From c25e1c55822f9b3b53ccbf88b85644317a525752 Mon Sep 17 00:00:00 2001 From: Masahiro Yamada Date: Fri, 27 May 2022 19:01:49 +0900 Subject: kbuild: do not create *.prelink.o for Clang LTO or IBT When CONFIG_LTO_CLANG=y, additional intermediate *.prelink.o is created for each module. Also, objtool is postponed until LLVM IR is converted to ELF. CONFIG_X86_KERNEL_IBT works in a similar way to postpone objtool until objects are merged together. This commit stops generating *.prelink.o, so the build flow will look similar with/without LTO. The following figures show how the LTO build currently works, and how this commit is changing it. Current build flow ================== [1] single-object module $(LD) $(CC) +objtool $(LD) foo.c --------------------> foo.o -----> foo.prelink.o -----> foo.ko (LLVM IR) (ELF) | (ELF) | foo.mod.o --/ (LLVM IR) [2] multi-object module $(LD) $(CC) $(AR) +objtool $(LD) foo1.c -----> foo1.o -----> foo.o -----> foo.prelink.o -----> foo.ko | (archive) (ELF) | (ELF) foo2.c -----> foo2.o --/ | (LLVM IR) foo.mod.o --/ (LLVM IR) One confusion is that foo.o in multi-object module is an archive despite of its suffix. New build flow ============== [1] single-object module Since there is only one object, there is no need to keep the LLVM IR. Use $(CC)+$(LD) to generate an ELF object in one build rule. When LTO is disabled, $(LD) is unneeded because $(CC) produces an ELF object. $(CC)+$(LD)+objtool $(LD) foo.c ----------------------------> foo.o ---------> foo.ko (ELF) | (ELF) | foo.mod.o --/ (LLVM IR) [2] multi-object module Previously, $(AR) was used to combine LLVM IR files into an archive, but there was no technical reason to do so. Use $(LD) to merge them into a single ELF object. $(LD) $(CC) +objtool $(LD) foo1.c ---------> foo1.o ---------> foo.o ---------> foo.ko | (ELF) | (ELF) foo2.c ---------> foo2.o ----/ | (LLVM IR) foo.mod.o --/ (LLVM IR) Signed-off-by: Masahiro Yamada Reviewed-by: Nicolas Schier Tested-by: Nathan Chancellor Reviewed-by: Sami Tolvanen Tested-by: Sedat Dilek # LLVM-14 (x86-64) Acked-by: Josh Poimboeuf --- scripts/Makefile.modpost | 9 ++------- 1 file changed, 2 insertions(+), 7 deletions(-) (limited to 'scripts/Makefile.modpost') diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost index 8b343480813d..911606496341 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) \ @@ -117,8 +114,6 @@ $(input-symdump): @echo >&2 ' Modules may not have dependencies or modversions.' @echo >&2 ' You may get many unresolved symbol warnings.' -modules := $(sort $(shell cat $(MODORDER))) - # KBUILD_MODPOST_WARN can be set to avoid error out in case of undefined symbols ifneq ($(KBUILD_MODPOST_WARN)$(filter-out $(existing-input-symdump), $(input-symdump)),) MODPOST += -w @@ -127,9 +122,9 @@ 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$$/$(mod-prelink-ext)\.o/' $< | $(MODPOST) -T - + cmd_modpost = sed 's/ko$$/o/' $< | $(MODPOST) -T - -$(output-symdump): $(MODORDER) $(input-symdump) $(modules:.ko=$(mod-prelink-ext).o) FORCE +$(output-symdump): $(MODORDER) $(input-symdump) FORCE $(call if_changed,modpost) targets += $(output-symdump) -- cgit v1.2.3