[PATCH ] PowerPC: fix for gdb.reverse/finish-precsave.exp and gdb.reverse/finish-reverse.exp

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

GDB maintainers:

I have reworked the PowerPC patch from the previous series to fix the
behavior of the reverse-finish command on PowerPC.  The patch does not
change the behavior of the reverse-finish command on other
architectures.  The patch simply make the command on PowerPC behave the
same as other architectures, specifically X86.

The issue with the reverse-finish command on PowerPC is the reverse-
finish command doesn't stop at the function call.  The issue is PowerPC
uses two entry points.  PowerPC calls the two entry points the local
entry point (LEP) and the global entry point (GEP).  The LEP is
normally used when calling a function.  The GEP is used when the table
of contents (TOC) needs to be setup before continuing execution at the
LEP.  GDB is not handling the two entry points correctly.  On systems
that don't use two entry points the LEP and the GEP are the same.

A new test case is added to verify the reverse-finish command works
properly.  It checks five cases for the reverse-finish command,
executing the command when stopped on the alternate entry point, the
normal entry point, between the entry points, the body of the function
when it is called via the normal entry point and finally the body of
the function when called via the alternate entry point.

The patch and new test have been run on Power 10, Intel X86 pre
generation 5 and an Intel X86 system with a generation 5 processor. 
The 5th generation X86 system is needed to run the btrace/tailcall.exp
and btrace/tailcall-only.exp tests that were an issue with the previous
patch series which was withdrawn from consideration.

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

                Carl 

----------------------------------------------------------
PowerPC: fix for gdb.reverse/finish-precsave.exp and gdb.reverse/finish-reverse.exp

PPC64 multiple entry points.  When executing in reverse the function
finish_backward sets the break point at the alternate entry point, known
as the global entry point (GEP) in PowerPC.  However if the forward
execution enters via the normal entry point, known as the local entry
point (LEP) on PowerPC, reverse execution never sees the break point at the
alternate entry point of the function.  Reverse execution continues until
the next break point is encountered thus stopping at the wrong place.

This patch adds a new address to struct execution_control_state to hold the
address of the alternate entry point (GEP).  The finish_backwards function
is updated, if the stopping point is between the normal entry point (LEP)
and the end of the function, a breakpoint is set at the normal entry point.
If the stopping point is between the entry points, a breakpoint is set to
the alternate entry point.

The patch fixes the behavior of the reverse-finish command on PowerPC to
match the behavior of the command on other platforms, specifically X86.
The patch does not change the behavior of the command on X86.

A new test is added to verify the reverse-finish command on PowerPC
correctly stops at the instruction where the function call is made.  A new
test, finish-reverse-next.exp, is added to verify the correct functionality
of the reverse-finish command.  The reverse-finish comand is expected to
stop on the instruction that jumps to the function.  Procedure
proc_step_until from test gdb.reverse/step-indirect-call-thunk.exp is moved
to lib/gdb.exp and renamed repeat_cmd_until.

The patch fixes 11 regression errors in test gdb.reverse/finish-precsave.exp
and 11 regression errors in test gdb.reverse/finish-reverse.exp.

The patch has been tested on Power 10 and X86 processor with no new
regression failures.
---
 gdb/infcmd.c                                  |  47 ++--
 gdb/infrun.c                                  |  26 ++
 .../gdb.reverse/finish-reverse-next.c         |  91 +++++++
 .../gdb.reverse/finish-reverse-next.exp       | 224 ++++++++++++++++++
 .../gdb.reverse/step-indirect-call-thunk.exp  |  33 ---
 gdb/testsuite/lib/gdb.exp                     |  33 +++
 6 files changed, 404 insertions(+), 50 deletions(-)
 create mode 100644 gdb/testsuite/gdb.reverse/finish-reverse-next.c
 create mode 100644 gdb/testsuite/gdb.reverse/finish-reverse-next.exp

diff --git a/gdb/infcmd.c b/gdb/infcmd.c
index 77206fcbfe8..a65cc700fc9 100644
--- a/gdb/infcmd.c
+++ b/gdb/infcmd.c
@@ -1728,28 +1728,41 @@ finish_backward (struct finish_command_fsm *sm)
      no way that a function up the stack can have a return address
      that's equal to its entry point.  */
 
