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c25e1c5582
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 <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # LLVM-14 (x86-64)
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
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|---|---|---|
| .. | ||
| atomic | ||
| basic | ||
| clang-tools | ||
| coccinelle | ||
| dtc | ||
| dummy-tools | ||
| gcc-plugins | ||
| gdb | ||
| genksyms | ||
| kconfig | ||
| ksymoops | ||
| mod | ||
| package | ||
| selinux | ||
| tracing | ||
| .gitignore | ||
| adjust_autoksyms.sh | ||
| as-version.sh | ||
| asn1_compiler.c | ||
| bin2c.c | ||
| bloat-o-meter | ||
| bootgraph.pl | ||
| bpf_doc.py | ||
| cc-can-link.sh | ||
| cc-version.sh | ||
| check-blacklist-hashes.awk | ||
| check-sysctl-docs | ||
| check_extable.sh | ||
| checkdeclares.pl | ||
| checkincludes.pl | ||
| checkkconfigsymbols.py | ||
| checkpatch.pl | ||
| checkstack.pl | ||
| checksyscalls.sh | ||
| checkversion.pl | ||
| cleanfile | ||
| cleanpatch | ||
| coccicheck | ||
| config | ||
| const_structs.checkpatch | ||
| decode_stacktrace.sh | ||
| decodecode | ||
| depmod.sh | ||
| dev-needs.sh | ||
| diffconfig | ||
| documentation-file-ref-check | ||
| export_report.pl | ||
| extract-ikconfig | ||
| extract-module-sig.pl | ||
| extract-sys-certs.pl | ||
| extract-vmlinux | ||
| extract_xc3028.pl | ||
| faddr2line | ||
| file-size.sh | ||
| find-unused-docs.sh | ||
| gcc-goto.sh | ||
| gcc-ld | ||
| gcc-x86_32-has-stack-protector.sh | ||
| gcc-x86_64-has-stack-protector.sh | ||
| gen-randstruct-seed.sh | ||
| gen_autoksyms.sh | ||
| gen_ksymdeps.sh | ||
| generate_initcall_order.pl | ||
| get_abi.pl | ||
| get_dvb_firmware | ||
| get_feat.pl | ||
| get_maintainer.pl | ||
| gfp-translate | ||
| headerdep.pl | ||
| headers_install.sh | ||
| insert-sys-cert.c | ||
| install.sh | ||
| jobserver-exec | ||
| kallsyms.c | ||
| Kbuild.include | ||
| Kconfig.include | ||
| kernel-doc | ||
| ld-version.sh | ||
| leaking_addresses.pl | ||
| Lindent | ||
| link-vmlinux.sh | ||
| Makefile | ||
| Makefile.asm-generic | ||
| Makefile.build | ||
| Makefile.clang | ||
| Makefile.clean | ||
| Makefile.compiler | ||
| Makefile.debug | ||
| Makefile.dtbinst | ||
| Makefile.extrawarn | ||
| Makefile.gcc-plugins | ||
| Makefile.headersinst | ||
| Makefile.host | ||
| Makefile.kasan | ||
| Makefile.kcov | ||
| Makefile.kcsan | ||
| Makefile.lib | ||
| Makefile.modfinal | ||
| Makefile.modinst | ||
| Makefile.modpost | ||
| Makefile.package | ||
| Makefile.randstruct | ||
| Makefile.ubsan | ||
| Makefile.userprogs | ||
| Makefile.vmlinux | ||
| makelst | ||
| markup_oops.pl | ||
| min-tool-version.sh | ||
| mkcompile_h | ||
| mksysmap | ||
| mkuboot.sh | ||
| module.lds.S | ||
| modules-check.sh | ||
| nsdeps | ||
| objdiff | ||
| objdump-func | ||
| pahole-flags.sh | ||
| pahole-version.sh | ||
| parse-maintainers.pl | ||
| patch-kernel | ||
| profile2linkerlist.pl | ||
| prune-kernel | ||
| recordmcount.c | ||
| recordmcount.h | ||
| recordmcount.pl | ||
| remove-stale-files | ||
| setlocalversion | ||
| show_delta | ||
| sign-file.c | ||
| sorttable.c | ||
| sorttable.h | ||
| spdxcheck-test.sh | ||
| spdxcheck.py | ||
| spelling.txt | ||
| sphinx-pre-install | ||
| split-man.pl | ||
| stackdelta | ||
| stackusage | ||
| subarch.include | ||
| syscallhdr.sh | ||
| syscallnr.sh | ||
| syscalltbl.sh | ||
| tags.sh | ||
| test_fortify.sh | ||
| tools-support-relr.sh | ||
| unifdef.c | ||
| ver_linux | ||
| xen-hypercalls.sh | ||
| xz_wrap.sh | ||