From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnaldo Carvalho de Melo Subject: Re: [PATCH v3] Allow user probes on versioned symbols Date: Tue, 4 Apr 2017 11:26:04 -0300 Message-ID: <20170404142604.GB12903@kernel.org> References: <20170331173123.GA18286@kernel.org> <095e1578-81c6-c62a-007f-1238445406a1@us.ibm.com> <20170403144658.GA3744@kernel.org> <20170404231802.711ac3e3346fa786259ddcde@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail.kernel.org ([198.145.29.136]:50560 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753921AbdDDO0K (ORCPT ); Tue, 4 Apr 2017 10:26:10 -0400 Content-Disposition: inline In-Reply-To: <20170404231802.711ac3e3346fa786259ddcde@kernel.org> Sender: linux-perf-users-owner@vger.kernel.org List-ID: To: Masami Hiramatsu Cc: Paul Clarke , LKML , David Ahern , linux-perf-users Em Tue, Apr 04, 2017 at 11:18:02PM +0900, Masami Hiramatsu escreveu: > On Mon, 3 Apr 2017 11:46:58 -0300 > Arnaldo Carvalho de Melo wrote: > > > > > But apart from those problems, I think that one should be able to ask > > > > for a versioned symbol, to probe just apps using that specific version, > > > > > I agree, but wasn't trying to tackle that at the moment. I can look into it, though. > > > > > > for instance, we should consider the whole name as two functions, which > > > > in fact, they are, no? > > > > > I'm not sure I understand what you mean here. Do you mean we should set a probe at every version of a given symbol name? For example, if there are symbols: > > > a@@V2 > > > a@V1.1 > > > a@V1 > > > > > ...for a request to set a probe at "a", we'd actually set a probe at all 3? > > > > I think that we should just probe the default for that symbol and have a > > way to probe all of them, perhaps using the wildcard, i.e.: > > > > [root@jouet linux]# nm /lib64/libpthread-2.24.so | grep ' pthread_cond_timedwait' > > 000000000000dd90 T pthread_cond_timedwait@GLIBC_2.2.5 > > 000000000000d6e0 T pthread_cond_timedwait@@GLIBC_2.3.2 > > [root@jouet linux]# > > > > # perf probe -x /lib64/libpthread-2.24.so pthread_cond_timedwait > > > > should be equivalent to: > > > > # perf probe -x /lib64/libpthread-2.24.so pthread_cond_timedwait@@GLIBC_2.3.2 > > > > Which matches how these versioned symbols are resolved by the linker, > > no? > > > > I.e. when 'pthread_cond_timedwait' is specified and the symbol table > > lookup fails, I think we should re-lookup for > > 'pthread_cond_timedwait@@*', i.e. we should have a > > symbol__find_default_by_name(), which will take the > > "pthread_cond_timedwait" and use a symbol comparison using > > strncmp(strlen(key)), matching, should then look at right after the > > common part looking for the double @@. > Hm, this 'fallback'process sounds good idea to me. This is just trying to keep the semantics used by the original user of this syntax, i.e. the linker. > BTW, how would we support other SYMBOL@VERSION, since we already > use '@' for specifying source code? > One possible way is to support it directly in perf-probe. If it > failed to find probe point from dwarf, try to find from symbol > map by using '@VERSION' suffix. Right, we would be overloading that @ symbol, since version numbers usually are very different of file source names :-) - Arnaldo