[PATCH] kbuild: add modules.builtin.objs

[Luis Chamberlain]

The file modules.builtin contains all modules that are built into
the kernel and this is used by modprobe to not fail when trying to
load something builtin. But for tools which want to see which object
files come from what modules we want to help them with such a mapping
as it is not easy to get this otherwise.

We do this by just extending scripts/Makefile.lib with a new variable
and define to capture all possible objects, and stuff this into a new
modinfo.

Note that this doesn't bloat the kernel as all because as you can see
in include/asm-generic/vmlinux.lds.h, the .modinfo section is discarded
at the link stage.

Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
---
 .gitignore                      |  2 +-
 Documentation/dontdiff          |  2 +-
 Documentation/kbuild/kbuild.rst |  5 +++++
 Makefile                        | 10 +++++++---
 include/linux/module.h          |  4 +++-
 scripts/Makefile.lib            |  5 ++++-
 scripts/Makefile.vmlinux_o      | 15 ++++++++++++++-
 7 files changed, 35 insertions(+), 8 deletions(-)

diff --git a/.gitignore b/.gitignore
index 5da004814678..ef8665c64f21 100644
--- a/.gitignore
+++ b/.gitignore
@@ -67,7 +67,7 @@ modules.order
 /System.map
 /Module.markers
 /modules.builtin
-/modules.builtin.modinfo
+/modules.builtin.*
 /modules.nsdeps
 
 #
diff --git a/Documentation/dontdiff b/Documentation/dontdiff
index 352ff53a2306..ed1fbc711f33 100644
--- a/Documentation/dontdiff
+++ b/Documentation/dontdiff
@@ -180,7 +180,7 @@ mkutf8data
 modpost
 modules-only.symvers
 modules.builtin
-modules.builtin.modinfo
+modules.builtin.*
 modules.nsdeps
 modules.order
 modversions.h*
diff --git a/Documentation/kbuild/kbuild.rst b/Documentation/kbuild/kbuild.rst
index 08f575e6236c..504f31517cb4 100644
--- a/Documentation/kbuild/kbuild.rst
+++ b/Documentation/kbuild/kbuild.rst
@@ -17,6 +17,11 @@ modules.builtin
 This file lists all modules that are built into the kernel. This is used
 by modprobe to not fail when trying to load something builtin.
 
+modules.builtin.objs
+-----------------------
+This file contains object mapping of modules that are built into the kernel
+to their corresponding object files used to build the module.
+
 modules.builtin.modinfo
 -----------------------
 This file contains modinfo from all modules that are built into the kernel.
diff --git a/Makefile b/Makefile
index d148a55bfd0f..cd563d9713c9 100644
--- a/Makefile
+++ b/Makefile
@@ -1228,7 +1228,11 @@ PHONY += vmlinux_o
 vmlinux_o: vmlinux.a $(KBUILD_VMLINUX_LIBS)
 	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.vmlinux_o
 
-vmlinux.o modules.builtin.modinfo modules.builtin: vmlinux_o
+MODULES_BUILTIN := modules.builtin.modinfo
+MODULES_BUILTIN += modules.builtin
+MODULES_BUILTIN += modules.builtin.objs
+
+vmlinux.o $(MODULES_BUILTIN): vmlinux_o
 	@:
 
 PHONY += vmlinux
@@ -1558,7 +1562,7 @@ __modinst_pre:
 	fi
 	@sed 's:^:kernel/:' modules.order > $(MODLIB)/modules.order
 	@cp -f modules.builtin $(MODLIB)/
-	@cp -f $(objtree)/modules.builtin.modinfo $(MODLIB)/
+	@cp -f $(objtree)/modules.builtin.* $(MODLIB)/
 
