linux-kernel - Re: [PATCH v2] tools/resolve_btfids: Tidy host CFLAGS forcing

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Date:   Wed, 1 Feb 2023 16:31:09 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Connor OBrien <connoro@...gle.com>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] tools/resolve_btfids: Tidy host CFLAGS forcing

On Wed, Feb 01, 2023 at 01:37:43PM -0800, Ian Rogers wrote:
> Avoid passing CROSS_COMPILE to submakes and ensure CFLAGS is forced to
> HOSTCFLAGS for submake builds. This fixes problems with cross
> compilation.
> 
> Tidy to not unnecessarily modify/export CFLAGS, make the override for
> prepare and build clearer.
> 
> Fixes: 13e07691a16f ("tools/resolve_btfids: Alter how HOSTCC is forced")
> Reported-by: Nathan Chancellor <nathan@...nel.org>
> Signed-off-by: Ian Rogers <irogers@...gle.com>

Tested-by: Nathan Chancellor <nathan@...nel.org>

I can test alternative solutions as well.

> ---
>  tools/bpf/resolve_btfids/Makefile | 49 ++++++++++++++++---------------
>  1 file changed, 26 insertions(+), 23 deletions(-)
> 
> diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
> index daed388aa5d7..3ed4e3be4e06 100644
> --- a/tools/bpf/resolve_btfids/Makefile
> +++ b/tools/bpf/resolve_btfids/Makefile
> @@ -17,12 +17,7 @@ else
>    MAKEFLAGS=--no-print-directory
>  endif
>  
> -# always use the host compiler
> -HOST_OVERRIDES := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)" ARCH="$(HOSTARCH)" \
> -		  EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"
> -
>  RM      ?= rm
> -CROSS_COMPILE =
>  
>  OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
>  
> @@ -43,8 +38,31 @@ SUBCMD_INCLUDE := $(SUBCMD_DESTDIR)include
>  BINARY     := $(OUTPUT)/resolve_btfids
>  BINARY_IN  := $(BINARY)-in.o
>  
> +LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null)
> +LIBELF_LIBS  := $(shell $(HOSTPKG_CONFIG) libelf --libs 2>/dev/null || echo -lelf)
> +
> +RESOLVE_BTFIDS_CFLAGS = -g \
> +          -I$(srctree)/tools/include \
> +          -I$(srctree)/tools/include/uapi \
> +          -I$(LIBBPF_INCLUDE) \
> +          -I$(SUBCMD_INCLUDE) \
> +          $(LIBELF_FLAGS)
> +
> +# Overrides for the prepare step libraries.
> +HOST_OVERRIDES_PREPARE := AR="$(HOSTAR)" CC="$(HOSTCC)" LD="$(HOSTLD)" \
> +	  ARCH="$(HOSTARCH)" CROSS_COMPILE=""
> +
> +# Overrides for Makefile.build C targets.
> +HOST_OVERRIDES_BUILD := $(HOST_OVERRIDES_PREPARE) \
> +	  CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS) $(RESOLVE_BTFIDS_CFLAGS)" \
> +
> +LIBS = $(LIBELF_LIBS) -lz
> +
>  all: $(BINARY)
>  
> +export srctree OUTPUT Q
> +include $(srctree)/tools/build/Makefile.include
> +
>  prepare: $(BPFOBJ) $(SUBCMDOBJ)
>  
>  $(OUTPUT) $(OUTPUT)/libsubcmd $(LIBBPF_OUT):
> @@ -53,31 +71,16 @@ $(OUTPUT) $(OUTPUT)/libsubcmd $(LIBBPF_OUT):
>  
>  $(SUBCMDOBJ): fixdep FORCE | $(OUTPUT)/libsubcmd
>  	$(Q)$(MAKE) -C $(SUBCMD_SRC) OUTPUT=$(SUBCMD_OUT) \
> -		    DESTDIR=$(SUBCMD_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
> +		    DESTDIR=$(SUBCMD_DESTDIR) $(HOST_OVERRIDES_PREPARE) prefix= subdir= \
>  		    $(abspath $@) install_headers
>  
>  $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OUT)
>  	$(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC) OUTPUT=$(LIBBPF_OUT)    \
> -		    DESTDIR=$(LIBBPF_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
> +		    DESTDIR=$(LIBBPF_DESTDIR) $(HOST_OVERRIDES_PREPARE) prefix= subdir= \
>  		    $(abspath $@) install_headers
>  
> -LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null)
> -LIBELF_LIBS  := $(shell $(HOSTPKG_CONFIG) libelf --libs 2>/dev/null || echo -lelf)
> -
> -CFLAGS += -g \
> -          -I$(srctree)/tools/include \
> -          -I$(srctree)/tools/include/uapi \
> -          -I$(LIBBPF_INCLUDE) \
> -          -I$(SUBCMD_INCLUDE) \
> -          $(LIBELF_FLAGS)
> -
> -LIBS = $(LIBELF_LIBS) -lz
> -
> -export srctree OUTPUT CFLAGS Q
> -include $(srctree)/tools/build/Makefile.include
> -
>  $(BINARY_IN): fixdep FORCE prepare | $(OUTPUT)
> -	$(Q)$(MAKE) $(build)=resolve_btfids $(HOST_OVERRIDES)
> +	$(Q)$(MAKE) $(build)=resolve_btfids $(HOST_OVERRIDES_BUILD)
>  
>  $(BINARY): $(BPFOBJ) $(SUBCMDOBJ) $(BINARY_IN)
>  	$(call msg,LINK,$@)
> -- 
> 2.39.1.519.gcb327c4b5f-goog
>