linux-kernel - [PATCH 22/22] x86, build: allow LTO

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Message-Id: <20200624203200.78870-23-samitolvanen@google.com>
Date:   Wed, 24 Jun 2020 13:32:00 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>,
        Will Deacon <will@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com,
        kernel-hardening@...ts.openwall.com, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        x86@...nel.org, Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH 22/22] x86, build: allow LTO_CLANG and THINLTO to be selected

Allow CONFIG_LTO_CLANG and CONFIG_THINLTO to be enabled.

Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
---
 arch/x86/Kconfig  | 2 ++
 arch/x86/Makefile | 5 +++++
 2 files changed, 7 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 6a0cc524882d..df335b1f9c31 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -92,6 +92,8 @@ config X86
 	select ARCH_SUPPORTS_ACPI
 	select ARCH_SUPPORTS_ATOMIC_RMW
 	select ARCH_SUPPORTS_NUMA_BALANCING	if X86_64
+	select ARCH_SUPPORTS_LTO_CLANG		if X86_64
+	select ARCH_SUPPORTS_THINLTO		if X86_64
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_QUEUED_RWLOCKS
 	select ARCH_USE_QUEUED_SPINLOCKS
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 00e378de8bc0..a1abc1e081ad 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -188,6 +188,11 @@ ifdef CONFIG_X86_64
 KBUILD_LDFLAGS += $(call ld-option, -z max-page-size=0x200000)
 endif
 
+ifdef CONFIG_LTO_CLANG
+KBUILD_LDFLAGS	+= -plugin-opt=-code-model=kernel \
+		   -plugin-opt=-stack-alignment=$(if $(CONFIG_X86_32),4,8)
+endif
+
 # Workaround for a gcc prelease that unfortunately was shipped in a suse release
 KBUILD_CFLAGS += -Wno-sign-compare
 #
-- 
2.27.0.212.ge8ba1cc988-goog