-  if (sal.pc != pc)
-    {
-      frame_info_ptr frame = get_selected_frame (nullptr);
-      struct gdbarch *gdbarch = get_frame_arch (frame);
+  CORE_ADDR alt_entry_point = sal.pc;
+  CORE_ADDR entry_point = alt_entry_point;
+  frame_info_ptr frame = get_selected_frame (nullptr);
+  struct gdbarch *gdbarch = get_frame_arch (frame);
 
-      /* Set a step-resume at the function's entry point.  Once that's
-	 hit, we'll do one more step backwards.  */
-      symtab_and_line sr_sal;
-      sr_sal.pc = sal.pc;
-      sr_sal.pspace = get_frame_program_space (frame);
-      insert_step_resume_breakpoint_at_sal (gdbarch,
-					    sr_sal, null_frame_id);
+  if (gdbarch_skip_entrypoint_p (gdbarch))
+    /* Some architectures, like PowerPC use local and global entry points.
+       There is only one Entry Point (GEP = LEP) for other architectures.
+       The GEP is an alternate entry point.  The LEP is the normal entry point.
+       The value of entry_point was initialized to the alternate entry point
+       (GEP).  It will be adjusted to the normal entry point if the function
+       has two entry points.  */
+    entry_point = gdbarch_skip_entrypoint (gdbarch, sal.pc);
+
+  if  ((pc >= alt_entry_point) && (pc <= entry_point))
+    /* We are either at one of the entry points or between the entry points.
+       If we are not at the alt_entry point, go back to the alt_entry_point
+       If we at the normal entry point step back one instruction, when we
+       stop we will determine if we entered via the entry point or the
+       alternate entry point.  If we are at the alternate entry point,
+       single step back to the function call.  */
+    tp->control.step_range_start = tp->control.step_range_end = 1;
 
-      proceed ((CORE_ADDR) -1, GDB_SIGNAL_DEFAULT);
-    }
   else
     {
-      /* We're almost there -- we just need to back up by one more
-	 single-step.  */
-      tp->control.step_range_start = tp->control.step_range_end = 1;
-      proceed ((CORE_ADDR) -1, GDB_SIGNAL_DEFAULT);
+      /* We are in the body of the function.  Set a breakpoint to backup to
+	 the normal entry point.  */
+      symtab_and_line sr_sal;
+      sr_sal.pc = entry_point;
+      sr_sal.pspace = get_frame_program_space (frame);
+      insert_step_resume_breakpoint_at_sal (gdbarch, sr_sal,
+					    null_frame_id);
     }
+
+  proceed ((CORE_ADDR) -1, GDB_SIGNAL_DEFAULT);
 }
 
 /* finish_forward -- helper function for finish_command.  FRAME is the
diff --git a/gdb/infrun.c b/gdb/infrun.c
index 87ab73c47a4..f0bd13fc219 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -1868,6 +1868,7 @@ struct execution_control_state
 
   struct target_waitstatus ws;
   int stop_func_filled_in = 0;
+  CORE_ADDR stop_func_alt_start = 0;
   CORE_ADDR stop_func_start = 0;
   CORE_ADDR stop_func_end = 0;
   const char *stop_func_name = nullptr;
@@ -4680,6 +4681,11 @@ fill_in_stop_func (struct gdbarch *gdbarch,
 	  ecs->stop_func_start
 	    += gdbarch_deprecated_function_start_offset (gdbarch);
 
+	  /* PowerPC functions have a Local Entry Point (LEP) and a Global
+	     Entry Point (GEP).  There is only one Entry Point (GEP = LEP) for
+	     other architectures.  */
+	  ecs->stop_func_alt_start = ecs->stop_func_start;
+
 	  if (gdbarch_skip_entrypoint_p (gdbarch))
 	    ecs->stop_func_start
 	      = gdbarch_skip_entrypoint (gdbarch, ecs->stop_func_start);
@@ -7269,6 +7275,26 @@ process_event_stop_test (struct execution_control_state *ecs)
 	}
     }
 
