[PATCH v2 1/6] kbuild: add modules.builtin.objs

[Kris Van Hees]

From: Luis Chamberlain <mcgrof@xxxxxxxxxx>

The file modules.builtin names all modules that are built into the
kernel; this is checked by modprobe to not fail when trying to load
something built-in. But for tools which want to see which object files
make up each module, 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 object files included in this module, store it
in a new objs= modinfo stanza, then extract it just before linking into
a new file modules.builtin.objs with a layout roughly modelled on a
makefile:

path/to/module.o: path/to/constituent.o path/to/other-constituent.o

Single-file built-in modules get a line reading

path/to/module.o:

Note that the .modinfo section is discarded at the link stage, so the
kernel is not bloated at all (see include/asm-generic/vmlinux.lds.h).

Orabug: 29891866
Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Signed-off-by: Nick Alcock <nick.alcock@xxxxxxxxxx>
Reviewed-by: Nick Alcock <nick.alcock@xxxxxxxxxx>
Reviewed-by: Kris Van Hees <kris.van.hees@xxxxxxxxxx>
---
Changes since v1:
 - None
---
 .gitignore                      |  2 +-
 Documentation/dontdiff          |  2 +-
 Documentation/kbuild/kbuild.rst |  5 +++++
 Makefile                        |  8 ++++++--
 include/linux/module.h          |  4 +++-
 scripts/Makefile.lib            |  5 ++++-
 scripts/Makefile.modinst        |  6 +++---
 scripts/Makefile.vmlinux_o      | 15 ++++++++++++++-
 8 files changed, 37 insertions(+), 10 deletions(-)

diff --git a/.gitignore b/.gitignore
index c59dc60ba62ef..62ede8565a2aa 100644
--- a/.gitignore
+++ b/.gitignore
@@ -69,7 +69,7 @@ modules.order
 /System.map
 /Module.markers
 /modules.builtin
-/modules.builtin.modinfo
+/modules.builtin.*
 /modules.nsdeps
 
 #
diff --git a/Documentation/dontdiff b/Documentation/dontdiff
index 3c399f132e2db..75b9655e57914 100644
--- a/Documentation/dontdiff
+++ b/Documentation/dontdiff
@@ -179,7 +179,7 @@ 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 9c8d1d046ea56..79e104ffee715 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 d51d411d44a82..cc979f9874f5a 100644
--- a/Makefile
+++ b/Makefile
@@ -1140,7 +1140,11 @@ 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
@@ -1476,7 +1480,7 @@ endif # CONFIG_MODULES
 
 # Directories & files removed with 'make clean'
 CLEAN_FILES += 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-project.json .vmlinux.objs .vmlinux.export.c
 
diff --git a/include/linux/module.h b/include/linux/module.h
index 1153b0d99a808..cbfff06e00cd6 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -180,7 +180,9 @@ 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 3179747cbd2cc..3b3baa78d4fbd 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -118,6 +118,8 @@ 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
@@ -131,7 +133,8 @@ 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.modinst b/scripts/Makefile.modinst
index 0afd75472679f..b45586aa1de49 100644
--- a/scripts/Makefile.modinst
+++ b/scripts/Makefile.modinst
@@ -30,10 +30,10 @@ $(MODLIB)/modules.order: modules.order FORCE
 quiet_cmd_install_modorder = INSTALL $@
       cmd_install_modorder = sed 's:^\(.*\)\.o$$:kernel/\1.ko:' $< > $@
 
-# Install modules.builtin(.modinfo) even when CONFIG_MODULES is disabled.
-install-y += $(addprefix $(MODLIB)/, modules.builtin modules.builtin.modinfo)
+# Install modules.builtin(.modinfo,.objs) even when CONFIG_MODULES is disabled.
+install-y += $(addprefix $(MODLIB)/, modules.builtin modules.builtin.modinfo modules.builtin.objs)
 
-$(addprefix $(MODLIB)/, modules.builtin modules.builtin.modinfo): $(MODLIB)/%: % FORCE
+$(addprefix $(MODLIB)/, modules.builtin modules.builtin.modinfo modules.builtin.objs): $(MODLIB)/%: % FORCE
 	$(call cmd,install)
 
 endif
diff --git a/scripts/Makefile.vmlinux_o b/scripts/Makefile.vmlinux_o
index 6de297916ce68..508b3294e2cf1 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
@@ -87,6 +87,19 @@ 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.
 # ---------------------------------------------------------------------------
 
-- 
2.43.0