/ (slash) command : fast way to temporarily change setting(s) to run a command

/ (slash) command : fast way to temporarily change setting(s) to run a command

[Philippe Waroquiers]

GDB has a lot of settings related to how commands behaves and/or print things.
    
There is however currently no easy way to temporarily change a setting
for a command.

The proposed new / command allows to temporarily change
the settings in order to execute another command.
A simple example:
 By default, 'set print pretty on|off' is off.
 To temporarily pretty
print something, today, you have to do:
   (gdb) set print pretty on
   (gdb) print
something
   (gdb) set print pretty off
 With the / command:
   (gdb) /p print something


The objective for this / command is to be fast to type, so it uses
1 or 2 letters codes to identify which settings(s) to temporarily set.
See the proposed user manual at
https://sourceware.org/ml/gdb-patches/2019-04/msg00245.html
and the patch at
https://sourceware.org/ml/gdb-patches/2019-04/msg00244.html


Several settings can be changed at once:
   (gdb) /lAai print some_array
is the equivalent of:
   (gdb) set language ada
   (gdb) set print array on
   (gdb) set print array-indexes on
   (gdb) print some_array
   (gdb) set language auto
   (gdb) set print array off
   (gdb) set print array-indexes off

An advantage of this approach is that the same options
are usable for all commands.
For example, you can use:
   (gdb) /lAai backtrace full
so that what backtrace prints is temporarily using
the settings identified by /lAai.

The full list of currently changeable settings is given
in the 'help /' below.

Feedback/comments/... welcome

Thank
Philippe


(gdb) help /
Usage: /SETTING... COMMAND
Temporarily changes settings according to SETTING, run COMMAND,
and then restore the settings to their previous values.
Each temporarily changeable setting is identified by a unique sequence
of one or more letters.
A boolean setting is temporarily activated (set to "on") by giving
its sequence of letters.  If the boolean sequence of letters is prefixed
by !, the boolean setting is deactivated (set to "off").
An integer setting is temporarily changed by using its sequence of letters
optionally prefixed by the temporary value desired.
If no prefix value is given before the integer setting letters,
the integer setting is temporarily changed to an unlimited value.
An enum setting is temporarily changed by giving its sequence of letters
followed by a letter designating the chosen enum value.
Example:
  /100e!ai print some_array
is equivalent to:
  # save current values of the settings set print elements/array/array-index.
  set print elements 100
  set print array off
  set print array-index on
  print some_array
  # restore the saved values of the changed settings.
The temporarily changeable settings are:
/Be       set backtrace past-entry       Boolean on|off
/Bl       set backtrace limit            Unsigned integer (0 means unlimited)
/Bm       set backtrace past-main        Boolean on|off
/Co       set print object               Boolean on|off
/Cs       set print static-members       Boolean on|off
/Cv       set print vtbl                 Boolean on|off
/Pa       set print address              Boolean on|off
/Ps       set print symbol               Boolean on|off
/Rf       set print raw frame-arguments  Boolean on|off
/a        set print array                Boolean on|off
/e        set print elements             Unsigned integer (0 means unlimited)
/f[asn]   set print frame-arguments      Enum, a = all, s = scalars, n = none
/i        set print array-indexes        Boolean on|off
/l[aluAscCdfgmMOo] set language          Enum, a = auto, l = local,
                                u = unknown, A = ada, s = asm, c = c, C = c++,
                                d = d, f = fortran, g = go, m = minimal,
                                M = modula-2, O = objective-c, o = opencl
/n        set print null-stop            Boolean on|off
/p        set print pretty               Boolean on|off
/r        set print repeats              Unsigned integer (0 means unlimited)
/u        set print union                Boolean on|off
/v        set varsize-limit              Unsigned integer (0 means unlimited)
(gdb) 

Re: / (slash) command : fast way to temporarily change setting(s) to run a command

[Simon Marchi]

