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

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Message-ID: <CAP-5=fUP07h=RFQ7n0pwzeK4-DgD2st3tfYxT0_e-y9GOst4fA@mail.gmail.com>
Date: Mon, 30 Sep 2024 22:11:34 -0700
From: Ian Rogers <irogers@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
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 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?

Thanks,
Ian