Re: [PATCH] lib/Kconfig.debug: Add check for non-constant .{s,u}leb128 support to DWARF5

From: Masahiro Yamada <masahiroy@kernel.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Nathan Chancellor <nathan@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Tom Rix <trix@redhat.com>, Palmer Dabbelt <palmer@dabbelt.com>,
	linux-kbuild@vger.kernel.org, linux-riscv@lists.infradead.org,
	linux-kernel@vger.kernel.org, patches@lists.linux.dev,
	llvm@lists.linux.dev, Conor Dooley <conor.dooley@microchip.com>
Subject: Re: [PATCH] lib/Kconfig.debug: Add check for non-constant .{s,u}leb128 support to DWARF5
Date: Mon, 3 Oct 2022 02:59:13 +0900	[thread overview]
Message-ID: <CAK7LNAQtS_cVVjsV32S8hQJNER3jN9frnRosz4rfQ6+TkXKUtg@mail.gmail.com> (raw)
In-Reply-To: <CAKwvOdk87wRWoiVjswZPwoLbSm+sYsMW6FHZv+r6MHxLHn0Trw@mail.gmail.com>

On Thu, Sep 29, 2022 at 6:53 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Wed, Sep 28, 2022 at 2:36 PM Nathan Chancellor <nathan@kernel.org> wrote:
> >
> > On Wed, Sep 28, 2022 at 02:13:47PM -0700, Nick Desaulniers wrote:
> > > Reraising my concern from
> > > https://github.com/ClangBuiltLinux/linux/issues/1719#issuecomment-1258678969
> >
> > Sorry, I thought I addressed your concern with my comment right below it
> > but I probably should have worded it better.
>
> No, I just missed your point about other architectures.
>
> > > We've put a fair amount of work into getting CC=clang LLVM_IAS=0 to
> > > work for DWARF v5 (both on the GNU binutils side, and Kbuild), I'd
> > > hate to see that effectively knee-capped because of an issue in GNU
> > > binutils that is only relevant for one architecture.
> >
> > Sure, that is a completely reasonable concern. However...
> >
> > > I'd concede support for ARCH=riscv, but not for all other
> > > architectures, which this effectively does.
> >
> > No, it does not, CONFIG_AS_HAS_NON_CONST_LEB128 can still be enabled
> > when GNU as supports this construct for a particular architecture; as
> > far as I can tell, RISC-V is the only one that doesn't. See the tests
> > with ARCH=arm64 and ARCH=x86_64 compared with ARCH=riscv below.
>
> Ah, sorry for the noise then. Thanks for the patch.
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
>
> --
> Thanks,
> ~Nick Desaulniers

This patch is incomplete.

It looks like Clang 14 switched to DWARF v5 by default.

I see the same errors for
CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y

masahiro@zoe:~/ref/linux$ clang --version | head -n1
Ubuntu clang version 14.0.0-1ubuntu1
masahiro@zoe:~/ref/linux$ grep DEBUG_INFO_DWARF .config
CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
# CONFIG_DEBUG_INFO_DWARF4 is not set
# CONFIG_DEBUG_INFO_DWARF5 is not set
masahiro@zoe:~/ref/linux$ make ARCH=riscv LLVM=1 LLVM_IAS=0
CROSS_COMPILE=riscv64-linux-gnu- -j24
  CALL    scripts/atomic/check-atomics.sh
  CALL    scripts/checksyscalls.sh
  CC      arch/riscv/kernel/vdso/vgettimeofday.o
/tmp/vgettimeofday-5997b4.s: Assembler messages:
/tmp/vgettimeofday-5997b4.s:2698: Error: non-constant .uleb128 is not supported
/tmp/vgettimeofday-5997b4.s:2699: Error: non-constant .uleb128 is not supported
/tmp/vgettimeofday-5997b4.s:2705: Error: non-constant .uleb128 is not supported
/tmp/vgettimeofday-5997b4.s:2706: Error: non-constant .uleb128 is not supported
/tmp/vgettimeofday-5997b4.s:2712: Error: non-constant .uleb128 is not supported
/tmp/vgettimeofday-5997b4.s:2713: Error: non-constant .uleb128 is not supported
/tmp/vgettimeofday-5997b4.s:2719: Error: non-constant .uleb128 is not supported
/tmp/vgettimeofday-5997b4.s:2720: Error: non-constant .uleb128 is not supported
/tmp/vgettimeofday-5997b4.s:2726: Error: non-constant .uleb128 is not supported
/tmp/vgettimeofday-5997b4.s:2727: Error: non-constant .uleb128 is not supported
/tmp/vgettimeofday-5997b4.s:2731: Error: non-constant .uleb128 is not supported
/tmp/vgettimeofday-5997b4.s:2732: Error: non-constant .uleb128 is not supported
/tmp/vgettimeofday-5997b4.s:2736: Error: non-constant .uleb128 is not supported
/tmp/vgettimeofday-5997b4.s:2737: Error: non-constant .uleb128 is not supported
/tmp/vgettimeofday-5997b4.s:2743: Error: non-constant .uleb128 is not supported
/tmp/vgettimeofday-5997b4.s:2744: Error: non-constant .uleb128 is not supported
/tmp/vgettimeofday-5997b4.s:2748: Error: non-constant .uleb128 is not supported
/tmp/vgettimeofday-5997b4.s:2749: Error: non-constant .uleb128 is not supported
/tmp/vgettimeofday-5997b4.s:2755: Error: non-constant .uleb128 is not supported
/tmp/vgettimeofday-5997b4.s:2756: Error: non-constant .uleb128 is not supported
/tmp/vgettimeofday-5997b4.s:2760: Error: non-constant .uleb128 is not supported
/tmp/vgettimeofday-5997b4.s:2761: Error: non-constant .uleb128 is not supported
/tmp/vgettimeofday-5997b4.s:2765: Error: non-constant .uleb128 is not supported
   ...

-- 
Best Regards
Masahiro Yamada