[PATCH v2 08/13] kbuild: build modules in the same way with/without Clang LTO

[Masahiro Yamada <masahiroy@kernel.org>]

When Clang LTO is enabled, additional intermediate files *.lto.o are
created because LLVM bitcode must be converted to ELF before modpost.

For non-LTO builds:

         $(LD)             $(LD)
  objects ---> <modname>.o -----> <modname>.ko
                             |
          <modname>.mod.o ---/

For Clang LTO builds:

         $(AR)            $(LD)                 $(LD)
  objects ---> <modname>.o ---> <modname>.lto.o -----> <modname>.ko
                                                  |
                                <modname>.mod.o --/

Since the Clang LTO introduction, Kbuild code is complicated due to
CONFIG_LTO_CLANG conditionals sprinkled everywhere.

Another confusion for Clang LTO builds is, <modname>.o is an archive
that contains LLVM bitcode files. The suffix should be .a instead of .o

To clean up the code, unify the build process of modules, as follows:

         $(AR)            $(LD)                     $(LD)
  objects ---> <modname>.a ---> <modname>.prelink.o -----> <modname>.ko
                                                      |
                                <modname>.mod.o ------/

Here, 'objects' are either ELF or LLVM bitcode. <modname>.a is an archive,
<modname>.prelink.o is ELF.

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

 scripts/Makefile.build    | 100 +++++++++++++++++---------------------
 scripts/Makefile.lib      |  11 ++---
 scripts/Makefile.modfinal |   4 +-
 scripts/Makefile.modpost  |   7 +--
 scripts/mod/modpost.c     |   6 +--
 5 files changed, 56 insertions(+), 72 deletions(-)

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 3ad1b1227371..cdc09e9080ca 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -88,9 +88,7 @@ endif
 
 targets-for-modules := $(patsubst %.o, %.mod, $(filter %.o, $(obj-m)))
 
-ifdef CONFIG_LTO_CLANG
-targets-for-modules += $(patsubst %.o, %.lto.o, $(filter %.o, $(obj-m)))
-endif
+targets-for-modules += $(patsubst %.o, %.prelink.o, $(filter %.o, $(obj-m)))
 
 ifdef need-modorder
 targets-for-modules += $(obj)/modules.order
@@ -243,9 +241,12 @@ endif # CONFIG_STACK_VALIDATION
 
 ifdef CONFIG_LTO_CLANG
 
-# Skip objtool for LLVM bitcode
+# Skip objtool LLVM bitcode
 $(obj)/%o: objtool-enabled :=
 
+# Run objtool now that we have compiled modules into native code
+$(obj)/%.prelink.o: objtool-enabled := y
+
 else
 
 # 'OBJECT_FILES_NON_STANDARD := y': skip objtool checking for a directory
@@ -255,6 +256,8 @@ else
 $(obj)/%o: objtool-enabled = $(if $(filter-out y%, \
 	$(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$(OBJECT_FILES_NON_STANDARD)n),y)
 
+$(obj)/%.prelink.o: objtool-enabled :=
+
 endif
 
 ifdef CONFIG_TRIM_UNUSED_KSYMS
@@ -287,32 +290,12 @@ $(obj)/%.o: $(src)/%.c $(recordmcount_source) FORCE
 	$(call if_changed_rule,cc_o_c)
 	$(call cmd,force_checksrc)
 
-ifdef CONFIG_LTO_CLANG
-# Module .o files may contain LLVM bitcode, compile them into native code
-# before ELF processing
-quiet_cmd_cc_lto_link_modules = LTO [M] $@
-cmd_cc_lto_link_modules =						\
-	$(LD) $(ld_flags) -r -o $@					\
-		$(shell [ -s $(@:.lto.o=.o.symversions) ] &&		\
-			echo -T $(@:.lto.o=.o.symversions))		\
-		--whole-archive $(filter-out FORCE,$^)			\
-		$(cmd_objtool)
-
-# objtool was skipped for LLVM bitcode, run it now that we have compiled
-# modules into native code
-$(obj)/%.lto.o: objtool-enabled = y
-$(obj)/%.lto.o: part-of-module := y
-
-$(obj)/%.lto.o: $(obj)/%.o FORCE
-	$(call if_changed,cc_lto_link_modules)
-endif
-
 cmd_mod = { \
 	echo $(if $($*-objs)$($*-y)$($*-m), $(addprefix $(obj)/, $($*-objs) $($*-y) $($*-m)), $(@:.mod=.o)); \
 	$(undefined_syms) echo; \
 	} > $@
 
