x86/build: Fix compiler support check for CONFIG_RETPOLINE

It is troublesome to add a diagnostic like this to the Makefile
parse stage because the top-level Makefile could be parsed with
a stale include/config/auto.conf.

Once you are hit by the error about non-retpoline compiler, the
compilation still breaks even after disabling CONFIG_RETPOLINE.

The easiest fix is to move this check to the "archprepare" like
this commit did:

  829fe4aa9ac1 ("x86: Allow generating user-space headers without a compiler")

Reported-by: Meelis Roos <mroos@linux.ee>
Tested-by: Meelis Roos <mroos@linux.ee>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")
Link: http://lkml.kernel.org/r/1543991239-18476-1-git-send-email-yamada.masahiro@socionext.com
Link: https://lkml.org/lkml/2018/12/4/206
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 25896d073d8a0403b07e6dec56f58e6c33678207)

Orabug: 29211617

Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>
Conflicts:
	arch/x86/Makefile
The archprepare rule is different in UEK and upstream makefiles

Signed-off-by: Brian Maly <brian.maly@oracle.com>

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index dfc305b91e2a45226155eb7c2b5e5455c1a5abb9..a53d1f150bea1ad6527fa5e3ba08c92a4b1b5fae 100644 (file)
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -174,9 +174,6 @@ KBUILD_AFLAGS += $(mflags-y)
 # Avoid indirect branches in kernel to deal with Spectre
 ifdef CONFIG_RETPOLINE
     RETPOLINE_CFLAGS += $(call cc-option,-mindirect-branch=thunk-extern -mindirect-branch-register)
-    ifeq ($(RETPOLINE_CFLAGS),)
-        $(error You are building kernel with non-retpoline compiler, please update your compiler.)
-    endif
     KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)
 endif
 
@@ -193,6 +190,13 @@ 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