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Date:   Fri, 20 Nov 2020 16:08:43 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Masahiro Yamada <masahiroy@kernel.org>
Cc:     Nathan Chancellor <natechancellor@gmail.com>,
        Michal Marek <michal.lkml@markovi.net>,
        Russell King <linux@armlinux.org.uk>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, Nick Desaulniers <ndesaulniers@google.com>,
        Arvind Sankar <nivedita@alum.mit.edu>,
        linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linuxppc-dev@lists.ozlabs.org, clang-built-linux@googlegroups.com
Subject: Re: [PATCH v2 1/2] kbuild: Hoist '--orphan-handling' into Kconfig
Message-ID: <202011201607.75FA476@keescook>
References: <20201113195553.1487659-1-natechancellor@gmail.com>
 <20201119204656.3261686-1-natechancellor@gmail.com>
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On Thu, Nov 19, 2020 at 01:46:56PM -0700, Nathan Chancellor wrote:
> Currently, '--orphan-handling=warn' is spread out across four different
> architectures in their respective Makefiles, which makes it a little
> unruly to deal with in case it needs to be disabled for a specific
> linker version (in this case, ld.lld 10.0.1).
> 
> To make it easier to control this, hoist this warning into Kconfig and
> the main Makefile so that disabling it is simpler, as the warning will
> only be enabled in a couple places (main Makefile and a couple of
> compressed boot folders that blow away LDFLAGS_vmlinx) and making it
> conditional is easier due to Kconfig syntax. One small additional
> benefit of this is saving a call to ld-option on incremental builds
> because we will have already evaluated it for CONFIG_LD_ORPHAN_WARN.
> 
> To keep the list of supported architectures the same, introduce
> CONFIG_ARCH_WANT_LD_ORPHAN_WARN, which an architecture can select to
> gain this automatically after all of the sections are specified and size
> asserted. A special thanks to Kees Cook for the help text on this
> config.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/1187
> Acked-by: Kees Cook <keescook@chromium.org>
> Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> Tested-by: Nick Desaulniers <ndesaulniers@google.com>
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>

Masahiro, do you want to take these to get them to Linus for v5.10? I
can send them if you'd prefer.

-Kees

-- 
Kees Cook