[PATCH V2 3/9] New commands `enable probe' and `disable probe'.

Pedro Alves palves@redhat.com
Fri Oct 17 11:23:00 GMT 2014

On 10/17/2014 03:31 AM, Sergio Durigan Junior wrote:
> On Thursday, October 16 2014, Pedro Alves wrote:
>> This also raises the question, can't we have both a stap
>> probe and a dtrace probe with the name provider and name?  Like,
>> using the proposed output that doesn't distinguish the probe types,
>> can't the user end up with the confusing:
>> Provider Name             Where              Semaphore Enabled Object
>> demo     am-main          0x0000000000400c96           n/a     /home/jemarch/oracle/usdt/demo
>> demo     am-main          0x0000000000400c8b n/a       always  /home/jemarch/oracle/usdt/demo
>> Does GDB cope correctly with this?  Will the user have
>> trouble specifying the probe he wants with the current UI?
> Aha, a good question :-P.
> Well, you can actually test this with current GDB, without even needing
> dtrace:
>   (gdb) info probes
>   Provider Name Where              Semaphore Object                                                                    
>   test    bla  0x00000000004004f4           a.out
>   test    bla  0x00000000004004f5           a.out
>   (gdb) b -p bla
>   Breakpoint 1 at 0x4004f4 (2 locations)
> You have basically two ways of specifying where the probe breakpoint is
> going to be located: either by using -probe (or -p), or using
> -probe-[type] (or -p[type]).  The second way is not problematic, because
> you tell GDB that type you want explicitly, so there is no confusion.
> However, in the first way, you put a breakpoint in a "probe" (the type
> is not important here, only the probe name/provider).  GDB will then try
> to see if any of the probe backends have probes with this name, and will
> put a breakpoint on every probe it finds (again, no matter which type).
> The logic for this is in gdb/probe.c:parse_probes, if you are
> interested.
> This is already working (as you can see in my example above), and Jose's
> patch does not touch it, so we are pretty much covered in this area.

Excellent, thank you.

> Nonetheless, I think it is a good idea to add one more field to the
> output of 'info probes', specifying the probe type.

Pedro Alves

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