linux-kernel - [PATCH v2] tools/build: Add clang cross-compilation flags to feature detection

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Date:   Thu,  2 Nov 2023 11:32:52 +0100
From:   Björn Töpel <bjorn@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...hat.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        linux-kernel@...r.kernel.org
Cc:     Björn Töpel <bjorn@...osinc.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, bpf@...r.kernel.org,
        Anders Roxell <anders.roxell@...aro.org>, llvm@...ts.linux.dev,
        Jiri Olsa <olsajiri@...il.com>
Subject: [PATCH v2] tools/build: Add clang cross-compilation flags to feature detection

From: Björn Töpel <bjorn@...osinc.com>

When a tool cross-build has LLVM=1 set, the clang cross-compilation
flags are not passed to the feature detection build system. This
results in the host's features are detected instead of the targets.

E.g, triggering a cross-build of bpftool:

  cd tools/bpf/bpftool
  make ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu- LLVM=1

would report the host's, and not the target's features.

Correct the issue by passing the CLANG_CROSS_FLAGS variable to the
feature detection makefile.

Fixes: cebdb7374577 ("tools: Help cross-building with clang")
Signed-off-by: Björn Töpel <bjorn@...osinc.com>
---
 tools/build/Makefile.feature |  2 +-
 tools/build/feature/Makefile | 12 ++++++------
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/tools/build/Makefile.feature b/tools/build/Makefile.feature
index 934e2777a2db..25b009a6c05f 100644
--- a/tools/build/Makefile.feature
+++ b/tools/build/Makefile.feature
@@ -8,7 +8,7 @@ endif
 
 feature_check = $(eval $(feature_check_code))
 define feature_check_code
-  feature-$(1) := $(shell $(MAKE) OUTPUT=$(OUTPUT_FEATURES) CC="$(CC)" CXX="$(CXX)" CFLAGS="$(EXTRA_CFLAGS) $(FEATURE_CHECK_CFLAGS-$(1))" CXXFLAGS="$(EXTRA_CXXFLAGS) $(FEATURE_CHECK_CXXFLAGS-$(1))" LDFLAGS="$(LDFLAGS) $(FEATURE_CHECK_LDFLAGS-$(1))" -C $(feature_dir) $(OUTPUT_FEATURES)test-$1.bin >/dev/null 2>/dev/null && echo 1 || echo 0)
+  feature-$(1) := $(shell $(MAKE) OUTPUT=$(OUTPUT_FEATURES) CC="$(CC)" CXX="$(CXX)" CFLAGS="$(EXTRA_CFLAGS) $(FEATURE_CHECK_CFLAGS-$(1))" CXXFLAGS="$(EXTRA_CXXFLAGS) $(FEATURE_CHECK_CXXFLAGS-$(1))" LDFLAGS="$(LDFLAGS) $(FEATURE_CHECK_LDFLAGS-$(1))" CLANG_CROSS_FLAGS="$(CLANG_CROSS_FLAGS)" -C $(feature_dir) $(OUTPUT_FEATURES)test-$1.bin >/dev/null 2>/dev/null && echo 1 || echo 0)
 endef
 
 feature_set = $(eval $(feature_set_code))
diff --git a/tools/build/feature/Makefile b/tools/build/feature/Makefile
index dad79ede4e0a..c4458345e564 100644
--- a/tools/build/feature/Makefile
+++ b/tools/build/feature/Makefile
@@ -84,12 +84,12 @@ PKG_CONFIG ?= $(CROSS_COMPILE)pkg-config
 
 all: $(FILES)
 
-__BUILD = $(CC) $(CFLAGS) -MD -Wall -Werror -o $@ $(patsubst %.bin,%.c,$(@F)) $(LDFLAGS)
+__BUILD = $(CC) $(CFLAGS) $(CLANG_CROSS_FLAGS) -MD -Wall -Werror -o $@ $(patsubst %.bin,%.c,$(@F)) $(LDFLAGS)
   BUILD = $(__BUILD) > $(@:.bin=.make.output) 2>&1
   BUILD_BFD = $(BUILD) -DPACKAGE='"perf"' -lbfd -ldl
   BUILD_ALL = $(BUILD) -fstack-protector-all -O2 -D_FORTIFY_SOURCE=2 -ldw -lelf -lnuma -lelf -lslang $(FLAGS_PERL_EMBED) $(FLAGS_PYTHON_EMBED) -DPACKAGE='"perf"' -lbfd -ldl -lz -llzma -lzstd -lcap
 
-__BUILDXX = $(CXX) $(CXXFLAGS) -MD -Wall -Werror -o $@ $(patsubst %.bin,%.cpp,$(@F)) $(LDFLAGS)
+__BUILDXX = $(CXX) $(CXXFLAGS) $(CLANG_CROSS_FLAGS) -MD -Wall -Werror -o $@ $(patsubst %.bin,%.cpp,$(@F)) $(LDFLAGS)
   BUILDXX = $(__BUILDXX) > $(@:.bin=.make.output) 2>&1
 
 ###############################
@@ -259,10 +259,10 @@ $(OUTPUT)test-reallocarray.bin:
 	$(BUILD)
 
 $(OUTPUT)test-libbfd-liberty.bin:
-	$(CC) $(CFLAGS) -Wall -Werror -o $@ test-libbfd.c -DPACKAGE='"perf"' $(LDFLAGS) -lbfd -ldl -liberty
+	$(CC) $(CFLAGS) $(CLANG_CROSS_FLAGS) -Wall -Werror -o $@ test-libbfd.c -DPACKAGE='"perf"' $(LDFLAGS) -lbfd -ldl -liberty
 
 $(OUTPUT)test-libbfd-liberty-z.bin:
-	$(CC) $(CFLAGS) -Wall -Werror -o $@ test-libbfd.c -DPACKAGE='"perf"' $(LDFLAGS) -lbfd -ldl -liberty -lz
+	$(CC) $(CFLAGS) $(CLANG_CROSS_FLAGS) -Wall -Werror -o $@ test-libbfd.c -DPACKAGE='"perf"' $(LDFLAGS) -lbfd -ldl -liberty -lz
 
 $(OUTPUT)test-cplus-demangle.bin:
 	$(BUILD) -liberty
@@ -283,10 +283,10 @@ $(OUTPUT)test-libbabeltrace.bin:
 	$(BUILD) # -lbabeltrace provided by $(FEATURE_CHECK_LDFLAGS-libbabeltrace)
 
 $(OUTPUT)test-compile-32.bin:
-	$(CC) -m32 -o $@ test-compile.c
+	$(CC) $(CLANG_CROSS_FLAGS) -m32 -o $@ test-compile.c
 
 $(OUTPUT)test-compile-x32.bin:
-	$(CC) -mx32 -o $@ test-compile.c
+	$(CC) $(CLANG_CROSS_FLAGS) -mx32 -o $@ test-compile.c
 
 $(OUTPUT)test-zlib.bin:
 	$(BUILD) -lz

base-commit: 21e80f3841c01aeaf32d7aee7bbc87b3db1aa0c6
-- 
2.40.1