commit e501ce957a786ecd076ea0cfb10b114e6e4d0f40
author Peter Zijlstra <peterz@infradead.org> Wed Jan 17 11:42:07 2018 +0100
committer Thomas Gleixner <tglx@linutronix.de> Tue Mar 20 10:58:02 2018 +0100
tree 93beb08eb9a78f81c80866baf25f7472df35b955
parent edc39c9b4589a4ce9a69273b5a27a1459c3423d4

x86: Force asm-goto

We want to start using asm-goto to guarantee the absence of dynamic
branches (and thus speculation).

A primary prerequisite for this is of course that the compiler
supports asm-goto. This effecively lifts the minimum GCC version to
build an x86 kernel to gcc-4.5.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: torvalds@linux-foundation.org
Link: https://lkml.kernel.org/r/20180319201327.GJ4043@hirez.programming.kicks-ass.net

arch/x86/Makefile

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 498c1b8..d798e36 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -181,6 +181,10 @@
   endif
 endif
 
+ifndef CC_HAVE_ASM_GOTO
+  $(error Compiler lacks asm-goto support.)
+endif
+
 #
 # Jump labels need '-maccumulate-outgoing-args' for gcc < 4.5.2 to prevent a
 # GCC bug (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=46226).  There's no way