RE: [PATCH 2/2 v5] Fix reverse stepping multiple contiguous PC ranges over the line table.

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

Simon:

On Mon, 2023-06-19 at 13:58 -0400, Simon Marchi wrote:
<snip>

> 
100644
> > --- a/gdb/infrun.c
> > +++ b/gdb/infrun.c
> > @@ -114,6 +114,9 @@ static struct async_event_handler
> > *infrun_async_inferior_event_token;
> >     Starts off as -1, indicating "never enabled/disabled".  */
> >  static int infrun_is_async = -1;
> >  
> > +static CORE_ADDR update_line_range_start (CORE_ADDR pc,
> > +					  struct
> > execution_control_state *ecs);
> > +
> 
> This forward-declaration is not needed.

I tried removing the forward-declaration and the compile fails with the
message:

   ../../binutils-gdb-reverse-multiple-contiguous/gdb/infrun.c:6773:1:
   error: no previous declaration for ‘CORE_ADDR
   update_line_range_start(CORE_ADDR, execution_control_state*)’ [-
   Werror=missing-declarations]
    6773 | update_line_range_start (CORE_ADDR pc, struct
   execution_control_state *ecs)
         | ^~~~~~~~~~~~~~~~~~~~~~~
   cc1plus: all warnings being treated as errors
   make[2]: *** [Makefile:1922: infrun.o] Error 1
   make[2]: Leaving directory '/home/carll/GDB/build-reverse-multiple-
   contiguous/gdb'
   make[1]: *** [Makefile:13569: all-gdb] Error 2
   make[1]: Leaving directory '/home/carll/GDB/build-reverse-multiple-
   contiguous'
   make: *** [Makefile:1005: all] Error 2

Leaving the forward declaration in the code.

   > 
> >  /* See infrun.h.  */
> >  
> >  void
> > @@ -6769,6 +6772,25 @@ handle_signal_stop (struct
> > execution_control_state *ecs)
> >    process_event_stop_test (ecs);
> >  }
> >  
> > +CORE_ADDR
> > +update_line_range_start (CORE_ADDR pc, struct
> > execution_control_state *ecs)
> 
> Please add a comment for the function.

Done.

