x86, build: allow LTO to be selected

Pass code model and stack alignment to the linker as these are not
stored in LLVM bitcode, and allow CONFIG_LTO_CLANG* to be enabled.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 9cd9bd6..c15d16f 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -95,6 +95,8 @@ config X86
        select ARCH_SUPPORTS_DEBUG_PAGEALLOC
        select ARCH_SUPPORTS_NUMA_BALANCING     if X86_64
        select ARCH_SUPPORTS_KMAP_LOCAL_FORCE_MAP       if NR_CPUS <= 4096
+       select ARCH_SUPPORTS_LTO_CLANG          if X86_64
+       select ARCH_SUPPORTS_LTO_CLANG_THIN     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 7116da3..845baf5 100644 (file)
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -166,6 +166,11 @@ ifeq ($(ACCUMULATE_OUTGOING_ARGS), 1)
        KBUILD_CFLAGS += $(call cc-option,-maccumulate-outgoing-args,)
 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
 #