Messages in this thread Patch in this message | | | From | Masahiro Yamada <> | Subject | [PATCH v3] kbuild: use -fmacro-prefix-map to make __FILE__ a relative path | Date | Fri, 30 Mar 2018 13:15:26 +0900 |
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The __FILE__ macro is used everywhere in the kernel to locate the file printing the log message, such as WARN_ON(), etc. If the kernel is built out of tree, this can be a long absolute path, like this:
WARNING: CPU: 1 PID: 1 at /path/to/build/directory/arch/arm64/kernel/foo.c:...
This is because Kbuild runs in the objtree instead of the srctree, then __FILE__ is expanded to a file path prefixed with $(srctree)/.
Commit 9da0763bdd82 ("kbuild: Use relative path when building in a subdir of the source tree") improved this to some extent; $(srctree) becomes ".." if the objtree is a child of the srctree.
For other cases of out-of-tree build, __FILE__ is still the absolute path. It also means the kernel image depends on where it was built.
A brand-new option from GCC, -fmacro-prefix-map, solves this problem. If your compiler supports it, __FILE__ is the relative path from the srctree regardless of O= option. This provides more readable log and more reproducible builds.
Please note __FILE__ is always an absolute path for external modules.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> ---
I tested this on GCC 8. (not released yet, but you can get the source code from the trunk.)
Changes in v3: - It is harmless to always set this option. Remove ifneq ifneq ($(KBUILD_SRC),)
Changes in v2: - Comment-in the ifeq
Makefile | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/Makefile b/Makefile index 7ba478a..83d25c9 100644 --- a/Makefile +++ b/Makefile @@ -856,6 +856,9 @@ KBUILD_CFLAGS += $(call cc-option,-Werror=incompatible-pointer-types) # Require designated initializers for all marked structures KBUILD_CFLAGS += $(call cc-option,-Werror=designated-init) +# change __FILE__ to the relative path from the srctree +KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=) + # use the deterministic mode of AR if available KBUILD_ARFLAGS := $(call ar-option,D) -- 2.7.4
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