+  if (execution_direction == EXEC_REVERSE
+      && ecs->event_thread->control.proceed_to_finish)
+    {
+      /* We are executing the reverse-finish command.  */
+      if (ecs->event_thread->stop_pc () >= ecs->stop_func_alt_start
+	  && ecs->event_thread->stop_pc () < ecs->stop_func_start
+	  && ecs->stop_func_alt_start != ecs->stop_func_start)
+	/* If the system supports multiple entry points and we are finishing a
+	   function in reverse.   If we are between the entry points singe-step
+	   back to the alternate entry point.  If we are at the alternate entry
+	   point -- just   need to back up by one more single-step, which
+	   should take us back to the function call.  */
+	{
+	  ecs->event_thread->control.step_range_start
+	    = ecs->event_thread->control.step_range_end = 1;
+	  keep_going (ecs);
+	  return;
+	}
+    }
+
   if (ecs->event_thread->control.step_range_end == 1)
     {
       /* It is stepi or nexti.  We always want to stop stepping after
diff --git a/gdb/testsuite/gdb.reverse/finish-reverse-next.c b/gdb/testsuite/gdb.reverse/finish-reverse-next.c
new file mode 100644
index 00000000000..e95ee8e33a6
--- /dev/null
+++ b/gdb/testsuite/gdb.reverse/finish-reverse-next.c
@@ -0,0 +1,91 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2012-2023 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/>.  */
+
+/* The reverse finish command should return from a function and stop on
+   the first instruction of the source line where the function call is made.
+   Specifically, the behavior should match doing a reverse next from the
+   first instruction in the function.  GDB should only require one reverse
+   step or next statement to reach the previous source code line.
+
+   This test verifies the fix for gdb bugzilla:
+
+   https://sourceware.org/bugzilla/show_bug.cgi?id=29927
+
+   PowerPC supports two entry points to a function.  The normal entry point
+   is called the local entry point (LEP).  The alternate entry point is called
+   the global entry point (GEP).  The GEP is only used if the table of
+   contents (TOC) value stored in register r2 needs to be setup prior to
+   execution starting at the LEP.  A function call via a function pointer
+   will entry via the GEP.  A normal function call will enter via the LEP.
+
+   This test has been expanded to include tests to verify the reverse-finish
+   command works properly if the function is called via the GEP.  The original
+   test only verified the reverse-finish command for a normal call that used
+   the LEP.  */
+
+int
+function2 (int a, int b)
+{
+  int ret = 0;
+  ret = ret + a + b;
+  return ret;
+}
+
+int
+function1 (int a, int b)   // FUNCTION1
+{
+  int ret = 0;
+  int (*funp) (int, int) = &function2;
+  /* The assembly code for this function when compiled for PowerPC is as
+     follows:
+
+     0000000010000758 <function1>:
+     10000758:	02 10 40 3c 	lis     r2,4098        <- GEP
+     1000075c:	00 7f 42 38 	addi    r2,r2,32512
+     10000760:	a6 02 08 7c 	mflr    r0             <- LEP
+     10000764:	10 00 01 f8 	std     r0,16(r1)
+     ....
+
+     When the function is called on PowerPC with function1 (a, b) the call
+     enters at the Local Entry Point (LEP).  When the function is called via
+     a function pointer, the Global Entry Point (GEP) for function1 is used.
+     The GEP sets up register 2 before reaching the LEP.
+  */
+  ret = funp (a + 1, b + 2);
+  return ret;
+}
+
+int
+main(int argc, char* argv[])
+{
+  int a, b;
+  int (*funp) (int, int) = &function1;
+
+  /* Call function via Local Entry Point (LEP).  */
+
+  a = 1;
+  b = 5;
+
+  function1 (a, b);   // CALL VIA LEP
+
+  /* Call function via Global Entry Point (GEP).  */
+  a = 10;
+  b = 50;
+
+  funp (a, b);        // CALL VIA GEP
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.reverse/finish-reverse-next.exp b/gdb/testsuite/gdb.reverse/finish-reverse-next.exp
new file mode 100644
index 00000000000..6e08530c970
--- /dev/null
+++ b/gdb/testsuite/gdb.reverse/finish-reverse-next.exp
@@ -0,0 +1,224 @@
+# Copyright 2008-2023 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/>.  */
+
+# This file is part of the GDB testsuite.  It tests reverse stepping.
+# Lots of code borrowed from "step-test.exp".
+
+# The reverse finish command should return from a function and stop on
+# the first instruction of the source line where the function call is made.
+# Specifically, the behavior should match doing a reverse next from the
