| Message ID | 1522337766-6476-1-git-send-email-yamada.masahiro@socionext.com |
|---|---|
| State | New |
| Headers | show |
| Series | kbuild: use -fmacro-prefix-map to make __FILE__ a relative path | expand |
diff --git a/Makefile b/Makefile index 7ba478a..d2d44f9 100644 --- a/Makefile +++ b/Makefile @@ -813,6 +813,11 @@ KBUILD_CFLAGS += $(call cc-option,-ffunction-sections,) KBUILD_CFLAGS += $(call cc-option,-fdata-sections,) endif +#ifneq ($(KBUILD_SRC),) +# Change __FILE__ to a relative path from the srctree +KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=) +#endif + # arch Makefile may override CC so keep this after arch Makefile is included NOSTDINC_FLAGS += -nostdinc -isystem $(call shell-cached,$(CC) -print-file-name=include) CHECKFLAGS += $(NOSTDINC_FLAGS)
The __FILE__ macro is used everywhere in the kernel to locate the file path printing the log message. The biggest users of this macro are WARN_ON() and friends. If the kernel is built out of tree, this could 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. Commit 9da0763bdd82 ("kbuild: Use relative path when building in a subdir of the source tree") mitigated the pain 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 solves this problem. -fmacro-prefix-map=<old>=<new> When preprocessing files residing in directory <old>, expand the __FILE__ and __BASE_FILE__ macros as if the files resided in directory <new> instead. This can be used to change an absolute path to a relative path by using . for <new> which can result in more reproducible builds that are location independent. This option also affects __builtin_FILE() during compilation. If your compiler supports this option, __FILE__ is the relative path from the root of srctree regardless of O= option. 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.) Makefile | 5 +++++ 1 file changed, 5 insertions(+) -- 2.7.4