kbuild: Add new Kbuild variable KBUILD_EXTRA_SYMBOLS

This patch adds a new (Kbuild) Makefile variable KBUILD_EXTRA_SYMBOLS.
The space separated list of file names assigned to KBUILD_EXTRA_SYMBOLS
is used when calling scripts/mod/modpost during stage 2 of the Kbuild
process for non-kernel-tree modules.

Signed-off-by: Richard Hacker <lerichi@gmx.net>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

2 files changed, 16 insertions, 1 deletions

diff --git a/Documentation/kbuild/modules.txt b/Documentation/kbuild/modules.txt
index 1d247d59ad56..1821c077b435 100644
--- a/Documentation/kbuild/modules.txt
+++ b/Documentation/kbuild/modules.txt
@@ -486,7 +486,7 @@ Module.symvers contains a list of all exported symbols from a kernel build.
         Sometimes, an external module uses exported symbols from another
         external module. Kbuild needs to have full knowledge on all symbols
         to avoid spitting out warnings about undefined symbols.
-        Two solutions exist to let kbuild know all symbols of more than
+        Three solutions exist to let kbuild know all symbols of more than
         one external module.
         The method with a top-level kbuild file is recommended but may be
         impractical in certain situations.
@@ -523,6 +523,13 @@ Module.symvers contains a list of all exported symbols from a kernel build.
                 containing the sum of all symbols defined and not part of the
                 kernel.
 
+        Use make variable KBUILD_EXTRA_SYMBOLS in the Makefile
+                If it is impractical to copy Module.symvers from another
+                module, you can assign a space separated list of files to
+                KBUILD_EXTRA_SYMBOLS in your Makfile. These files will be
+                loaded by modpost during the initialisation of its symbol
+                tables.
+
 === 8. Tips & Tricks
 
 --- 8.1 Testing for CONFIG_FOO_BAR
diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index 2d20640854b7..24b3c8fe6bca 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -42,6 +42,13 @@ _modpost: __modpost
 
 include include/config/auto.conf
 include scripts/Kbuild.include
+
+ifneq ($(KBUILD_EXTMOD),)
+# Include the module's Makefile to find KBUILD_EXTRA_SYMBOLS
+include $(if $(wildcard $(KBUILD_EXTMOD)/Kbuild), \
+             $(KBUILD_EXTMOD)/Kbuild, $(KBUILD_EXTMOD)/Makefile)
+endif
+
 include scripts/Makefile.lib
 
 kernelsymfile := $(objtree)/Module.symvers
@@ -69,6 +76,7 @@ modpost = scripts/mod/modpost                    \
  $(if $(CONFIG_MODULE_SRCVERSION_ALL),-a,)       \
  $(if $(KBUILD_EXTMOD),-i,-o) $(kernelsymfile)   \
  $(if $(KBUILD_EXTMOD),-I $(modulesymfile))      \
+ $(if $(iKBUILD_EXTRA_SYMBOLS), $(patsubst %, -e %,$(EXTRA_SYMBOLS))) \
  $(if $(KBUILD_EXTMOD),-o $(modulesymfile))      \
  $(if $(CONFIG_DEBUG_SECTION_MISMATCH),,-S)      \
  $(if $(CONFIG_MARKERS),-K $(kernelmarkersfile)) \