linux-pci.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Arnd Bergmann <arnd@kernel.org>
To: Fangrui Song <maskray@google.com>
Cc: Sami Tolvanen <samitolvanen@google.com>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Will Deacon <will@kernel.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	linux-arch <linux-arch@vger.kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	linux-pci <linux-pci@vger.kernel.org>
Subject: Re: [PATCH v8 00/16] Add support for Clang LTO
Date: Wed, 9 Dec 2020 10:19:44 +0100	[thread overview]
Message-ID: <CAK8P3a1p8yKMKXB1cUpy-5PjehJGPX0SPNEx4VsMmqgOeR6fZg@mail.gmail.com> (raw)
In-Reply-To: <20201209045554.fxlzrmxknakl2gdr@google.com>

On Wed, Dec 9, 2020 at 5:56 AM 'Fangrui Song' via Clang Built Linux
<clang-built-linux@googlegroups.com> wrote:
> On 2020-12-08, 'Sami Tolvanen' via Clang Built Linux wrote:
> >On Tue, Dec 8, 2020 at 4:15 AM Arnd Bergmann <arnd@kernel.org> wrote:
> >> So far I have
> >> not managed to get a working build out of it, the main problem so far being
> >> that it is really slow to build because the link stage only uses one CPU.
> >> These are the other issues I've seen so far:
>
> ld.lld ThinLTO uses the number of (physical cores enabled by affinity) by default.

Ah, I see.  Do you know if it's also possible to do something like
-flto=jobserver
to integrate better with the kernel build system?

I tend to run multiple builds under a top-level makefile with 'make
-j30' in order
to use 30 of the 32 threads and leave the scheduling to jobserver instead of
the kernel. If the linker itself is multithreaded but the jobserver
thinks it is a
single thread, could end up with 30 concurrent linkers each trying to use
16 cores.

> >> - CONFIG_CPU_BIG_ENDIAN doesn't seem to work with lld, and LTO
> >>   doesn't work with ld.bfd.
> >>   I've added a CPU_LITTLE_ENDIAN dependency to
> >>   ARCH_SUPPORTS_LTO_CLANG{,THIN}
> >
> >Ah, good point. I'll fix this in v9.
>
> Full/Thin LTO should work with GNU ld and gold with LLVMgold.so built from
> llvm-project (https://llvm.org/docs/GoldPlugin.html ). You'll need to make sure
> that LLVMgold.so is newer than clang. (Newer clang may introduce bitcode
> attributes which are unrecognizable by older LLVMgold.so/ld.lld)

The current patch series requires LLD:

config HAS_LTO_CLANG
       def_bool y
       depends on CC_IS_CLANG && CLANG_VERSION >= 110000 && LD_IS_LLD

Is this something we should change then, or try to keep it simple with the
current approach, leaving LTO disabled for big-endian builds and hosts without
a working lld?

