Re: [PATCH v5] gdb: Add new 'print nibbles' feature

[Bruno Larsen <blarsen@redhat.com>]

On 10/7/21 11:44, Enze Li via Gdb-patches wrote:
> Make an introduction of a new print setting that can be set by 'set
> print nibbles [on|off]'.  The default value is OFF, and it would be
> changed by users manually.
> 
> Of course, 'show print nibbles' is also included in the patch.
> 
> The new feature could display binary values in groups, and each group
> has four bits.
> 
> The motivation behind this work is to enable users to more quickly
> distinguish the position of any bit on the binary value.
> 
> Here's a GDB session before this patch is applied.
>    (gdb) print var_a
>    $1 = 1230
>    (gdb) print/t var_a
>    $2 = 10011001110
> 
> With this patch applied, we have a new print setting to use.
>    (gdb) print var_a
>    $1 = 1230
>    (gdb) print/t var_a
>    $2 = 10011001110
>    (gdb) set print nibbles on
>    (gdb) print/t a
>    $3 = 100 1100 1110
> 
> Tested on x86_64-linux(little-endian) and mips-linux(big-endian).
> 
> gdb/ChangeLog:
> 2021-09-03  Enze Li  <lienze2010@hotmail.com>
> 
> 	* NEWS: Metion new command.
> 	* printcmd.c (print_scalar_formatted): Add new parameter and pass
> 	it to print_binary_chars.
> 	* valprint.c (struct value_print_options) <nibblesprint>:
> 	New member.
> 	(show_binary_groups): New function.
> 	(print_binary_chars): Add new parameter `value_print_option *`
> 	and use it.
> 	* valprint.h (struct value_print_options):
> 	(print_binary_chars): Add new parameter to declaration.
> 
> gdb/doc/ChangeLog:
> 2021-09-03  Enze Li  <lienze2010@hotmail.com>
> 
> 	* gdb.texinfo (Print Settings): Document 'print nibbles'.
> 
> gdb/testsuite/ChangeLog:
> 2021-09-03  Enze Li  <lienze2010@hotmail.com>
> 
> 	* gdb.base/printcmds.exp: Update to use new
> 	'print nibbles' command.
> 	* gdb.base/options.exp: Add -nibbles in the print completion list.
> ---
>   gdb/NEWS                             |  5 ++++
>   gdb/doc/gdb.texinfo                  | 35 ++++++++++++++++++++++++----
>   gdb/printcmd.c                       |  2 +-
>   gdb/testsuite/gdb.base/options.exp   |  1 +
>   gdb/testsuite/gdb.base/printcmds.exp | 14 +++++++++++
>   gdb/valprint.c                       | 28 +++++++++++++++++++++-
>   gdb/valprint.h                       |  6 ++++-
>   7 files changed, 84 insertions(+), 7 deletions(-)
> 
> diff --git a/gdb/NEWS b/gdb/NEWS
> index 7ca1f842cb1..ef1127da27b 100644
> --- a/gdb/NEWS
> +++ b/gdb/NEWS
> @@ -170,6 +170,11 @@ set debug event-loop
>   show debug event-loop
>     Control the display of debug output about GDB's event loop.
>   
> +set print nibbles [on|off]
> +show print nibbles
> +  This controls whether the 'print/t' command will display binary values
> +  in groups of four bits, known as "nibbles".  The default is 'off'.
> +
>   set print memory-tag-violations
>   show print memory-tag-violations
>     Control whether to display additional information about memory tag violations
> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
> index a6f207a41a7..d59fbe13457 100644
> --- a/gdb/doc/gdb.texinfo
> +++ b/gdb/doc/gdb.texinfo
> @@ -2141,10 +2141,10 @@ on @code{-} after the command name.  For example:
>   
>   @smallexample
>   (@value{GDBP}) print -@key{TAB}@key{TAB}
> --address         -max-depth       -raw-values      -union
> --array           -null-stop       -repeats         -vtbl
> --array-indexes   -object          -static-members
> --elements        -pretty          -symbol
> +-address         -max-depth       -pretty          -symbol
> +-array           -nibbles         -raw-values      -union
> +-array-indexes   -null-stop       -repeats         -vtbl
> +-elements        -object          -static-members