> 
> > +{
> > +  /* The line table may have multiple entries for the same source
> > code line.
> > +     Given the PC, check the line table and return the PC that
> > corresponds
> > +     to the line table entry for the source line that PC is
> > in.  */
> > +  CORE_ADDR start_line_pc = ecs->event_thread-
> > >control.step_range_start;
> > +  gdb::optional<CORE_ADDR> real_range_start;
> > +
> > +  /* Call find_line_range_start to get the smallest address in the
> > +     linetable for multiple Line X entries in the line table.  */
> > +  real_range_start = find_line_range_start (pc);
> > +
> > +  if (real_range_start.has_value ())
> > +    start_line_pc = *real_range_start;
> > +
> > +  return start_line_pc;
> 
> When I read this, I wonder: why was control.step_range_start not set
> to
> the "real" range start in the first place (not only in the context of
> reverse execution, every time it is set)?  It would seem more robust
> than patching it afterwards in some very specific spots.
> 
> I could see some benefits for range-stepping uses cases too (relevant
> when debugging remotely).  Using your example here:
> 
>    Line X - [0x0 - 0x8]
>    Line X - [0x8 - 0x10]
>    Line X - [0x10 - 0x18]
> 
> Imagine we are stopped at 0x14, and we type "next", and 0x14 is a
> conditional jump to 0x5.  It seems like current GDB would send a
> "range
> step" request to GDBserver, to step in the [0x10, 0x18[ range.  When
> reaching 0x5, execution would stop, and GDB would resume it again
> with
> the [0x0,0x8[ range.  When reaching 0x8, it would stop again, GDB
> would
> resume it with [0x8,0x10[, and so on.  If GDB could send a "range
> step"
> request with the [0x0,0x18[ range, it would avoid those unnecessary
> intermediary stop.
> 
> > +}
> > +
> >  /* Come here when we've got some debug event / signal we can
> > explain
> >     (IOW, not a random signal), and test whether it should cause a
> >     stop, or whether we should resume the inferior (transparently).
> > @@ -7570,6 +7592,28 @@ process_event_stop_test (struct
> > execution_control_state *ecs)
> >  
> >        if (stop_pc_sal.is_stmt)
> >  	{
> > +	  if (execution_direction == EXEC_REVERSE)
> > +	    {
> > +	      /* We are stepping backwards make sure we have reached
> > the
> > +		 beginning of the line.  */
> > +	      CORE_ADDR stop_pc = ecs->event_thread->stop_pc ();
> > +	      CORE_ADDR start_line_pc
> > +		= update_line_range_start (stop_pc, ecs);
> > +
> > +	      if (stop_pc != start_line_pc)
> > +		{
> > +		  /* Have not reached the beginning of the source code
> > line.
> > +		     Set a step range.  Execution should stop in any
> > function
> > +		     calls we execute back into before reaching the
> > beginning
> > +		     of the line.  */
> > +		  ecs->event_thread->control.step_range_start =
> > start_line_pc;
> > +		  ecs->event_thread->control.step_range_end = stop_pc;
> > +		  set_step_info (ecs->event_thread, frame,
> > stop_pc_sal);
> > +		  keep_going (ecs);
> > +		  return;
> > +		}
> > +	    }
> > +
> >  	  /* We are at the start of a statement.
> >  
> >  	     So stop.  Note that we don't stop if we step into the
> > middle of a
> > @@ -7632,6 +7676,19 @@ process_event_stop_test (struct
> > execution_control_state *ecs)
> >      set_step_info (ecs->event_thread, frame, stop_pc_sal);
> >  
> >    infrun_debug_printf ("keep going");
> > +
> > +  if (execution_direction == EXEC_REVERSE)
> > +    {
> > +      CORE_ADDR stop_pc = ecs->event_thread->stop_pc ();
> > +
> > +      /* Make sure the stop_pc is set to the beginning of the
> > line.  */
> > +      if (stop_pc != ecs->event_thread->control.step_range_start)
> > +	{
> > +	  stop_pc = update_line_range_start (stop_pc, ecs);
> > +	  ecs->event_thread->control.step_range_start = stop_pc;
> > +	}
> > +    }
> > +
> >    keep_going (ecs);
> >  }
> >  
> > diff --git a/gdb/symtab.c b/gdb/symtab.c
> > index 27611a34ec4..91d35616eb9 100644
> > --- a/gdb/symtab.c
> > +++ b/gdb/symtab.c
> > @@ -3282,6 +3282,55 @@ find_pc_line (CORE_ADDR pc, int notcurrent)
> >    return sal;
> >  }
> >  
> > +/* Compare two symtab_and_line entries.  Return true if both have
> > +   the same line number and the same symtab pointer.  That means
> > we
> > +   are dealing with two entries from the same line and from the
> > same
> > +   source file.
> > +
> > +   Return false otherwise.  */
> > +
> > +static bool
> > +sal_line_symtab_matches_p (const symtab_and_line &sal1,
> > +			   const symtab_and_line &sal2)
> > +{
> > +  return (sal1.line == sal2.line && sal1.symtab == sal2.symtab);
> 
> Unnecessary parenthesis.

Removed unnecessary parenthesis.

