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From: Arnd Bergmann <arnd@kernel.org>
To: Sami Tolvanen <samitolvanen@google.com>
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: Wed, 9 Dec 2020 18:51:34 +0100	[thread overview]
Message-ID: <CAK8P3a04nQwJkK-CPWNzvfKavZnHQYzKX5OGB7Rm3Ee_62oXhA@mail.gmail.com> (raw)
In-Reply-To: <CABCJKud7ZC7_rXVmrF5PnDOMZTJX9iB7uYAa03YF-dkEojnBxg@mail.gmail.com>

On Wed, Dec 9, 2020 at 5:25 PM 'Sami Tolvanen' via Clang Built Linux
<clang-built-linux@googlegroups.com> wrote:
>
> On Wed, Dec 9, 2020 at 4:36 AM Arnd Bergmann <arnd@kernel.org> wrote:
> >
> > On Tue, Dec 8, 2020 at 1:15 PM Arnd Bergmann <arnd@kernel.org> wrote:
> >
> >
> > It seems to happen because of CONFIG_TRIM_UNUSED_KSYMS,
> > which is a shame, since I think that is an option we'd always want to
> > have enabled with LTO, to allow more dead code to be eliminated.
>
> Ah yes, this is a known issue. We use TRIM_UNUSED_KSYMS with LTO in
> Android's Generic Kernel Image and the problem is that bitcode doesn't
> yet contain calls to these functions, so autoksyms won't see them. The
> solution is to use a symbol whitelist with LTO to prevent these from
> being trimmed. I suspect we would need a default whitelist for LTO
> builds.

A built-in allowlist sounds good to me. FWIW, in the randconfigs so far, I only
saw five symbols that would need to be on it:

memcpy(), memmove(), memset(), __stack_chk_fail() and __stack_chk_guard

       Arnd

      reply	other threads:[~2020-12-09 17:53 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
2020-12-09 12:35   ` Arnd Bergmann
2020-12-09 16:25     ` Sami Tolvanen
2020-12-09 17:51       ` Arnd Bergmann [this message]

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