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Subject[PATCH 3/3] kbuild: add a flag to force absolute path for srctree
In old days, Kbuild always used an absolute path for $(srctree).

Since commit 890676c65d69 ("kbuild: Use relative path when building in
the source tree"), $(srctree) is '.' when not using O=.

Yet, using absolute paths is useful in some cases even without O=, for
instance, to create a cscope file with absolute path tags.

O=. was used as an idiom to force Kbuild to use absolute paths even
when you are building in the source tree.

Since commit 25b146c5b8ce ("kbuild: allow Kbuild to start from any
directory"), Kbuild is too clever to be tricked. Even if you pass O=.
Kbuild notices you are building in the source tree, then use '.' for

So, "make O=. cscope" is no help to create absolute path tags.

We cannot force one or the other according to commit e93bc1a0cab3
("Revert "kbuild: specify absolute paths for cscope""). Both of
relative path and absolute path have pros and cons.

This commit adds a new flag KBUILD_ABS_SRCTREE to allow users to
choose the absolute path for $(srctree).

"make KBUILD_ABS_SRCTREE=1 cscope" will work as a replacement of
"make O=. cscope".

I added Fixes since that commit broke some users' workflow.

Fixes: 25b146c5b8ce ("kbuild: allow Kbuild to start from any directory")
Reported-by: Pawan Gupta <>
Signed-off-by: Masahiro Yamada <>

Documentation/kbuild/kbuild.txt | 9 +++++++++
Makefile | 4 ++++
scripts/ | 3 +--
3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/Documentation/kbuild/kbuild.txt b/Documentation/kbuild/kbuild.txt
index 7a7e2aa2fab5..3ef42f87f275 100644
--- a/Documentation/kbuild/kbuild.txt
+++ b/Documentation/kbuild/kbuild.txt
@@ -182,6 +182,15 @@ The output directory is often set using "O=..." on the commandline.

The value can be overridden in which case the default value is ignored.

+Kbuild uses a relative path to point to the tree when possible. For instance,
+when building in the source tree, the source tree path is '.'
+Setting this flag requests Kbuild to use absolute path to the source tree.
+There are some useful cases to do so, like when generating tag files with
+absolute path entries etc.
This variable allows a passphrase or PIN to be passed to the sign-file
diff --git a/Makefile b/Makefile
index 534a5dc796b1..6dc453f86f00 100644
--- a/Makefile
+++ b/Makefile
@@ -244,6 +244,10 @@ else
building_out_of_srctree := 1

+srctree := $(abs_srctree)
objtree := .
VPATH := $(srctree)

diff --git a/scripts/ b/scripts/
index 7fea4044749b..4e18ae5282a6 100755
--- a/scripts/
+++ b/scripts/
@@ -17,8 +17,7 @@ ignore="$(echo "$RCS_FIND_IGNORE" | sed 's|\\||g' )"
# tags and cscope files should also ignore MODVERSION *.mod.c files
ignore="$ignore ( -name *.mod.c ) -prune -o"

-# Do not use full path if we do not use O=.. builds
-# Use make O=. {tags|cscope}
+# Use make KBUILD_ABS_SRCTREE=1 {tags|cscope}
# to force full paths for a non-O= build
if [ "${srctree}" = "." -o -z "${srctree}" ]; then
 \ /
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