>   @end smallexample
>   
>   Completion will in some cases guide you with a suggestion of what kind
> @@ -10003,6 +10003,10 @@ Set limit on string chars or array elements to print.  The value
>   Set the threshold after which nested structures are replaced with
>   ellipsis.  Related setting: @ref{set print max-depth}.
>   
> +@item -nibbles [@code{on}|@code{off}]
> +Set whether to print binary values in groups of four bits, known
> +as ``nibbles''. @xref{set print nibbles}.
> +
>   @item -null-stop [@code{on}|@code{off}]
>   Set printing of char arrays to stop at first null char.  Related
>   setting: @ref{set print null-stop}.
> @@ -11361,6 +11365,29 @@ Stop printing element indexes when displaying arrays.
>   Show whether the index of each element is printed when displaying
>   arrays.
>   
> +@anchor{set print nibbles}
> +@item set print nibbles
> +@itemx set print nibbles on
> +@cindex print binary values in groups of four bits
> +Print binary values in groups of four bits, known as @dfn{nibbles},
> +when using the print command of @value{GDBN} with the option @samp{/t}.
> +For example, this is what it looks like with @code{set print nibbles on}:
> +
> +@smallexample
> +@group
> +(@value{GDBP}) print val_flags
> +$1 = 1230
> +(@value{GDBP}) print/t val_flags
> +$2 = 100 1100 1110
> +@end group
> +@end smallexample
> +
> +@item set print nibbles off
> +Don't printing binary values in groups.  This is the default.
> +
> +@item show print nibbles
> +Show whether to print binary values in groups of four bits.
> +
>   @anchor{set print elements}
>   @item set print elements @var{number-of-elements}
>   @itemx set print elements unlimited
> diff --git a/gdb/printcmd.c b/gdb/printcmd.c
> index 2fe3f4b0cc5..62713f1a91f 100644
> --- a/gdb/printcmd.c
> +++ b/gdb/printcmd.c
> @@ -490,7 +490,7 @@ print_scalar_formatted (const gdb_byte *valaddr, struct type *type,
>         break;
>   
>       case 't':
> -      print_binary_chars (stream, valaddr, len, byte_order, size > 0);
> +      print_binary_chars (stream, valaddr, len, byte_order, size > 0, options);
>         break;
>       case 'x':
>         print_hex_chars (stream, valaddr, len, byte_order, size > 0);
> diff --git a/gdb/testsuite/gdb.base/options.exp b/gdb/testsuite/gdb.base/options.exp
> index 94372aa9fc7..1a680a3baf4 100644
> --- a/gdb/testsuite/gdb.base/options.exp
> +++ b/gdb/testsuite/gdb.base/options.exp
> @@ -168,6 +168,7 @@ proc_with_prefix test-print {{prefix ""}} {
>   	"-elements"
>   	"-max-depth"
>   	"-memory-tag-violations"
> +	"-nibbles"
>   	"-null-stop"
>   	"-object"
>   	"-pretty"
> diff --git a/gdb/testsuite/gdb.base/printcmds.exp b/gdb/testsuite/gdb.base/printcmds.exp
> index b2f90aaff10..75abe79a70d 100644
> --- a/gdb/testsuite/gdb.base/printcmds.exp
> +++ b/gdb/testsuite/gdb.base/printcmds.exp
> @@ -690,6 +690,19 @@ proc test_print_char_arrays {} {
>       gdb_test_no_output "set print address off" "address off char arrays"
>   }
>   
> +proc test_print_nibbles {} {
> +    gdb_test_no_output "set print nibbles on"
> +    gdb_test "p/t 0"		" = 0"
> +    gdb_test "p/t 0x0"		" = 0"
> +    gdb_test "p/t 0x30"		" = 11 0000"
> +    gdb_test "p/t 0xff"		" = 1111 1111"
> +    gdb_test "p/t 0x0f"		" = 1111"
> +    gdb_test "p/t 0x01"		" = 1"
> +    gdb_test "p/t 0xf0f"	" = 1111 0000 1111"
> +    gdb_test "p/t 0x70f"	" = 111 0000 1111"
> +    gdb_test_no_output "set print nibbles off"
> +}
> +
>   proc test_print_string_constants {} {
>       global gdb_prompt
>   
> @@ -1067,6 +1080,7 @@ test_print_int_arrays
>   test_print_typedef_arrays
>   test_artificial_arrays
>   test_print_char_arrays
> +test_print_nibbles
>   # We used to do the runto main here.
>   test_print_string_constants
