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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Mon, 23 Nov 2020 10:42:10 -0800
Message-ID: <CAKwvOdn0qoa_F-qX10Hu7Cr8eeCjcK23i10zw4fty32u1aBPSw@mail.gmail.com>
Subject: Re: [PATCH v3] Kbuild: do not emit debug info for assembly with LLVM_IAS=1
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>
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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 long=
er 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 (wi=
th 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=3D1 LLVM_IAS=3D1 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   +=3D -g
>> >  endif
>> >
>> > +ifneq ($(LLVM_IAS),1)
>> >  KBUILD_AFLAGS  +=3D -Wa,-gdwarf-2
>> > +endif
>> >
>> >  ifdef CONFIG_DEBUG_INFO_DWARF4
>> >  DEBUG_CFLAGS   +=3D -gdwarf-4
>> > --
>> > 2.29.2.222.g5d2a92d10f8-goog
>> >
>>
>>
>> --
>> Thanks,
>> ~Nick Desaulniers
>>
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--=20
Thanks,
~Nick Desaulniers