From: Thomas Hebb tommyhebb@gmail.com
[ Upstream commit e3232c2f39acafd5a29128425bc30b9884642cfa ]
commit c8c188679ccf ("tools build: Use the same CC for feature detection and actual build") changed these assignments from unconditional (:=) to conditional (?=) so that they wouldn't clobber values from the environment. However, conditional assignment does not work properly for variables that Make implicitly sets, among which are CC and CXX. To quote tools/scripts/Makefile.include, which handles this properly:
# Makefiles suck: This macro sets a default value of $(2) for the # variable named by $(1), unless the variable has been set by # environment or command line. This is necessary for CC and AR # because make sets default values, so the simpler ?= approach # won't work as expected.
In other words, the conditional assignments will not run even if the variables are not overridden in the environment; Make will set CC to "cc" and CXX to "g++" when it starts[1], meaning the variables are not empty by the time the conditional assignments are evaluated. This breaks cross-compilation when CROSS_COMPILE is set but CC isn't, since "cc" gets used for feature detection instead of the cross compiler (and likewise for CXX).
To fix the issue, just pass down the values of CC and CXX computed by the parent Makefile, which gets included by the Makefile that actually builds whatever we're detecting features for and so is guaranteed to have good values. This is a better solution anyway, since it means we aren't trying to replicate the logic of the parent build system and so don't risk it getting out of sync.
Leave PKG_CONFIG alone, since 1) there's no common logic to compute it in Makefile.include, and 2) it's not an implicit variable, so conditional assignment works properly.
[1] https://www.gnu.org/software/make/manual/html_node/Implicit-Variables.html
Fixes: c8c188679ccf ("tools build: Use the same CC for feature detection and actual build") Signed-off-by: Thomas Hebb tommyhebb@gmail.com Acked-by: Jiri Olsa jolsa@kernel.org Cc: David Carrillo-Cisneros davidcc@google.com Cc: Ian Rogers irogers@google.com Cc: Igor Lubashev ilubashe@akamai.com Cc: Namhyung Kim namhyung@kernel.org Cc: Quentin Monnet quentin@isovalent.com Cc: Song Liu songliubraving@fb.com Cc: Stephane Eranian eranian@google.com Cc: thomas hebb tommyhebb@gmail.com Link: http://lore.kernel.org/lkml/0a6e69d1736b0fa231a648f50b0cce5d8a6734ef.1595822... Signed-off-by: Arnaldo Carvalho de Melo acme@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- tools/build/Makefile.feature | 2 +- tools/build/feature/Makefile | 2 -- 2 files changed, 1 insertion(+), 3 deletions(-)
diff --git a/tools/build/Makefile.feature b/tools/build/Makefile.feature index c71a05b9c984f..a2389f0c0b1c0 100644 --- a/tools/build/Makefile.feature +++ b/tools/build/Makefile.feature @@ -7,7 +7,7 @@ endif
feature_check = $(eval $(feature_check_code)) define feature_check_code - feature-$(1) := $(shell $(MAKE) OUTPUT=$(OUTPUT_FEATURES) CFLAGS="$(EXTRA_CFLAGS) $(FEATURE_CHECK_CFLAGS-$(1))" CXXFLAGS="$(EXTRA_CXXFLAGS) $(FEATURE_CHECK_CXXFLAGS-$(1))" LDFLAGS="$(LDFLAGS) $(FEATURE_CHECK_LDFLAGS-$(1))" -C $(feature_dir) $(OUTPUT_FEATURES)test-$1.bin >/dev/null 2>/dev/null && echo 1 || echo 0) + feature-$(1) := $(shell $(MAKE) OUTPUT=$(OUTPUT_FEATURES) CC=$(CC) CXX=$(CXX) CFLAGS="$(EXTRA_CFLAGS) $(FEATURE_CHECK_CFLAGS-$(1))" CXXFLAGS="$(EXTRA_CXXFLAGS) $(FEATURE_CHECK_CXXFLAGS-$(1))" LDFLAGS="$(LDFLAGS) $(FEATURE_CHECK_LDFLAGS-$(1))" -C $(feature_dir) $(OUTPUT_FEATURES)test-$1.bin >/dev/null 2>/dev/null && echo 1 || echo 0) endef
feature_set = $(eval $(feature_set_code)) diff --git a/tools/build/feature/Makefile b/tools/build/feature/Makefile index 96982640fbf88..26316749e594a 100644 --- a/tools/build/feature/Makefile +++ b/tools/build/feature/Makefile @@ -55,8 +55,6 @@ FILES= \
FILES := $(addprefix $(OUTPUT),$(FILES))
-CC ?= $(CROSS_COMPILE)gcc -CXX ?= $(CROSS_COMPILE)g++ PKG_CONFIG ?= $(CROSS_COMPILE)pkg-config LLVM_CONFIG ?= llvm-config