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

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Message-ID: <ZUNsFkZWxws6c5Vx@krava>
Date:   Thu, 2 Nov 2023 10:29:58 +0100
From:   Jiri Olsa <olsajiri@...il.com>
To:     Björn Töpel <bjorn@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...hat.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        linux-kernel@...r.kernel.org,
        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
Subject: Re: [PATCH] tools/build: Add clang cross-compilation flags to
 feature detection

On Thu, Nov 02, 2023 at 09:14:41AM +0100, Björn Töpel wrote:
> 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 | 8 ++++----
>  2 files changed, 5 insertions(+), 5 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..0231a53024c7 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

should we add this also to test-compile-32.bin/test-compile-x32.bin
targets?

jirka

>  
>  $(OUTPUT)test-cplus-demangle.bin:
>  	$(BUILD) -liberty
> 
> base-commit: 21e80f3841c01aeaf32d7aee7bbc87b3db1aa0c6
> -- 
> 2.40.1
> 
>