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* [PATCH] kbuild: warn if a different compiler is used for external module builds
@ 2021-08-01 2:53 Masahiro Yamada
0 siblings, 0 replies; only message in thread
From: Masahiro Yamada @ 2021-08-01 2:53 UTC (permalink / raw)
To: linux-kbuild; +Cc: Masahiro Yamada, Josh Poimboeuf, Michal Marek, linux-kernel
It is always safe to use the same compiler for the kernel and external
modules, but in reality, some distributions such as Fedora release a
different version of GCC from the one used for building the kernel.
There was a long discussion about mixing different compilers .
I do not repeat it here, but at least, showing a heads up in that
case is better than nothing.
Linus suggested :
And a warning might be more palatable even if different compiler
version work fine together. Just a heads up on "it looks like you
might be mixing compiler versions" is a valid note, and isn't
necessarily wrong. Even when they work well together, maybe you want
to have people at least _aware_ of it.
This commit shows a warning unless the compiler is exactly the same.
warning: the compiler differs from the one used to build the kernel
The kernel was built by: gcc (GCC) 11.1.1 20210531 (Red Hat 11.1.1-3)
You are using: gcc (GCC) 11.2.1 20210728 (Red Hat 11.2.1-1)
Check the difference, and if it is OK with you, please proceed at your
To avoid the locale issue as in commit bcbcf50f5218 ("kbuild: fix
ld-version.sh to not be affected by locale"), pass LC_ALL=C to
Acked-by: Josh Poimboeuf <firstname.lastname@example.org>
Signed-off-by: Masahiro Yamada <email@example.com>
Makefile | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/Makefile b/Makefile
index 6b555f64df06..f4cc77a10413 100644
@@ -583,7 +583,7 @@ endif
# Some architectures define CROSS_COMPILE in arch/$(SRCARCH)/Makefile.
# CC_VERSION_TEXT is referenced from Kconfig (so it needs export),
# and from include/config/auto.conf.cmd to detect the compiler upgrade.
-CC_VERSION_TEXT = $(subst $(pound),,$(shell $(CC) --version 2>/dev/null | head -n 1))
+CC_VERSION_TEXT = $(subst $(pound),,$(shell LC_ALL=C $(CC) --version 2>/dev/null | head -n 1))
ifneq ($(findstring clang,$(CC_VERSION_TEXT)),)
@@ -1731,6 +1731,16 @@ clean-dirs := $(KBUILD_EXTMOD)
clean: rm-files := $(KBUILD_EXTMOD)/Module.symvers $(KBUILD_EXTMOD)/modules.nsdeps \
+PHONY += prepare
+# now expand this into a simple variable to reduce the cost of shell evaluations
+prepare: CC_VERSION_TEXT := $(CC_VERSION_TEXT)
+ @if [ "$(CC_VERSION_TEXT)" != $(CONFIG_CC_VERSION_TEXT) ]; then \
+ echo >&2 "warning: the compiler differs from the one used to build the kernel"; \
+ echo >&2 " The kernel was built by: "$(CONFIG_CC_VERSION_TEXT); \
+ echo >&2 " You are using: $(CC_VERSION_TEXT)"; \
PHONY += help
@echo ' Building external modules.'
@@ -1742,7 +1752,7 @@ help:
# no-op for external module builds
-PHONY += prepare modules_prepare
+PHONY += modules_prepare
endif # KBUILD_EXTMOD
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2021-08-01 2:53 [PATCH] kbuild: warn if a different compiler is used for external module builds Masahiro Yamada
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