> 
> > +}
> > +
> > +/* See symtah.h.  */
> > +
> > +gdb::optional<CORE_ADDR>
> > +find_line_range_start (CORE_ADDR pc)
> > +{
> > +  struct symtab_and_line current_sal = find_pc_line (pc, 0);
> > +
> > +  if (current_sal.line == 0)
> > +    return {};
> > +
> > +  struct symtab_and_line prev_sal = find_pc_line (current_sal.pc -
> > 1, 0);
> > +
> > +  /* If the previous entry is for a different line, that means we
> > are already
> > +     at the entry with the start PC for this line.  */
> > +  if (!sal_line_symtab_matches_p (prev_sal, current_sal))
> > +    return current_sal.pc;
> > +
> > +  /* Otherwise, keep looking for entries for the same line but
> > with
> > +     smaller PC's.  */
> > +  bool done = false;
> > +  CORE_ADDR prev_pc;
> > +  while (!done)
> > +    {
> > +      prev_pc = prev_sal.pc;
> > +
> > +      prev_sal = find_pc_line (prev_pc - 1, 0);
> > +
> > +      /* Did we notice a line change?  If so, we are done with the
> > search.  */
> > +      if (!sal_line_symtab_matches_p (prev_sal, current_sal))
> > +	done = true;
> > +    }
> > +
> > +  return prev_pc;
> 
> Algorithmic complexity question: given that line tables are sorted by
> address, would it work to start at the current line table item, and
> go
> look at the previous ones until we find one that is no longer
> contiguous and same line?  find_pc_line is somewhat heavy, so if we
> don't need to do it repeatedly...
> 
> > +}
> > +
> >  /* See symtab.h.  */
> >  
> >  struct symtab *
> > diff --git a/gdb/symtab.h b/gdb/symtab.h
> > index 404d0ab30a8..f54305636da 100644
> > --- a/gdb/symtab.h
> > +++ b/gdb/symtab.h
> > @@ -2346,6 +2346,22 @@ extern struct symtab_and_line find_pc_line
> > (CORE_ADDR, int);
> >  extern struct symtab_and_line find_pc_sect_line (CORE_ADDR,
> >  						 struct obj_section *,
> > int);
> >  
> > +/* Given PC, and assuming it is part of a range of addresses that
> > is part of a
> > +   line, go back through the linetable and find the starting PC of
> > that
> > +   line.
> > +
> > +   For example, suppose we have 3 PC ranges for line X:
> > +
> > +   Line X - [0x0 - 0x8]
> > +   Line X - [0x8 - 0x10]
> > +   Line X - [0x10 - 0x18]
> > +
> > +   If we call the function with PC == 0x14, we want to return 0x0,
> > as that is
> > +   the starting PC of line X, and the ranges are contiguous.
> 
> I think that putting this example in the comment is great.  It makes
> it
> much more obvious what the function specifically does.
> 
> > +*/
> > +
> > +extern gdb::optional<CORE_ADDR> find_line_range_start (CORE_ADDR
> > pc);
> > +
> >  /* Wrapper around find_pc_line to just return the symtab.  */
> >  
> >  extern struct symtab *find_pc_line_symtab (CORE_ADDR);
> > diff --git a/gdb/testsuite/gdb.reverse/func-map-to-same-line.c
> > b/gdb/testsuite/gdb.reverse/func-map-to-same-line.c
> > new file mode 100644
> > index 00000000000..da944874e86
> > --- /dev/null
> > +++ b/gdb/testsuite/gdb.reverse/func-map-to-same-line.c
> > @@ -0,0 +1,36 @@
> > +/* 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 test is used to test the reverse-step and reverse-next
> > instruction
> > +   execution for a source line that contains multiple function
> > calls.  */
> > +
> > +void
> > +func1 ()
> > +{
> > +} /* END FUNC1 */
> > +
> > +void
> > +func2 ()
> > +{
> > +} /* END FUNC2 */
> > +
> > +int main ()
> 
> int
> main (void)
> 

Fixed.

