Re: [PATCH v3] Fix reverse stepping multiple contiguous PC ranges over the line table.

Luis Machado via Gdb-patches
2023-05-05T15:00:58Z

On 5/4/23 16:59, Carl Love wrote:
>
> Bruno, GDB maintainers:
f>
> Version 3, added the gcc version check as discussed further from
> version 2 of the patch. Also updated the tests to check for supporting
> reverse execution rather than requiring recording. I also noticed
> there were a couple more instances of a requirement check, i.e. if []
> which I changed to "require" per the current style for checking on the
> test requirements.
>
>
> The following patch fixes issues on PowerPC with the reverse-step and
> reverse-next instructions when there are multiple assignment statements
> on the same line and when there are multiple function calls on the same
> line. The commit log below discusses these issues in further depth.
> The discussion included what the correct operation should be for these
> commands based on the GDB documentation. The proposed patch at that
> time changed how the commands worked on other platforms such as X86 in
> a way they no longer matched the documentation.
>
> The issue is the line table contains multiple entries for the same
> source line. The patch adds a function to search the line table to
> find the address of the first instruction of a line. When setup up the
> reverse stepping range, the function is called to make sure the start
> of the range corresponds to the address of the first instruction for
> the line. This approach was used. When Luis initially developed the
> patch, he considered merging the contiguous ranges in the line table
> when reading the line tables. He decided it was better to work with the
> data directly in the line table rather than creating and using a
> modified version of the line table.
>
> The following patch fixes the execution of the reveres-step and
> reverse-next commands for both senarios of multiple statements on the
> same line for PowerPC and aarch64-linux. Unlike the previous patch, it
> does not change the operation of the commands on other platforms, i.e.
> X86. The patch adds new test cases for both scenarios to verify they
> work correctly.
>
> The patch has been tested on PowerPC, Intel X86 and aarch64-linux with
> no new regression failures.
>
> Please let me know if the patch is acceptable for mainline. Thanks.
>
> Carl
>
> ---------------------------------------------------------------
> Fix reverse stepping multiple contiguous PC ranges over the line table.
>
> There are a couple of scenarios where the GDB reverse-step and reverse-next
> commands do not work correctly.
>
> Scenario 1 issue description by Luis Machado:
>
> When running GDB's testsuite on aarch64-linux/Ubuntu 20.04 (also spotted on
> the ppc backend), I noticed some failures in gdb.reverse/solib-precsave.exp
> and gdb.reverse/solib-reverse.exp.
>
> The failure happens around the following code:
>
> 38 b[1] = shr2(17); /* middle part two */
> 40 b[0] = 6; b[1] = 9; /* generic statement, end part two */
> 42 shr1 ("message 1\n"); /* shr1 one */
>
> Normal execution:
>
> - step from line 38 will land on line 40.
> - step from line 40 will land on line 42.
>
> Reverse execution:
> - step from line 42 will land on line 40.
> - step from line 40 will land on line 40.
> - step from line 40 will land on line 38.
>
> The problem here is that line 40 contains two contiguous but distinct
> PC ranges in the line table, like so:
>
> Line 40 - [0x7ec ~ 0x7f4]
> Line 40 - [0x7f4 ~ 0x7fc]
>
> The two distinct ranges are generated because GCC started outputting source
> column information, which GDB doesn't take into account at the moment.
>
> When stepping forward from line 40, we skip both of these ranges and land on
> line 42. When stepping backward from line 42, we stop at the start PC of the
> second (or first, going backwards) range of line 40.
>
> Since we've reached ecs->event_thread->control.step_range_start, we stop
> stepping backwards.
>
> ---------------------------------------------------------
>
> Scenario 2 issue described by Pedro Alves:
>
> The following explanation of the issue was taken from the gdb mailing list
> discussion of the withdrawn patch to change the behavior of the reverse-step
> and reverse-next commands. Specifically, message from Pedro Alves
> <pedro@palves.net> where he demonstrates the issue where you have multiple
> function calls on the same source code line:
>
> https://sourceware.org/pipermail/gdb-patches/2023-January/196110.html
>
> The source line looks like:
>
> func1 (); func2 ();
>
> so stepping backwards over that line should always stop at the first
> instruction of the line, not in the middle. Let's simplify this.
>
> Here's the full source code of my example:
