All of lore.kernel.org
 help / color / mirror / Atom feed
From: Sami Tolvanen <samitolvanen@google.com>
To: Masahiro Yamada <masahiroy@kernel.org>
Cc: linux-kbuild <linux-kbuild@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Nicolas Schier <nicolas@fjasle.eu>,
	Peter Zijlstra <peterz@infradead.org>,
	linux-modules@vger.kernel.org, linux-s390@vger.kernel.org,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	Ard Biesheuvel <ardb@kernel.org>
Subject: Re: [PATCH v4 09/14] kbuild: do not create *.prelink.o for Clang LTO or IBT
Date: Mon, 9 May 2022 16:13:11 -0700	[thread overview]
Message-ID: <CABCJKudnbTS=_2WgX63xb_3oCwt_6jwotqfoV5wSjkmfjuUJZQ@mail.gmail.com> (raw)
In-Reply-To: <20220508190631.2386038-10-masahiroy@kernel.org>

On Sun, May 8, 2022 at 12:10 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> When CONFIG_LTO_CLANG=y, additional intermediate *.prelink.o is created
> for each module. Also, objtool is postponed until LLVM bitcode 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
> the same 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 bitcode)        (ELF)       |
>                                                              |
>                                                  foo.mod.o --/
>
>  [2] multi-object module
>                                       $(LD)
>            $(CC)         $(AR)       +objtool               $(LD)
>     foo1.c -----> foo1.o -----> foo.o -----> foo.prelink.o -----> foo.ko
>                            |  (archive)          (ELF)       |
>     foo2.c -----> foo2.o --/                                 |
>                 (LLVM bitcode)                   foo.mod.o --/
>
>   One confusion is 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, we do not need to have the LLVM
>   bitcode stage. 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)    |
>                                              |
>                                  foo.mod.o --/
>
>  [2] multi-object module
>
>   Previously, $(AR) was used to combine LLVM bitcode into an archive,
>   but there was no technical reason to do so.
>   This commit just uses $(LD) to combine and convert them into a single
>   ELF object.
>
>                             $(LD)
>             $(CC)          +objtool        $(LD)
>     foo1.c -------> foo1.o -------> foo.o -------> foo.ko
>                               |     (ELF)    |
>     foo2.c -------> foo2.o ---/              |
>                 (LLVM bitcode)   foo.mod.o --/
>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
> Tested-by: Nathan Chancellor <nathan@kernel.org>

Looks good, thanks for cleaning this up!

Reviewed-by: Sami Tolvanen <samitolvanen@google.com>

Sami

WARNING: multiple messages have this Message-ID
From: Sami Tolvanen <samitolvanen@google.com>
To: Masahiro Yamada <masahiroy@kernel.org>
Cc: linux-s390@vger.kernel.org, Nicolas Schier <nicolas@fjasle.eu>,
	linux-kbuild <linux-kbuild@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Nathan Chancellor <nathan@kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	Ard Biesheuvel <ardb@kernel.org>,
	linux-modules@vger.kernel.org
Subject: Re: [PATCH v4 09/14] kbuild: do not create *.prelink.o for Clang LTO or IBT
Date: Mon, 9 May 2022 16:13:11 -0700	[thread overview]
Message-ID: <CABCJKudnbTS=_2WgX63xb_3oCwt_6jwotqfoV5wSjkmfjuUJZQ@mail.gmail.com> (raw)
In-Reply-To: <20220508190631.2386038-10-masahiroy@kernel.org>

On Sun, May 8, 2022 at 12:10 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> When CONFIG_LTO_CLANG=y, additional intermediate *.prelink.o is created
> for each module. Also, objtool is postponed until LLVM bitcode 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
> the same 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 bitcode)        (ELF)       |
>                                                              |
>                                                  foo.mod.o --/
>
>  [2] multi-object module
>                                       $(LD)
>            $(CC)         $(AR)       +objtool               $(LD)
>     foo1.c -----> foo1.o -----> foo.o -----> foo.prelink.o -----> foo.ko
>                            |  (archive)          (ELF)       |
>     foo2.c -----> foo2.o --/                                 |
>                 (LLVM bitcode)                   foo.mod.o --/
>
>   One confusion is 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, we do not need to have the LLVM
>   bitcode stage. 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)    |
>                                              |
>                                  foo.mod.o --/
>
>  [2] multi-object module
>
>   Previously, $(AR) was used to combine LLVM bitcode into an archive,
>   but there was no technical reason to do so.
>   This commit just uses $(LD) to combine and convert them into a single
>   ELF object.
>
>                             $(LD)
>             $(CC)          +objtool        $(LD)
>     foo1.c -------> foo1.o -------> foo.o -------> foo.ko
>                               |     (ELF)    |
>     foo2.c -------> foo2.o ---/              |
>                 (LLVM bitcode)   foo.mod.o --/
>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
> Tested-by: Nathan Chancellor <nathan@kernel.org>

Looks good, thanks for cleaning this up!

