Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Wed, 4 Nov 2020 23:58:44 -0700
From:   Nathan Chancellor <natechancellor@gmail.com>
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     Masahiro Yamada <masahiroy@kernel.org>,
        Jakub Jelinek <jakub@redhat.com>,
        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>,
        Sedat Dilek <sedat.dilek@gmail.com>,
        Dmitry Golovin <dima@golovin.in>,
        Alistair Delva <adelva@google.com>, stable@vger.kernel.org
Subject: Re: [PATCH v2 2/4] Kbuild: do not emit debug info for assembly with
 LLVM_IAS=1
Message-ID: <20201105065844.GA3243074@ubuntu-m3-large-x86>
References: <CAK7LNAST0Ma4bGGOA_HATzYAmRhZG=x_X=8p_9dKGX7bYc2FMA@mail.gmail.com>
 <20201104005343.4192504-1-ndesaulniers@google.com>
 <20201104005343.4192504-3-ndesaulniers@google.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20201104005343.4192504-3-ndesaulniers@google.com>
Precedence: bulk

On Tue, Nov 03, 2020 at 04:53:41PM -0800, Nick Desaulniers 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.  This

Is this something that should be called out somewhere? If I understand
this correctly, LLVM_IAS=1 + CONFIG_DEBUG_INFO=y won't work? Maybe this
should be handled in Kconfig?

> will be re-enabled for new 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: Nathan Chancellor <natechancellor@gmail.com>
> Suggested-by: Dmitry Golovin <dima@golovin.in>

If you happen to respin, Dmitry deserves a Reported-by tag too :)

> Suggested-by: Sedat Dilek <sedat.dilek@gmail.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>

Regardless of the other two comments, this is fine as is as a fix for
stable to unblock Android + CrOS since we have been running something
similar to it in CI:

Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>

> ---
>  Makefile | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/Makefile b/Makefile
> index f353886dbf44..75b1a3dcbf30 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -826,7 +826,9 @@ else
>  DEBUG_CFLAGS	+= -g
>  endif
>  
> +ifndef LLVM_IAS

Nit: this should probably match the existing LLVM_IAS check

ifneq ($(LLVM_IAS),1)

>  KBUILD_AFLAGS	+= -Wa,-gdwarf-2
> +endif
>  
>  ifdef CONFIG_DEBUG_INFO_DWARF4
>  DEBUG_CFLAGS	+= -gdwarf-4
> -- 
> 2.29.1.341.ge80a0c044ae-goog
>