[DTrace-devel] [PATCH 1/5] kbuild: add modules.builtin.objs

Mon Oct 30 22:05:28 UTC 2023

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 at kernel.org>
Signed-off-by: Nick Alcock <nick.alcock at oracle.com>
Reviewed-by: Nick Alcock <nick.alcock at oracle.com>
---
 .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 9fd4c9533b3d..59baf691631b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -68,7 +68,7 @@ modules.order
 /System.map
 /Module.markers
 /modules.builtin
-/modules.builtin.modinfo
+/modules.builtin.*
 /modules.nsdeps
 
 #
diff --git a/Documentation/dontdiff b/Documentation/dontdiff
index 3c399f132e2d..75b9655e5791 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 bd906407e307..15d1b61d9454 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 fc83c079c471..a893f1500003 100644
--- a/Makefile
+++ b/Makefile
@@ -1230,7 +1230,11 @@ 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
@@ -1583,7 +1587,7 @@ ifdef CONFIG_MODULES
 	@sed 's:^\(.*\)\.o$$:kernel/\1.ko:' modules.order > $(MODLIB)/modules.order
 endif
 	@cp -f modules.builtin $(MODLIB)/
-	@cp -f $(objtree)/modules.builtin.modinfo $(MODLIB)/
+	@cp -f $(objtree)/modules.builtin.* $(MODLIB)/
 
 ###
 # Cleaning is done on three levels.
@@ -1594,7 +1598,7 @@ endif
 
 # 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-project.json .vmlinux.objs .vmlinux.export.c
 
diff --git a/include/linux/module.h b/include/linux/module.h
index a98e188cf37b..53323e94b96e 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 68d0134bdbf9..40803f8faa5e 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.
 # ---------------------------------------------------------------------------
 
-- 
2.39.2