On 2019-04-15 3:32 a.m., Philippe Waroquiers wrote:
> GDB has a lot of settings related to how commands behaves and/or print things.
>     
> There is however currently no easy way to temporarily change a setting
> for a command.
> 
> The proposed new / command allows to temporarily change
> the settings in order to execute another command.
> A simple example:
>  By default, 'set print pretty on|off' is off.
>  To temporarily pretty
> print something, today, you have to do:
>    (gdb) set print pretty on
>    (gdb) print
> something
>    (gdb) set print pretty off
>  With the / command:
>    (gdb) /p print something
> 
> 
> The objective for this / command is to be fast to type, so it uses
> 1 or 2 letters codes to identify which settings(s) to temporarily set.
> See the proposed user manual at
> https://sourceware.org/ml/gdb-patches/2019-04/msg00245.html
> and the patch at
> https://sourceware.org/ml/gdb-patches/2019-04/msg00244.html
> 
> 
> Several settings can be changed at once:
>    (gdb) /lAai print some_array
> is the equivalent of:
>    (gdb) set language ada
>    (gdb) set print array on
>    (gdb) set print array-indexes on
>    (gdb) print some_array
>    (gdb) set language auto
>    (gdb) set print array off
>    (gdb) set print array-indexes off
> 
> An advantage of this approach is that the same options
> are usable for all commands.
> For example, you can use:
>    (gdb) /lAai backtrace full
> so that what backtrace prints is temporarily using
> the settings identified by /lAai.
> 
> The full list of currently changeable settings is given
> in the 'help /' below.
> 
> Feedback/comments/... welcome
> 
> Thank
> Philippe
> 
> 
> (gdb) help /
> Usage: /SETTING... COMMAND
> Temporarily changes settings according to SETTING, run COMMAND,
> and then restore the settings to their previous values.
> Each temporarily changeable setting is identified by a unique sequence
> of one or more letters.
> A boolean setting is temporarily activated (set to "on") by giving
> its sequence of letters.  If the boolean sequence of letters is prefixed
> by !, the boolean setting is deactivated (set to "off").
> An integer setting is temporarily changed by using its sequence of letters
> optionally prefixed by the temporary value desired.
> If no prefix value is given before the integer setting letters,
> the integer setting is temporarily changed to an unlimited value.
> An enum setting is temporarily changed by giving its sequence of letters
> followed by a letter designating the chosen enum value.
> Example:
>   /100e!ai print some_array
> is equivalent to:
>   # save current values of the settings set print elements/array/array-index.
>   set print elements 100
>   set print array off
>   set print array-index on
>   print some_array
>   # restore the saved values of the changed settings.
> The temporarily changeable settings are:
> /Be       set backtrace past-entry       Boolean on|off
> /Bl       set backtrace limit            Unsigned integer (0 means unlimited)
> /Bm       set backtrace past-main        Boolean on|off
> /Co       set print object               Boolean on|off
> /Cs       set print static-members       Boolean on|off
> /Cv       set print vtbl                 Boolean on|off
> /Pa       set print address              Boolean on|off
> /Ps       set print symbol               Boolean on|off
> /Rf       set print raw frame-arguments  Boolean on|off
> /a        set print array                Boolean on|off
> /e        set print elements             Unsigned integer (0 means unlimited)
> /f[asn]   set print frame-arguments      Enum, a = all, s = scalars, n = none
> /i        set print array-indexes        Boolean on|off
> /l[aluAscCdfgmMOo] set language          Enum, a = auto, l = local,
>                                 u = unknown, A = ada, s = asm, c = c, C = c++,
>                                 d = d, f = fortran, g = go, m = minimal,
>                                 M = modula-2, O = objective-c, o = opencl
> /n        set print null-stop            Boolean on|off
> /p        set print pretty               Boolean on|off
> /r        set print repeats              Unsigned integer (0 means unlimited)
> /u        set print union                Boolean on|off
> /v        set varsize-limit              Unsigned integer (0 means unlimited)
> (gdb) 

Hi Philippe,

I like the idea, I would probably use it most with /e (for long strings) and /p.
I just tried it a little bit, and I appreciate the fact that it's easy to apply
to your previous command.  Just type up and add the prefix to the beginning of the
line.

About that help, I would just add a few newlines here and there to space things
out and ease the reading.  Other than that, it's quite clear.

