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

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Message-Id: <20230105090155.357604-4-irogers@google.com>
Date:   Thu,  5 Jan 2023 01:01:55 -0800
From:   Ian Rogers <irogers@...gle.com>
To:     Josh Poimboeuf <jpoimboe@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nicolas Schier <nicolas@...sle.eu>,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Cc:     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>,
        Ian Rogers <irogers@...gle.com>
Subject: [PATCH v3 3/3] objtool: Alter how HOSTCC is forced

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>
---
 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