linux-kernel - [PATCH 4.19 44/44] x86/build: Fix compiler support check for CONFIG

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Date:   Tue, 18 Dec 2018 17:39:56 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Meelis Roos <mroos@...ux.ee>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Zhenzhong Duan <zhenzhong.duan@...cle.com>,
        Borislav Petkov <bp@...en8.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Sasha Levin <sashal@...nel.org>,
        Gi-Oh Kim <gi-oh.kim@...ud.ionos.com>
Subject: [PATCH 4.19 44/44] x86/build: Fix compiler support check for CONFIG_RETPOLINE

4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Masahiro Yamada <yamada.masahiro@...ionext.com>

commit 25896d073d8a0403b07e6dec56f58e6c33678207 upstream.

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>
Tested-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>
Signed-off-by: Sasha Levin <sashal@...nel.org>
Cc: Gi-Oh Kim <gi-oh.kim@...ud.ionos.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/Makefile |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -223,9 +223,6 @@ KBUILD_CFLAGS += -fno-asynchronous-unwin
 
 # 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
 
@@ -303,6 +300,13 @@ 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