linux-kernel - [PATCH v2] x86/boot: define CC_HAVE_ASM

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Date:   Thu, 27 Sep 2018 13:47:58 -0700
From:   ndesaulniers@...gle.com
To:     bp@...en8.de, mingo@...hat.com, tglx@...utronix.de
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Kees Cook <keescook@...omium.org>,
        Cao jin <caoj.fnst@...fujitsu.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2] x86/boot: define CC_HAVE_ASM_GOTO

Early prototypes of Clang with asm goto support produce 6 instances of
the following warning:

In file included from arch/x86/boot/compressed/misc.h:20:
In file included from ./include/linux/elf.h:5:
In file included from ./arch/x86/include/asm/elf.h:8:
In file included from ./include/linux/thread_info.h:38:
In file included from ./arch/x86/include/asm/thread_info.h:53:
./arch/x86/include/asm/cpufeature.h:150:2: warning: "Compiler lacks
ASM_GOTO support. Add -D __BPF_TRACING__ to your compiler arguments"
[-W#warnings]
your compiler arguments"
 ^

Since 6 files under arch/x86/boot/compressed/ include
arch/x86/boot/compressed/misc.h AND
arch/x86/boot/compressed/Makefile happens to redefine KBUILD_CFLAGS,
which set these variables in the top level MAKEFILE.

Suggested-by: Borislav Petkov <bp@...e.de>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
v1 -> v2:
  Updated commit message to provide more context as per Borislav.

 arch/x86/boot/compressed/Makefile | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index 28764dacf018..158c0b4e178a 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -56,6 +56,13 @@ KBUILD_LDFLAGS += $(shell $(LD) --help 2>&1 | grep -q "\-z noreloc-overflow" \
 endif
 LDFLAGS_vmlinux := -T

+# check for 'asm goto'
+ifeq ($(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-goto.sh $(CC) $(KBUILD_CFLAGS)), y)
+  CC_HAVE_ASM_GOTO := 1
+  KBUILD_CFLAGS += -DCC_HAVE_ASM_GOTO
+  KBUILD_AFLAGS += -DCC_HAVE_ASM_GOTO
+endif
+
 hostprogs-y	:= mkpiggy
 HOST_EXTRACFLAGS += -I$(srctree)/tools/include

-- 
2.19.0.605.g01d371f741-goog