Re: [PATCH v2 2/4] Kbuild: do not emit debug info for assembly with LLVM_IAS=1

Nathan Chancellor
2020-11-05T06:58:49Z

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
>