netdev - Re: [PATCH bpf-next] kbuild: add ability to generate BTF type info for vmlinux

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Date:   Wed, 3 Apr 2019 11:04:28 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Jiri Olsa <jolsa@...hat.com>, andrii.nakryiko@...il.com
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org, kernel-team@...com,
        Andrii Nakryiko <andriin@...com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Alexei Starovoitov <ast@...com>, Yonghong Song <yhs@...com>,
        Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH bpf-next] kbuild: add ability to generate BTF type info
 for vmlinux

On 04/03/2019 10:46 AM, Jiri Olsa wrote:
> On Tue, Apr 02, 2019 at 09:49:50AM -0700, andrii.nakryiko@...il.com wrote:
>> From: Andrii Nakryiko <andriin@...com>
>>
>> This patch adds new config option to trigger generation of BTF type
>> information from DWARF debuginfo for vmlinux and kernel modules through
>> pahole, which in turn relies on libbpf for btf_dedup() algorithm.
>>
>> The intent is to record compact type information of all types used
>> inside kernel, including all the structs/unions/typedefs/etc. This
>> enables BPF's compile-once-run-everywhere ([0]) approach, in which
>> tracing programs that are inspecting kernel's internal data (e.g.,
>> struct task_struct) can be compiled on a system running some kernel
>> version, but would be possible to run on other kernel versions (and
>> configurations) without recompilation, even if the layout of structs
>> changed and/or some of the fields were added, removed, or renamed.
>>
>> This is only possible if BPF loader can get kernel type info to adjust
>> all the offsets correctly. This patch is a first time in this direction,
>> making sure that BTF type info is part of Linux kernel image in
>> non-loadable ELF section.
>>
>> BTF deduplication ([1]) algorithm typically provides 100x savings
>> compared to DWARF data, so resulting .BTF section is not big as is
>> typically about 2MB in size.
> 
> hi,
> I'm using the latest pahole from git tree:
>   https://github.com/acmel/dwarves.git
> 
> and getting pahole crash:
> 
>   LD      vmlinux
>   BTF     vmlinux
> die__process_inline_expansion: DW_TAG_label (0xa) @ <0x3eef8> not handled!
> scripts/link-vmlinux.sh: line 96: 31222 Segmentation fault      (core dumped) LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1}
> make[1]: *** [/home/jolsa/linux/Makefile:1025: vmlinux] Error 139
> make: *** [Makefile:170: sub-make] Error 2
> 
> is there some other source/dependency I'm missing?

Yesterday night, I've tested with [0] but seems to have the same HEAD as
the github repo you pointed out. Seems the above is coming from pahole's
__die__process_tag() bailing out with default for DW_TAG_label?

On my side worked fine:

# rm vmlinux
# make -j8
  DESCEND  objtool
  CALL    scripts/atomic/check-atomics.sh
  CALL    scripts/checksyscalls.sh
  CHK     include/generated/compile.h
  GEN     .version
  CHK     include/generated/compile.h
  UPD     include/generated/compile.h
  CC      init/version.o
  AR      init/built-in.a
  LD      vmlinux.o
  MODPOST vmlinux.o
  KSYM    .tmp_kallsyms1.o
  KSYM    .tmp_kallsyms2.o
  LD      vmlinux
  BTF     vmlinux                              <--
  SORTEX  vmlinux
  SYSMAP  System.map
  Building modules, stage 2.
  CC      arch/x86/boot/version.o
  VOFFSET arch/x86/boot/compressed/../voffset.h
  OBJCOPY arch/x86/boot/compressed/vmlinux.bin
  RELOCS  arch/x86/boot/compressed/vmlinux.relocs
  CC      arch/x86/boot/compressed/kaslr.o
  CC      arch/x86/boot/compressed/misc.o
  GZIP    arch/x86/boot/compressed/vmlinux.bin.gz
  MKPIGGY arch/x86/boot/compressed/piggy.S
  AS      arch/x86/boot/compressed/piggy.o
  LD      arch/x86/boot/compressed/vmlinux
  ZOFFSET arch/x86/boot/zoffset.h
  OBJCOPY arch/x86/boot/vmlinux.bin
  AS      arch/x86/boot/header.o
  LD      arch/x86/boot/setup.elf
  OBJCOPY arch/x86/boot/setup.bin
  BUILD   arch/x86/boot/bzImage
Setup is 17660 bytes (padded to 17920 bytes).
System is 9245 kB
CRC 24cd7eff
Kernel: arch/x86/boot/bzImage is ready  (#15)
  MODPOST 4979 modules

  [0] https://git.kernel.org/pub/scm/devel/pahole/pahole.git/