Re: [PATCH,v4] Fix reverse stepping multiple contiguous PC ranges over the line table

Bruno Larsen via Gdb-patches
2022-05-06T15:05:45Z

Hi Luis and Carl!

Sorry about not answering about this earlier, I had a few rushed weeks, but I have some nits about the .exp file

On 5/6/22 05:55, Luis Machado wrote:
> v4:
> - Updated testcase to make it a bit longer so it can exercise reverse-stepping
> multiple times.
> - Cleaned up debugging prints.
>

<snip>

> 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..efaa60a957f
> --- /dev/null
> +++ b/gdb/testsuite/gdb.reverse/map-to-same-line.exp
> @@ -0,0 +1,136 @@
> +# Copyright 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/>.
> +
> +# 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.
> +

Could you add a comment here after the copyright blurb explaining why this testcase exists? Something similar to the find_line_range_start comment should be enough, jsut so the next unrelated person who looks at this code in 2 years has some context as to what is going on.

> +load_lib dwarf.exp
> +
> +# This test can only be run on targets which support DWARF-2 and use gas.
> +if {![dwarf2_support]} {
> + unsupported "dwarf2 support required for this test"
> + return 0
> +}
> +
> +if [get_compiler_info] {
> + return -1
> +}
> +
> +# The DWARF assembler requires the gcc compiler.
> +if {!$gcc_compiled} {
> + unsupported "gcc is required for this test"
> + return 0
> +}

There should probably be a test here for supports_reverse. Or supports_process_record. I'm not sure what the difference is between these 2 checks.

> +
> +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_end_sequence
> + }
> + }
> +}
> +
> +if { [prepare_for_testing "failed to prepare" ${testfile} \
> + [list $srcfile $asm_file] {nodebug} ] } {
> + return -1
> +}
> +
> +if ![runto_main] {
> + return -1
> +}
> +
> +if [supports_process_record] {
> + # Activate process record/replay
> + gdb_test_no_output "record" "turn on process record"
> +}
since we would have tested above if the target supports recording/reversing, we should be good to just use record here, without the if clause. I suggest doing it this way because there is no point in this whole test if the target doesn't support reverse execution.

> +
> +gdb_test "tbreak main_return" "Temporary breakpoint .*" "breakpoint at return"
> +gdb_test "continue" "Temporary breakpoint .*" "run to end of main"
> +
> +# 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"
> +}

Cheers!
Bruno Larsen