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

[Nathan Chancellor]

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@xxxxxxxxxxxxxxx>
> Link: https://github.com/ClangBuiltLinux/linux/issues/716
> Reported-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
> Suggested-by: Dmitry Golovin <dima@xxxxxxxxxx>

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

> Suggested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx>
> Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>

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@xxxxxxxxx>

> ---
>  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
>