Re: [PATCH v3 0/2] Kbuild: DWARF v5 support

From: Nick Desaulniers <ndesaulniers@google.com>
To: Sedat Dilek <sedat.dilek@gmail.com>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Jiri Olsa <jolsa@kernel.org>, Andrii Nakryiko <andrii@kernel.org>,
	Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Caroline Tice <cmtice@google.com>,
	Arvind Sankar <nivedita@alum.mit.edu>,
	Jakub Jelinek <jakub@redhat.com>,
	Fangrui Song <maskray@google.com>,
	Clang-Built-Linux ML <clang-built-linux@googlegroups.com>,
	Nick Clifton <nickc@redhat.com>, bpf <bpf@vger.kernel.org>
Subject: Re: [PATCH v3 0/2] Kbuild: DWARF v5 support
Date: Thu, 14 Jan 2021 10:53:06 -0800	[thread overview]
Message-ID: <CAKwvOd=+g88AEDO9JRrV-gwggsqx5p-Ckiqon3=XLcx8L-XaKg@mail.gmail.com> (raw)
In-Reply-To: <CA+icZUUtAVBvpU8M0PONnNSiOATgeL9Ym24nYUcRPoWhsQj8Ug@mail.gmail.com>

On Wed, Jan 13, 2021 at 10:18 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
>
> On Wed, Jan 13, 2021 at 11:25 PM Caroline Tice <cmtice@google.com> wrote:
> >
> > On Tue, Jan 12, 2021 at 3:17 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
> >>
> >> Unfortunately, I see with CONFIG_DEBUG_INFO_DWARF5=y and
> >> CONFIG_DEBUG_INFO_BTF=y:
> >>
> >> die__process_inline_expansion: DW_TAG_INVALID (0x48) @ <0x3f0dd5a> not handled!
> >> die__process_function: DW_TAG_INVALID (0x48) @ <0x3f0dd69> not handled!

I can confirm that I see a stream of these warnings when building with
this patch series applied, and those two configs enabled.

rebuilding with `make ... V=1`, it looks like the call to:

+ pahole -J .tmp_vmlinux.btf

is triggering these.

Shall I send a v4 that adds a Kconfig dependency on !DEBUG_INFO_BTF?
Does pahole have a bug tracker?

> >>
> >> In /usr/include/dwarf.h I found:
> >>
> >> 498:    DW_OP_lit24 = 0x48,                /* Literal 24.  *
> >
> >
> > There are multiple dwarf objects with the value 0x48, depending on which section of the dwarf.h file you search:
> >
> > DW_TAG_call_site = 0x48
> > DW_AT_static_link = 0x48
> > DW_OP_lit24 = 0x48.
> >
> > In this case, since the error message was about a DW_TAG, it would be complaining about DW_TAG_call_site, which is new to DWARF v5.
> >
> Example for "DW_TAG_INVALID (0x48)" from my build-log:
>
> die__process_inline_expansion: DW_TAG_INVALID (0x48) @ <0x1f671e7> not handled!
>
> $ llvm-dwarfdump-11 --debug-info=0x1f671e7 vmlinux
> vmlinux:        file format elf64-x86-64
>
> .debug_info contents:
>
> 0x01f671e7: DW_TAG_call_site
>              DW_AT_call_return_pc      (0xffffffff811b16f2)
>              DW_AT_call_origin (0x01f67f1d)
>
> Looking for "DW_AT_call_origin (0x01f67f1d)":
>
> $ llvm-dwarfdump-11 --debug-info=0x01f67f1d vmlinux
> vmlinux:        file format elf64-x86-64
>
> .debug_info contents:
>
> 0x01f67f1d: DW_TAG_subprogram
>              DW_AT_external    (true)
>              DW_AT_declaration (true)
>              DW_AT_linkage_name        ("fput")
>              DW_AT_name        ("fput")
>              DW_AT_decl_file
> ("/home/dileks/src/linux-kernel/git/./include/linux/file.h")
>              DW_AT_decl_line   (16)
>              DW_AT_decl_column (0x0d)

That's a neat trick (using --debug-info=offset to print one element
from the stream).
-- 
Thanks,
~Nick Desaulniers