linux-kernel - Re: [PATCH v1 0/3] 2 memory fixes and a build fix

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Message-ID: <ZvyMw2xwnyEnMaSa@google.com>
Date: Tue, 1 Oct 2024 16:58:59 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Kan Liang <kan.liang@...ux.intel.com>,
	Kajol Jain <kjain@...ux.ibm.com>,
	Athira Rajeev <atrajeev@...ux.vnet.ibm.com>,
	"Steinar H. Gunderson" <sesse@...gle.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	Alexander Lobakin <aleksander.lobakin@...el.com>,
	Hemant Kumar <hemant@...ux.vnet.ibm.com>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	Yang Jihong <yangjihong@...edance.com>, leo.yan@....com
Subject: Re: [PATCH v1 0/3] 2 memory fixes and a build fix

On Mon, Sep 30, 2024 at 10:11:34PM -0700, Ian Rogers wrote:
> On Tue, Sep 24, 2024 at 11:25 AM Namhyung Kim <namhyung@...nel.org> wrote:
> >
> > On Mon, Sep 23, 2024 at 05:37:17PM -0700, Ian Rogers wrote:
> > > I was looking into some lsan regressions and a latent issue with
> > > libdw, creating these fixes.
> > >
> > > A thought, we should probably simplify the libdw logic but rather than
> > > do it here I'll do it as a separate series on top of these. The issues
> > > I see are:
> > >
> > > 1) dwfl_thread_getframes is used to test for the presence of
> > >    libdw-dwarf-unwind. The blame date on this function is
> > >    2013-05-30. As the function is 10 years old I think having libdw
> > >    implies having dwfl_thread_getframes and so we can just merge the
> > >    two pieces of logic instead of having different feature tests and
> > >    ifdefs.
> > >
> > > 2) similarly, dwarf_getlocations has a blame date of 2013-08-23 so
> > >    let's just make libdw tests test for this and make having libdw
> > >    imply dwarf_getlocations support.
> > >
> > > 3) similarly, dwarf_getcfi has a blame date of 2009-06-24 so let's
> > >    just make libdw tests test for this and make having libdw imply
> > >    dwarf_getcfi support.
> > >
> > > 4) in Makefie.config feature-dwarf is a synonym for libdw support. I
> > >    think using the name libdw is more intention revealing as dwarf can
> > >    mean multiple things. Let's change HAVE_DWARF_SUPPORT to
> > >    HAVE_LIBDW_SUPPORT and all similar dwarf vs libdw names.
> > >
> > > 5) We have "#if _ELFUTILS_PREREQ(0, 142)" testing for elfutils version
> > >    0.142. Elfutils 0.142 was released around 2009-06-13 (via git blame
> > >    on the NEWS file). Let's remove the #if and ensure elfutils feature
> > >    tests for at least 0.142. If someone were using an incredibly old
> > >    version then they'd lose some elfutils support, but given the 15
> > >    year old age of the library I find it unlikely anyone is doing
> > >    this. They can also just move to a newer version.
> >
> > Looking at the map file in libdw, the latest addition was 0.158 for
> > dwfl_thread_getframes().  Probably we can add the version check to the
> > feature test to make sure if it has all the required APIs.
> >
> > https://sourceware.org/git/?p=elfutils.git;a=blob;f=libdw/libdw.map;h=552588a94c0c1a1f2fd5b973553c784026e6de14;hb=HEAD#l274
> >
> > >
> > > From the mailing list I notice also overlap with the last patch and
> > > this series:
> > > https://lore.kernel.org/lkml/20240919013513.118527-1-yangjihong@bytedance.com/
> > > Simplifying the libdw support will address some of those issues too.
> >
> > Yeah I noticed that too and feel like it should go to perf-tools tree.
> > Probably it doesn't clash with this so I think it's ok to have this in
> > perf-tools-next.
> 
> I think the comments wrt libdw are covered in the series cleaning up libdw:
> https://lore.kernel.org/lkml/20240924160418.1391100-1-irogers@google.com/
> so these fixes should be good to land?

Sure, I'll just adjust the errno.h part as it's picked up by Arnaldo
to the perf-tools already.  I'll merge the branch later.

Thanks,
Namhyung