linux-kernel - Re: [PATCH v3] Allow user probes on versioned symbols

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Message-Id: <095e1578-81c6-c62a-007f-1238445406a1@us.ibm.com>
Date:   Fri, 31 Mar 2017 14:38:11 -0500
From:   Paul Clarke <pc@...ibm.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        David Ahern <dsahern@...il.com>,
        linux-perf-users <linux-perf-users@...r.kernel.org>
Subject: Re: [PATCH v3] Allow user probes on versioned symbols

On 03/31/2017 12:31 PM, Arnaldo Carvalho de Melo wrote:
> Em Fri, Mar 31, 2017 at 11:06:16AM -0500, Paul Clarke escreveu:
>> Symbol versioning, as in glibc, results in symbols being defined as:
>> <real symbol>@[@]<version>
>> (Note that "@@" identifies a default symbol, if the symbol name
>> is repeated.)
>>
>> perf is currently unable to deal with this, and is unable to create
>> user probes at such symbols:
>
> On top of what tree/branch should I try to apply this?

I worked from torvalds/linux.

> Trying on acme/perf/core:

Pardon my ignorance, but where can I find that tree?

> [acme@...et linux]$ patch -p1 < /wb/1.patch
> patching file tools/perf/util/auxtrace.c
> Hunk #1 FAILED at 1875.
[...]

> Apart from that, you are not checking the return of strndup, that
> however unlikely, can fail, so must be checked.

It's in the middle of strcmp-type function, so all return values are valid.  Shall I emit a message and call exit()?

> On the style front you sometimes add a space after commas, sometimes
> not, please make sure you add one.

Ack.

> 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@...1
a@V1

...for a request to set a probe at "a", we'd actually set a probe at all 3?

> Additionaly, I can't reproduce your problem here, on x86_64:

I just cloned from acme/linux, and will rebase to there, if that's the best tree.

PC