[PATCH v2] gdb: add 'maintenance print record-instruction' command

[PATCH v2] gdb: add 'maintenance print record-instruction' command

[Bruno Larsen]

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.  */
+	  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);
+	      gdb_printf ("Register %%%s changed:",
+			  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]);
+	      gdb_printf ("\n");
+	      break;
+	    }
+	  case record_full_mem:
+	    {
+	      gdb_byte* b = record_full_get_loc (to_print);
+	      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]);
+	      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

Re: [PATCH v2] gdb: add 'maintenance print record-instruction' command

[Eli Zaretskii]

> Cc: Bruno Larsen <blarsen@redhat.com>
> Date: Mon, 12 Dec 2022 11:44:17 +0100
> From: Bruno Larsen via Gdb-patches <gdb-patches@sourceware.org>
> 
> 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(+)

Thanks.

> --- 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.

This part is OK.

> --- 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
   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Some editing snafu happened here, it seems?

> +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.

In all places where you use "M" (upper-case), you should use "@var{n}"
(with @var and in lower-case).

The gdb.texinfo part is OK with those nits fixed.

Re: [PATCH v2] gdb: add 'maintenance print record-instruction' command

[Lancelot SIX]

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
> 

Re: [PATCH v2] gdb: add 'maintenance print record-instruction' command

[Lancelot SIX]

>     struct value_print_options opts;
>     get_user_print_options (&opts);
>     auto mark = value_mark ();

Hi,

I forgot about scoped_value_mark which is probably much better than
manually doing the value_mark () ; value_free_to_mark () dance.

Lancelot.

>     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);

Re: [PATCH v2] gdb: add 'maintenance print record-instruction' command

[Tom Tromey]

Lancelot> I forgot about scoped_value_mark which is probably much better than
Lancelot> manually doing the value_mark () ; value_free_to_mark () dance.

You don't normally need to bother with this at all, it's automatically
managed by the command loop.

Tom

Re: [PATCH v2] gdb: add 'maintenance print record-instruction' command

[Bruno Larsen]

On 14/12/2022 01:46, Lancelot SIX wrote:
> 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.

Hi Lancelot,

Thanks for the review, I've fixed all the style nits.

I wasn't aware of how to do this, thanks for explaining! I was a bit 
reticent of using the value_as_long option specifically because I wanted 
to handle all types of registers, but if I can make value_print work it 
will definitely be better. However, when I tried this I got the 
following output:

(gdb) maint print record-instruction
8 bytes of memory at address 0x00007fffffffde48 changed from: e0 de ff 
ff ff 7f 00 00
(gdb) Register rip changed: (void (*)()) 0x40113e <main+8>

I see a few issues here:
* The casting at the front is pretty confusing. I want the printing to 
be raw so the user can see what is going on
* I'm not necessary fond of the <main+8> at the end, mostly because I am 
worried that it might be misplaced in other instances
* it is being printed after the gdb prompt

I'm saying this mostly because it will probably take me a while to make 
a new version, but I really appreciate your feedback!

-- 
Cheers,
Bruno

>
>> +	      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
>>

Re: [PATCH v2] gdb: add 'maintenance print record-instruction' command

[Pedro Alves]

On 2022-12-12 10:44 a.m., 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.

Please include an example of this working in the commit log.

> ---
>  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.

I noticed missing double space after period in the sentences above.