linux-kernel - [PATCH v2 19/26] kbuild: embed symbol versions at final link of vmlinux or modules

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Date:   Sun,  1 May 2022 17:40:25 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-kbuild@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: [PATCH v2 19/26] kbuild: embed symbol versions at final link of vmlinux or modules

Do not update objects with version CRCs while the directory descending.

Do it at the final link stage.

Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
---

(no changes since v1)

 scripts/Makefile.build    | 22 +++-------------------
 scripts/Makefile.modfinal |  3 ++-
 scripts/link-vmlinux.sh   |  4 +++-
 3 files changed, 8 insertions(+), 21 deletions(-)

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index a1023868775f..cec17b28de42 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -162,15 +162,9 @@ ifdef CONFIG_MODVERSIONS
 # o if <file>.o doesn't contain a __ksymtab version, i.e. does
 #   not export symbols, it's done.
 # o otherwise, we calculate symbol versions using the good old
-#   genksyms on the preprocessed source and postprocess them in a way
-#   that they are usable as a linker script
-# o generate .tmp_<file>.o from <file>.o using the linker to
-#   replace the unresolved symbols __crc_exported_symbol with
-#   the actual value of the checksum generated by genksyms
-# o remove .tmp_<file>.o to <file>.o
-
-# Generate .o.symversions files for each .o with exported symbols, and link these
-# to the kernel and/or modules at the end.
+#   genksyms on the preprocessed source and dump them into the .cmd file.
+# o modpost will extract versions from the .cmd file and create linker
+#   scripts used to link the kernel and/or modules.
 
 genksyms_format_rel_crc := [^_]*__crc_\([^ ]*\) = \.; LONG(\([^)]*\)).*
 genksyms_format_normal := __crc_\(.*\) = \(.*\);
@@ -188,12 +182,6 @@ gen_symversions =								\
 
 cmd_gen_symversions_c =	$(call gen_symversions,c)
 
-cmd_modversions =								\
-	if [ -r $@...mversions ]; then						\
-		$(LD) $(KBUILD_LDFLAGS) -r -o $(@D)/.tmp_$(@F) $@ 		\
-			-T $@...mversions;					\
-		mv -f $(@D)/.tmp_$(@F) $@;					\
-	fi
 endif
 
 ifdef CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT
@@ -273,7 +261,6 @@ define rule_cc_o_c
 	$(call cmd,checkdoc)
 	$(call cmd,gen_objtooldep)
 	$(call cmd,gen_symversions_c)
-	$(if $(CONFIG_LTO_CLANG),,$(call cmd,modversions))
 	$(call cmd,record_mcount)
 endef
 
@@ -282,7 +269,6 @@ define rule_as_o_S
 	$(call cmd,gen_ksymdeps)
 	$(call cmd,gen_objtooldep)
 	$(call cmd,gen_symversions_S)
-	$(call cmd,modversions)
 endef
 
 # Built-in and composite module parts
@@ -296,8 +282,6 @@ ifneq ($(CONFIG_LTO_CLANG)$(CONFIG_X86_KERNEL_IBT),)
 quiet_cmd_cc_prelink_modules = LD [M]  $@
       cmd_cc_prelink_modules =						\
 	$(LD) $(ld_flags) -r -o $@					\
-               $(shell [ -s $(@:.prelink.o=.o.symversions) ] &&		\
-                       echo -T $(@:.prelink.o=.o.symversions))		\
 		--whole-archive $(filter-out FORCE,$^)			\
 		$(cmd_objtool)
 
diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
index 7f39599e9fae..d429e3f9ae1d 100644
--- a/scripts/Makefile.modfinal
+++ b/scripts/Makefile.modfinal
@@ -34,6 +34,7 @@ quiet_cmd_ld_ko_o = LD [M]  $@
       cmd_ld_ko_o +=							\
 	$(LD) -r $(KBUILD_LDFLAGS)					\
 		$(KBUILD_LDFLAGS_MODULE) $(LDFLAGS_MODULE)		\
+		$(addprefix -T, $(filter %.symver.lds, $(real-prereqs)))\
 		-T scripts/module.lds -o $@ $(filter %.o, $^);		\
 	$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
 
@@ -56,7 +57,7 @@ if_changed_except = $(if $(call newer_prereqs_except,$(2))$(cmd-check),      \
 
 
 # Re-generate module BTFs if either module's .ko or vmlinux changed
-$(modules): %.ko: %$(mod-prelink-ext).o %.mod.o scripts/module.lds $(if $(KBUILD_BUILTIN),vmlinux) FORCE
+$(modules): %.ko: %$(mod-prelink-ext).o %.mod.o $(if $(CONFIG_MODVERSIONS), %.symver.lds) scripts/module.lds $(if $(KBUILD_BUILTIN),vmlinux) FORCE
 	+$(call if_changed_except,ld_ko_o,vmlinux)
 ifdef CONFIG_DEBUG_INFO_BTF_MODULES
 	+$(if $(newer-prereqs),$(call cmd,btf_ko))
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index eceb3ee7ec06..8da5c0182665 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -90,7 +90,6 @@ modpost_link()
 
 		if is_enabled CONFIG_MODVERSIONS; then
 			gen_symversions
-			lds="${lds} -T .tmp_symversions.lds"
 		fi
 
 		# This might take a while, so indicate that we're doing
@@ -196,6 +195,9 @@ vmlinux_link()
 	fi
 
 	ldflags="${ldflags} ${wl}--script=${objtree}/${KBUILD_LDS}"
+	if is_enabled CONFIG_MODVERSIONS; then
+		ldflags="${ldflags} ${wl}--script=vmlinux.symver.lds"
+	fi
 
 	# The kallsyms linking does not need debug symbols included.
 	if [ "$output" != "${output#.tmp_vmlinux.kallsyms}" ] ; then
-- 
2.32.0