How to compare $arg0 with string literal?

How to compare $arg0 with string literal?

[Aleksey Midenkov]

F.ex.

define logging
    if $argc == 1
        if $arg0 == off
            set logging off
            set logging file gdb.log
        else if $arg0 == stop
            set logging off
        else
            set logging $arg0
        end
    else
        set logging $arg0 $arg1
    end
    show logging
end

When type 'logging off' I get error about no such symbol 'off'...

Re: How to compare $arg0 with string literal?

[Doug Evans]

On Thu, Mar 26, 2015 at 9:27 AM, Aleksey Midenkov <midenok@gmail.com> wrote:
> F.ex.
>
> define logging
>     if $argc == 1
>         if $arg0 == off
>             set logging off
>             set logging file gdb.log
>         else if $arg0 == stop
>             set logging off
>         else
>             set logging $arg0
>         end
>     else
>         set logging $arg0 $arg1
>     end
>     show logging
> end
>
> When type 'logging off' I get error about no such symbol 'off'...

Such things are not supported in gdb's own scripting language.
However, with a bit of Python-provided magic ($_streq):

define logging
    if $argc == 1
        if $_streq("$arg0", "off")
            set logging off
            set logging file gdb.log
        else
            if $_streq("$arg0", "stop")
                set logging off
            else
                set logging $arg0
            end
        end
    else
        set logging $arg0 $arg1
    end
    show logging
end

Note that gdb's if/else syntax is a pain.

Re: How to compare $arg0 with string literal?

[Aleksey Midenkov]

On Thu, Mar 26, 2015 at 9:28 PM, Doug Evans <dje@google.com> wrote:
> Such things are not supported in gdb's own scripting language.
> However, with a bit of Python-provided magic ($_streq):
>
> define logging
>     if $argc == 1
>         if $_streq("$arg0", "off")
>             set logging off
>             set logging file gdb.log
>         else
>             if $_streq("$arg0", "stop")
>                 set logging off
>             else
>                 set logging $arg0
>             end
>         end
>     else
>         set logging $arg0 $arg1
>     end
>     show logging
> end
>
> Note that gdb's if/else syntax is a pain.

Sure thing, gdb's syntax could be a bit richer... Also, if I get this
error message does that mean that my gdb is not Python-powered?

(gdb)  p $_streq("off", "off")
Invalid data type for function to be called.

Re: How to compare $arg0 with string literal?

[Doug Evans]

On Thu, Mar 26, 2015 at 11:35 PM, Aleksey Midenkov <midenok@gmail.com> wrote:
> On Thu, Mar 26, 2015 at 9:28 PM, Doug Evans <dje@google.com> wrote:
>> Such things are not supported in gdb's own scripting language.
>> However, with a bit of Python-provided magic ($_streq):
>>
>> define logging
>>     if $argc == 1
>>         if $_streq("$arg0", "off")
>>             set logging off
>>             set logging file gdb.log
>>         else
>>             if $_streq("$arg0", "stop")
>>                 set logging off
>>             else
>>                 set logging $arg0
>>             end
>>         end
>>     else
>>         set logging $arg0 $arg1
>>     end
>>     show logging
>> end
>>
>> Note that gdb's if/else syntax is a pain.
>
> Sure thing, gdb's syntax could be a bit richer... Also, if I get this
> error message does that mean that my gdb is not Python-powered?
>
> (gdb)  p $_streq("off", "off")
> Invalid data type for function to be called.

I'd use "py print 42" or some such as a more direct test of whether
python is present.

btw, which version of gdb are you using?

Re: How to compare $arg0 with string literal?

[Aleksey Midenkov]

On Fri, Mar 27, 2015 at 7:25 PM, Doug Evans <dje@google.com> wrote:
> On Thu, Mar 26, 2015 at 11:35 PM, Aleksey Midenkov <midenok@gmail.com> wrote:
>> On Thu, Mar 26, 2015 at 9:28 PM, Doug Evans <dje@google.com> wrote:
>>> Such things are not supported in gdb's own scripting language.
>>> However, with a bit of Python-provided magic ($_streq):
>>>
>>> define logging
>>>     if $argc == 1
>>>         if $_streq("$arg0", "off")
>>>             set logging off
>>>             set logging file gdb.log
>>>         else
>>>             if $_streq("$arg0", "stop")
>>>                 set logging off
>>>             else
>>>                 set logging $arg0
>>>             end
>>>         end
>>>     else
>>>         set logging $arg0 $arg1
>>>     end
>>>     show logging
>>> end
>>>
>>> Note that gdb's if/else syntax is a pain.
>>
>> Sure thing, gdb's syntax could be a bit richer... Also, if I get this
>> error message does that mean that my gdb is not Python-powered?
>>
>> (gdb)  p $_streq("off", "off")
>> Invalid data type for function to be called.
>
> I'd use "py print 42" or some such as a more direct test of whether
> python is present.
>
> btw, which version of gdb are you using?

That host where this error occurs is always outdated. 7.2-60.el6_4.1
On my local machine is latest version and $_streq() works.
On 7.2 'py print' :

(gdb) py print 42
42
(gdb) py prind 42
  File "<string>", line 1
    prind 42
          ^
SyntaxError: unexpected EOF while parsing
Error while executing Python code.