[PATCH 2/8] kbuild: Support for Symbols.list creation

[Joao Moreira]

For automatic resolution of livepatch relocations, a file called
Symbols.list is used. This file maps symbols within every compiled
kernel object allowing the identification of symbols whose name is
unique, thus relocation can be automatically inferred, or providing
information that helps developers when code annotation is required for
solving the matter.

Add support for creating Symbols.list in the main Makefile. First,
ensure that built-in is compiled when CONFIG_LIVEPATCH is enabled (as
required to achieve a complete Symbols.list file). Define the command to
build Symbols.list (cmd_klp_map) and hook it in the modules rule.

As it is undesirable to have symbols from livepatch objects inside
Symbols.list, make livepatches discernible by modifying
scripts/Makefile.build to create a .livepatch file for each livepatch
in $(MODVERDIR). This file is then used by cmd_klp_map to identify and
bypass livepatches.

For identifying livepatches during the build process, a flag variable
LIVEPATCH_$(basetarget).o is considered in scripts/Makefile.build. This
way, set this flag for the livepatch sample Makefile in
samples/livepatch/Makefile.

Finally, Add a clean rule to ensure that Symbols.list is removed during
clean.

Notes:

To achieve a correct Symbols.list file, all kernel objects must be
considered, thus, its construction require these objects to be priorly
built. On the other hand, invoking scripts/Makefile.modpost without
having a complete Symbols.list in place would occasionally lead to
in-tree livepatches being post-processed incorrectly. To prevent this
from becoming a circular dependency, the construction of Symbols.list
uses non-post-processed kernel objects and such does not cause harm as
the symbols normally referenced from within livepatches are visible at
this stage. Also due to these requirements, the spot in-between modules
compilation and the invocation of scripts/Makefile.modpost was picked
for hooking cmd_klp_map.

The approach based on .livepatch files was proposed as an alternative
to using MODULE_INFO statementes. This approach was originally
proposed by Miroslav Benes as a workaround for identifying livepathces
without depending on modinfo during the modpost stage. It was moved to
this patch as the approach also shown to be useful while building
Symbols.list.

Signed-off-by: Joao Moreira <jmoreira@xxxxxxx>
---
 .gitignore                 |  1 +
 Makefile                   | 27 ++++++++++++++++++++++++---
 samples/livepatch/Makefile |  1 +
 scripts/Makefile.build     |  6 ++++++
 4 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/.gitignore b/.gitignore
index 0c39aa20b6ba..e6a67517a3bc 100644
--- a/.gitignore
+++ b/.gitignore
@@ -39,6 +39,7 @@ Module.symvers
 *.dwo
 *.su
 *.c.[012]*.*
+Symbols.list
 
 #
 # Top-level generic files
diff --git a/Makefile b/Makefile
index e40c471abe29..e1d315e585d8 100644
--- a/Makefile
+++ b/Makefile
@@ -320,10 +320,13 @@ KBUILD_BUILTIN := 1
 # If we have only "make modules", don't compile built-in objects.
 # When we're building modules with modversions, we need to consider
 # the built-in objects during the descend as well, in order to
-# make sure the checksums are up to date before we record them.
+# make sure the checksums are up to date before we record them. The
+# same applies for building livepatches, as built-in objects may hold
+# symbols which are referenced from livepatches and are required by
+# klp-convert post-processing tool for resolving these cases.
 
 ifeq ($(MAKECMDGOALS),modules)
-  KBUILD_BUILTIN := $(if $(CONFIG_MODVERSIONS),1)
+  KBUILD_BUILTIN := $(if $(or $(CONFIG_MODVERSIONS), $(CONFIG_LIVEPATCH)),1)
 endif
 
 # If we have "make <whatever> modules", compile modules
@@ -1207,9 +1210,24 @@ all: modules
 # duplicate lines in modules.order files.  Those are removed
 # using awk while concatenating to the final file.
 
+quiet_cmd_klp_map = LIVEPATCH	Symbols.list
+SLIST = $(objtree)/Symbols.list
+
+define cmd_klp_map
+	$(shell echo "*vmlinux" > $(SLIST))						\
+	$(shell nm -f posix $(objtree)/vmlinux | cut -d\  -f1 >> $(SLIST))		\
+	$(foreach m, $(wildcard $(MODVERDIR)/*.mod),					\
+		$(eval mod = $(patsubst %.ko,%.o,$(shell head -n1 $(m))))		\
+		$(if $(wildcard $(MODVERDIR)/$(shell basename -s .o $(mod)).livepatch),,\
+			$(eval fmod = $(subst $(quote),_,$(subst -,_,$(mod))))		\
+			$(shell echo "*$(shell basename -s .o $(fmod))" >> $(SLIST))	\
+			$(shell nm -f posix $(mod) | cut -d\  -f1 >> $(SLIST))))
+endef
+
 PHONY += modules
 modules: $(vmlinux-dirs) $(if $(KBUILD_BUILTIN),vmlinux) modules.builtin
 	$(Q)$(AWK) '!x[$$0]++' $(vmlinux-dirs:%=$(objtree)/%/modules.order) > $(objtree)/modules.order
+	$(if $(CONFIG_LIVEPATCH), $(call cmd,klp_map))
 	@$(kecho) '  Building modules, stage 2.';
 	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost
 	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.fwinst obj=firmware __fw_modbuild
@@ -1306,7 +1324,10 @@ vmlinuxclean:
 	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/link-vmlinux.sh clean
 	$(Q)$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) clean)
 
-clean: archclean vmlinuxclean
+klpclean:
+	$(Q) rm -f $(objtree)/Symbols.list
+
+clean: archclean vmlinuxclean klpclean
 
 # mrproper - Delete all generated files, including .config
 #
diff --git a/samples/livepatch/Makefile b/samples/livepatch/Makefile
index 10319d7ea0b1..955e7ac12d2b 100644
--- a/samples/livepatch/Makefile
+++ b/samples/livepatch/Makefile
@@ -1 +1,2 @@
+LIVEPATCH_livepatch-sample.o := y
 obj-$(CONFIG_SAMPLE_LIVEPATCH) += livepatch-sample.o
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 733e044fff8b..d0c32a50cce7 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -276,6 +276,11 @@ objtool_obj = $(if $(patsubst y%,, \
 endif # SKIP_STACK_VALIDATION
 endif # CONFIG_STACK_VALIDATION
 
+ifdef CONFIG_LIVEPATCH
+cmd_livepatch = $(if $(LIVEPATCH_$(basetarget).o),			\
+	$(shell touch $(MODVERDIR)/$(basetarget).livepatch))
+endif
+
 define rule_cc_o_c
 	$(call echo-cmd,checksrc) $(cmd_checksrc)			  \
 	$(call cmd_and_fixdep,cc_o_c)					  \
@@ -309,6 +314,7 @@ $(single-used-m): $(obj)/%.o: $(src)/%.c $(recordmcount_source) $(objtool_obj) F
 	$(call if_changed_rule,cc_o_c)
 	@{ echo $(@:.o=.ko); echo $@; \
 	   $(cmd_undef_syms); } > $(MODVERDIR)/$(@F:.o=.mod)
+	$(call cmd_livepatch)
 
 quiet_cmd_cc_lst_c = MKLST   $@
       cmd_cc_lst_c = $(CC) $(c_flags) -g -c -o $*.o $< && \
-- 
2.12.0