Re: 5.4 and 4.19 warning fix for LLVM_IAS

[Nick Desaulniers <ndesaulniers@google.com>]

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On Wed, Dec 9, 2020 at 2:58 AM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Tue, Dec 08, 2020 at 04:43:34PM -0800, Nick Desaulniers wrote:
> > Dear stable kernel maintainers,
> > (Woah, two in one day; have I exceeded my limit?)
> >
> > Please consider the attached patch for 5.4 and 4.19 for commit
> > b8a9092330da ("Kbuild: do not emit debug info for assembly with
> > LLVM_IAS=1"), which fixes a significant number of warnings under arch/
> > when assembling a kernel with Clang.
>
> I also need a version of this for 5.9.y before we can take this for
> older kernels.  Can you provide that as well?

Yes, apologies.  It's similar to the 5.4.y patch, but with a shorter
set of conflicts as noted in the commit message.  Attached.
-- 
Thanks,
~Nick Desaulniers

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From afb10106a6b8ea979463daf0a613352bfdf642f3 Mon Sep 17 00:00:00 2001
From: Nick Desaulniers <ndesaulniers@google.com>
Date: Mon, 9 Nov 2020 10:35:28 -0800
Subject: [PATCH] Kbuild: do not emit debug info for assembly with LLVM_IAS=1

commit b8a9092330da2030496ff357272f342eb970d51b upstream.

Clang's integrated assembler produces the warning for assembly files:

warning: DWARF2 only supports one section per compilation unit

If -Wa,-gdwarf-* is unspecified, then debug info is not emitted for
assembly sources (it is still emitted for C sources).  This will be
re-enabled for newer DWARF versions in a follow up patch.

Enables defconfig+CONFIG_DEBUG_INFO to build cleanly with
LLVM=1 LLVM_IAS=1 for x86_64 and arm64.

Cc: <stable@vger.kernel.org>
Link: https://github.com/ClangBuiltLinux/linux/issues/716
Reported-by: Dmitry Golovin <dima@golovin.in>
Reported-by: Nathan Chancellor <natechancellor@gmail.com>
Suggested-by: Dmitry Golovin <dima@golovin.in>
Suggested-by: Nathan Chancellor <natechancellor@gmail.com>
Suggested-by: Sedat Dilek <sedat.dilek@gmail.com>
Reviewed-by: Fangrui Song <maskray@google.com>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
[nd: backport to avoid conflicts from:
  commit 695afd3d7d58 ("kbuild: Simplify DEBUG_INFO Kconfig handling")]
---
 Makefile | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Makefile b/Makefile
index b98b54758b20..8f8a39624320 100644
--- a/Makefile
+++ b/Makefile
@@ -821,8 +821,11 @@ DEBUG_CFLAGS	+= -gsplit-dwarf
 else
 DEBUG_CFLAGS	+= -g
 endif
+ifneq ($(LLVM_IAS),1)
 KBUILD_AFLAGS	+= -Wa,-gdwarf-2
 endif
+endif
+
 ifdef CONFIG_DEBUG_INFO_DWARF4
 DEBUG_CFLAGS	+= -gdwarf-4
 endif
-- 
2.29.2.576.ga3fc446d84-goog