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

From: Namhyung Kim
Date: Tue Sep 24 2024 - 14:25:41 EST


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@xxxxxxxxxxxxx/
> 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
>