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

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Message-Id: <20241028193619.247727-1-irogers@google.com>
Date: Mon, 28 Oct 2024 12:36:19 -0700
From: Ian Rogers <irogers@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, 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: [PATCH v2] perf build: Make libunwind opt-in rather than opt-out

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.

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