>
> (gdb) list 1
> 1 void func1 ()
> 2 {
> 3 }
> 4
> 5 void func2 ()
> 6 {
> 7 }
> 8
> 9 int main ()
> 10 {
> 11 func1 (); func2 ();
> 12 }
>
> Compiled with:
>
> $ gcc reverse.c -o reverse -g3 -O0
> $ gcc -v
> ...
> gcc version 11.3.0 (Ubuntu 11.3.0-1ubuntu1~22.04)
>
> Now let's debug it with target record, using current gdb git master (f3d8ae90b236),
> without your patch:
>
> $ gdb ~/reverse
> GNU gdb (GDB) 14.0.50.20230124-git
> ...
> Reading symbols from /home/pedro/reverse...
> (gdb) start
> Temporary breakpoint 1 at 0x1147: file reverse.c, line 11.
> Starting program: /home/pedro/reverse
> [Thread debugging using libthread_db enabled]
> Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
>
> Temporary breakpoint 1, main () at reverse.c:11
> 11 func1 (); func2 ();
> (gdb) record
>
> (gdb) disassemble /s
> Dump of assembler code for function main:
> reverse.c:
> 10 {
> 0x000055555555513f <+0>: endbr64
> 0x0000555555555143 <+4>: push %rbp
> 0x0000555555555144 <+5>: mov %rsp,%rbp
>
> 11 func1 (); func2 ();
> => 0x0000555555555147 <+8>: mov $0x0,%eax
> 0x000055555555514c <+13>: call 0x555555555129 <func1>
> 0x0000555555555151 <+18>: mov $0x0,%eax
> 0x0000555555555156 <+23>: call 0x555555555134 <func2>
> 0x000055555555515b <+28>: mov $0x0,%eax
>
> 12 }
> 0x0000555555555160 <+33>: pop %rbp
> 0x0000555555555161 <+34>: ret
> End of assembler dump.
>
> (gdb) n
> 12 }
>
> So far so good, a "next" stepped over the whole of line 11 and stopped at line 12.
>
> Let's confirm where we are now:
>
> (gdb) disassemble /s
> Dump of assembler code for function main:
> reverse.c:
> 10 {
> 0x000055555555513f <+0>: endbr64
> 0x0000555555555143 <+4>: push %rbp
> 0x0000555555555144 <+5>: mov %rsp,%rbp
>
> 11 func1 (); func2 ();
> 0x0000555555555147 <+8>: mov $0x0,%eax
> 0x000055555555514c <+13>: call 0x555555555129 <func1>
> 0x0000555555555151 <+18>: mov $0x0,%eax
> 0x0000555555555156 <+23>: call 0x555555555134 <func2>
> 0x000055555555515b <+28>: mov $0x0,%eax
>
> 12 }
> => 0x0000555555555160 <+33>: pop %rbp
> 0x0000555555555161 <+34>: ret
> End of assembler dump.
>
> Good, we're at the first instruction of line 12.
>
> Now let's undo the "next", with "reverse-next":
>
> (gdb) reverse-next
> 11 func1 (); func2 ();
>
> Seemingly stopped at line 11. Let's see exactly where:
>
> (gdb) disassemble /s
> Dump of assembler code for function main:
> reverse.c:
> 10 {
> 0x000055555555513f <+0>: endbr64
> 0x0000555555555143 <+4>: push %rbp
> 0x0000555555555144 <+5>: mov %rsp,%rbp
>
> 11 func1 (); func2 ();
> 0x0000555555555147 <+8>: mov $0x0,%eax
> 0x000055555555514c <+13>: call 0x555555555129 <func1>
> => 0x0000555555555151 <+18>: mov $0x0,%eax
> 0x0000555555555156 <+23>: call 0x555555555134 <func2>
> 0x000055555555515b <+28>: mov $0x0,%eax
>
> 12 }
> 0x0000555555555160 <+33>: pop %rbp
> 0x0000555555555161 <+34>: ret
> End of assembler dump.
> (gdb)
>
> And lo, we stopped in the middle of line 11! That is a bug, we should have
> stepped back all the way to the beginning of the line. The "reverse-next"
> should have fully undone the prior "next" command.
>
> The above issues were fixed by introducing a new function that looks for
> adjacent PC ranges for the same line, until we notice a line change. Then
> we take that as the start PC of the range. The new start PC for the range
> is used for the control.step_range_start when setting up a step range.
>
> The test case gdb.reverse/map-to-same-line.exp is added to test the fix
> for the issues in scenario 1.
>
> The test case gdb.reverse/func-map-to-same-line.exp was added to test the
> fix for scenario 2 when the binary was compiled with and without line
> table information.
>
> bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28426
>
> Co-authored-by: Luis Machado <luis.machado@arm.com>
> Co-authored-by: Carl Love <cel@us.ibm.com>
> ---
> gdb/infrun.c | 57 +++++++
> gdb/symtab.c | 49 ++++++
> gdb/symtab.h | 16 ++
> .../gdb.reverse/func-map-to-same-line.c | 36 ++++
> .../gdb.reverse/func-map-to-same-line.exp | 146 ++++++++++++++++
> gdb/testsuite/gdb.reverse/map-to-same-line.c | 58 +++++++
> .../gdb.reverse/map-to-same-line.exp | 156 ++++++++++++++++++
> 7 files changed, 518 insertions(+)
> create mode 100644 gdb/testsuite/gdb.reverse/func-map-to-same-line.c
> create mode 100644 gdb/testsuite/gdb.reverse/func-map-to-same-line.exp
> create mode 100644 gdb/testsuite/gdb.reverse/map-to-same-line.c
> create mode 100644 gdb/testsuite/gdb.reverse/map-to-same-line.exp
>
> diff --git a/gdb/infrun.c b/gdb/infrun.c
> index efe2c00c489..8555e3c979f 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);
> +
> /* 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)
> +{
> + /* 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 smallest address in the

