-sr.exp
index 6ef56d30e7b..671b1c09dd4 100644
--- a/gdb/testsuite/gdb.reverse/next-reverse-bkpt-over-sr.exp
+++ b/gdb/testsuite/gdb.reverse/next-reverse-bkpt-over-sr.exp
@@ -14,20 +14,37 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
 # This file is part of the GDB testsuite.  It tests reverse stepping.
-# Lots of code borrowed from "step-test.exp".
-
 #
 # reverse-next over a function call sets a step-resume breakpoint at
 # callee's entry point, runs to it, and then does an extra single-step
 # to get at the callee's caller.  Test that a user breakpoint set at
 # the same location as the step-resume breakpoint isn't ignored.
 #
+# The test sets a breakpoint with the command break *callee to set a
+# breakpoint on the first instruction of the function.  The issue is on
+# PowerPC it uses Global Entry Points (GEP) and Local Entry Points (LEP).
+# The GEP is the first instruction in the function.  It sets up register
+# r2 and then reaches the LEP.
+#
+#  <callee>:
+#   lis     r2,4098        <- GEP
+#   addi    r2,r2,32512
+#   mflr    r0             <- LEP
+#   std     r0,16(r1)
+
+#
+# The command break *callee sets the breakpoint on the GEP.  Calling
+# the function with callee() will enter the function via the LEP.  So,
+# this test needs to use a function pointer to call callee() so the
+# function will be entered via the GEP to work as designed on PowerPC in
+# addition to non-PowerPC systems.  On non-PowerPC systems, the GEP and LEP
+# are the same.
 
 if ![supports_reverse] {
     return
 }
 
-standard_testfile step-reverse.c
+standard_testfile
 
 if { [prepare_for_testing "failed to prepare" $testfile $srcfile] } {
     return -1
@@ -42,8 +59,12 @@ if [supports_process_record] {
     gdb_test_no_output "record" "turn on process record"
 }
 
-set lineno [gdb_get_line_number "STEP INTO THIS CALL"]
-gdb_test "advance $lineno" ".*STEP INTO THIS CALL.*" "get past callee call"
+# Move to the function pointer call to the callee call after the function
+# pointer call to callee to begin the test.  The function pointer call to
+# callee will use the Global Entry Point on Power.
+set lineno [gdb_get_line_number "STEP INTO CALL AFTER FUNP CALL"]
+gdb_test "advance $lineno" ".*STEP INTO CALL AFTER FUNP CALL.*" \
+    "get past callee call"
 
 gdb_test "b \*callee" "" "set breakpoint at callee's entry"
 
@@ -53,5 +74,5 @@ gdb_test "reverse-next" \
     "reverse-next over call trips user breakpoint at function entry"
 
 gdb_test "up" \
-    ".*NEXT OVER THIS CALL.*" \
+    ".*FUNCTION PTR CALL TO CALLEE.*" \
     "stopped at the right callee call"
-- 
2.37.2