Reviewed-by: Sami Tolvanen <samitolvanen@google.com>

Sami

  reply	other threads:[~2022-05-09 23:13 UTC|newest]

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-08 19:06 [PATCH v4 00/14] kbuild: yet another series of cleanups (modpost, LTO, MODULE_REL_CRCS, export.h) Masahiro Yamada
2022-05-08 19:06 ` Masahiro Yamada
2022-05-08 19:06 ` [PATCH v4 01/14] modpost: remove left-over cross_compile declaration Masahiro Yamada
2022-05-08 19:06   ` Masahiro Yamada
2022-05-09 17:08   ` Nick Desaulniers
2022-05-09 17:08     ` Nick Desaulniers
2022-05-12  4:35   ` Masahiro Yamada
2022-05-12  4:35     ` Masahiro Yamada
2022-05-08 19:06 ` [PATCH v4 02/14] modpost: change the license of EXPORT_SYMBOL to bool type Masahiro Yamada
2022-05-08 19:06   ` Masahiro Yamada
2022-05-12  4:36   ` Masahiro Yamada
2022-05-12  4:36     ` Masahiro Yamada
2022-05-08 19:06 ` [PATCH v4 03/14] modpost: split the section mismatch checks into section-check.c Masahiro Yamada
2022-05-08 19:06   ` Masahiro Yamada
2022-05-09 17:19   ` Nick Desaulniers
2022-05-09 17:19     ` Nick Desaulniers
2022-05-10  6:55     ` Masahiro Yamada
2022-05-10  6:55       ` Masahiro Yamada
2022-05-11 18:47       ` Nick Desaulniers
2022-05-11 18:47         ` Nick Desaulniers
2022-05-11 19:27         ` Masahiro Yamada
2022-05-11 19:27           ` Masahiro Yamada
2022-05-11 19:51           ` Jeff Johnson
2022-05-11 19:51             ` Jeff Johnson
2022-05-11 20:01             ` Nick Desaulniers
2022-05-11 20:01               ` Nick Desaulniers
2022-05-08 19:06 ` [PATCH v4 04/14] modpost: add sym_find_with_module() helper Masahiro Yamada
2022-05-08 19:06   ` Masahiro Yamada
2022-05-08 19:06 ` [PATCH v4 05/14] modpost: extract symbol versions from *.cmd files Masahiro Yamada
2022-05-08 19:06   ` Masahiro Yamada
2022-05-09 21:52   ` Sami Tolvanen
2022-05-09 21:52     ` Sami Tolvanen
2022-05-08 19:06 ` [PATCH v4 06/14] kbuild: link symbol CRCs at final link, removing CONFIG_MODULE_REL_CRCS Masahiro Yamada
2022-05-08 19:06   ` Masahiro Yamada
2022-05-09 17:50   ` Nick Desaulniers
2022-05-09 17:50     ` Nick Desaulniers
2022-05-10 13:03     ` Masahiro Yamada
2022-05-10 13:03       ` Masahiro Yamada
2022-05-08 19:06 ` [PATCH v4 07/14] kbuild: stop merging *.symversions Masahiro Yamada
2022-05-08 19:06   ` Masahiro Yamada
2022-05-08 19:06 ` [PATCH v4 08/14] genksyms: adjust the output format to modpost Masahiro Yamada
2022-05-08 19:06   ` Masahiro Yamada
2022-05-08 19:06 ` [PATCH v4 09/14] kbuild: do not create *.prelink.o for Clang LTO or IBT Masahiro Yamada
2022-05-08 19:06   ` Masahiro Yamada
2022-05-09 23:13   ` Sami Tolvanen [this message]
2022-05-09 23:13     ` Sami Tolvanen
2022-05-08 19:06 ` [PATCH v4 10/14] kbuild: check static EXPORT_SYMBOL* by script instead of modpost Masahiro Yamada
2022-05-08 19:06   ` Masahiro Yamada
2022-05-09 18:05   ` Nick Desaulniers
2022-05-09 18:05     ` Nick Desaulniers
2022-05-10 13:53     ` Masahiro Yamada
2022-05-10 13:53       ` Masahiro Yamada
2022-05-08 19:06 ` [PATCH v4 11/14] kbuild: make built-in.a rule robust against too long argument error Masahiro Yamada
2022-05-08 19:06   ` Masahiro Yamada
2022-05-08 19:06 ` [PATCH v4 12/14] kbuild: make *.mod " Masahiro Yamada
2022-05-08 19:06   ` Masahiro Yamada
2022-05-08 19:06 ` [PATCH v4 13/14] kbuild: add cmd_and_savecmd macro Masahiro Yamada
2022-05-08 19:06   ` Masahiro Yamada
2022-05-08 19:06 ` [PATCH v4 14/14] kbuild: rebuild multi-object modules when objtool is updated Masahiro Yamada
2022-05-08 19:06   ` Masahiro Yamada
2022-05-09  4:24 ` [PATCH v4 00/14] kbuild: yet another series of cleanups (modpost, LTO, MODULE_REL_CRCS, export.h) Masahiro Yamada
2022-05-09  4:24   ` Masahiro Yamada
2022-05-09 22:13   ` Nathan Chancellor
2022-05-09 22:13     ` Nathan Chancellor
2022-05-10  6:55     ` Masahiro Yamada
2022-05-10  6:55       ` Masahiro Yamada
2022-05-09 22:19   ` Nathan Chancellor
2022-05-09 22:19     ` Nathan Chancellor

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CABCJKudnbTS=_2WgX63xb_3oCwt_6jwotqfoV5wSjkmfjuUJZQ@mail.gmail.com' \
    --to=samitolvanen@google.com \
    --cc=ardb@kernel.org \
    --cc=clang-built-linux@googlegroups.com \
    --cc=linux-kbuild@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-modules@vger.kernel.org \
    --cc=linux-s390@vger.kernel.org \
    --cc=linuxppc-dev@lists.ozlabs.org \
    --cc=masahiroy@kernel.org \
    --cc=nathan@kernel.org \
    --cc=ndesaulniers@google.com \
    --cc=nicolas@fjasle.eu \
    --cc=peterz@infradead.org \
    --subject='Re: [PATCH v4 09/14] kbuild: do not create *.prelink.o for Clang LTO or IBT' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.