Re: [PATCH v2] x86/build: fix compiler support check for CONFIG_RETPOLINE

[Zhenzhong Duan]

On 2018/12/5 14:27, Masahiro Yamada wrote:

It is troublesome to add a diagnostic like this to the Makefile
parse stage because the top-level Makefile could be parsed with
a stale include/config/auto.conf.

Once you are hit by the error about non-retpoline compiler, the
compilation still breaks even after disabling CONFIG_RETPOLINE.

The easiest fix is to move this check to the "archprepare" like commit
829fe4aa9ac1 ("x86: Allow generating user-space headers without a
compiler") did.

Link: https://lkml.org/lkml/2018/12/4/206
Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler 
support")
Reported-by: Meelis Roos <mr...@linux.ee>
Signed-off-by: Masahiro Yamada <yamada.masah...@socionext.com>
---

Changes in v2:
   - Revive ifdef CONFIG_RETPOLINE surrounding the KBUILD_CFLAGS addition
   - Rephase the commit log a bit, hoping the cause of the issue will be clearer

  arch/x86/Makefile | 10 +++++++---
  1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index f5d7f41..75ef499 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -220,9 +220,6 @@ KBUILD_CFLAGS += -fno-asynchronous-unwind-tables

# Avoid indirect branches in kernel to deal with Spectre

  ifdef CONFIG_RETPOLINE
-ifeq ($(RETPOLINE_CFLAGS),)
-  $(error You are building kernel with non-retpoline compiler, please update 
your compiler.)
-endif
    KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)
  endif

@@ -307,6 +304,13 @@ ifndef CC_HAVE_ASM_GOTO

        @echo Compiler lacks asm-goto support.
        @exit 1
  endif
+ifdef CONFIG_RETPOLINE
+ifeq ($(RETPOLINE_CFLAGS),)
+       @echo "You are building kernel with non-retpoline compiler." >&2
+       @echo "Please update your compiler." >&2
+       @false
+endif
+endif

archclean:

        $(Q)rm -rf $(objtree)/arch/i386

Acked-by: Zhenzhong Duan <zhenzhong.d...@oracle.com>

--
Regards
Zhenzhong