Re: [PATCH 2/2] ptype: add option to use hexadecimal notation

[John Baldwin <jhb@FreeBSD.org>]

On 12/31/20 4:53 AM, Lancelot SIX via Gdb-patches wrote:
> This commit adds a flag to the ptype command in order to print the
> offsets and sizes of struct members using the hexadecimal notation. The
> 'x' flag ensures use of the hexadecimal notation while the 'X' flag
> ensures use of the decimal notation. The default is to use decimal
> notation.
> 
> Before this patch, gdb only uses decimal notation, as pointed out in bug
> cli/22640.
> 
> Here is an example of this new behavior with hex output turned on:
> 
> 	(gdb) ptype /ox struct type_print_options
> 	/* offset    |  size */  type = struct type_print_options {
> 	/* 0x00: 0   |  0x04 */    unsigned int raw : 1;
> 	/* 0x00: 1   |  0x04 */    unsigned int print_methods : 1;
> 	/* 0x00: 2   |  0x04 */    unsigned int print_typedefs : 1;
> 	/* 0x00: 3   |  0x04 */    unsigned int print_offsets : 1;
> 	/* 0x00: 4   |  0x04 */    unsigned int print_in_hex : 1;
> 	/* XXX  3-bit hole   */
> 	/* XXX  3-byte hole  */
> 	/* 0x04      |  0x04 */    int print_nested_type_limit;
> 	/* 0x08      |  0x08 */    typedef_hash_table *local_typedefs;
> 	/* 0x10      |  0x08 */    typedef_hash_table *global_typedefs;
> 	/* 0x18      |  0x08 */    ext_lang_type_printers *global_printers;
> 
> 	                           /* total size (bytes):   32 */
> 	                         }
> 
> This patch also adds the 'set print type hex' and 'show print type hex'
> commands in order to set and inspect the default behavior regarding the
> use of decimal or hexadecimal notation when printing struct sizes and
> offsets.
> 
> Tested using 'runtest -tool gdb ptype-offsets.exp'

Thanks for working on this.  In general I think this looks fine in
terms of new print flags, etc.  My only concern might be that a
single byte worth of space might be a bit short.  I frequently
use ptype with some larger data structures whose sizes in hex
run to 3 digits and would distort the formatting as a result.

What would you think of using 6 character fields for hex values
such as 0x%04x?  It would mean the entire display would shift left
by 4 characters and the header would have to be adjusted.  Alternatively
if you are really concerned about horizontal space you could perhaps
only expand the offset portion to 4 hex digits?

The other possible consideration is to not print leading zeroes
but instead use '%6s' with hex_string() for the hex fields.

-- 
John Baldwin