-$(obj)/%.mod: $(obj)/%$(mod-prelink-ext).o FORCE
+$(obj)/%.mod: $(obj)/%.prelink.o FORCE
 	$(call if_changed,mod)
 
 quiet_cmd_cc_lst_c = MKLST   $@
@@ -416,17 +399,6 @@ $(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
-ifeq ($(CONFIG_LTO_CLANG) $(CONFIG_MODVERSIONS),y y)
-      cmd_update_lto_symversions =					\
-	rm -f $@.symversions						\
-	$(foreach n, $(filter-out FORCE,$^),				\
-		$(if $(shell test -s $(n).symversions && echo y),	\
-			; 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)
 #
@@ -446,10 +418,10 @@ $(obj)/built-in.a: $(real-obj-y) FORCE
 # modules.order unless contained modules are updated.
 
 cmd_modules_order = { $(foreach m, $(real-prereqs), \
-	$(if $(filter %/modules.order, $m), cat $m, echo $(patsubst %.o,%.ko,$m));) :; } \
+	$(if $(filter %/modules.order, $m), cat $m, echo $(patsubst %.a,%.ko,$m));) :; } \
 	| $(AWK) '!x[$$0]++' - > $@
 
-$(obj)/modules.order: $(obj-m) FORCE
+$(obj)/modules.order: $(modules) FORCE
 	$(call if_changed,modules_order)
 
 #
@@ -458,26 +430,44 @@ $(obj)/modules.order: $(obj-m) FORCE
 $(obj)/lib.a: $(lib-y) FORCE
 	$(call if_changed,ar)
 
-# NOTE:
-# Do not replace $(filter %.o,^) with $(real-prereqs). When a single object
-# module is turned into a multi object module, $^ will contain header file
-# dependencies recorded in the .*.cmd file.
-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
-quiet_cmd_link_multi-m = LD [M]  $@
-      cmd_link_multi-m = $(LD) $(ld_flags) -r -o $@ $(filter %.o,$^)
+#
+# Rule to prelink modules
+#
+
+ifeq ($(CONFIG_LTO_CLANG) $(CONFIG_MODVERSIONS),y y)
+
+cmd_merge_symver = $(PERL) scripts/merge-symvers.pl -a $(AR) -o $@ $<
+
+$(obj)/%.prelink.symversions: $(obj)/%.a FORCE
+	$(call if_changed,merge_symver)
+
+targets += $(patsubst %.a, %.prelink.symversions, $(modules))
+
+$(obj)/%.prelink.o: ld_flags += --script=$(filter %.symversions,$^)
+module-symver = $(obj)/%.prelink.symversions
+
 endif
 
-$(multi-obj-m): FORCE
-	$(call if_changed,link_multi-m)
-$(call multi_depend, $(multi-obj-m), .o, -objs -y -m)
+quiet_cmd_ld_o_a = LD [M]  $@
+      cmd_ld_o_a = $(LD) $(ld_flags) -r -o $@ --whole-archive $< $(cmd_objtool)
+
+$(obj)/%.prelink.o: part-of-module := y
+
+$(obj)/%.prelink.o: $(obj)/%.a $(module-symver) FORCE
+	$(call if_changed,ld_o_a)
+
+quiet_cmd_ar_module = AR [M]  $@
+      cmd_ar_module = rm -f $@; $(AR) cDPrST $@ $(real-prereqs)
+
+$(modules-single): %.a: %.o FORCE
+	$(call if_changed,ar_module)
+
+$(modules-multi): FORCE
+	$(call if_changed,ar_module)
+$(call multi_depend, $(modules-multi), .a, -objs -y -m)
+
+targets += $(modules-single) $(modules-multi)
 
