From: Lancelot SIX <lsix@lancelotsix.com>
To: Bruno Larsen <blarsen@redhat.com>
Cc: gdb-patches@sourceware.org
Subject: Re: [PATCH v2] gdb: add 'maintenance print record-instruction' command
Date: Wed, 14 Dec 2022 00:46:22 +0000 [thread overview]
Message-ID: <20221214004529.3hgz2yuhv6rx2r4c@ubuntu.lan> (raw)
In-Reply-To: <20221212104417.136536-1-blarsen@redhat.com>
Hi Bruno,
I have a couple more comments and suggestions below.
On Mon, Dec 12, 2022 at 11:44:17AM +0100, Bruno Larsen via Gdb-patches wrote:
> While chasing some reverse debugging bugs, I found myself wondering what
> was recorded by GDB to undo and redo a certain instruction. This commit
> implements a simple way of printing that information.
> ---
> gdb/NEWS | 6 ++++
> gdb/doc/gdb.texinfo | 8 +++++
> gdb/record-full.c | 81 +++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 95 insertions(+)
>
> diff --git a/gdb/NEWS b/gdb/NEWS
> index c4ccfcc9e32..d6ce6bf86a0 100644
> --- a/gdb/NEWS
> +++ b/gdb/NEWS
> @@ -103,6 +103,12 @@
>
> * New commands
>
> +maintenance print record-instruction [ N ]
> + Print the recorded information for a given instruction. If N is not given
> + prints how GDB would undo the last instruction executed. If N is negative,
> + prints how GDB would undo the N-th previous instruction, and if N is
> + positive, it prints how GDB will redo the N-th following instruction.
> +
> maintenance set ignore-prologue-end-flag on|off
> maintenance show ignore-prologue-end-flag
> This setting, which is off by default, controls whether GDB ignores the
> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
> index 5b566669975..807af351e79 100644
> --- a/gdb/doc/gdb.texinfo
> +++ b/gdb/doc/gdb.texinfo
> @@ -40531,6 +40531,14 @@ that symbol is described. The type chain produced by this command is
> a recursive definition of the data type as stored in @value{GDBN}'s
> data structures, including its flags and contained types.
>
> +@kindex maint print record-instruction
> +@item maint print record-instruction
> +@itemx maint print record-instruction @var{N}
> +@cindex print how GDB recorded a given instruction. If N is not positive
> +number, it prints the values stored by the inferior before the N-th previous
> +instruction was exectued. If N is positive, print the values after the N-th
> +following instruction is executed. If N is not given, 0 is assumed.
> +
> @kindex maint selftest
> @cindex self tests
> @item maint selftest @r{[}-verbose@r{]} @r{[}@var{filter}@r{]}
> diff --git a/gdb/record-full.c b/gdb/record-full.c
> index 48b92281fe6..25e1fd22c6f 100644
> --- a/gdb/record-full.c
> +++ b/gdb/record-full.c
> @@ -2764,6 +2764,79 @@ set_record_full_insn_max_num (const char *args, int from_tty,
> }
> }
>
> +/* Implement the 'maintenance print record-instruction' command. */
> +
> +static void
> +maintenance_print_record_instruction (const char *args, int from_tty)
> +{
> + struct record_full_entry* to_print = record_full_list;
> +
> + if (args != nullptr)
> + {
> + int offset = value_as_long (parse_and_eval (args));
> + if (offset > 0)
> + {
> + /* Move forward OFFSET instructions. We know we found the
> + end of an instruction when to_print->type is 0. */
I think the literal 0 in the comment is a left-over from V1, right?
