linux-kernel - [PATCH v3] Kbuild: do not emit debug info for assembly with LLVM

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Message-Id: <20201109183528.1391885-1-ndesaulniers@google.com>
Date:   Mon,  9 Nov 2020 10:35:28 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-toolchains@...r.kernel.org,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Fangrui Song <maskray@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Dmitry Golovin <dima@...ovin.in>,
        Alistair Delva <adelva@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        stable@...r.kernel.org
Subject: [PATCH v3] Kbuild: do not emit debug info for assembly with LLVM_IAS=1

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>
---
 Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Makefile b/Makefile
index f353886dbf44..7e899d356902 100644
--- a/Makefile
+++ b/Makefile
@@ -826,7 +826,9 @@ else
 DEBUG_CFLAGS	+= -g
 endif
 
+ifneq ($(LLVM_IAS),1)
 KBUILD_AFLAGS	+= -Wa,-gdwarf-2
+endif
 
 ifdef CONFIG_DEBUG_INFO_DWARF4
 DEBUG_CFLAGS	+= -gdwarf-4
-- 
2.29.2.222.g5d2a92d10f8-goog