linux-kernel - Re: [PATCH v2] perf build: Make libunwind opt-in rather than opt-out

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Message-ID: <ZyAG4kSqZk8Fpu1A@x1>
Date: Mon, 28 Oct 2024 18:49:22 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Namhyung Kim <namhyung@...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>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] perf build: Make libunwind opt-in rather than opt-out

On Mon, Oct 28, 2024 at 12:36:19PM -0700, Ian Rogers wrote:
> Having multiple unwinding libraries makes the perf code harder to
> understand and we have unused/untested code paths.
 
> Perf made BPF support an opt-out rather than opt-in feature. As libbpf
> has a libelf dependency, elfutils that provides libelf will also
> provide libdw. When libdw is present perf will use libdw unwinding
> rather than libunwind unwinding even if libunwind support is compiled
> in.
 
> Rather than have libunwind built into perf and never used, explicitly
> disable the support and make it opt-in.

Looks ok and testing it does what is advertised:

⬢ [acme@...lbox perf-tools-next]$ ldd ~/bin/perf | grep libunwind
⬢ [acme@...lbox perf-tools-next]$ perf check feature libunwind
             libunwind: [ OFF ]  # HAVE_LIBUNWIND_SUPPORT
⬢ [acme@...lbox perf-tools-next]$

Since I have libunwind-devel installed:

Auto-detecting system features:
<SNIP
...                               libunwind: [ on  ]
<SNIP

If I uninstall libunwind-devel, just to complete the cycle, even this
patch not touching that part:

Auto-detecting system features:
<SNIP>
...                               libunwind: [ OFF ]
<SNIP>

Tested-by: Arnaldo Carvalho de Melo <acme@...hat.com>

- Arnaldo
 
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> Closes: https://lore.kernel.org/linux-perf-users/CAP-5=fUXkp-d7gkzX4eF+nbjb2978dZsiHZ9abGHN=BN1qAcbg@mail.gmail.com/
> ---
> v2: update build tests.
> ---
>  tools/perf/Makefile.config | 4 ++++
>  tools/perf/Makefile.perf   | 2 +-
>  tools/perf/tests/make      | 6 +++---
>  3 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
> index b93ed2b7623f..707d7355ff18 100644
> --- a/tools/perf/Makefile.config
> +++ b/tools/perf/Makefile.config
> @@ -91,6 +91,10 @@ ifneq ($(SRCARCH),$(filter $(SRCARCH),x86 arm arm64 powerpc s390 csky riscv loon
>    NO_LIBDW_DWARF_UNWIND := 1
>  endif
>  
> +ifneq ($(LIBUNWIND),1)
> +  NO_LIBUNWIND := 1
> +endif
> +
>  ifeq ($(LIBUNWIND_LIBS),)
>    NO_LIBUNWIND := 1
>  endif
> diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
> index b4dee7c20ed1..d74241a15131 100644
> --- a/tools/perf/Makefile.perf
> +++ b/tools/perf/Makefile.perf
> @@ -52,7 +52,7 @@ include ../scripts/utilities.mak
>  #
>  # Define NO_LIBELF if you do not want libelf dependency (e.g. cross-builds)
>  #
> -# Define NO_LIBUNWIND if you do not want libunwind dependency for dwarf
> +# Define LIBUNWIND if you do not want libunwind dependency for dwarf
>  # backtrace post unwind.
>  #
>  # Define NO_BACKTRACE if you do not want stack backtrace debug feature
> diff --git a/tools/perf/tests/make b/tools/perf/tests/make
> index a5040772043f..a7fcbd589752 100644
> --- a/tools/perf/tests/make
> +++ b/tools/perf/tests/make
> @@ -81,7 +81,7 @@ make_no_gtk2        := NO_GTK2=1
>  make_no_ui          := NO_SLANG=1 NO_GTK2=1
>  make_no_demangle    := NO_DEMANGLE=1
>  make_no_libelf      := NO_LIBELF=1
> -make_no_libunwind   := NO_LIBUNWIND=1
> +make_libunwind      := LIBUNWIND=1
>  make_no_libdw_dwarf_unwind := NO_LIBDW_DWARF_UNWIND=1
>  make_no_backtrace   := NO_BACKTRACE=1
>  make_no_libcapstone := NO_CAPSTONE=1
> @@ -121,7 +121,7 @@ make_static         := LDFLAGS=-static NO_PERF_READ_VDSO32=1 NO_PERF_READ_VDSOX3
>  
>  # all the NO_* variable combined
>  make_minimal        := NO_LIBPERL=1 NO_LIBPYTHON=1 NO_GTK2=1
> -make_minimal        += NO_DEMANGLE=1 NO_LIBELF=1 NO_LIBUNWIND=1 NO_BACKTRACE=1
> +make_minimal        += NO_DEMANGLE=1 NO_LIBELF=1 NO_BACKTRACE=1
>  make_minimal        += NO_LIBNUMA=1 NO_LIBAUDIT=1 NO_LIBBIONIC=1
>  make_minimal        += NO_LIBDW_DWARF_UNWIND=1 NO_AUXTRACE=1 NO_LIBBPF=1
>  make_minimal        += NO_LIBCRYPTO=1 NO_SDT=1 NO_JVMTI=1 NO_LIBZSTD=1
> @@ -153,7 +153,7 @@ run += make_no_gtk2
>  run += make_no_ui
>  run += make_no_demangle
>  run += make_no_libelf
> -run += make_no_libunwind
> +run += make_libunwind
>  run += make_no_libdw_dwarf_unwind
>  run += make_no_backtrace
>  run += make_no_libcapstone
> -- 
> 2.47.0.163.g1226f6d8fa-goog