       Arnd

  reply	other threads:[~2020-12-09  9:21 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-01 21:36 [PATCH v8 00/16] Add support for Clang LTO Sami Tolvanen
2020-12-01 21:36 ` [PATCH v8 01/16] tracing: move function tracer options to Kconfig Sami Tolvanen
2020-12-01 21:47   ` Steven Rostedt
2020-12-01 21:36 ` [PATCH v8 02/16] kbuild: add support for Clang LTO Sami Tolvanen
2020-12-02  2:59   ` Masahiro Yamada
2020-12-03  0:07   ` Nick Desaulniers
2020-12-01 21:36 ` [PATCH v8 03/16] kbuild: lto: fix module versioning Sami Tolvanen
2020-12-01 21:36 ` [PATCH v8 04/16] kbuild: lto: limit inlining Sami Tolvanen
2020-12-01 21:36 ` [PATCH v8 05/16] kbuild: lto: merge module sections Sami Tolvanen
2020-12-01 21:36 ` [PATCH v8 06/16] kbuild: lto: remove duplicate dependencies from .mod files Sami Tolvanen
2020-12-01 21:36 ` [PATCH v8 07/16] init: lto: ensure initcall ordering Sami Tolvanen
2020-12-01 21:36 ` [PATCH v8 08/16] init: lto: fix PREL32 relocations Sami Tolvanen
2020-12-01 21:37 ` [PATCH v8 09/16] PCI: Fix PREL32 relocations for LTO Sami Tolvanen
2020-12-01 21:37 ` [PATCH v8 10/16] modpost: lto: strip .lto from module names Sami Tolvanen
2020-12-01 21:37 ` [PATCH v8 11/16] scripts/mod: disable LTO for empty.c Sami Tolvanen
2020-12-01 21:37 ` [PATCH v8 12/16] efi/libstub: disable LTO Sami Tolvanen
2020-12-01 21:37 ` [PATCH v8 13/16] drivers/misc/lkdtm: disable LTO for rodata.o Sami Tolvanen
2020-12-01 21:37 ` [PATCH v8 14/16] arm64: vdso: disable LTO Sami Tolvanen
2020-12-01 21:37 ` [PATCH v8 15/16] arm64: disable recordmcount with DYNAMIC_FTRACE_WITH_REGS Sami Tolvanen
2020-12-01 21:37 ` [PATCH v8 16/16] arm64: allow LTO to be selected Sami Tolvanen
2020-12-03  0:01 ` [PATCH v8 00/16] Add support for Clang LTO Nick Desaulniers
2020-12-03 11:26 ` Will Deacon
2020-12-03 17:07   ` Sami Tolvanen
2020-12-03 18:21     ` Nathan Chancellor
2020-12-03 18:22     ` Will Deacon
2020-12-03 22:32       ` Nick Desaulniers
2020-12-04  9:35         ` Will Deacon
2020-12-04 22:52         ` Sami Tolvanen
2020-12-06  6:50           ` Nathan Chancellor
2020-12-06 20:09             ` Sami Tolvanen
2020-12-08  0:46               ` Nathan Chancellor
2020-12-08 12:15 ` Arnd Bergmann
2020-12-08 13:54   ` Arnd Bergmann
2020-12-08 16:53     ` Sami Tolvanen
2020-12-08 16:56       ` Arnd Bergmann
2020-12-08 16:43   ` Sami Tolvanen
     [not found]     ` <CAK8P3a1Xfpt7QLkvxjtXKcgzcWkS8g9bmxD687+rqjTafTzKrg@mail.gmail.com>
2020-12-08 21:09       ` Nick Desaulniers
2020-12-08 22:20         ` Arnd Bergmann
2020-12-09 16:11           ` Sami Tolvanen
     [not found]       ` <CAK8P3a3O65m6Us=YvCP3QA+0kqAeEqfi-DLOJa+JYmBqs8-JcA@mail.gmail.com>
2020-12-09  5:23         ` Fāng-ruì Sòng
2020-12-09  9:07           ` Arnd Bergmann
2020-12-09 16:09         ` Sami Tolvanen
2020-12-09 19:24           ` Arnd Bergmann
2020-12-09  4:55     ` Fangrui Song
2020-12-09  9:19       ` Arnd Bergmann [this message]
2020-12-09 12:35   ` Arnd Bergmann
2020-12-09 16:25     ` Sami Tolvanen
2020-12-09 17:51       ` Arnd Bergmann

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=CAK8P3a1p8yKMKXB1cUpy-5PjehJGPX0SPNEx4VsMmqgOeR6fZg@mail.gmail.com \
    --to=arnd@kernel.org \
    --cc=clang-built-linux@googlegroups.com \
    --cc=gregkh@linuxfoundation.org \
    --cc=jpoimboe@redhat.com \
    --cc=keescook@chromium.org \
    --cc=kernel-hardening@lists.openwall.com \
    --cc=linux-arch@vger.kernel.org \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kbuild@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-pci@vger.kernel.org \
    --cc=masahiroy@kernel.org \
    --cc=maskray@google.com \
    --cc=ndesaulniers@google.com \
    --cc=paulmck@kernel.org \
    --cc=peterz@infradead.org \
    --cc=rostedt@goodmis.org \
    --cc=samitolvanen@google.com \
    --cc=will@kernel.org \
    /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
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).