x86/build: Add -Wnoaddress-of-packed-member to REALMODE_CFLAGS, to silence GCC9 build...

[mirror_ubuntu-bionic-kernel.git] / arch / x86 / Makefile

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index fad55160dcb94a28e60d537d3d69d471a1e10e2e..cd596ca6090107f5e565e1cc4a2d4738835c0ec3 100644 (file)
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -39,6 +39,7 @@ REALMODE_CFLAGS       := $(M16_CFLAGS) -g -Os -D__KERNEL__ \
 
 REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -ffreestanding)
 REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -fno-stack-protector)
+REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -Wno-address-of-packed-member)
 REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), $(cc_stack_align4))
 export REALMODE_CFLAGS
 
@@ -48,7 +49,7 @@ export REALMODE_CFLAGS
 export BITS
 
 ifdef CONFIG_X86_NEED_RELOCS
-        LDFLAGS_vmlinux := --emit-relocs
+        LDFLAGS_vmlinux := --emit-relocs --discard-none
 endif
 
 #
@@ -223,6 +224,15 @@ KBUILD_CFLAGS += $(cfi) $(cfi-sigframe) $(cfi-sections) $(asinstr) $(avx_instr)
 
 LDFLAGS := -m elf_$(UTS_MACHINE)
 
+#
+# The 64-bit kernel must be aligned to 2MB.  Pass -z max-page-size=0x200000 to
+# the linker to force 2MB page size regardless of the default page size used
+# by the linker.
+#
+ifdef CONFIG_X86_64
+LDFLAGS += $(call ld-option, -z max-page-size=0x200000)
+endif
+
 # Speed up the build
 KBUILD_CFLAGS += -pipe
 # Workaround for a gcc prelease that unfortunately was shipped in a suse release
@@ -232,10 +242,16 @@ KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
 
 # Avoid indirect branches in kernel to deal with Spectre
 ifdef CONFIG_RETPOLINE
-    RETPOLINE_CFLAGS += $(call cc-option,-mindirect-branch=thunk-extern -mindirect-branch-register)
-    ifneq ($(RETPOLINE_CFLAGS),)
-        KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) -DRETPOLINE
-    endif
+  KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)
+  # Additionally, avoid generating expensive indirect jumps which
+  # are subject to retpolines for small number of switch cases.
+  # clang turns off jump table generation by default when under
+  # retpoline builds, however, gcc does not for x86. This has
+  # only been fixed starting from gcc stable version 8.4.0 and
+  # onwards, but not for older ones. See gcc bug #86952.
+  ifndef CONFIG_CC_IS_CLANG
+    KBUILD_CFLAGS += $(call cc-option,-fno-jump-tables)
+  endif
 endif
 
 archscripts: scripts_basic
@@ -251,6 +267,13 @@ archprepare:
 ifeq ($(CONFIG_KEXEC_FILE),y)
        $(Q)$(MAKE) $(build)=arch/x86/purgatory arch/x86/purgatory/kexec-purgatory.c
 endif
+ifdef CONFIG_RETPOLINE
+ifeq ($(RETPOLINE_CFLAGS),)
+       @echo "You are building kernel with non-retpoline compiler." >&2
+       @echo "Please update your compiler." >&2
+       @false
+endif
+endif
 
 ###
 # Kernel objects