[Rpm-maint] debugedit: Implement DWARF-5. (#1332)

[Panu Matilainen]

On 2/15/21 1:29 PM, Mark Wielaard wrote:
> Hi,
> 
> It looks like the rpm-maint github bridge doesn't always work flawlessly
> with attached patches.

Lol, that's ... putting it nicely :D

> So here the whole series is using normal git
> send-email. They are also available at:
> https://code.wildebeest.org/git/user/mjw/rpm/log/?h=gcc-dwarf5
> 
> These patches are based on the original patches by Jan Kratochvil
> but rewritten a bit so each individual patch adds distinct new
> functionality and adding explicit DWARF4 and DWARF5 testcases using
> the default GCC compiler that should work whether or not the compiler
> defaults to DWARF4 or DWARF5 and whether or not the binutils assembler
> generates older or new .debug_line sections. The patches (except the
> new test cases) have been tested during the recent Fedora mass-rebuild
> that used a GCC11 pre-release that defaulted to DWARF5 by default
> using binutils 2.35.2. This resulted in one bug fix, a confusion of
> comparing the size of the .debug_str and the new .debug_line_str section.
> Those patches were against the rpm 4.16.1.2 release and can be found here:
> https://code.wildebeest.org/git/user/mjw/rpm/log/?h=gcc-dwarf5-4.16.1.2
> 
> Those 4.16.1.2 patches include two patches which were already applied
> to master:
> - [NFC] debugedit: Move code from edit_dwarf2() to edit_info().
> - debugedit: Fix missing relocation of .debug_types section.
> So those have been dropped in this series, which was rebased to
> current git trunk:
> 
>   [PATCH 1/5] [NFC] debugedit: Protect macro arguments by parentheses
>   [PATCH 2/5] [NFC] debugedit: Move code to separate functions.
>   [PATCH 3/5] debugedit: Implement DWARF-5 unit header and new forms
>   [PATCH 4/5] debugedit: Handle DWARF-5 debug_line and debug_line_str.
>   [PATCH 5/5] debugedit: Add DWARF5 tests
> 
> The first two [NFC] patches are unchanged just have a bit more explanation
> in the commit message about what is going on.
> 
> The original series contained one patch that was dropped:
> - debugedit: Fix handling in caller for errors in called read_dwarf2_line.
> It was needed when doing multiple passes of some phases when dealing
> with .debug_line, but the new patch handles things by doing each phase
> just once (that is the fourth patch).
> 
> The original patches:
> - debugedit: Implement DWARF-5 .debug_types (in .debug_info).
> - debugedit: Implement DWARF-5.
> were rewritten and split into the last three patches to have separate
> implementations of handling the new unit headers and forms, handling
> of the new .debug_line and .debug_line_str and adding new test cases.
> This also made the third patch testable independently with older GCC
> versions that support -gdwarf-5 but don't yet generate DWARF5 debug
> line tables.
> 
> One feature of the original patch was dropped, handling of DW_UT_types
> in .debug_info, which seemed to complicate the code a bit and wasn't
> necessary for the default GCC DWARF5 mode. It shouldn't be that hard
> to add that back if needed (although handling the partially linked
> variant might be slightly tricky since they require handling COMDAT
> .debug_info sections).
> 
> The original series added tests based on llvm tooling, which I have
> replaced by existing tests based on explicit -gdwarf-4 and -gdwarf-5
> tests that should work fine against both older and newer gcc versions
> which might have different DWARF version defaults.

Thanks for the detailed explanation. I think this has been already 
reviewed and tested to the extent it's going to get, merged via 
https://github.com/rpm-software-management/rpm/pull/1537 now. Thanks 
again for the effort!

	- Panu -