linux-kernel - [tip:x86/urgent] x86/build: Fix compiler support check for CONFIG

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Date:   Tue, 4 Dec 2018 23:45:53 -0800
From:   tip-bot for Masahiro Yamada <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     mingo@...nel.org, tglx@...utronix.de, linux-kernel@...r.kernel.org,
        zhenzhong.duan@...cle.com, torvalds@...ux-foundation.org,
        yamada.masahiro@...ionext.com, mroos@...ux.ee,
        peterz@...radead.org, bp@...en8.de, hpa@...or.com
Subject: [tip:x86/urgent] x86/build: Fix compiler support check for
 CONFIG_RETPOLINE

Commit-ID:  10b87bc9f630a38a7f0c1e7cf13ff23fea1692ec
Gitweb:     https://git.kernel.org/tip/10b87bc9f630a38a7f0c1e7cf13ff23fea1692ec
Author:     Masahiro Yamada <yamada.masahiro@...ionext.com>
AuthorDate: Wed, 5 Dec 2018 15:27:19 +0900
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 5 Dec 2018 08:42:09 +0100

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@...ux.ee>
Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
Acked-by: Zhenzhong Duan <zhenzhong.duan@...cle.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Zhenzhong Duan <zhenzhong.duan@...cle.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@...nel.org>
---
 arch/x86/Makefile | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index f5d7f4134524..75ef499a66e2 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -220,9 +220,6 @@ KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
 
 # Avoid indirect branches in kernel to deal with Spectre
 ifdef CONFIG_RETPOLINE
-ifeq ($(RETPOLINE_CFLAGS),)
-  $(error You are building kernel with non-retpoline compiler, please update your compiler.)
-endif
   KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)
 endif
 
@@ -307,6 +304,13 @@ ifndef CC_HAVE_ASM_GOTO
 	@echo Compiler lacks asm-goto support.
 	@exit 1
 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
 
 archclean:
 	$(Q)rm -rf $(objtree)/arch/i386