netdev - Re: [PATCH bpf-next] selftests/bpf: Cross-compile bpftool

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Date:   Mon, 13 Feb 2023 20:53:31 +0000
From:   Quentin Monnet <quentin@...valent.com>
To:     Björn Töpel <bjorn@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
        netdev@...r.kernel.org,
        Jean-Philippe Brucker <jean-philippe@...aro.org>
Cc:     Björn Töpel <bjorn@...osinc.com>,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf-next] selftests/bpf: Cross-compile bpftool

2023-02-10 09:43 UTC+0100 ~ Björn Töpel <bjorn@...nel.org>
> From: Björn Töpel <bjorn@...osinc.com>
> 
> When the BPF selftests are cross-compiled, only the a host version of
> bpftool is built. This version of bpftool is used to generate various
> intermediates, e.g., skeletons.
> 
> The test runners are also using bpftool. The Makefile will symlink
> bpftool from the selftest/bpf root, where the test runners will look
> for the tool:
> 
>   | ...
>   | $(Q)ln -sf $(if $2,..,.)/tools/build/bpftool/bootstrap/bpftool \
>   |    $(OUTPUT)/$(if $2,$2/)bpftool
> 
> There are two issues for cross-compilation builds:
> 
>  1. There is no native (cross-compilation target) build of bpftool
>  2. The bootstrap variant of bpftool is never cross-compiled (by
>     design)
> 
> Make sure that a native/cross-compiled version of bpftool is built,
> and if CROSS_COMPILE is set, symlink to the native/non-bootstrap
> version.
> 
> Signed-off-by: Björn Töpel <bjorn@...osinc.com>
> ---
>  tools/testing/selftests/bpf/Makefile | 28 +++++++++++++++++++++++++---
>  1 file changed, 25 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index b2eb3201b85a..b706750f71e2 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -157,8 +157,9 @@ $(notdir $(TEST_GEN_PROGS)						\
>  	 $(TEST_CUSTOM_PROGS)): %: $(OUTPUT)/% ;
>  
>  # sort removes libbpf duplicates when not cross-building
> -MAKE_DIRS := $(sort $(BUILD_DIR)/libbpf $(HOST_BUILD_DIR)/libbpf	       \
> -	       $(HOST_BUILD_DIR)/bpftool $(HOST_BUILD_DIR)/resolve_btfids      \
> +MAKE_DIRS := $(sort $(BUILD_DIR)/libbpf $(HOST_BUILD_DIR)/libbpf	\
> +	       $(BUILD_DIR)/bpftool $(HOST_BUILD_DIR)/bpftool		\
> +	       $(HOST_BUILD_DIR)/resolve_btfids				\
>  	       $(RUNQSLOWER_OUTPUT) $(INCLUDE_DIR))
>  $(MAKE_DIRS):
>  	$(call msg,MKDIR,,$@)
> @@ -208,6 +209,14 @@ $(OUTPUT)/bpf_testmod.ko: $(VMLINUX_BTF) $(wildcard bpf_testmod/Makefile bpf_tes
>  	$(Q)cp bpf_testmod/bpf_testmod.ko $@
>  
>  DEFAULT_BPFTOOL := $(HOST_SCRATCH_DIR)/sbin/bpftool
> +ifneq ($(CROSS_COMPILE),)
> +CROSS_BPFTOOL := $(SCRATCH_DIR)/sbin/bpftool
> +TRUNNER_BPFTOOL := $(CROSS_BPFTOOL)
> +USE_BOOTSTRAP := ""
> +else
> +TRUNNER_BPFTOOL := $(DEFAULT_BPFTOOL)
> +USE_BOOTSTRAP := "bootstrap"
> +endif
>  
>  $(OUTPUT)/runqslower: $(BPFOBJ) | $(DEFAULT_BPFTOOL) $(RUNQSLOWER_OUTPUT)
>  	$(Q)$(MAKE) $(submake_extras) -C $(TOOLSDIR)/bpf/runqslower	       \
> @@ -255,6 +264,18 @@ $(DEFAULT_BPFTOOL): $(wildcard $(BPFTOOLDIR)/*.[ch] $(BPFTOOLDIR)/Makefile)    \
>  		    LIBBPF_DESTDIR=$(HOST_SCRATCH_DIR)/			       \
>  		    prefix= DESTDIR=$(HOST_SCRATCH_DIR)/ install-bin
>  
> +ifneq ($(CROSS_COMPILE),)
> +$(CROSS_BPFTOOL): $(wildcard $(BPFTOOLDIR)/*.[ch] $(BPFTOOLDIR)/Makefile)	\
> +		    $(BPFOBJ) | $(BUILD_DIR)/bpftool
> +	$(Q)$(MAKE) $(submake_extras)  -C $(BPFTOOLDIR)				\
> +		    ARCH=$(ARCH) CROSS_COMPILE=$(CROSS_COMPILE)			\
> +		    EXTRA_CFLAGS='-g -O0'					\
> +		    OUTPUT=$(BUILD_DIR)/bpftool/				\
> +		    LIBBPF_OUTPUT=$(BUILD_DIR)/libbpf/				\
> +		    LIBBPF_DESTDIR=$(SCRATCH_DIR)/				\
> +		    prefix= DESTDIR=$(SCRATCH_DIR)/ install-bin
> +endif
> +
>  all: docs
>  
>  docs:
> @@ -518,11 +539,12 @@ endif
>  $(OUTPUT)/$(TRUNNER_BINARY): $(TRUNNER_TEST_OBJS)			\
>  			     $(TRUNNER_EXTRA_OBJS) $$(BPFOBJ)		\
>  			     $(RESOLVE_BTFIDS)				\
> +			     $(TRUNNER_BPFTOOL)				\
>  			     | $(TRUNNER_BINARY)-extras
>  	$$(call msg,BINARY,,$$@)
>  	$(Q)$$(CC) $$(CFLAGS) $$(filter %.a %.o,$$^) $$(LDLIBS) -o $$@
>  	$(Q)$(RESOLVE_BTFIDS) --btf $(TRUNNER_OUTPUT)/btf_data.bpf.o $$@
> -	$(Q)ln -sf $(if $2,..,.)/tools/build/bpftool/bootstrap/bpftool \
> +	$(Q)ln -sf $(if $2,..,.)/tools/build/bpftool/$(USE_BOOTSTRAP)/bpftool \

Nit: You'll have a double slash in this path when USE_BOOSTRAP is empty
(.../tools/build/bpftool//bpftool), but it probably doesn't matter much.

>  		   $(OUTPUT)/$(if $2,$2/)bpftool
>  
>  endef
> 
> base-commit: 06744f24696e1e7598412c3df61a538b57ebec22

The changes look good to me, thanks!

Acked-by: Quentin Monnet <quentin@...valent.com>

Jean-Philippe, I know you do some cross-compiling with bpftool, how does
this look from your side?