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

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Message-ID: <ZvMEGn5RIWMZNvFc@google.com>
Date: Tue, 24 Sep 2024 11:25:30 -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 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.

Thanks,
Namhyung

> 
> Ian Rogers (3):
>   perf disasm: Fix capstone memory leak
>   perf probe: Fix libdw memory leak
>   perf build: Fix !HAVE_DWARF_GETLOCATIONS_SUPPORT
> 
>  tools/perf/Makefile.config     |  6 ++++++
>  tools/perf/util/disasm.c       | 11 +++++++----
>  tools/perf/util/dwarf-aux.h    |  1 +
>  tools/perf/util/probe-finder.c |  5 +++++
>  4 files changed, 19 insertions(+), 4 deletions(-)
> 
> -- 
> 2.46.0.792.g87dc391469-goog
>