> > +{
> > +  int a, b;
> > +  a = 1;
> > +  b = 2;
> > +  func1 (); func2 ();
> > +  a = a + b;     /* START REVERSE TEST */
> > +}
> > diff --git a/gdb/testsuite/gdb.reverse/func-map-to-same-line.exp
> > b/gdb/testsuite/gdb.reverse/func-map-to-same-line.exp
> > new file mode 100644
> > index 00000000000..89e226b0f84
> > --- /dev/null
> > +++ b/gdb/testsuite/gdb.reverse/func-map-to-same-line.exp
> > @@ -0,0 +1,140 @@
> > +# 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".
> > +
> > +# This test checks to make sure there is no regression failures
> > for
> > +# the reverse-next command when stepping back over two functions
> > in
> > +# the same line.
> > +
> > +require supports_reverse
> > +
> > +# This test uses the gcc no-column-info command which was added in
> > gcc 7.1.
> > +
> > +proc run_tests {} {
> > +    global srcfile
> > +    global executable
> > +
> > +    runto_main
> 
> We typically check for runto_main's success:

Fixed two instances of runto_main in this test case and two in the
other test case.

> 
>   if { ![runto_main] } {
>       return
>   }
> 
> runto_main logs a FAIL on failure.  There are a few runto_mains in
> the
> patch.
> 
> > +    set target_remote [gdb_is_target_remote]
> 
> target_remote seems unused

Removed.

> 
> > +
> > +    with_test_prefix "test1" {
> > +	gdb_test_no_output "record" "turn on process record"
> > +    }
> 
> with_test_prefix with a single test in it is really just the same as:
> 
>   gdb_test_no_output "record" "test1: turn on process record"
> 
> In fact, you have some other tests with the "test1:" or "test2:"
> prefix,
> I think they should be moved to the with_test_prefix.  And maybe use
> "next" and "step" instead of "test1" and "test2".

Yup, cleaner to have the with_test_prefix cover the whole test. 
Changed test1 to next-test and test2 to step-next.

> 
> > +
> > +    # This regression test verifies the reverse-step and reverse-
> > next commands
> > +    # work properly when executing backwards thru a source line
> > containing
> > +    # two function calls on the same source line, i.e. func1 ();
> > func2 ();
> > +    # This test is compiled so the dwarf info not contain the line
> > table
> > +    # information.
> > +
> > +    # Test 1, reverse-next command
> > +    # Set breakpoint at the line after the function calls.
> > +    set bp_start_reverse_test [gdb_get_line_number "START REVERSE
> > TEST" \
> > +				   $srcfile]
> > +    gdb_breakpoint $srcfile:$bp_start_reverse_test temporary
> > +
> > +    # Continue to break point for reverse-next test.
> > +    # Command definition:  reverse-next [count]
> > +    #   Run backward to the beginning of the previous line
> > executed in the
> > +    #   current (innermost) stack frame. If the line contains
> > function calls,
> > +    #   they will be “un-executed” without stopping. Starting from
> > the first
> > +    #   line of a function, reverse-next will take you back to the
> > caller of
> > +    #   that function, before the function was called, just as the
> > normal next
> > +    #   command would take you from the last line of a function
> > back to its
> > +    #   return to its caller 2 .
> > +    gdb_continue_to_breakpoint \
> > +	"test1: stopped at command reverse-next test start location" \
> > +	".*$srcfile:$bp_start_reverse_test\r\n.*"
> > +
> > +    # The reverse-next should step all the way back to the
> > beginning of the
> > +    # line, i.e. at the beginning of the func1 call.
> > +    gdb_test "reverse-next" ".*func1 \\(\\); func2 \\(\\);.*" \
> > +	"test1: reverse-next to line with two functions"
> > +
> > +    # We should be stopped at the first instruction of the line. A
> > reverse-step
> > +    # should step back and stop at the beginning of the previous
> > line b = 2,
> > +    # i.e. not in func1 ().
> > +    gdb_test "reverse-stepi" ".*b = 2;.*" \
> > +	"test1: reverse-stepi to previous line b = 2"
> > +
> > +
> > +    # Setup for test 2
> > +    clean_restart $executable
> > +    runto_main
> > +
> > +    with_test_prefix "test2" {
> > +	gdb_test_no_output "record" "turn on process record"
> > +    }
> > +
> > +    # Test 2, reverse-step command
> > +    # Set breakpoint at the line after the function calls.
> > +    gdb_breakpoint $srcfile:$bp_start_reverse_test temporary
> > +
> > +    #  Continue to the start of the reverse-step test.
> > +    #  Command definition:  reverse-step [count]
> > +    #    Run the program backward until control reaches the start
> > of a
> > +    #    different source line; then stop it, and return control
> > to gdb.
> > +    #    Like the step command, reverse-step will only stop at the
> > beginning
> > +    #    of a source line. It “un-executes” the previously
> > executed source
> > +    #    line. If the previous source line included calls to
> > debuggable
> > +    #    functions, reverse-step will step (backward) into the
> > called function,
> > +    #    stopping at the beginning of the last statement in the
> > called
> > +    #    function (typically a return statement).  Also, as with
> > the step
> > +    #    command, if non-debuggable functions are called, reverse-
> > step will
> > +    #    run thru them backward without stopping.
> > +
> > +    gdb_continue_to_breakpoint \
> > +	"test2: stopped at command reverse-step test start location" \
> > +	".*$srcfile:$bp_start_reverse_test\r\n.*"
> > +
> > +    # The first reverse step should take us call of func2 ().
> > +    gdb_test "reverse-step" ".*END FUNC2.*" \
> > +	"test2: reverse-step into func2 "
> > +
> > +    # The second reverse step should take us into func1 ().
> > +    gdb_test "reverse-step" ".*END FUNC1.*" \
> > +	"test2: reverse-step into func1 "
> > +
> > +    # The third reverse step should take us call of func1 ().
> > +    gdb_test "reverse-step" ".*func1 \\(\\); func2 \\(\\);.*" \
> > +	"test2: reverse-step to line func1(); func2(), at call for
> > func1 "
> > +
> > +    # We should be stopped at the first instruction of the line. A
> > reverse
> > +    # stepi should take us to b = 2 ().
> > +    gdb_test "reverse-stepi" ".*b = 2;.*" \
> > +	"test2: reverse-stepi to line b = 2 "
> > +}
> > +
> > +set srcfile  func-map-to-same-line.c
> > +set executable func-map-to-same-line
> 
> Wondering if this test should use standard_testfile (like almost
> every
> other tests) to set these.

