kernel-hardening - Re: [PATCH 02/22] kbuild: add support for Clang LTO

Follow @Openwall on Twitter for new release announcements and other news

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200624212902.GA26253@google.com>
Date: Wed, 24 Jun 2020 14:29:02 -0700
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Masahiro Yamada <masahiroy@...nel.org>, Will Deacon <will@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Kees Cook <keescook@...omium.org>,
	clang-built-linux <clang-built-linux@...glegroups.com>,
	Kernel Hardening <kernel-hardening@...ts.openwall.com>,
	linux-arch <linux-arch@...r.kernel.org>,
	Linux ARM <linux-arm-kernel@...ts.infradead.org>,
	Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-pci@...r.kernel.org,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>
Subject: Re: [PATCH 02/22] kbuild: add support for Clang LTO

On Wed, Jun 24, 2020 at 01:53:52PM -0700, Nick Desaulniers wrote:
> On Wed, Jun 24, 2020 at 1:32 PM Sami Tolvanen <samitolvanen@...gle.com> wrote:
> >
> > diff --git a/Makefile b/Makefile
> > index ac2c61c37a73..0c7fe6fb2143 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -886,6 +886,22 @@ KBUILD_CFLAGS      += $(CC_FLAGS_SCS)
> >  export CC_FLAGS_SCS
> >  endif
> >
> > +ifdef CONFIG_LTO_CLANG
> > +ifdef CONFIG_THINLTO
> > +CC_FLAGS_LTO_CLANG := -flto=thin $(call cc-option, -fsplit-lto-unit)
> 
> The kconfig change gates this on clang-11; do we still need the
> cc-option check here, or can we hardcode the use of -fsplit-lto-unit?
> Playing with the flag in godbolt, it looks like clang-8 had support
> for this flag.

True, we don't need cc-option here anymore. I'll remove it, thanks.

> > +KBUILD_LDFLAGS += --thinlto-cache-dir=.thinlto-cache
> 
> It might be nice to have `make distclean` or even `make clean` scrub
> the .thinlto-cache?  Also, I verified that the `.gitignore` rule for
> `.*` properly ignores this dir.

Sure, distclean sounds appropriate to me.

Sami

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.