From: Sami Tolvanen <samitolvanen@google.com>
To: Arnd Bergmann <arnd@kernel.org>
Cc: 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: Tue, 8 Dec 2020 08:43:06 -0800 [thread overview]
Message-ID: <CABCJKueCHo2RYfx_A21m+=d1gQLR9QsOOxCsHFeicCqyHkb-Kg@mail.gmail.com> (raw)
In-Reply-To: <CAK8P3a1WEAo2SEgKUEs3SB7n7QeeHa0=cx_nO==rDK0jjDArow@mail.gmail.com>
On Tue, Dec 8, 2020 at 4:15 AM Arnd Bergmann <arnd@kernel.org> wrote:
>
> On Tue, Dec 1, 2020 at 10:37 PM 'Sami Tolvanen' via Clang Built Linux
> <clang-built-linux@googlegroups.com> wrote:
> >
> > This patch series adds support for building the kernel with Clang's
> > Link Time Optimization (LTO). In addition to performance, the primary
> > motivation for LTO is to allow Clang's Control-Flow Integrity (CFI)
> > to be used in the kernel. Google has shipped millions of Pixel
> > devices running three major kernel versions with LTO+CFI since 2018.
> >
> > Most of the patches are build system changes for handling LLVM
> > bitcode, which Clang produces with LTO instead of ELF object files,
> > postponing ELF processing until a later stage, and ensuring initcall
> > ordering.
> >
> > Note that arm64 support depends on Will's memory ordering patches
> > [1]. I will post x86_64 patches separately after we have fixed the
> > remaining objtool warnings [2][3].
> >
> > [1] https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/log/?h=for-next/lto
> > [2] https://lore.kernel.org/lkml/20201120040424.a3wctajzft4ufoiw@treble/
> > [3] https://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git/log/?h=objtool-vmlinux
> >
> > You can also pull this series from
> >
> > https://github.com/samitolvanen/linux.git lto-v8
>
> I've tried pull this into my randconfig test tree to give it a spin.
Great, thank you for testing this!
> 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:
You may want to limit your testing only to ThinLTO at first, because
full LTO is going to be extremely slow with larger configs, especially
when building arm64 kernels.
> - one build seems to take even longer to link. It's currently at 35GB RAM
> usage and 40 minutes into the final link, but I'm worried it might
> not complete
> before it runs out of memory. I only have 128GB installed, and google-chrome
> uses another 30GB of that, and I'm also doing some other builds in parallel.
> Is there a minimum recommended amount of memory for doing LTO builds?
When building arm64 defconfig, the maximum memory usage I measured
with ThinLTO was 3.5 GB, and with full LTO 20.3 GB. I haven't measured
larger configurations, but I believe LLD can easily consume 3-4x that
much with full LTO allyesconfig.
> - One build failed with
> ld.lld -EL -maarch64elf -mllvm -import-instr-limit=5 -r -o vmlinux.o
> -T .tmp_initcalls.lds --whole-archive arch/arm64/kernel/head.o
> init/built-in.a usr/built-in.a arch/arm64/built-in.a kernel/built-in.a
> certs/built-in.a mm/built-in.a fs/built-in.a ipc/built-in.a
> security/built-in.a crypto/built-in.a block/built-in.a
> arch/arm64/lib/built-in.a lib/built-in.a drivers/built-in.a
> sound/built-in.a net/built-in.a virt/built-in.a --no-whole-archive
> --start-group arch/arm64/lib/lib.a lib/lib.a
> ./drivers/firmware/efi/libstub/lib.a --end-group
> "ld.lld: error: arch/arm64/kernel/head.o: invalid symbol index"
> after about 30 minutes
That's interesting. Did you use LLVM_IAS=1?
> - 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.
[...]
> Not sure if these are all known issues. If there is one you'd like me try
> take a closer look at for finding which config options break it, I can try
No, none of these are known issues. I would be happy to take a closer
look if you can share configs that reproduce these.
Sami
next prev parent reply other threads:[~2020-12-08 16:44 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 [this message]
[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
2020-12-09 12:35 ` Arnd Bergmann
2020-12-09 16:25 ` Sami Tolvanen
2020-12-09 17:51 ` Arnd Bergmann
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