Simon

Simon

Re: / (slash) command : fast way to temporarily change setting(s) to run a command

[Philippe Waroquiers]

On Mon, 2019-04-15 at 23:06 -0400, Simon Marchi wrote:
> Hi Philippe,
> 
> I like the idea, I would probably use it most with /e (for long strings) and /p.
> I just tried it a little bit, and I appreciate the fact that it's easy to apply
> to your previous command.  Just type up and add the prefix to the beginning of the
> line.
Interesting, that was not the primary use case I was thinking to.

We could make this even easier by making COMMAND optional in:
   Usage: /SETTING... [COMMAND]
and giving no command means to repeat the previous command with the additional
given settings e.g. :
    (gdb) some command
    .... some command output
    (gdb) /e
        => executes /e some command

    (gdb) /e some command
    ... some command output
    (gdb) /p
       => executes  /ep some command

I guess we probably call dont_repeat () in / command
when no COMMAND is given.

> 
> About that help, I would just add a few newlines here and there to space things
> out and ease the reading.  Other than that, it's quite clear.
Ok, will add some new lines in the v2 of the patch.

Thanks for the feedback

Philippe

Re: / (slash) command : fast way to temporarily change setting(s) to run a command

[Simon Marchi]

On 2019-04-16 02:48, Philippe Waroquiers wrote:
> On Mon, 2019-04-15 at 23:06 -0400, Simon Marchi wrote:
>> Hi Philippe,
>> 
>> I like the idea, I would probably use it most with /e (for long 
>> strings) and /p.
>> I just tried it a little bit, and I appreciate the fact that it's easy 
>> to apply
>> to your previous command.  Just type up and add the prefix to the 
>> beginning of the
>> line.
> Interesting, that was not the primary use case I was thinking to.
> 
> We could make this even easier by making COMMAND optional in:
>    Usage: /SETTING... [COMMAND]
> and giving no command means to repeat the previous command with the 
> additional
> given settings e.g. :
>     (gdb) some command
>     .... some command output
>     (gdb) /e
>         => executes /e some command
> 
>     (gdb) /e some command
>     ... some command output
>     (gdb) /p
>        => executes  /ep some command
> 
> I guess we probably call dont_repeat () in / command
> when no COMMAND is given.

Ah yeah, that sounds good too, I would be consistent with the fact that 
just like you can do:

(gdb) p 10
$4 = 10
(gdb) p/x
$5 = 0xa

Does it mean that as a side-effect, "/" alone would repeat the previos 
command unaltered?

Simon

Re: / (slash) command : fast way to temporarily change setting(s) to run a command

[Philippe Waroquiers]

On Tue, 2019-04-16 at 08:20 -0400, Simon Marchi wrote:
> 
> Ah yeah, that sounds good too, I would be consistent with the fact that 
> just like you can do:
> 
> (gdb) p 10
> $4 = 10
> (gdb) p/x
> $5 = 0xa
> 
> Does it mean that as a side-effect, "/" alone would repeat the previos 
> command unaltered?
The previous command can be run by just typing Return,
so I think we can keep slash command checking that at least one
setting was given.

I thought that implementing a command that would re-run the
previous saved_command_line would mean to just look/use 
saved_command_line.
But when a command runs, saved_command_line already contains
the line of the currently running command.
Slightly unexpected but not a big deal:
it is very easy to add previous_saved_command_line.

Philippe

Re: / (slash) command : fast way to temporarily change setting(s) to run a command

[Kevin Buettner]

My first reaction to this proposal was that '/' is already used in
some commands to modify their behavior.  E.g. "print", "display", and
"x" all use /FMT to change the way that data is formatted.

That said, '/' seems to be used in only a handful of commands.  It
may be that its use is confined to the ones already mentioned.

I see that the "interrupt" command allows the use of -a to modify
its behavior.  Most commands have no modifiers at all.

I don't have a serious objection to Philippe's proposal, but I do
think that we ought to consider whether use of '/' in this context
might be confusing to the user.  Might some other character or command
name be less confusing?  I don't know the answer to this, but I do
think it's something which should be pondered before making this
proposal a part of GDB's CLI.

