linux-kernel - [PATCH 5.4 01/36] Kbuild: do not emit debug info for assembly with LLVM

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Date:   Mon, 14 Dec 2020 18:27:45 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dmitry Golovin <dima@...ovin.in>,
        Nathan Chancellor <natechancellor@...il.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Fangrui Song <maskray@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>
Subject: [PATCH 5.4 01/36] Kbuild: do not emit debug info for assembly with LLVM_IAS=1

From: Nick Desaulniers <ndesaulniers@...gle.com>

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@...r.kernel.org>
Link: https://github.com/ClangBuiltLinux/linux/issues/716
Reported-by: Dmitry Golovin <dima@...ovin.in>
Reported-by: Nathan Chancellor <natechancellor@...il.com>
Suggested-by: Dmitry Golovin <dima@...ovin.in>
Suggested-by: Nathan Chancellor <natechancellor@...il.com>
Suggested-by: Sedat Dilek <sedat.dilek@...il.com>
Reviewed-by: Fangrui Song <maskray@...gle.com>
Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
[nd: backport to avoid conflicts from:
  commit 10e68b02c861 ("Makefile: support compressed debug info")
  commit 7b16994437c7 ("Makefile: Improve compressed debug info support detection")
  commit 695afd3d7d58 ("kbuild: Simplify DEBUG_INFO Kconfig handling")]
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 Makefile |    3 +++
 1 file changed, 3 insertions(+)

--- a/Makefile
+++ b/Makefile
@@ -802,8 +802,11 @@ 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