dwarf_nextcu can't handle abbrev offset correctly ?

dwarf_nextcu can't handle abbrev offset correctly ?

[Hengqi Chen]

Hi,

I am using pahole (which relies on libelf) to process an elf file ([0]):

    LLVM_OBJCOPY="objcopy" pahole -J --btf_gen_floats --btf_base vmlinux adl_pci9111.ko

This failed with:

    die__process: DW_TAG_compile_unit, DW_TAG_type_unit, DW_TAG_partial_unit or DW_TAG_skeleton_unit expected got member (0xd)!

The .ko contains two CU, readelf says that the abbrev offsets are at 0 and 0x907,
but dwarf_nextcu reports that abbrev offsets are both at 0.

pahole expects to find DW_TAG_compile_unit, but seams that the wrong abbrev offset causes the failure.


  [0]: https://gitlab.com/chenhengqi/loong-debug


--
Hengqi

Re: dwarf_nextcu can't handle abbrev offset correctly ?

[Mark Wielaard]

Hi Hengqi,

On Thu, 2022-12-01 at 23:34 +0800, Hengqi Chen via Elfutils-devel
wrote:
> I am using pahole (which relies on libelf) to process an elf file
> ([0]):
> 
>     LLVM_OBJCOPY="objcopy" pahole -J --btf_gen_floats --btf_base
> vmlinux adl_pci9111.ko
> 
> This failed with:
> 
>     die__process: DW_TAG_compile_unit, DW_TAG_type_unit,
> DW_TAG_partial_unit or DW_TAG_skeleton_unit expected got member
> (0xd)!
> 
> The .ko contains two CU, readelf says that the abbrev offsets are at
> 0 and 0x907,
> but dwarf_nextcu reports that abbrev offsets are both at 0.
> 
> pahole expects to find DW_TAG_compile_unit, but seams that the wrong
> abbrev offset causes the failure.
> 
> 
>   [0]: https://gitlab.com/chenhengqi/loong-debug

I took a quick look at the adl_pci9111.ko there. And the issue is that
elfutils doesn't know how to handle the relocations for LoongArch yet.

Specifically the backend should implement the reloc_simple_type hook.

Cheers,

Mark

Re: dwarf_nextcu can't handle abbrev offset correctly ?

[Hengqi Chen]

Hi Mark,

On 2022/12/1 23:54, Mark Wielaard wrote:
> Hi Hengqi,
> 
> On Thu, 2022-12-01 at 23:34 +0800, Hengqi Chen via Elfutils-devel
> wrote:
>> I am using pahole (which relies on libelf) to process an elf file
>> ([0]):
>>
>>     LLVM_OBJCOPY="objcopy" pahole -J --btf_gen_floats --btf_base
>> vmlinux adl_pci9111.ko
>>
>> This failed with:
>>
>>     die__process: DW_TAG_compile_unit, DW_TAG_type_unit,
>> DW_TAG_partial_unit or DW_TAG_skeleton_unit expected got member
>> (0xd)!
>>
>> The .ko contains two CU, readelf says that the abbrev offsets are at
>> 0 and 0x907,
>> but dwarf_nextcu reports that abbrev offsets are both at 0.
>>
>> pahole expects to find DW_TAG_compile_unit, but seams that the wrong
>> abbrev offset causes the failure.
>>
>>
>>   [0]: https://gitlab.com/chenhengqi/loong-debug
> 
> I took a quick look at the adl_pci9111.ko there. And the issue is that
> elfutils doesn't know how to handle the relocations for LoongArch yet.
> 
> Specifically the backend should implement the reloc_simple_type hook.
> 
> Cheers,
> 
> Mark

That's great. Thanks for the pointer. Will try to implement it.


Cheers,
---
Hengqi