+# first instruction in the function.  GDB should only take one reverse step
+# or next statement to reach the previous source code line.
+
+# This testcase verifies the reverse-finish command stops at the first
+# instruction in the source code line where the function was called.  There
+# are two scenarios that must be checked:
+#   1) gdb is at the entry point instruction for the function
+#   2) gdb is in the body of the function.
+
+# This test verifies the fix for gdb bugzilla:
+#   https://sourceware.org/bugzilla/show_bug.cgi?id=29927
+
+# PowerPC supports two entry points to a function.  The normal entry point
+# is called the local entry point (LEP).  The alternate entry point is called
+# the global entry point (GEP).  A function call via a function pointer
+# will entry via the GEP.  A normal function call will enter via the LEP.
+#
+# This test has been expanded to include tests to verify the reverse-finish
+# command works properly if the function is called via the GEP.  The original
+# test only verified the reverse-finish command for a normal call that used
+# the LEP.
+
+if ![supports_reverse] {
+    return
+}
+
+standard_testfile
+
+if { [prepare_for_testing "failed to prepare" $testfile $srcfile] } {
+    return -1
+}
+
+runto_main
+set target_remote [gdb_is_target_remote]
+
+if [supports_process_record] {
+    # Activate process record/replay.
+    gdb_test_no_output "record" "turn on process record for test1"
+}
+
+
+### TEST 1: reverse finish from the entry point instruction (LEP) in
+### function1 when called using the normal entry point (LEP).
+
+# Set breakpoint at call to function1 in main.
+set bp_LEP_test [gdb_get_line_number "CALL VIA LEP" $srcfile]
+gdb_breakpoint $srcfile:$bp_LEP_test temporary
+
+# Continue to break point at function1 call in main.
+gdb_continue_to_breakpoint \
+    "stopped at function1 entry point instruction to stepi into function" \
+    ".*$srcfile:$bp_LEP_test\r\n.*"
+
+# stepi until we see "{" indicating we entered function1
+repeat_cmd_until "stepi" "CALL VIA LEP" "{" "stepi into function1 call"
+
+# The reverse-finish command should stop on the function call instruction
+# which is the last instruction in the source code line.  A reverse-next
+# instruction should then stop at the first instruction in the same source
+# code line.  Another revers-next instruction stops at the previous source
+# code line.
+gdb_test "reverse-finish" ".*function1 \\(a, b\\);   // CALL VIA LEP.*" \
+    "reverse-finish function1 LEP call from LEP "
+gdb_test "reverse-next" ".*function1 \\(a, b\\);   // CALL VIA LEP" \
+    "reverse next 1 LEP entry point function call from LEP"
+gdb_test "reverse-next" ".*b = 5;.*" "reverse next 2, at b = 5, call from LEP"
+
+
+gdb_test "reverse-continue" ".*" "setup for test 2"
+
+# Turn off record to clear logs and turn on again
+gdb_test "record stop"  "Process record is stopped.*" \
+    "turn off process record for test1"
+gdb_test_no_output "record" "turn on process record for test2"
+
+
+### TEST 2: reverse finish from the body of function1.
+
+# Set breakpoint at call to function1 in main.
+gdb_breakpoint $srcfile:$bp_LEP_test temporary
+
+# Continue to break point at function1 call in main.
+gdb_continue_to_breakpoint \
+    "at function1 entry point instruction to step to body of function" \
+    ".*$srcfile:$bp_LEP_test\r\n.*"
+
+# do a step instruction to get to the body of the function
+gdb_test "step" ".*int ret = 0;.*" "step test 1"
+
+# The reverse-finish command should stop on the function call instruction
+# which is the last instruction in the source code line.  A reverse-next
+# instruction should then stop at the first instruction in the same source
+# code line.  Another revers-next instruction stops at the previous source
+# code line.
+gdb_test "reverse-finish" ".*function1 \\(a, b\\);   // CALL VIA LEP.*" \
+    "reverse-finish function1 LEP call from function body"
+gdb_test "reverse-next" ".*function1 \\(a, b\\);   // CALL VIA LEP.*" \
+    "reverse next 1 LEP from function body"
+gdb_test "reverse-next" ".*b = 5;.*" \
+    "reverse next 2 at b = 5, from function body"
+
+gdb_test "reverse-continue" ".*" "setup for test 3"
+
+# Turn off record to clear logs and turn on again
+gdb_test "record stop"  "Process record is stopped.*" \
+    "turn off process record for test2"
+gdb_test_no_output "record" "turn on process record for test3"
+
+
+### TEST 3: reverse finish from the alternate entry point instruction (GEP) in
