[PATCH 4.14] x86/retpolines: Fix up backport of a9d57ef15cbe

[PATCH 4.14] x86/retpolines: Fix up backport of a9d57ef15cbe

[Nathan Chancellor]

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@gmail.com>
---
 arch/x86/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index cd596ca60901..3dc54d2f79c4 100644
--- 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
-- 
2.23.0

Re: [PATCH 4.14] x86/retpolines: Fix up backport of a9d57ef15cbe

[Greg Kroah-Hartman]

On Sun, Sep 29, 2019 at 11:32:06AM -0700, Nathan Chancellor wrote:
> 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@gmail.com>
> ---
>  arch/x86/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Now queued up, thanks!

greg k-h