linux-kernel - Re: [PATCH v3 10/10] perf: perf interface for uprobes.

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Date:	Fri, 07 May 2010 13:53:37 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
CC:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Mel Gorman <mel@....ul.ie>,
	Randy Dunlap <rdunlap@...otime.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Roland McGrath <roland@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Mark Wielaard <mjw@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v3 10/10] perf: perf interface for uprobes.

Srikar Dronamraju wrote:
>>
>> Could you also rebase your patch on the latest tip tree? :)
>> (and remove die() too)
> 
> I was aware that I have to rebase the patch to the latest tip.
> However I wanted to get a working set out.
> Please expect the rebased version in the next version of the posting.
> 
>>
>>> Here is a terminal snapshot of placing, using and removing a probe on a
>>> process with pid 3329 (corresponding to zsh)
>>>
>>> [ Probing a function in the executable using function name  ]
>>> -------------------------------------------------------------
>>> [root@...D]# perf probe -p 3329 zfree@zsh
>>
>> Hmm, I'm not sure why we have to specify both of PID and exec name.
>> Is that possible to give a symbol as below? (omit exec name)
>>
>> # perf probe -p 3329 zfree
> 
> Yes, If the symbol name belongs to th execfile then we can omit the
> execfile part. However for symbols outside the execname, the
> execfile(library file) is a must(atleast for now).

Good!:)

>>> Added new event:
>>>   probe:p_3329_zfree                       (on 0x446420)
>>
>> Hmm, the event name should be simpler, as like as zfree_3329.
>> or, we might better make a new event group for each process, as like as
>> 'probe_3329:zfree'
>>
> 
> Either zfree_3329 or having a new event group for each process is
> possible.

I think adding new groups make controlling those event easier.
(e.g. deleting all probes on exited process)


>> Hmm, if user gave --list with -p, what happened?
>> We need to check a bad combination and warn it.
>>
> 
> Currently it would ignore -p option. i.e --list overrides.
> We could either warn, or error out. What do you suggest?
> 
>>>  
>>> +	if (session.pid)
>>> +		goto end_dwarf;
>>> +
>>
>> Again, it must be checked that the combination of -p option and dwarf requirement.
>> The latest code has perf_probe_event_need_dwarf(), so you can check it easier.
>>
> 
> Okay, 
> 
>> [...]
>>> +	else
>>> +		free(pp->function);
>>> +	pp->function = zalloc(sizeof(char *) * 20);
>>> +	if (!pp->function)
>>> +		die("Failed to allocate memory by zalloc.");
>>> +	e_snprintf(pp->function, 20, "0x%llx", vaddr);
>>> +}
>>
>> Well, after rebasing, you'll need to remove die()s from here and
>> make it returns errors. 
>>
> 
> Okay. 
> 
> 
>> [...]
>>> @@ -383,7 +450,11 @@ int synthesize_trace_kprobe_event(struct probe_point *pp)
>>>  	pp->probes[0] = buf = zalloc(MAX_CMDLEN);
>>>  	if (!buf)
>>>  		die("Failed to allocate memory by zalloc.");
>>> -	ret = e_snprintf(buf, MAX_CMDLEN, "%s+%d", pp->function, pp->offset);
>>> +	if (pp->offset)
>>> +		ret = e_snprintf(buf, MAX_CMDLEN, "%s+%d", pp->function,
>>> +					pp->offset);
>>> +	else
>>> +		ret = e_snprintf(buf, MAX_CMDLEN, "%s", pp->function);
>>>  	if (ret <= 0)
>>>  		goto error;
>>>  	len = ret;
>>
>> Isn't it a cleanup ?
> 
> Can you please elaborate?

symbol+offset is always allowed even if offset == 0,
so I think this change isn't needed. I guessed it is just for cleanup.

>>> +void add_trace_uprobe_events(struct probe_point *probes, int nr_probes,
>>> +			     bool force_add, pid_t pid)
>>> +{
>>> +	int fd = open_uprobe_events(O_RDWR, O_APPEND);
>>> +	add_trace_probe_events(fd, probes, nr_probes, force_add, pid);
>>> +}
>>
>> Please close fd in the function which opened it.
>>
> 
> Okay.
> 
>>
>>>  	memset(&sym, 0, sizeof(sym));
>>> -	if (!self->kernel) {
>>> +	if (self->kernel || symbol_conf.sort_by_name)
>>> +		self->adjust_symbols = 0;
>>> +	else {
>>>  		self->adjust_symbols = (ehdr.e_type == ET_EXEC ||
>>>  				elf_section_by_name(elf, &ehdr, &shdr,
>>>  						     ".gnu.prelink_undo",
>>>  						     NULL) != NULL);
>>> -	} else self->adjust_symbols = 0;
>>> +	}
>>>  
>>>  	elf_symtab__for_each_symbol(syms, nr_syms, idx, sym) {
>>>  		struct symbol *f;
>>
>> This one changes the symbol.c, so I think you'd better make a
>> separate patch for this change.
> 
> Okay, I will separate it in the next version.
> Thanks Masami for the review.


Thank you!

-- 
Masami Hiramatsu
e-mail: mhiramat@...hat.com
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