OK, changed to use the standard_testfile.

> 
> > +
> > +# test with and without gcc column info enabled
> > +foreach_with_prefix with_column_info {yes no} {
> > +    if {$with_column_info == "yes"} {
> > +	set options [list debug column-info]
> > +    } else {
> > +	set options [list debug no-column-info]
> > +    }
> 
> I didn't think of this when proposing the foreach_with_prefix, but
> you
> could perhaps use:
> 
>   foreach_with_prefix column_info_flag {column-info no-column-info}
> 
> ... to avoid this boilerplate.  You can then use $column_info_flag
> directly when setting options.
> 
OK, that cleans things up a bit.  Changed.
+
+    if {[build_executable "failed to prepare" $executable $srcfile
\
+	     $options] == -1} {
+	return -1
+    }
+
+    clean_restart $executable

clean_restart can go in run_tests.


+    run_tests
+}
diff --git a/gdb/testsuite/gdb.reverse/map-to-same-line.c
b/gdb/testsuite/gdb.reverse/map-to-same-line.c
new file mode 100644
index 00000000000..f20d778f40e
--- /dev/null
+++ b/gdb/testsuite/gdb.reverse/map-to-same-line.c
@@ -0,0 +1,58 @@
+/* Copyright 2008-2023 Free Software Foundation, Inc.

Just wondering if the copyright years are right.

New files so yea, should just start with 2023.
> 
+
+   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 purpose of this test is to create a DWARF line table that
contains two
+   or more entries for the same line.  When stepping (forwards or
backwards),
+   GDB should step over the entire line and not just a particular
entry in the
+   line table.  */
+
+int
+main ()

void in the parenthesis

Fixed in both test files.

