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Thu, 10 Dec 2020 02:16:10 +0000 Subject: Re: [PATCH bpf-next] selftests/bpf: Drop the need for LLVM's llc To: Andrew Delgadillo , CC: Alexei Starovoitov , Daniel Borkmann References: <20201209205301.2586678-1-adelg@google.com> From: Yonghong Song Message-ID: Date: Wed, 9 Dec 2020 18:16:08 -0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.5.1 In-Reply-To: <20201209205301.2586678-1-adelg@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Originating-IP: [2620:10d:c090:400::5:bc44] X-ClientProxiedBy: BY5PR17CA0063.namprd17.prod.outlook.com (2603:10b6:a03:167::40) To BYAPR15MB4088.namprd15.prod.outlook.com (2603:10b6:a02:c3::18) X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2620:10d:c085:21c8::113f] (2620:10d:c090:400::5:bc44) by BY5PR17CA0063.namprd17.prod.outlook.com (2603:10b6:a03:167::40) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3654.12 via Frontend Transport; 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Consequently, it > exposes many low level options about its backend. To avoid future bugs > introduced by using the raw LLC tool, use clang directly so that all > appropriate options are passed to the back end. Agree that this indeed make build system simpler. > > Additionally, the native clang build rule was not being use in the > selftests Makefile, so remove it. This is true too. Otherwise, native clang build will require both clang and llc runs. The patch looks good and I have a few comments and hopefully you can accommodate. > > Signed-off-by: Andrew Delgadillo > --- > tools/testing/selftests/bpf/Makefile | 20 ++++---------------- > 1 file changed, 4 insertions(+), 16 deletions(-) > > diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile > index 944ae17a39ed..74870d365b62 100644 > --- a/tools/testing/selftests/bpf/Makefile > +++ b/tools/testing/selftests/bpf/Makefile > @@ -19,7 +19,6 @@ ifneq ($(wildcard $(GENHDR)),) > endif > > CLANG ?= clang > -LLC ?= llc > LLVM_OBJCOPY ?= llvm-objcopy > BPF_GCC ?= $(shell command -v bpf-gcc;) > SAN_CFLAGS ?= > @@ -256,24 +255,13 @@ $(OUTPUT)/flow_dissector_load.o: flow_dissector_load.h > # $3 - CFLAGS > # $4 - LDFLAGS > define CLANG_BPF_BUILD_RULE > - $(call msg,CLNG-LLC,$(TRUNNER_BINARY),$2) > - $(Q)($(CLANG) $3 -O2 -target bpf -emit-llvm \ > - -c $1 -o - || echo "BPF obj compilation failed") | \ > - $(LLC) -mattr=dwarfris -march=bpf -mcpu=v3 $4 -filetype=obj -o $2 > + $(call msg,CLNG-BPF,$(TRUNNER_BINARY),$2) > + $(Q)$(CLANG) $3 -O2 -target bpf -c $1 -o $2 -Xclang -target-feature -Xclang +dwarfris -mcpu=v3 $4 Yes, we still use +dwarfris here. The original llvm patch which introduded +dwarfris is: https://github.com/llvm/llvm-project/commit/03e1c8b8f9cc7b898217b7789d3887a903443c93 it is to workaround an elfutils/libdw issue as it does not support bpf backend so pahole cannot display debuginfo structures properly. Subsequently, the elfutils/libdw bpf support is added at https://sourceware.org/git/?p=elfutils.git;a=commitdiff;h=c1990d36cfe37a30bcc49422c37a6767fd190559 Any recent pahole should already build with the above fix. I tested with pahole 1.16 it works fine for binaries built without +dwarfris. Also BTF now can be used to dump structures. So could you also accommodate the change to remove +dwarfris option? > endef > # Similar to CLANG_BPF_BUILD_RULE, but with disabled alu32 > define CLANG_NOALU32_BPF_BUILD_RULE > - $(call msg,CLNG-LLC,$(TRUNNER_BINARY),$2) > - $(Q)($(CLANG) $3 -O2 -target bpf -emit-llvm \ > - -c $1 -o - || echo "BPF obj compilation failed") | \ > - $(LLC) -march=bpf -mcpu=v2 $4 -filetype=obj -o $2 > -endef > -# Similar to CLANG_BPF_BUILD_RULE, but using native Clang and bpf LLC > -define CLANG_NATIVE_BPF_BUILD_RULE > $(call msg,CLNG-BPF,$(TRUNNER_BINARY),$2) > - $(Q)($(CLANG) $3 -O2 -emit-llvm \ > - -c $1 -o - || echo "BPF obj compilation failed") | \ > - $(LLC) -march=bpf -mcpu=v3 $4 -filetype=obj -o $2 > + $(Q)$(CLANG) $3 -O2 -target bpf -c $1 -o $2 -mcpu=v2 $4 > endef > # Build BPF object using GCC > define GCC_BPF_BUILD_RULE > @@ -402,7 +390,7 @@ TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read $(OUTPUT)/bpf_testmod.ko \ > $(wildcard progs/btf_dump_test_case_*.c) > TRUNNER_BPF_BUILD_RULE := CLANG_BPF_BUILD_RULE > TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS) > -TRUNNER_BPF_LDFLAGS := -mattr=+alu32 > +TRUNNER_BPF_LDFLAGS := -Xclang -target-feature -Xclang +alu32 The +alu32 is only used for non-alu32 case where -mcpu=v3 actually implies alu32. So let us remove TRUNNER_BPF_LDFLAGS flag from Makefile too. > $(eval $(call DEFINE_TEST_RUNNER,test_progs)) > > # Define test_progs-no_alu32 test runner. >