llvm dev - May 2020 - RFC: Add DWARF support for yaml2obj

Hi folks,

I am going to implement DWARF support for yaml2obj. I really
appreciate it that many of you have given me a lot of useful comments
and suggestions in the previous thread [1]. I've had some offline
discussions with James and done some updates to the previous proposal.

This proposal addresses the issue of properly describing the DWARF
sections in YAML both at a high level and at a low level. We add some
extra value types (Tag/Value/Address/String) in the "debug_info"
entry, which helps describe the DWARF sections at a high level by
providing the logical structure of the DIEs. "yaml2obj" will traverse
these DIEs and emit other debug sections properly. We are also able to
hand-craft debug sections at a low level by hardcoding the contents,
offsets, values, etc.

Here's the proposal [2] which gives a brief introduction to the DWARF
YAML. Any thoughts on that? Thanks in advance!

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[1] https://lists.llvm.org/pipermail/llvm-dev/2020-March/140518.html
[2]
https://docs.google.com/document/d/13wNr4JbXtzaOly-UsFt7vxI3LKXzik_lVU58ICqslWM/edit?usp=sharing

-- 
Cheers,
Xing

I think the example looks like it would be really useful for many categories of
testcases!
Will it still be possible to manually specify the .debug_abbrev section when
this is desired after you are done?

-- adrian

On 5/21/20, Adrian Prantl <aprantl at apple.com>
wrote:
> I think the example looks like it would be really useful for many
categories
> of testcases!
> Will it still be possible to manually specify the .debug_abbrev section
when
> this is desired after you are done?
Yes, I think it works. There are two ways to edit the .debug_abbrev section.

i) Edit the "Attr:" and "Form:" entries of a DIE in the
".debug_info"
section. This controls the generation of the ".debug_abbrev" section
at a high level since "yaml2obj" generates the
".debug_abbrev" section
according to the contents from debug information entries.

ii) Edit the ".debug_abbrev" directly. This controls the generation of
the ".debug_abbrev" section at a low level. We will have to hardcode
the tag and attributes for each DIE. Editing the section in this way
doesn't need a "debug_info" entry in the "DWARF".

Additionally, if we have the "debug_info" entry and the
"debug_abbrev"
entry at the same time, the latter one will overwrite the tags and
attributes generated by the former one.

Does it make sense?

-- 
Cheers,
Xing