Re: [PATCH v3] Kbuild: do not emit debug info for assembly with LLVM_IAS=1

From: Nick Desaulniers <ndesaulniers@google.com>
To: Masahiro Yamada <masahiroy@kernel.org>,
	Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-toolchains@vger.kernel.org,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	Fangrui Song <maskray@google.com>,
	Nathan Chancellor <natechancellor@gmail.com>,
	Sedat Dilek <sedat.dilek@gmail.com>,
	Dmitry Golovin <dima@golovin.in>,
	Alistair Delva <adelva@google.com>,
	"# 3.4.x" <stable@vger.kernel.org>, Jian Cai <jiancai@google.com>
Subject: Re: [PATCH v3] Kbuild: do not emit debug info for assembly with LLVM_IAS=1
Date: Mon, 23 Nov 2020 10:42:10 -0800	[thread overview]
Message-ID: <CAKwvOdn0qoa_F-qX10Hu7Cr8eeCjcK23i10zw4fty32u1aBPSw@mail.gmail.com> (raw)
In-Reply-To: <CA+SOCLJTg6U+Ddop_5O-baVR42va3vGAvMQ62o9H6rd+10aKrw@mail.gmail.com>

Hi Masahiro,
I would appreciate any feedback you have on this patch.

On Fri, Nov 20, 2020 at 3:58 PM Jian Cai <jiancai@google.com> wrote:
>
> I also verified that with this patch Chrome OS devices booted with either GNU assembler or LLVM's integrated assembler. With this patch, IAS no longer produces extra warnings compared to GNU as on Chrome OS and would remove the last blocker of enabling IAS on it.
>
> Tested-by: Jian Cai <jiancai@google.com> # Compile-tested on mainline (with defconfig) and boot-tested on ChromeOS (with olddefconfig).
>
>
> On Mon, Nov 16, 2020 at 3:41 PM 'Nick Desaulniers' via Clang Built Linux <clang-built-linux@googlegroups.com> wrote:
>>
>> Hi Masahiro, have you had time to review v3 of this patch?
>>
>> On Mon, Nov 9, 2020 at 10:35 AM Nick Desaulniers
>> <ndesaulniers@google.com> wrote:
>> >
>> > 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>
>> > ---
>> >  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
>> >
>>
>>
>> --
>> Thanks,
>> ~Nick Desaulniers
>>
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-- 
Thanks,
~Nick Desaulniers