-targets += $(multi-obj-m)
 targets := $(filter-out $(PHONY), $(targets))
 
 # Add intermediate targets:
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 34c4c11c4bc1..5074922db82d 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -106,6 +106,10 @@ multi-dtb-y	:= $(addprefix $(obj)/, $(multi-dtb-y))
 real-dtb-y	:= $(addprefix $(obj)/, $(real-dtb-y))
 subdir-ym	:= $(addprefix $(obj)/,$(subdir-ym))
 
+modules		:= $(patsubst %.o, %.a, $(obj-m))
+modules-multi	:= $(sort $(patsubst %.o, %.a, $(multi-obj-m)))
+modules-single	:= $(sort $(filter-out $(modules-multi), $(filter %.a, $(modules))))
+
 # Finds the multi-part object the current object will be linked into.
 # If the object belongs to two or more multi-part objects, list them all.
 modname-multi = $(sort $(foreach m,$(multi-obj-ym),\
@@ -225,13 +229,6 @@ dtc_cpp_flags  = -Wp,-MMD,$(depfile).pre.tmp -nostdinc                    \
 		 $(addprefix -I,$(DTC_INCLUDE))                          \
 		 -undef -D__DTS__
 
-ifeq ($(CONFIG_LTO_CLANG),y)
-# With CONFIG_LTO_CLANG, .o files in modules might be LLVM bitcode, so we
-# need to run LTO to compile them into native code (.lto.o) before further
-# processing.
-mod-prelink-ext := .lto
-endif
-
 # Useful for describing the dependency of composite objects
 # Usage:
 #   $(call multi_depend, multi_used_targets, suffix_to_remove, suffix_to_add)
diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
index ff805777431c..1b6401f53662 100644
--- a/scripts/Makefile.modfinal
+++ b/scripts/Makefile.modfinal
@@ -9,7 +9,7 @@ __modfinal:
 include include/config/auto.conf
 include $(srctree)/scripts/Kbuild.include
 
-# for c_flags and mod-prelink-ext
+# for c_flags
 include $(srctree)/scripts/Makefile.lib
 
 # find all modules listed in modules.order
@@ -55,7 +55,7 @@ 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: %.prelink.o %.mod.o 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/Makefile.modpost b/scripts/Makefile.modpost
index eef56d629799..11883b31c615 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -41,9 +41,6 @@ __modpost:
 include include/config/auto.conf
 include $(srctree)/scripts/Kbuild.include
 
-# for mod-prelink-ext
-include $(srctree)/scripts/Makefile.lib
-
 MODPOST = scripts/mod/modpost								\
 	$(if $(CONFIG_MODVERSIONS),-m)							\
 	$(if $(CONFIG_MODULE_SRCVERSION_ALL),-a)					\
@@ -128,9 +125,9 @@ endif
 # Read out modules.order to pass in modpost.
 # Otherwise, allmodconfig would fail with "Argument list too long".
 quiet_cmd_modpost = MODPOST $@
-      cmd_modpost = sed 's/\.ko$$/$(mod-prelink-ext)\.o/' $< | $(MODPOST) -T -
+      cmd_modpost = sed 's/ko$$/prelink.o/' $< | $(MODPOST) -T -
 
-$(output-symdump): $(MODORDER) $(input-symdump) $(modules:.ko=$(mod-prelink-ext).o) FORCE
+$(output-symdump): $(MODORDER) $(input-symdump) $(modules:ko=prelink.o) FORCE
 	$(call if_changed,modpost)
 
 targets += $(output-symdump)
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index a26139aa57fd..56cd9b7a5dd0 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -2000,9 +2000,9 @@ static void read_symbols(const char *modname)
 		/* strip trailing .o */
 		tmp = NOFAIL(strdup(modname));
 		tmp[strlen(tmp) - 2] = '\0';
-		/* strip trailing .lto */
-		if (strends(tmp, ".lto"))
-			tmp[strlen(tmp) - 4] = '\0';
+		/* strip trailing .prelink */
+		if (strends(tmp, ".prelink"))
+			tmp[strlen(tmp) - 8] = '\0';
 		mod = new_module(tmp);
 		free(tmp);
 	}
-- 
2.30.2