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authorMasahiro Yamada <yamada.masahiro@socionext.com>2018-03-30 13:15:26 +0900
committerMasahiro Yamada <yamada.masahiro@socionext.com>2018-04-07 19:04:02 +0900
commita73619a845d5625079cc1b3b820f44c899618388 (patch)
tree18ba6bd224aa6e2f7475d2675b292d2dbdf29728 /Makefile
parent54a702f70589926acf687f0cd5df24d07230c80e (diff)
downloadlinux-a73619a845d5625079cc1b3b820f44c899618388.tar.bz2
kbuild: use -fmacro-prefix-map to make __FILE__ a relative path
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>
Diffstat (limited to 'Makefile')
-rw-r--r--Makefile3
1 files changed, 3 insertions, 0 deletions
diff --git a/Makefile b/Makefile
index b259dd64ce95..74567b0ec2f0 100644
--- a/Makefile
+++ b/Makefile
@@ -846,6 +846,9 @@ 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)