Commit 38e89184 authored by Sami Tolvanen's avatar Sami Tolvanen Committed by Kees Cook
Browse files

kbuild: lto: fix module versioning 



With CONFIG_MODVERSIONS, version information is linked into each
compilation unit that exports symbols. With LTO, we cannot use this
method as all C code is compiled into LLVM bitcode instead. This
change collects symbol versions into .symversions files and merges
them in link-vmlinux.sh where they are all linked into vmlinux.o at
the same time.

Signed-off-by: default avatarSami Tolvanen <samitolvanen@google.com>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20201211184633.3213045-4-samitolvanen@google.com
parent dc5723b0

.gitignore

+1 −0
Original line number Diff line number Diff line
@@ -41,6 +41,7 @@ 
*.so.dbg

*.su

*.symtypes

*.symversions

*.tab.[ch]

*.tar

*.xz

Makefile

+2 −1
Original line number Diff line number Diff line
@@ -1837,7 +1837,8 @@ clean: $(clean-dirs) 
		-o -name '.tmp_*.o.*' \

		-o -name '*.c.[012]*.*' \

		-o -name '*.ll' \

		-o -name '*.gcno' \) -type f -print | xargs rm -f

		-o -name '*.gcno' \

		-o -name '*.*.symversions' \) -type f -print | xargs rm -f



# Generate tags for editors

# ---------------------------------------------------------------------------

arch/Kconfig

+0 −1
Original line number Diff line number Diff line
@@ -668,7 +668,6 @@ config HAS_LTO_CLANG 
	depends on !FTRACE_MCOUNT_USE_RECORDMCOUNT

	depends on !KASAN

	depends on !GCOV_KERNEL

	depends on !MODVERSIONS

	help

	  The compiler and Kconfig options support building with Clang's

	  LTO.

scripts/Makefile.build

+31 −2
Original line number Diff line number Diff line
@@ -166,6 +166,15 @@ ifdef CONFIG_MODVERSIONS 
#   the actual value of the checksum generated by genksyms

# o remove .tmp_<file>.o to <file>.o



ifdef CONFIG_LTO_CLANG

# Generate .o.symversions files for each .o with exported symbols, and link these

# to the kernel and/or modules at the end.

cmd_modversions_c =								\

	if $(NM) $@ 2>/dev/null | grep -q __ksymtab; then			\

		$(call cmd_gensymtypes_c,$(KBUILD_SYMTYPES),$(@:.o=.symtypes))	\

		    > $@.symversions;						\

	fi;

else

cmd_modversions_c =								\

	if $(OBJDUMP) -h $@ | grep -q __ksymtab; then				\

		$(call cmd_gensymtypes_c,$(KBUILD_SYMTYPES),$(@:.o=.symtypes))	\
@@ -177,6 +186,7 @@ cmd_modversions_c = \ 
		rm -f $(@D)/.tmp_$(@F:.o=.ver);					\

	fi

endif

endif



ifdef CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT

# compiler will not generate __mcount_loc use recordmcount or recordmcount.pl
@@ -386,6 +396,18 @@ $(obj)/%.asn1.c $(obj)/%.asn1.h: $(src)/%.asn1 $(objtree)/scripts/asn1_compiler 
$(subdir-builtin): $(obj)/%/built-in.a: $(obj)/% ;

$(subdir-modorder): $(obj)/%/modules.order: $(obj)/% ;



# combine symversions for later processing

quiet_cmd_update_lto_symversions = SYMVER  $@

ifeq ($(CONFIG_LTO_CLANG) $(CONFIG_MODVERSIONS),y y)

      cmd_update_lto_symversions =					\

	rm -f $@.symversions						\

	$(foreach n, $(filter-out FORCE,$^),				\

		$(if $(wildcard $(n).symversions),			\

			; cat $(n).symversions >> $@.symversions))

else

      cmd_update_lto_symversions = echo >/dev/null

endif



#

# Rule to compile a set of .o files into one .a file (without symbol table)

#
@@ -393,8 +415,11 @@ $(subdir-modorder): $(obj)/%/modules.order: $(obj)/% ; 
quiet_cmd_ar_builtin = AR      $@

      cmd_ar_builtin = rm -f $@; $(AR) cDPrST $@ $(real-prereqs)



quiet_cmd_ar_and_symver = AR      $@

      cmd_ar_and_symver = $(cmd_update_lto_symversions); $(cmd_ar_builtin)



$(obj)/built-in.a: $(real-obj-y) FORCE

	$(call if_changed,ar_builtin)

	$(call if_changed,ar_and_symver)



#

# Rule to create modules.order file
@@ -414,8 +439,11 @@ $(obj)/modules.order: $(obj-m) FORCE 
#

# Rule to compile a set of .o files into one .a file (with symbol table)

#

quiet_cmd_ar_lib = AR      $@

      cmd_ar_lib = $(cmd_update_lto_symversions); $(cmd_ar)



$(obj)/lib.a: $(lib-y) FORCE

	$(call if_changed,ar)

	$(call if_changed,ar_lib)



# NOTE:

# Do not replace $(filter %.o,^) with $(real-prereqs). When a single object
@@ -424,6 +452,7 @@ $(obj)/lib.a: $(lib-y) FORCE 
ifdef CONFIG_LTO_CLANG

quiet_cmd_link_multi-m = AR [M]  $@

cmd_link_multi-m =						\

	$(cmd_update_lto_symversions);				\

	rm -f $@; 						\

	$(AR) cDPrsT $@ $(filter %.o,$^)

else

scripts/Makefile.modpost

+5 −1
Original line number Diff line number Diff line
@@ -111,7 +111,11 @@ ifdef CONFIG_LTO_CLANG 
prelink-ext := .lto



quiet_cmd_cc_lto_link_modules = LTO [M] $@

cmd_cc_lto_link_modules = $(LD) $(ld_flags) -r -o $@ --whole-archive $^

cmd_cc_lto_link_modules =						\

	$(LD) $(ld_flags) -r -o $@					\

		$(shell [ -s $(@:.lto.o=.o.symversions) ] &&		\

			echo -T $(@:.lto.o=.o.symversions))		\

		--whole-archive $^



%.lto.o: %.o

	$(call if_changed,cc_lto_link_modules)