+### function1 when called using the alternate entry point (GEP).
+
+# Set breakpoint at call to funp in main.
+set bp_GEP_test  [gdb_get_line_number "CALL VIA GEP" $srcfile]
+gdb_breakpoint $srcfile:$bp_GEP_test temporary
+
+# Continue to break point at funp call in main.
+gdb_continue_to_breakpoint \
+    "stopped at function1 entry point instruction to stepi into funp" \
+    ".*$srcfile:$bp_GEP_test\r\n.*"
+
+# stepi until we see "{" indicating we entered function.
+repeat_cmd_until "stepi" "CALL VIA GEP" "{" "stepi into funp call"
+
+# The reverse-finish command should stop on the function call instruction
+# which is the last instruction in the source code line.  A reverse-next
+# instruction should then stop at the first instruction in the same source
+# code line.  Another revers-next instruction stops at the previous source
+# code line.
+gdb_test "reverse-finish" ".*funp \\(a, b\\);.*" \
+    "function1 GEP call call from GEP"
+gdb_test "reverse-next" ".*funp \\(a, b\\);.*" \
+    "reverse next 1 GEP entry point function call from GEP"
+gdb_test "reverse-next" ".*b = 50;.*" "reverse next 2 at b = 50, call from GEP"
+
+gdb_test "reverse-continue" ".*" "setup for test 4"
+
+# Turn off record to clear logs and turn on again
+gdb_test "record stop"  "Process record is stopped.*" \
+    "turn off process record for test3"
+gdb_test_no_output "record" "turn on process record for test4"
+
+### TEST 4: reverse finish from between the GEP and LEP in
+### function1 when called using the alternate entry point (GEP).
+
+# Set breakpoint at call to funp in main.
+set bp_GEP_test  [gdb_get_line_number "CALL VIA GEP" $srcfile]
+gdb_breakpoint $srcfile:$bp_GEP_test temporary
+
+# Continue to break point at funp call in main.
+gdb_continue_to_breakpoint \
+    "stopped at function1 entry point instruction to stepi into funp again" \
+    ".*$srcfile:$bp_GEP_test\r\n.*"
+
+# stepi until we see "{" indicating we entered function.
+repeat_cmd_until "stepi" "CALL VIA GEP" "{" "stepi into funp call again"
+
+# do one more stepi so we are between the GEP and LEP.
+gdb_test "stepi" "{" "stepi to between GEP and LEP"
+
+# The reverse-finish command should stop on the function call instruction
+# which is the last instruction in the source code line.  A reverse-next
+# instruction should then stop at the first instruction in the same source
+# code line.  Another revers-next instruction stops at the previous source
+# code line.
+gdb_test "reverse-finish" ".*funp \\(a, b\\);.*" \
+    "function1 GEP call call from GEP again"
+gdb_test "reverse-next" ".*funp \\(a, b\\);.*" \
+    "reverse next 1 GEP entry point function call from GEP again"
+gdb_test "reverse-next" ".*b = 50;.*" \
+    "reverse next 2 at b = 50, call from GEP again"
+
+gdb_test "reverse-continue" ".*" "setup for test 5"
+
+# Turn off record to clear logs and turn on again
+gdb_test "record stop"  "Process record is stopped.*" \
+    "turn off process record for test4"
+gdb_test_no_output "record" "turn on process record for test5"
+
+
+### TEST 5: reverse finish from the body of function 1 when calling using the
+### alternate entrypoint (GEP).
+gdb_breakpoint $srcfile:$bp_GEP_test temporary
+
+# Continue to break point at funp call.
+gdb_continue_to_breakpoint \
+    "at function1 entry point instruction to step to body of funp call" \
+    ".*$srcfile:$bp_GEP_test\r\n.*"
+
+# Step into body of funp, called via GEP.
+gdb_test "step" ".*int ret = 0;.*" "step test 2"
+
+# The reverse-finish command should stop on the function call instruction
+# which is the last instruction in the source code line.  A reverse-next
+# instruction should then stop at the first instruction in the same source
+# code line.  Another revers-next instruction stops at the previous source
+# code line.
+gdb_test "reverse-finish" ".*funp \\(a, b\\);.*" \
+    "reverse-finish function1 GEP call, from function body  "
+gdb_test "reverse-next" ".*funp \\(a, b\\);.*" \
+    "reverse next 1 GEP call from function body"
+gdb_test "reverse-next" ".*b = 50;.*" \
+    "reverse next 2 at b = 50 from function body"
diff --git a/gdb/testsuite/gdb.reverse/step-indirect-call-thunk.exp b/gdb/testsuite/gdb.reverse/step-indirect-call-thunk.exp
index 94292d5eb9b..dc5cf097511 100644
--- a/gdb/testsuite/gdb.reverse/step-indirect-call-thunk.exp
+++ b/gdb/testsuite/gdb.reverse/step-indirect-call-thunk.exp
@@ -36,39 +36,6 @@ if { ![runto_main] } {
     return -1
 }
 
