perf build: Convert llvm-config shell queries to simply expanded variables

In Makefile.config, CFLAGS, CXXFLAGS, LIBLLVM, and EXTLIBS were assigned
using recursive expansion or appended with raw $(shell $(LLVM_CONFIG) ...)
calls. Because these variables were expanded during dependency evaluation
across every single object file compilation rule, Kbuild continuously
re-executed llvm-config forks nearly 200 times during incremental builds.

Convert llvm-config shell queries to simply expanded variables (:=) to
ensure Make evaluates LLVM compiler flags and library paths exactly once
when Makefile.config is parsed, eliminating ~185 redundant sub-processes
during build startup.

Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Assisted-by: Gemini:gemini-3.1-pro-preview
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Ankur Arora <ankur.a.arora@oracle.com>
Cc: Collin Funk <collin.funk1@gmail.com>
Cc: Costa Shulyupin <costa.shul@redhat.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Dapeng Mi <dapeng1.mi@linux.intel.com>
Cc: David Sterba <dsterba@suse.com>
Cc: Dmitrii Dolgov <9erthalion6@gmail.com>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Howard Chu <howardchu95@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: Leo Yan <leo.yan@arm.com>
Cc: Markus Mayer <mmayer@broadcom.com>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Terrell <terrelln@fb.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <pjw@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Quentin Monnet <qmo@kernel.org>
Cc: Ricky Ringler <ricky.ringler@proton.me>
Cc: Song Liu <song@kernel.org>
Cc: Swapnil Sapkal <swapnil.sapkal@amd.com>
Cc: Thomas Falcon <thomas.falcon@intel.com>
Cc: Tomas Glozar <tglozar@redhat.com>
Cc: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
index 26de7528d6ce7851ad84cc1d8b5c48e0b567239c..b56fa8419f7d021a3f21c85f396c27b56c224a83 100644 (file)
--- a/tools/perf/Makefile.config
+++ b/tools/perf/Makefile.config
@@ -925,11 +925,14 @@ ifndef NO_LIBLLVM
   $(call feature_check,llvm-perf)
   ifeq ($(feature-llvm-perf), 1)
     CFLAGS += -DHAVE_LIBLLVM_SUPPORT
-    CFLAGS += $(shell $(LLVM_CONFIG) --cflags)
-    CXXFLAGS += -DHAVE_LIBLLVM_SUPPORT
-    CXXFLAGS += $(shell $(LLVM_CONFIG) --cxxflags)
-    LIBLLVM = $(shell $(LLVM_CONFIG) --libs all) $(shell $(LLVM_CONFIG) --system-libs)
-    EXTLIBS += -L$(shell $(LLVM_CONFIG) --libdir) $(LIBLLVM)
+    LLVM_CFLAGS := $(shell $(LLVM_CONFIG) --cflags 2>/dev/null)
+    LLVM_CXXFLAGS := $(shell $(LLVM_CONFIG) --cxxflags 2>/dev/null)
+    LLVM_LIBLLVM := $(shell $(LLVM_CONFIG) --libs all 2>/dev/null) $(shell $(LLVM_CONFIG) --system-libs 2>/dev/null)
+    LLVM_LIBDIR := $(shell $(LLVM_CONFIG) --libdir 2>/dev/null)
+    CFLAGS += $(LLVM_CFLAGS)
+    CXXFLAGS += -DHAVE_LIBLLVM_SUPPORT $(LLVM_CXXFLAGS)
+    LIBLLVM := $(LLVM_LIBLLVM)
+    EXTLIBS += -L$(LLVM_LIBDIR) $(LIBLLVM)
     EXTLIBS += -lstdc++
     $(call detected,CONFIG_LIBLLVM)
   else