> 
+{     /* TAG: main prologue */
+  asm ("main_label: .globl main_label");
+  int i = 1, j = 2, k;
+  float f1 = 2.0, f2 = 4.1, f3;
+  const char *str_1 = "foo", *str_2 = "bar", *str_3;
+
+  asm ("line1: .globl line1");
+  k = i; f3 = f1; str_3 = str_1;    /* TAG: line 1 */
+
+  asm ("line2: .globl line2");
+  k = j; f3 = f2; str_3 = str_2;    /* TAG: line 2 */
+
+  asm ("line3: .globl line3");
+  k = i; f3 = f1; str_3 = str_1;    /* TAG: line 3 */
+
+  asm ("line4: .globl line4");
+  k = j; f3 = f2; str_3 = str_2;    /* TAG: line 4 */
+
+  asm ("line5: .globl line5");
+  k = i; f3 = f1; str_3 = str_1;    /* TAG: line 5 */
+
+  asm ("line6: .globl line6");
+  k = j; f3 = f2; str_3 = str_2;    /* TAG: line 6 */
+
+  asm ("line7: .globl line7");
+  k = i; f3 = f1; str_3 = str_1;    /* TAG: line 7 */
+
+  asm ("line8: .globl line8");
+  k = j; f3 = f2; str_3 = str_2;    /* TAG: line 8 */
+
+  asm ("main_return: .globl main_return");
+  k = j; f3 = f2; str_3 = str_2;    /* TAG: main return */
+
+  asm ("end_of_sequence: .globl end_of_sequence");
+  return 0; /* TAG: main return */
+}
diff --git a/gdb/testsuite/gdb.reverse/map-to-same-line.exp
b/gdb/testsuite/gdb.reverse/map-to-same-line.exp
new file mode 100644
index 00000000000..16a359d90ec
--- /dev/null
+++ b/gdb/testsuite/gdb.reverse/map-to-same-line.exp
@@ -0,0 +1,156 @@
+# 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/
=  >.
+
+# When stepping (forwards or backwards), GDB should step over the
entire line
+# and not just a particular entry in the line table. This test was
added to
+# verify the find_line_range_start function properly sets the step
range for a
+# line that consists of multiple statements, i.e. multiple entries
in the line
+# table.  This test creates a DWARF line table that contains two
entries for
+# the same line to do the needed testing.
+
+# This test can only be run on targets which support DWARF-2 and
use gas.
+load_lib dwarf.exp
+require dwarf2_support
+
+# The DWARF assembler requires the gcc compiler.
+require is_c_compiler_gcc
+
+# This test suitable only for process that can do reverse
execution
+require supports_reverse
+
+standard_testfile .c .S
+
+if { [prepare_for_testing "failed to prepare" ${testfile}
${srcfile}] } {
+    return -1
+}
+
+set asm_file [standard_output_file $srcfile2]
+Dwarf::assemble $asm_file {
+    global srcdir subdir srcfile
+    declare_labels integer_label L
+
+    # Find start address and length of program
+    lassign [function_range main [list
${srcdir}/${subdir}/$srcfile]] \
+	main_start main_len
+    set main_end "$main_start + $main_len"
+
+    cu {} {
+	compile_unit {
+	    {language @DW_LANG_C}
+	    {name map-to-same-line.c}
+	    {stmt_list $L DW_FORM_sec_offset}
+	    {low_pc 0 addr}
+	} {
+	    subprogram {
+		{external 1 flag}
+		{name main}
+		{low_pc $main_start addr}
+		{high_pc $main_len DW_FORM_data4}
+	    }
+	}
+    }
+
+    lines {version 2 default_is_stmt 1} L {
+	include_dir "${srcdir}/${subdir}"
+	file_name "$srcfile" 1
+
+	# Generate the line table program with distinct source lines
being
+	# mapped to the same line entry. Line 1, 5 and 8 contain 1
statement
+	# each.  Line 2 contains 2 statements.  Line 3 contains 3