-# Do repeated stepping COMMANDs in order to reach TARGET from CURRENT
-#
-#  COMMAND is a stepping command
-#  CURRENT is a string matching the current location
-#  TARGET  is a string matching the target location
-#  TEST    is the test name
-#
-# The function issues repeated COMMANDs as long as the location matches
-# CURRENT up to a maximum of 100 steps.
-#
-# TEST passes if the resulting location matches TARGET and fails
-# otherwise.
-#
-proc step_until { command current target test } {
-    global gdb_prompt
-
-    set count 0
-    gdb_test_multiple "$command" "$test" {
-        -re "$current.*$gdb_prompt $" {
-            incr count
-            if { $count < 100 } {
-                send_gdb "$command\n"
-                exp_continue
-            } else {
-                fail "$test"
-            }
-        }
-        -re "$target.*$gdb_prompt $" {
-            pass "$test"
-        }
-    }
-}
-
 gdb_test_no_output "record"
 gdb_test "next" ".*" "record trace"
 
diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index faa0ac05a9a..c156982a674 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -9295,6 +9295,39 @@ proc gdb_step_until { regexp {test_name ""} {max_steps 10} } {
     }
 }
 
+# Do repeated stepping COMMANDs in order to reach TARGET from CURRENT
+#
+#  COMMAND is a stepping command
+#  CURRENT is a string matching the current location
+#  TARGET  is a string matching the target location
+#  TEST    is the test name
+#
+# The function issues repeated COMMANDs as long as the location matches
+# CURRENT up to a maximum of 100 steps.
+#
+# TEST passes if the resulting location matches TARGET and fails
+# otherwise.
+#
+proc repeat_cmd_until { command current target test } {
+    global gdb_prompt
+
+    set count 0
+    gdb_test_multiple "$command" "$test" {
+	-re "$current.*$gdb_prompt $" {
+	    incr count
+	    if { $count < 100 } {
+		send_gdb "$command\n"
+		exp_continue
+	    } else {
+		fail "$test"
+	    }
+	}
+	-re "$target.*$gdb_prompt $" {
+	    pass "$test"
+	}
+    }
+}
+
 # Check if the compiler emits epilogue information associated
 # with the closing brace or with the last statement line.
 #
-- 
2.37.2