 endif # CONFIG_MODULES
 
@@ -1571,7 +1575,7 @@ endif # CONFIG_MODULES
 
 # Directories & files removed with 'make clean'
 CLEAN_FILES += include/ksym vmlinux.symvers modules-only.symvers \
-	       modules.builtin modules.builtin.modinfo modules.nsdeps \
+	       modules.builtin modules.builtin.* modules.nsdeps \
 	       compile_commands.json .thinlto-cache rust/test rust/doc \
 	       .vmlinux.objs .vmlinux.export.c
 
diff --git a/include/linux/module.h b/include/linux/module.h
index ec61fb53979a..ce044cffd43d 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -179,7 +179,9 @@ extern void cleanup_module(void);
 #ifdef MODULE
 #define MODULE_FILE
 #else
-#define MODULE_FILE	MODULE_INFO(file, KBUILD_MODFILE);
+#define MODULE_FILE					                      \
+			MODULE_INFO(file, KBUILD_MODFILE);                    \
+			MODULE_INFO(objs, KBUILD_MODOBJS);
 #endif
 
 /*
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 3aa384cec76b..f7e5a83572fa 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -112,6 +112,8 @@ modname-multi = $(sort $(foreach m,$(multi-obj-ym),\
 __modname = $(or $(modname-multi),$(basetarget))
 
 modname = $(subst $(space),:,$(__modname))
+modname-objs = $($(modname)-objs) $($(modname)-y) $($(modname)-Y)
+modname-objs-prefixed = $(sort $(strip $(addprefix $(obj)/, $(modname-objs))))
 modfile = $(addprefix $(obj)/,$(__modname))
 
 # target with $(obj)/ and its suffix stripped
@@ -125,7 +127,8 @@ name-fix = $(call stringify,$(call name-fix-token,$1))
 basename_flags = -DKBUILD_BASENAME=$(call name-fix,$(basetarget))
 modname_flags  = -DKBUILD_MODNAME=$(call name-fix,$(modname)) \
 		 -D__KBUILD_MODNAME=kmod_$(call name-fix-token,$(modname))
-modfile_flags  = -DKBUILD_MODFILE=$(call stringify,$(modfile))
+modfile_flags  = -DKBUILD_MODFILE=$(call stringify,$(modfile)) \
+                 -DKBUILD_MODOBJS=$(call stringify,$(modfile).o:$(subst $(space),|,$(modname-objs-prefixed)))
 
 _c_flags       = $(filter-out $(CFLAGS_REMOVE_$(target-stem).o), \
                      $(filter-out $(ccflags-remove-y), \
diff --git a/scripts/Makefile.vmlinux_o b/scripts/Makefile.vmlinux_o
index 0edfdb40364b..9b4ca83f0695 100644
--- a/scripts/Makefile.vmlinux_o
+++ b/scripts/Makefile.vmlinux_o
@@ -1,7 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 
 PHONY := __default
-__default: vmlinux.o modules.builtin.modinfo modules.builtin
+__default: vmlinux.o modules.builtin.modinfo modules.builtin modules.builtin.objs
 
 include include/config/auto.conf
 include $(srctree)/scripts/Kbuild.include
@@ -86,6 +86,19 @@ targets += modules.builtin
 modules.builtin: modules.builtin.modinfo FORCE
 	$(call if_changed,modules_builtin)
 
+# module.builtin.objs
+# ---------------------------------------------------------------------------
+quiet_cmd_modules_builtin_objs = GEN     $@
+      cmd_modules_builtin_objs = \
+	tr '\0' '\n' < $< | \
+	sed -n 's/^[[:alnum:]:_]*\.objs=//p' | \
+	tr ' ' '\n' | uniq | sed -e 's|:|: |' -e 's:|: :g' | \
+	tr -s ' ' > $@
+
+targets += modules.builtin.objs
+modules.builtin.objs: modules.builtin.modinfo FORCE
+	$(call if_changed,modules_builtin_objs)
+
 # Add FORCE to the prequisites of a target to force it to be always rebuilt.
 # ---------------------------------------------------------------------------
 
-- 
2.35.1