From: Masahiro Yamada yamada.masahiro@socionext.com
[ Upstream commit a73619a845d5625079cc1b3b820f44c899618388 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- Makefile | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/Makefile b/Makefile index 19c7e30684077..62ce3766032c9 100644 --- a/Makefile +++ b/Makefile @@ -837,6 +837,9 @@ 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)