kbuild: use $(src) instead of $(srctree)/$(src) for source directory

Kbuild conventionally uses $(obj)/ for generated files, and $(src)/ for
checked-in source files. It is merely a convention without any functional
difference. In fact, $(obj) and $(src) are exactly the same, as defined
in scripts/Makefile.build:

    src := $(obj)

When the kernel is built in a separate output directory, $(src) does
not accurately reflect the source directory location. While Kbuild
resolves this discrepancy by specifying VPATH=$(srctree) to search for
source files, it does not cover all cases. For example, when adding a
header search path for local headers, -I$(srctree)/$(src) is typically
passed to the compiler.

This introduces inconsistency between upstream and downstream Makefiles
because $(src) is used instead of $(srctree)/$(src) for the latter.

To address this inconsistency, this commit changes the semantics of
$(src) so that it always points to the directory in the source tree.

Going forward, the variables used in Makefiles will have the following
meanings:

  $(obj)     - directory in the object tree
  $(src)     - directory in the source tree  (changed by this commit)
  $(objtree) - the top of the kernel object tree
  $(srctree) - the top of the kernel source tree

Consequently, $(srctree)/$(src) in upstream Makefiles need to be replaced
with $(src).

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

1 files changed, 6 insertions, 6 deletions

diff --git a/Documentation/kbuild/makefiles.rst b/Documentation/kbuild/makefiles.rst
index ad118b7a1806..991ce6081e35 100644
--- a/Documentation/kbuild/makefiles.rst
+++ b/Documentation/kbuild/makefiles.rst
@@ -346,7 +346,7 @@ ccflags-y, asflags-y and ldflags-y
   Example::
 
     #arch/cris/boot/compressed/Makefile
-    ldflags-y += -T $(srctree)/$(src)/decompress_$(arch-y).lds
+    ldflags-y += -T $(src)/decompress_$(arch-y).lds
 
 subdir-ccflags-y, subdir-asflags-y
   The two flags listed above are similar to ccflags-y and asflags-y.
@@ -426,14 +426,14 @@ path to prerequisite files and target files.
 Two variables are used when defining custom rules:
 
 $(src)
-  $(src) is a relative path which points to the directory
-  where the Makefile is located. Always use $(src) when
+  $(src) is the directory where the Makefile is located. Always use $(src) when
   referring to files located in the src tree.
 
 $(obj)
-  $(obj) is a relative path which points to the directory
-  where the target is saved. Always use $(obj) when
-  referring to generated files.
+  $(obj) is the directory where the target is saved. Always use $(obj) when
+  referring to generated files. Use $(obj) for pattern rules that need to work
+  for both generated files and real sources (VPATH will help to find the
+  prerequisites not only in the object tree but also in the source tree).
 
   Example::