Kevin

Re: / (slash) command : fast way to temporarily change setting(s) to run a command

[Philippe Waroquiers]

On Wed, 2019-04-17 at 01:14 -0700, Kevin Buettner wrote:
> My first reaction to this proposal was that '/' is already used in
> some commands to modify their behavior.  E.g. "print", "display", and
> "x" all use /FMT to change the way that data is formatted.
> 
> That said, '/' seems to be used in only a handful of commands.  It
> may be that its use is confined to the ones already mentioned.
> 
> I see that the "interrupt" command allows the use of -a to modify
> its behavior.  Most commands have no modifiers at all.
> 
> I don't have a serious objection to Philippe's proposal, but I do
> think that we ought to consider whether use of '/' in this context
> might be confusing to the user.  Might some other character or command
> name be less confusing?  I don't know the answer to this, but I do
> think it's something which should be pondered before making this
> proposal a part of GDB's CLI.
Yes, for sure, getting the user interface correct is critical:
it is always possible to improve the implementation/code in the next
release, but changing the user interface in a next release
is a lot more difficult.

Maybe we need to identify first what kind of confusion
can happen with the '/' command ?
In fact, one of the reasons I started with '/' is that I find this
easy to remember and not confusing, as '/' is already used
to indicate 'some options or settings' in various GDB commands.
I did not want to use '-' as today, the '-' options of
commands that use this cannot be combined, while the / options
can (both in the slash command, and in commands that use /
as option such as print).

We could use another character, e.g. ':', but other characters
IMO do not ring a bell that it is related to settings or options.

If really we need to use another character, of course, the code
to change is quite trivial (mostly name changes, as currently,
many variables and args are called 'slash_...').

But / seems a reasonable (the best?)  option :)

Thanks

Philippe

Re: / (slash) command : fast way to temporarily change setting(s) to run a command

[John Baldwin]

On 4/17/19 1:14 AM, Kevin Buettner wrote:
> My first reaction to this proposal was that '/' is already used in
> some commands to modify their behavior.  E.g. "print", "display", and
> "x" all use /FMT to change the way that data is formatted.
> 
> That said, '/' seems to be used in only a handful of commands.  It
> may be that its use is confined to the ones already mentioned.
> 
> I see that the "interrupt" command allows the use of -a to modify
> its behavior.  Most commands have no modifiers at all.
> 
> I don't have a serious objection to Philippe's proposal, but I do
> think that we ought to consider whether use of '/' in this context
> might be confusing to the user.  Might some other character or command
> name be less confusing?  I don't know the answer to this, but I do
> think it's something which should be pondered before making this
> proposal a part of GDB's CLI.

I find using / to make sense actually.  A leading / applies "global"
settings to the following command, so you have a general syntax that
is something like:

[/global settings] [command] [/command-specific settings] [arguments]

Where moving from left to right consistently "narrows" the scope.
This is not unlike the syntax used in certain command line programs
that reuse getopt-like interfaces for subcommand options while also
supporting "global" options.  git is an example of this (you have
global options before the verb and then command-specific options
after the verb both of which use the same getopt syntax) as well as
svn, etc.

-- 
John Baldwin

Re: / (slash) command : fast way to temporarily change setting(s) to run a command

[Kevin Buettner]

On Fri, 19 Apr 2019 09:52:43 -0700
John Baldwin <jhb@FreeBSD.org> wrote:

> On 4/17/19 1:14 AM, Kevin Buettner wrote:
> > My first reaction to this proposal was that '/' is already used in
> > some commands to modify their behavior.  E.g. "print", "display", and
> > "x" all use /FMT to change the way that data is formatted.
> > 
> > That said, '/' seems to be used in only a handful of commands.  It
> > may be that its use is confined to the ones already mentioned.
> > 
> > I see that the "interrupt" command allows the use of -a to modify
> > its behavior.  Most commands have no modifiers at all.
> > 
> > I don't have a serious objection to Philippe's proposal, but I do
> > think that we ought to consider whether use of '/' in this context
> > might be confusing to the user.  Might some other character or command
> > name be less confusing?  I don't know the answer to this, but I do
> > think it's something which should be pondered before making this
> > proposal a part of GDB's CLI.  
> 
> I find using / to make sense actually.  A leading / applies "global"
> settings to the following command, so you have a general syntax that
> is something like:
> 
> [/global settings] [command] [/command-specific settings] [arguments]
> 
> Where moving from left to right consistently "narrows" the scope.
> This is not unlike the syntax used in certain command line programs
> that reuse getopt-like interfaces for subcommand options while also
> supporting "global" options.  git is an example of this (you have
> global options before the verb and then command-specific options
> after the verb both of which use the same getopt syntax) as well as
> svn, etc.

