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.
These backports have already been shipped in Android; I would like to
revert them and take them from syncing with stable. CrOS also has the
patches staged, but I would prefer for them to sync them from stable
as well.
b8a9092330da just landed in v5.10-rc7. I recently read
https://lwn.net/Articles/838819/, which mentions a discussion about
letting patches have more time to soak in mainline, so I accept if
your decision is to wait, though I'll note these have been soaking in
Android for 2 days shy of one month (Nov 10).
There were minor conflicts due to missing Kbuild support for
compressed debug info, which is a feature I implemented but don't plan
to backport to stable.
We plan to use Clang's integrated assembler for Android and CrOS for 4.19+.
See also: https://github.com/ClangBuiltLinux/linux/issues/716.
--
Thanks,
~Nick Desaulniers
From 125bcd1867e6b59f4eb364522276bc273e2648e2 Mon Sep 17 00:00:00 2001
From: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
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@xxxxxxxxxxxxxxx>
Link: https://github.com/ClangBuiltLinux/linux/issues/716
Reported-by: Dmitry Golovin <dima@xxxxxxxxxx>
Reported-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Suggested-by: Dmitry Golovin <dima@xxxxxxxxxx>
Suggested-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Suggested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx>
Reviewed-by: Fangrui Song <maskray@xxxxxxxxxx>
Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
[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")]
---
Makefile | 3 +++
1 file changed, 3 insertions(+)
diff --git a/Makefile b/Makefile
index e520dee34490..f8c766b35b71 100644
--- 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
--
2.29.2.576.ga3fc446d84-goog
From 17369ed6faa2ebdf4c10accfd6ca9075fdcbb4a2 Mon Sep 17 00:00:00 2001
From: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
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@xxxxxxxxxxxxxxx>
Link: https://github.com/ClangBuiltLinux/linux/issues/716
Reported-by: Dmitry Golovin <dima@xxxxxxxxxx>
Reported-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Suggested-by: Dmitry Golovin <dima@xxxxxxxxxx>
Suggested-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Suggested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx>
Reviewed-by: Fangrui Song <maskray@xxxxxxxxxx>
Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
[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")]
---
Makefile | 3 +++
1 file changed, 3 insertions(+)
diff --git a/Makefile b/Makefile
index 71e55c5cd74a..4c6ac3c6995f 100644
--- a/Makefile
+++ b/Makefile
@@ -745,8 +745,11 @@ KBUILD_CFLAGS += $(call cc-option, -gsplit-dwarf, -g)
else
KBUILD_CFLAGS += -g
endif
+ifneq ($(LLVM_IAS),1)
KBUILD_AFLAGS += -Wa,-gdwarf-2
endif
+endif
+
ifdef CONFIG_DEBUG_INFO_DWARF4
KBUILD_CFLAGS += $(call cc-option, -gdwarf-4,)
endif
--
2.29.2.576.ga3fc446d84-goog