s/smallest/the smallest

> + 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;
> +}
> +
> /* 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);
> +}
> +
> +/* 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;
> +}
> +
> /* 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.
> +*/
> +
> +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..412ab180943
> --- /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 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..4eae042a6bf
> --- /dev/null
> +++ b/gdb/testsuite/gdb.reverse/func-map-to-same-line.exp
> @@ -0,0 +1,146 @@
> +# 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.
> +require get_compiler_info "gcc-7-*"
> +
> +proc run_tests {msg} {
> + global srcfile
> + global executable
> +
> + runto_main
> + set target_remote [gdb_is_target_remote]
> +
> + gdb_test_no_output "record" "turn on process record"
> +
> + # 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 \
> + "$msg: test1: stopped at command reverse-next test start location" \
> + ".*$srcfile:$bp_start_reverse_test\r\n.*"
> +
> + # The reverse-next should step all the way back to the beginning of the
> + # line, i.e. at the beginning of the func1 call.
> + gdb_test "reverse-next" ".*func1 \\(\\); func2 \\(\\);.*" \
> + "$msg: 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;.*" \
> + "$msg: test1: reverse-stepi to previous line b = 2"
> +
> +
> + # Setup for test 2
> + clean_restart $executable
> + runto_main
> +
> + 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 \
> + "$msg: test2: stopped at command reverse-step test start location" \
> + ".*$srcfile:$bp_start_reverse_test\r\n.*"
> +
> + # The first reverse step should take us call of func2 ().
> + gdb_test "reverse-step" ".*END FUNC2.*" \
> + "$msg: test2: reverse-step into func2 "
> +
> + # The second reverse step should take us into func1 ().
> + gdb_test "reverse-step" ".*END FUNC1.*" \
> + "$msg: test2: reverse-step into func1 "
> +
> + # The third reverse step should take us call of func1 ().
> + gdb_test "reverse-step" ".*func1 \\(\\); func2 \\(\\);.*" \
> + "$msg: 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;.*" \
> + "$msg: test2: reverse-stepi to line b = 2 "
> +}
> +
> +set srcfile func-map-to-same-line.c
> +set executable func-map-to-same-line
> +
> +# test with gcc column info enabled
> +set options [list debug additional_flags=]
> +
> +if {[build_executable "failed to prepare" $executable $srcfile $options] == -1}\
> + {
> + return -1
> +}
> +
> +clean_restart $executable
> +
> +run_tests {"with-column-info"}
> +
> +
> +#test with gcc column info disabled
> +set options [list debug additional_flags=-gno-column-info]
> +
> +if {[build_executable "failed to prepare" $executable $srcfile $options] == -1}\
> + {
> + return -1
> +}
> +
> +set $executable executable_without_column_info
> +clean_restart $executable
> +
> +run_tests {"no-column-info"}
> 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.
> +
> + 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 ()
> +{ /* 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..02f3f4d8c9c
> --- /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.
> +require dwarf2_support
> +load_lib dwarf.exp
> +
> +# The DWARF assembler requires the gcc compiler.
> +require is_c_compiler_gcc
> +
> +# This test suitable only for process that can do reverse execution
> +requires 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"
> +}

Other than the nit, this LGTM. Thanks for picking this one up and improving it to fix other issues.

Reviewed-by: Luis Machado <luis.machado@arm.com>