>   test_print_array_constants
> diff --git a/gdb/valprint.c b/gdb/valprint.c
> index c6ea0d82e40..1e79cc73beb 100644
> --- a/gdb/valprint.c
> +++ b/gdb/valprint.c
> @@ -108,6 +108,7 @@ struct value_print_options user_print_options =
>     0,				/* vtblprint */
>     1,				/* unionprint */
>     1,				/* addressprint */
> +  false,			/* nibblesprint */
>     0,				/* objectprint */
>     PRINT_MAX_DEFAULT,		/* print_max */
>     10,				/* repeat_count_threshold */
> @@ -260,6 +261,17 @@ show_unionprint (struct ui_file *file, int from_tty,
>   		    value);
>   }
>   
> +/* Controls the format of printing binary values.  */
> +
> +static void
> +show_nibbles (struct ui_file *file, int from_tty,
> +		       struct cmd_list_element *c, const char *value)
> +{
> +  fprintf_filtered (file,
> +		    _("Printing binary values in groups is %s.\n"),
> +		    value);
> +}
> +
>   /* If nonzero, causes machine addresses to be printed in certain contexts.  */
>   
>   static void
> @@ -1367,7 +1379,8 @@ print_floating (const gdb_byte *valaddr, struct type *type,
>   
>   void
>   print_binary_chars (struct ui_file *stream, const gdb_byte *valaddr,
> -		    unsigned len, enum bfd_endian byte_order, bool zero_pad)
> +		    unsigned len, enum bfd_endian byte_order, bool zero_pad,
> +		    const struct value_print_options *options)
>   {
>     const gdb_byte *p;
>     unsigned int i;
> @@ -1390,6 +1403,8 @@ print_binary_chars (struct ui_file *stream, const gdb_byte *valaddr,
>   
>   	  for (i = 0; i < (HOST_CHAR_BIT * sizeof (*p)); i++)
>   	    {
> +	      if (options->nibblesprint && seen_a_one && i % 4 == 0)
> +		fputc_filtered (' ', stream);
>   	      if (*p & (mask >> i))
>   		b = '1';
>   	      else
> @@ -1410,6 +1425,8 @@ print_binary_chars (struct ui_file *stream, const gdb_byte *valaddr,
>   	{
>   	  for (i = 0; i < (HOST_CHAR_BIT * sizeof (*p)); i++)
>   	    {
> +	      if (options->nibblesprint && seen_a_one && i % 4 == 0)
> +		fputc_filtered (' ', stream);
>   	      if (*p & (mask >> i))
>   		b = '1';
>   	      else
> @@ -3016,6 +3033,15 @@ static const gdb::option::option_def value_print_option_defs[] = {
>       NULL, /* help_doc */
>     },
>   
> +  boolean_option_def {
> +    "nibbles",
> +    [] (value_print_options *opt) { return &opt->nibblesprint; },
> +    show_nibbles, /* show_cmd_cb */
> +    N_("Set whether to print binary values in groups of four bits."),
> +    N_("Show whether to print binary values in groups of four bits."),
> +    NULL, /* help_doc */
> +  },
> +
>     uinteger_option_def {
>       "elements",
>       [] (value_print_options *opt) { return &opt->print_max; },
> diff --git a/gdb/valprint.h b/gdb/valprint.h
> index e1dae2cc8fc..bb19c41ab68 100644
> --- a/gdb/valprint.h
> +++ b/gdb/valprint.h
> @@ -44,6 +44,9 @@ struct value_print_options
>     /* Controls printing of addresses.  */
>     bool addressprint;
>   
> +  /* Controls printing of nibbles.  */
> +  bool nibblesprint;
> +
>     /* Controls looking up an object's derived type using what we find
>        in its vtables.  */
>     bool objectprint;
> @@ -149,7 +152,8 @@ extern void value_print_scalar_formatted
>      int size, struct ui_file *stream);
>   
>   extern void print_binary_chars (struct ui_file *, const gdb_byte *,
> -				unsigned int, enum bfd_endian, bool);
> +				unsigned int, enum bfd_endian, bool,
> +				const struct value_print_options *options);
>   
>   extern void print_octal_chars (struct ui_file *, const gdb_byte *,
>   			       unsigned int, enum bfd_endian);
> 

This code LGTM, and doesn't introduce any regressions as far as I could see.

That said, I'm a new contributor, so I'm not sure this means all that much.

-- 
Cheers!
Bruno Larsen