> + while (to_print->next != nullptr && offset > 0)
> + {
> + to_print = to_print->next;
> + if (to_print->type == record_full_end)
> + offset--;
> + }
> + if (offset != 0)
> + error (_("Not enough recorded history"));
> + }
> + else
> + {
> + while (to_print->prev != nullptr && offset < 0)
> + {
> + to_print = to_print->prev;
> + if (to_print->type == record_full_end)
> + offset++;
> + }
> + if (offset != 0)
> + error (_("Not enough recorded history"));
> + }
> + }
> + gdb_assert (to_print != nullptr);
> +
> + /* Go back to the start of the instruction. */
> + while (to_print->prev != nullptr && to_print->prev->type != record_full_end)
> + to_print = to_print->prev;
> +
> + while (to_print->type != record_full_end)
> + {
> + switch (to_print->type)
> + {
> + case record_full_reg:
> + {
> + gdb_byte* b = record_full_get_loc (to_print);
^^
The space comes before the * here.
> + gdb_printf ("Register %%%s changed:",
The '%' prefix for register names is specific to the att assembler
syntax. Do we want this here? I think in most places GDB uses the
plain register name without such prefix.
> + gdbarch_register_name (target_gdbarch (),
> + to_print->u.reg.num));
> + for (int i = 0; i < to_print->u.reg.len; i++)
> + gdb_printf (" %02x",b[i]);
^
Space after the ",".
> + gdb_printf ("\n");
Did you consider printing the register value instead of the bytes
composing the value? I think something like this could do:
auto mark = value_mark ();
type *regtype = gdbarch_register_type (target_gdbarch (),
to_print->u.reg.num);
value *val
= value_from_contents (regtype, record_full_get_loc (to_print));
gdb_printf ("Register %s changed: %s\n",
gdbarch_register_name (target_gdbarch (),
to_print->u.reg.num),
hex_string (value_as_long (val)));
value_free_to_mark (mark);
This would however not work for vector registers (anything which does
not fit in a long long). You might want to use something like
`value_print` to handle all cases, unless its output is too fancy:
struct value_print_options opts;
get_user_print_options (&opts);
auto mark = value_mark ();
type *regtype = gdbarch_register_type (target_gdbarch (),
to_print->u.reg.num);
value *val
= value_from_contents (regtype, record_full_get_loc (to_print));
gdb_printf ("Register %s changed: %s\n",
gdbarch_register_name (target_gdbarch (),
to_print->u.reg.num));
value_print (val, gdb_stdout, &opts);
gdb_printf ("\n");
value_free_to_mark (mark);
Not sure if there is a cleaner way to achieve this, but it should do the
trick.
> + break;
> + }
> + case record_full_mem:
> + {
> + gdb_byte* b = record_full_get_loc (to_print);
Same here, the space shoud be before the "*".
> + gdb_printf ("%d bytes of memory at address %s changed from:",
> + to_print->u.mem.len,
> + print_core_address (target_gdbarch (),
> + to_print->u.mem.addr));
> + for (int i = 0; i < to_print->u.mem.len; i++)
> + gdb_printf (" %02x",b[i]);
Space after the ",".
Best,
Lancelot.
> + gdb_printf ("\n");
> + break;
> + }
> + }
> + to_print = to_print->next;
> + }
> +}
> +
> void _initialize_record_full ();
> void
> _initialize_record_full ()
> @@ -2868,4 +2941,12 @@ When ON, query if PREC cannot record memory change of next instruction."),
> c = add_alias_cmd ("memory-query", record_full_memory_query_cmds.show,
> no_class, 1,&show_record_cmdlist);
> deprecate_cmd (c, "show record full memory-query");
> +
> + add_cmd ("record-instruction", class_maintenance,
> + maintenance_print_record_instruction,
> + _("\
> +Print a recorded instruction.\nIf no argument is provided, print the last \
> +instruction recorded.\nIf a negative argument is given, prints how the nth \
> +previous instruction will be undone.\nIf a positive argument is given, prints \
> +how the nth following instruction will be redone."), &maintenanceprintlist);
> }
> --
> 2.38.1
>
next prev parent reply other threads:[~2022-12-14 0:46 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-12 10:44 Bruno Larsen
2022-12-12 13:54 ` Eli Zaretskii
2022-12-14 0:46 ` Lancelot SIX [this message]
2022-12-14 10:04 ` Lancelot SIX
2022-12-14 16:30 ` Tom Tromey
2022-12-16 10:03 ` Bruno Larsen
2022-12-16 13:25 ` Pedro Alves
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