Re: [PATCH v2 08/13] kbuild: build modules in the same way with/without Clang LTO
From: Nick Desaulniers <hidden>
Date: 2021-08-31 17:46:42
Also in:
lkml
On Tue, Aug 31, 2021 at 12:40 AM Masahiro Yamada [off-list ref] wrote:
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 --/Is it worth modifying the diagram to note that objects in non-LTO builds are <objects>.o, while for LTO builds, they are <objects>.bc? If we're not using the .bc file suffix, can we?
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 ------/And here, too.
quoted hunk ↗ jump to hunk
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
I agree with Kees here; drop this comment change.
quoted hunk ↗ jump to hunk
$(obj)/%o: objtool-enabled := +# Run objtool now that we have compiled modules into native code +$(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 :=
Can we use the canonical .bc file suffix for LLVM bitcode, rather than .prelink.o?
quoted hunk ↗ jump to hunk
+ 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
-- Thanks, ~Nick Desaulniers