x86/boot: Restrict header scope to make Clang happy

The inclusion of <linux/kernel.h> was causing issue as the definition of
__arch_hweight64 from arch/x86/include/asm/arch_hweight.h eventually gets
included. The definition is problematic when compiled with -m16 (all code
in arch/x86/boot/ is) as the "D" inline assembly constraint is rejected
by both compilers when passed an argument of type long long (regardless
of signedness, anything smaller is fine).

Because GCC performs inlining before semantic analysis, and
__arch_hweight64 is dead in this translation unit, GCC does not report
any issues at compile time.  Clang does the semantic analysis in the
front end, before inlining (run in the middle) can determine the code is
dead. I consider this another case of PR33587, which I think we can do
more work to solve.

It turns out that arch/x86/boot/string.c doesn't actually need
linux/kernel.h, simply linux/limits.h and linux/compiler.h.

Suggested-by: Stephen Rothwell <[email protected]>
Signed-off-by: Nick Desaulniers <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Tested-by: Nathan Chancellor <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: "H. Peter Anvin" <[email protected]>
Cc: Chao Fan <[email protected]>
Cc: Uros Bizjak <[email protected]>
Link: https://bugs.llvm.org/show_bug.cgi?id=33587
Link: https://github.com/ClangBuiltLinux/linux/issues/347
Link: https://lkml.kernel.org/r/[email protected]

1 files changed, 2 insertions, 1 deletions

diff --git a/arch/x86/boot/string.c b/arch/x86/boot/string.c
index 315a67b8896b..90154df8f125 100644
--- a/arch/x86/boot/string.c
+++ b/arch/x86/boot/string.c
@@ -13,8 +13,9 @@
  */
 
 #include <linux/types.h>
-#include <linux/kernel.h>
+#include <linux/compiler.h>
 #include <linux/errno.h>
+#include <linux/limits.h>
 #include <asm/asm.h>
 #include "ctype.h"
 #include "string.h"