linux-kernel - [PATCH 11/13] kbuild: always postpone CRC links for module versioning

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Date:   Thu, 19 Aug 2021 09:57:42 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-kbuild@...r.kernel.org
Cc:     Sami Tolvanen <samitolvanen@...gle.com>,
        linux-kernel@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com
Subject: [PATCH 11/13] kbuild: always postpone CRC links for module versioning

When CONFIG_MODVERSIONS=y, the CRCs of EXPORT_SYMBOL are linked into
*.o files in-place.

It is impossible for Clang LTO because *.o files are not ELF, but LLVM
bitcode. The CRCs are stored in separate *.symversions files, and then
supplied to the modpost link.

Let's do so for CONFIG_LTO_CLANG=n is possible, and unify the module
versioning code.

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

 scripts/Makefile.build  | 32 ++++++--------------------------
 scripts/link-vmlinux.sh | 22 ++++++++++++++--------
 2 files changed, 20 insertions(+), 34 deletions(-)

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 957addea830b..874e84a1f3fc 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -158,17 +158,12 @@ quiet_cmd_cc_o_c = CC $(quiet_modtag)  $@
 ifdef CONFIG_MODVERSIONS
 # When module versioning is enabled the following steps are executed:
 # o compile a <file>.o from <file>.c
-# o if <file>.o doesn't contain a __ksymtab version, i.e. does
-#   not export symbols, it's done.
+# o if <file>.o doesn't contain __ksymtab* symbols, i.e. does
+#   not export symbols, create an empty *.symversions
 # 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
 
-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 =								\
@@ -178,18 +173,6 @@ cmd_modversions_c =								\
 	else									\
 		rm -f $@...mversions;						\
 	fi;
-else
-cmd_modversions_c =								\
-	if $(OBJDUMP) -h $@ | grep -q __ksymtab; then				\
-		$(call cmd_gensymtypes_c,$(KBUILD_SYMTYPES),$(@:.o=.symtypes))	\
-		    > $(@D)/.tmp_$(@F:.o=.ver);					\
-										\
-		$(LD) $(KBUILD_LDFLAGS) -r -o $(@D)/.tmp_$(@F) $@ 		\
-			-T $(@D)/.tmp_$(@F:.o=.ver);				\
-		mv -f $(@D)/.tmp_$(@F) $@;					\
-		rm -f $(@D)/.tmp_$(@F:.o=.ver);					\
-	fi
-endif
 endif
 
 ifdef CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT
@@ -348,12 +331,9 @@ ifdef CONFIG_ASM_MODVERSIONS
 cmd_modversions_S =								\
 	if $(OBJDUMP) -h $@ | grep -q __ksymtab; then				\
 		$(call cmd_gensymtypes_S,$(KBUILD_SYMTYPES),$(@:.o=.symtypes))	\
-		    > $(@D)/.tmp_$(@F:.o=.ver);					\
-										\
-		$(LD) $(KBUILD_LDFLAGS) -r -o $(@D)/.tmp_$(@F) $@ 		\
-			-T $(@D)/.tmp_$(@F:.o=.ver);				\
-		mv -f $(@D)/.tmp_$(@F) $@;					\
-		rm -f $(@D)/.tmp_$(@F:.o=.ver);					\
+		    > $@...mversions;						\
+	else									\
+		rm -rf $@...mversions;						\
 	fi
 endif
 
@@ -424,7 +404,7 @@ $(obj)/lib.a: $(lib-y) FORCE
 # Rule to prelink modules
 #
 
-ifeq ($(CONFIG_LTO_CLANG) $(CONFIG_MODVERSIONS),y y)
+ifdef CONFIG_MODVERSIONS
 
 cmd_merge_symver =					\
 	rm -f $@;					\
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 17976609c2d8..66ced6ff8e65 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -59,8 +59,7 @@ append_symversion()
 	fi
 }
 
-# If CONFIG_LTO_CLANG is selected, collect generated symbol versions into
-# .tmp_symversions.lds
+# Collect generated symbol versions into .tmp_symversions.lds
 gen_symversions()
 {
 	info GEN .tmp_symversions.lds
@@ -94,14 +93,13 @@ modpost_link()
 		${KBUILD_VMLINUX_LIBS}				\
 		--end-group"
 
+	if [ -n "${CONFIG_MODVERSIONS}" ]; then
+		lds="${lds} -T .tmp_symversions.lds"
+	fi
+
 	if [ -n "${CONFIG_LTO_CLANG}" ]; then
 		gen_initcalls
-		lds="-T .tmp_initcalls.lds"
-
-		if [ -n "${CONFIG_MODVERSIONS}" ]; then
-			gen_symversions
-			lds="${lds} -T .tmp_symversions.lds"
-		fi
+		lds="${lds} -T .tmp_initcalls.lds"
 
 		# This might take a while, so indicate that we're doing
 		# an LTO link
@@ -198,6 +196,10 @@ vmlinux_link()
 
 	ldflags="${ldflags} ${wl}--script=${objtree}/${KBUILD_LDS}"
 
+	if [ -n "${CONFIG_MODVERSIONS}" ]; then
+		ldflags="${ldflags} ${wl}--script=.tmp_symversions.lds"
+	fi
+
 	# The kallsyms linking does not need debug symbols included.
 	if [ "$output" != "${output#.tmp_vmlinux.kallsyms}" ] ; then
 		ldflags="${ldflags} ${wl}--strip-debug"
@@ -351,6 +353,10 @@ fi;
 # final build of init/
 ${MAKE} -f "${srctree}/scripts/Makefile.build" obj=init need-builtin=1
 
+if [ -n "${CONFIG_MODVERSIONS}" ]; then
+	gen_symversions
+fi
+
 #link vmlinux.o
 modpost_link vmlinux.o
 objtool_link vmlinux.o
-- 
2.30.2