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

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Message-ID: <871qd81ny2.fsf@all.your.base.are.belong.to.us>
Date:   Thu, 02 Nov 2023 10:53:09 +0100
From:   Björn Töpel <bjorn@...nel.org>
To:     Jiri Olsa <olsajiri@...il.com>
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

Jiri Olsa <olsajiri@...il.com> writes:

> 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?

Ah, yes!

I'll spin a v2 with:
diff --git a/tools/build/feature/Makefile b/tools/build/feature/Makefile
index 0231a53024c7..c4458345e564 100644
--- a/tools/build/feature/Makefile
+++ b/tools/build/feature/Makefile
@@ -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


Thanks for having a look, jirka!


Björn