statements.
+	program {
+	    DW_LNE_set_address $main_start
+	    line [gdb_get_line_number "TAG: main prologue"]
+	    DW_LNS_copy
+	    DW_LNE_set_address line1
+	    line [gdb_get_line_number "TAG: line 1" ]
+	    DW_LNS_copy
+	    DW_LNE_set_address line2
+	    line [gdb_get_line_number "TAG: line 2" ]
+	    DW_LNS_copy
+	    DW_LNE_set_address line3
+	    line [gdb_get_line_number "TAG: line 2" ]
+	    DW_LNS_copy
+	    DW_LNE_set_address line4
+	    line [gdb_get_line_number "TAG: line 3" ]
+	    DW_LNS_copy
+	    DW_LNE_set_address line5
+	    line [gdb_get_line_number "TAG: line 3" ]
+	    DW_LNS_copy
+	    DW_LNE_set_address line6
+	    line [gdb_get_line_number "TAG: line 3" ]
+	    DW_LNS_copy
+	    DW_LNE_set_address line7
+	    line [gdb_get_line_number "TAG: line 5" ]
+	    DW_LNS_copy
+	    DW_LNE_set_address line8
+	    line [gdb_get_line_number "TAG: line 8" ]
+	    DW_LNS_copy
+	    DW_LNE_set_address main_return
+	    line [gdb_get_line_number "TAG: main return"]
+	    DW_LNS_copy
+	    DW_LNE_set_address end_of_sequence
+	    DW_LNE_end_sequence
+	}
+    }
+}
+
+if { [prepare_for_testing "failed to prepare" ${testfile} \
+	[list $srcfile $asm_file] {nodebug} ] } {
+    return -1
+}
+
+runto_main
+
+# Print the line table
+gdb_test_multiple "maint info line-table ${testfile}" "" {
+    -re "\r\n$decimal\[ \t\]+$decimal\[ \t\]+($hex)\[
\t\]+Y\[^\r\n\]*" {
+	lappend is_stmt $expect_out(1,string)
+	exp_continue
+    }
+    -re -wrap "" {
+    }
+}
+
+# Do the reverse-step test
+gdb_test_no_output "record" "turn on process record"
+
+set bp_main_return [gdb_get_line_number "TAG: main return"
$srcfile]
+gdb_breakpoint $srcfile:$bp_main_return
+gdb_continue_to_breakpoint  "run to end of main, reverse-step
test" ".*$srcfile:$bp_main_return.*"
+gdb_test "display \$pc" ".*pc =.*" "display pc, reverse-step test"
+
+# At this point, GDB has already recorded the execution up until
the return
+# statement.  Reverse-step and test if GDB transitions between
lines in the
+# expected order.  It should reverse-step across lines 8, 5, 3, 2
and 1.
+foreach line {8 5 3 2 1} {
+    gdb_test "reverse-step" ".*TAG: line $line.*" "reverse step to
line $line"
+}
+
+## Clean restart, test reverse-next command
+clean_restart ${testfile}
+runto_main
+gdb_test_no_output "record" "turn on process record, reverst-next
test"
+
+set bp_main_return [gdb_get_line_number "TAG: main return"
$srcfile]
+gdb_breakpoint $srcfile:$bp_main_return
+gdb_continue_to_breakpoint  "run to end of main, reverse-next
test" ".*$srcfile:$bp_main_return.*"
+gdb_test "display \$pc" ".*pc =.*" "display pc, reverse-next test"
+
+# At this point, GDB has already recorded the execution up until
the return
+# statement.  Reverse-next and test if GDB transitions between
lines in the
+# expected order.  It should reverse-next across lines 8, 5, 3, 2
and 1.
+foreach line {8 5 3 2 1} {
+    gdb_test "reverse-next" ".*TAG: line $line.*" "reverse next to
line $line"
+}

It seems like the step and next tests are identical, so I guess it
could
be factored out using:

  foreach_with_prefix method {step next} {
      ...
  }

?

Yup, redid the code using the foreach_with_prefix.

> 
Simon
> yR