linux-kernel - [PATCH 4.14 149/185] x86/retpolines: Fix up backport of a9d57ef15cbe

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Message-Id: <20191003154512.704851856@linuxfoundation.org>
Date:   Thu,  3 Oct 2019 17:53:47 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "stable@...r.kernel.org, x86@...nel.org,
        clang-built-linux@...glegroups.com, Nathan Chancellor" 
        <natechancellor@...il.com>,
        Nathan Chancellor <natechancellor@...il.com>
Subject: [PATCH 4.14 149/185] x86/retpolines: Fix up backport of a9d57ef15cbe

From: Nathan Chancellor <natechancellor@...il.com>

Commit a9d57ef15cbe ("x86/retpolines: Disable switch jump tables when
retpolines are enabled") added -fno-jump-tables to workaround a GCC issue
while deliberately avoiding adding this flag when CONFIG_CC_IS_CLANG is
set, which is defined by the kconfig system when CC=clang is provided.

However, this symbol was added in 4.18 in commit 469cb7376c06 ("kconfig:
add CC_IS_CLANG and CLANG_VERSION") so it is always undefined in 4.14,
meaning -fno-jump-tables gets added when using Clang.

Fix this up by using the equivalent $(cc-name) comparison, which matches
what upstream did until commit 076f421da5d4 ("kbuild: replace cc-name
test with CONFIG_CC_IS_CLANG").

Fixes: e28951100515 ("x86/retpolines: Disable switch jump tables when retpolines are enabled")
Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/Makefile |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -249,7 +249,7 @@ ifdef CONFIG_RETPOLINE
   # 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
+  ifneq ($(cc-name), clang)
     KBUILD_CFLAGS += $(call cc-option,-fno-jump-tables)
   endif
 endif