linux-kernel - Re: [PATCH v3 3/3] objtool: Alter how HOSTCC is forced

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Message-ID: <CAKwvOdnagfhgdi7LoggNwu5hjj1NHqCSF6oqe=CR5SgUwEX8UQ@mail.gmail.com>
Date:   Mon, 9 Jan 2023 15:05:53 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Ian Rogers <irogers@...gle.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Nathan Chancellor <nathan@...nel.org>, Tom Rix <trix@...hat.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nicolas Schier <nicolas@...sle.eu>,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        Stephane Eranian <eranian@...gle.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH v3 3/3] objtool: Alter how HOSTCC is forced

On Thu, Jan 5, 2023 at 1:02 AM Ian Rogers <irogers@...gle.com> wrote:
>
> HOSTCC is always wanted when building objtool. 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. To avoid mixing CFLAGS from different compilers just
> the objtool CFLAGS are determined with the exception of
> EXTRA_WARNINGS. HOSTCFLAGS is added to these so that command line
> flags can add to the CFLAGS.
>
> Signed-off-by: Ian Rogers <irogers@...gle.com>

Thanks Ian, and happy new year! Sorry for delays reviewing this; I'm
just getting back online today.  Assuming Peter and Josh may be too,
otherwise can Peter or Josh PTAL?

Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>

(I'm happy that this allows me to now pass HOSTCFLAGS on to objtool
successfully)

> ---
>  tools/objtool/Makefile | 25 +++++++++++++++----------
>  1 file changed, 15 insertions(+), 10 deletions(-)
>
> diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile
> index 61a00b7acae9..49956f4f58b9 100644
> --- a/tools/objtool/Makefile
> +++ b/tools/objtool/Makefile
> @@ -2,16 +2,12 @@
>  include ../scripts/Makefile.include
>  include ../scripts/Makefile.arch
>
> -# always use the host compiler
> -AR      = $(HOSTAR)
> -CC      = $(HOSTCC)
> -LD      = $(HOSTLD)
> -
>  ifeq ($(srctree),)
>  srctree := $(patsubst %/,%,$(dir $(CURDIR)))
>  srctree := $(patsubst %/,%,$(dir $(srctree)))
>  endif
>
> +MAKE = make -S
>  LIBSUBCMD_DIR = $(srctree)/tools/lib/subcmd/
>  ifneq ($(OUTPUT),)
>    LIBSUBCMD_OUTPUT = $(abspath $(OUTPUT))/libsubcmd
> @@ -37,12 +33,19 @@ INCLUDES := -I$(srctree)/tools/include \
>             -I$(srctree)/tools/objtool/arch/$(SRCARCH)/include \
>             -I$(LIBSUBCMD_OUTPUT)/include
>  WARNINGS := $(EXTRA_WARNINGS) -Wno-switch-default -Wno-switch-enum -Wno-packed -Wno-nested-externs
> -CFLAGS   := -Werror $(WARNINGS) $(KBUILD_HOSTCFLAGS) -g $(INCLUDES) $(LIBELF_FLAGS)
> -LDFLAGS  += $(LIBELF_LIBS) $(LIBSUBCMD) $(KBUILD_HOSTLDFLAGS)
> +OBJTOOL_CFLAGS := -Werror $(WARNINGS) -g $(INCLUDES) $(LIBELF_FLAGS) $(HOSTCFLAGS)
> +OBJTOOL_LDFLAGS := $(LIBELF_LIBS) $(LIBSUBCMD)
>
>  # Allow old libelf to be used:
>  elfshdr := $(shell echo '$(pound)include <libelf.h>' | $(CC) $(CFLAGS) -x c -E - | grep elf_getshdr)
> -CFLAGS += $(if $(elfshdr),,-DLIBELF_USE_DEPRECATED)
> +OBJTOOL_CFLAGS += $(if $(elfshdr),,-DLIBELF_USE_DEPRECATED)
> +
> +# Always want host compilation.
> +HOST_OVERRIDES := CC="$(HOSTCC)" EXTRA_CFLAGS="$(OBJTOOL_CFLAGS)" \
> +                 LD="$(HOSTLD)" AR="$(HOSTAR)"
> +BUILD_HOST_OVERRIDES := CC="$(HOSTCC)" CFLAGS="$(OBJTOOL_CFLAGS)" \
> +                       LD="$(HOSTLD)" LDFLAGS="$(OBJTOOL_LDFLAGS)" \
> +                       AR="$(HOSTAR)"
>
>  AWK = awk
>  MKDIR = mkdir
> @@ -65,10 +68,11 @@ include $(srctree)/tools/build/Makefile.include
>
>  $(OBJTOOL_IN): fixdep FORCE
>         $(Q)$(CONFIG_SHELL) ./sync-check.sh
> -       $(Q)$(MAKE) $(build)=objtool
> +       $(Q)$(MAKE) $(build)=objtool $(BUILD_HOST_OVERRIDES)
> +
>
>  $(OBJTOOL): $(LIBSUBCMD) $(OBJTOOL_IN)
> -       $(QUIET_LINK)$(CC) $(OBJTOOL_IN) $(LDFLAGS) -o $@
> +       $(QUIET_LINK)$(HOSTCC) $(OBJTOOL_IN) $(KBUILD_HOSTLDFLAGS) $(OBJTOOL_LDFLAGS) -o $@
>
>
>  $(LIBSUBCMD_OUTPUT):
> @@ -77,6 +81,7 @@ $(LIBSUBCMD_OUTPUT):
>  $(LIBSUBCMD): fixdep FORCE $(LIBSUBCMD_OUTPUT)
>         $(Q)$(MAKE) -C $(LIBSUBCMD_DIR) O=$(LIBSUBCMD_OUTPUT) \
>                 DESTDIR=$(LIBSUBCMD_DESTDIR) prefix= subdir= \
> +               $(HOST_OVERRIDES) \
>                 $@ install_headers
>
>  $(LIBSUBCMD)-clean:
> --
> 2.39.0.314.g84b9a713c41-goog
>


-- 
Thanks,
~Nick Desaulniers