linux-kernel - Re: [PATCH v2 2/2] tools/resolve_btfids: Alter how HOSTCC is forced

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Date:   Thu, 19 Jan 2023 15:51:22 +0100
From:   Jiri Olsa <olsajiri@...il.com>
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>,
        Connor OBrien <connoro@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] tools/resolve_btfids: Alter how HOSTCC is forced

On Mon, Jan 16, 2023 at 01:57:51PM -0800, Ian Rogers wrote:
> HOSTCC is always wanted when building. Setting CC to HOSTCC happens
> after tools/scripts/Makefile.include is included, meaning flags are
> set assuming say CC is gcc, but then it can be later set to HOSTCC
> which may be clang. tools/scripts/Makefile.include is needed for host
> set up and common macros in objtool's Makefile. Rather than override
> CC to HOSTCC, just pass CC as HOSTCC to Makefile.build, the libsubcmd
> builds and the linkage step. This means the Makefiles don't see things
> like CC changing and tool flag determination, and similar, work
> properly.
> 
> Also, clear the passed subdir as otherwise an outer build may break by
> inadvertently passing an inappropriate value.

I tested with cross builds for s390/ppc/arm64 and it was ok

some comments below

thanks,
jirka


> 
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
>  tools/bpf/resolve_btfids/Makefile | 17 +++++++----------
>  1 file changed, 7 insertions(+), 10 deletions(-)
> 
> diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
> index 76b737b2560d..515d87b32fb8 100644
> --- a/tools/bpf/resolve_btfids/Makefile
> +++ b/tools/bpf/resolve_btfids/Makefile
> @@ -18,14 +18,11 @@ else
>  endif
>  
>  # always use the host compiler
> -AR       = $(HOSTAR)
> -CC       = $(HOSTCC)
> -LD       = $(HOSTLD)
> -ARCH     = $(HOSTARCH)

I wonder all the tools should use HOSTCC in the first place?
seems more clear than forcing it from other makefiles

subcmd even has:

CC ?= $(CROSS_COMPILE)gcc
LD ?= $(CROSS_COMPILE)ld
AR ?= $(CROSS_COMPILE)ar

which seems wrong unless I'm missing something.. should be always
the host compiler, right?

> +HOST_OVERRIDES := AR=$(HOSTAR) CC="$(HOSTCC)" LD="$(HOSTLD)" AR="$(HOSTAR)" \
> +		  ARCH=$(HOSTARCH) EXTRA_CFLAGS="$(HOSTCFLAGS) $(KBUILD_HOSTCFLAGS)"

there's extra AR set and ARCH value is not in ""

> +
>  RM      ?= rm
>  CROSS_COMPILE =
> -CFLAGS  := $(KBUILD_HOSTCFLAGS)
> -LDFLAGS := $(KBUILD_HOSTLDFLAGS)
>  
>  OUTPUT ?= $(srctree)/tools/bpf/resolve_btfids/
>  
> @@ -56,12 +53,12 @@ $(OUTPUT) $(OUTPUT)/libsubcmd $(LIBBPF_OUT):
>  
>  $(SUBCMDOBJ): fixdep FORCE | $(OUTPUT)/libsubcmd
>  	$(Q)$(MAKE) -C $(SUBCMD_SRC) OUTPUT=$(SUBCMD_OUT) \
> -		    DESTDIR=$(SUBCMD_DESTDIR) prefix= \
> +		    DESTDIR=$(SUBCMD_DESTDIR) $(HOST_OVERRIDES) 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=$(LIBBPF_DESTDIR) prefix= EXTRA_CFLAGS="$(CFLAGS)" \
> +		    DESTDIR=$(LIBBPF_DESTDIR) $(HOST_OVERRIDES) prefix= subdir= \
>  		    $(abspath $@) install_headers
>  
>  CFLAGS += -g \
> @@ -76,11 +73,11 @@ export srctree OUTPUT CFLAGS Q
>  include $(srctree)/tools/build/Makefile.include
>  
>  $(BINARY_IN): fixdep FORCE prepare | $(OUTPUT)
> -	$(Q)$(MAKE) $(build)=resolve_btfids
> +	$(Q)$(MAKE) $(build)=resolve_btfids $(HOST_OVERRIDES)
>  
>  $(BINARY): $(BPFOBJ) $(SUBCMDOBJ) $(BINARY_IN)
>  	$(call msg,LINK,$@)
> -	$(Q)$(CC) $(BINARY_IN) $(LDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
> +	$(Q)$(HOSTCC) $(BINARY_IN) $(KBUILD_HOSTLDFLAGS) -o $@ $(BPFOBJ) $(SUBCMDOBJ) $(LIBS)
>  
>  clean_objects := $(wildcard $(OUTPUT)/*.o                \
>                              $(OUTPUT)/.*.o.cmd           \
> -- 
> 2.39.0.314.g84b9a713c41-goog
>