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/Kbuild.include | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'scripts/Kbuild.include') diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include index 3514c2149e9d..455a0a6ce12d 100644 --- a/scripts/Kbuild.include +++ b/scripts/Kbuild.include @@ -15,6 +15,10 @@ pound := \# # Name of target with a '.' as filename prefix. foo/bar.o => foo/.bar.o dot-target = $(dir $@).$(notdir $@) +### +# Name of target with a '.tmp_' as filename prefix. foo/bar.o => foo/.tmp_bar.o +tmp-target = $(dir $@).tmp_$(notdir $@) + ### # The temporary file to save gcc -MMD generated dependencies must not # contain a comma -- cgit v1.2.3 From ebd191b38c5ea177318543a08e544cf2f7df944d Mon Sep 17 00:00:00 2001 From: Masahiro Yamada Date: Fri, 27 May 2022 19:01:54 +0900 Subject: kbuild: add cmd_and_savecmd macro Separate out the command execution part of if_changed, as we did for if_changed_dep. This allows us to reuse it in if_changed_rule. define rule_foo $(call cmd_and_savecmd,foo) $(call cmd,bar) endef Signed-off-by: Masahiro Yamada Reviewed-by: Kees Cook Tested-by: Nathan Chancellor Reviewed-by: Nicolas Schier Tested-by: Sedat Dilek # LLVM-14 (x86-64) --- scripts/Kbuild.include | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) (limited to 'scripts/Kbuild.include') diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include index 455a0a6ce12d..ece44b735061 100644 --- a/scripts/Kbuild.include +++ b/scripts/Kbuild.include @@ -142,9 +142,11 @@ check-FORCE = $(if $(filter FORCE, $^),,$(warning FORCE prerequisite is missing) if-changed-cond = $(newer-prereqs)$(cmd-check)$(check-FORCE) # Execute command if command has changed or prerequisite(s) are updated. -if_changed = $(if $(if-changed-cond), \ +if_changed = $(if $(if-changed-cond),$(cmd_and_savecmd),@:) + +cmd_and_savecmd = \ $(cmd); \ - printf '%s\n' 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd, @:) + printf '%s\n' 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd # Execute the command and also postprocess generated .d dependencies file. if_changed_dep = $(if $(if-changed-cond),$(cmd_and_fixdep),@:) -- cgit v1.2.3