I like this rationale for the global / command.

I'd like to wait a bit longer before reviewing Philippe's patch, however.
I know that one of my colleagues has some thoughts on the interface
and I'd like to give him a little extra time to express them here...

Kevin

Re: / (slash) command : fast way to temporarily change setting(s) to run a command

[Pedro Alves]

On 5/3/19 4:10 AM, Kevin Buettner wrote:
> On Fri, 19 Apr 2019 09:52:43 -0700
> John Baldwin <jhb@FreeBSD.org> wrote:
> 
>> On 4/17/19 1:14 AM, Kevin Buettner wrote:
>>> My first reaction to this proposal was that '/' is already used in
>>> some commands to modify their behavior.  E.g. "print", "display", and
>>> "x" all use /FMT to change the way that data is formatted.
>>>
>>> That said, '/' seems to be used in only a handful of commands.  It
>>> may be that its use is confined to the ones already mentioned.
>>>
>>> I see that the "interrupt" command allows the use of -a to modify
>>> its behavior.  Most commands have no modifiers at all.
>>>
>>> I don't have a serious objection to Philippe's proposal, but I do
>>> think that we ought to consider whether use of '/' in this context
>>> might be confusing to the user.  Might some other character or command
>>> name be less confusing?  I don't know the answer to this, but I do
>>> think it's something which should be pondered before making this
>>> proposal a part of GDB's CLI.  
>>
>> I find using / to make sense actually.  A leading / applies "global"
>> settings to the following command, so you have a general syntax that
>> is something like:
>>
>> [/global settings] [command] [/command-specific settings] [arguments]
>>
>> Where moving from left to right consistently "narrows" the scope.
>> This is not unlike the syntax used in certain command line programs
>> that reuse getopt-like interfaces for subcommand options while also
>> supporting "global" options.  git is an example of this (you have
>> global options before the verb and then command-specific options
>> after the verb both of which use the same getopt syntax) as well as
>> svn, etc.
> 
> I like this rationale for the global / command.
> 
> I'd like to wait a bit longer before reviewing Philippe's patch, however.
> I know that one of my colleagues has some thoughts on the interface
> and I'd like to give him a little extra time to express them here...

That was me.  :-)  See here:

 https://sourceware.org/ml/gdb-patches/2019-05/msg00002.html

I'll follow up when I have a chance.  Yesterday I fixed the
regressions that Philippe pointed at (fixes already in the branch) -- I
wanted to see if it was possible to get to a clean slate for better
experimenting / better ground for discussion.

Thanks,
Pedro Alves

Re: / (slash) command : fast way to temporarily change setting(s) to run a command

[Philippe Waroquiers]

On Fri, 2019-05-03 at 09:23 +0100, Pedro Alves wrote:
> > 
> > I like this rationale for the global / command.
> > 
> > I'd like to wait a bit longer before reviewing Philippe's patch, however.
> > I know that one of my colleagues has some thoughts on the interface
> > and I'd like to give him a little extra time to express them here...
> 
> That was me.  :-)  See here:
> 
>  https://sourceware.org/ml/gdb-patches/2019-05/msg00002.html
> 
> I'll follow up when I have a chance.  Yesterday I fixed the
> regressions that Philippe pointed at (fixes already in the branch) -- I
> wanted to see if it was possible to get to a clean slate for better
> experimenting / better ground for discussion.
Thanks for this.
Note that  I have listed some points for the discussion in
https://sourceware.org/ml/gdb-patches/2019-05/msg00019.html

IMO, a (the?) major question I still have about keeping (or not) the "/"
patch is for options that have a 'wide' impact.
The "/" command avoids that this option has to be added as a specific
argument to all the commands that are impacted directly or indirectly.
An example is the new max-depth.
As far as I understand, max-depth will at least impact:
   backtrace
   print
   frame
   info args
   ...
(in fact all commands that are printing directly or indirectly
some variables).
With the "/" command, you have a way to influence all these commands.
Otherwise, as far as I understand, an option --max-depth has
to be added to all these commands.
(or the user has to do set/launch command/reset).

Philippe