== Summary ==
Fedora 18 implemented [[Features/DwarfCompressor]]. As the format did
not get widespread and the tool is not much maintained it became
burden to make existing debugging tools compatible with Fedora debug
== Owner ==
* Name: [[User:jankratochvil| Jan Kratochvil ]]
* Email: jan.kratochvil(a)redhat.com
== Detailed Description ==
Debug info files *.debug contained in *-debuginfo.rpm are very big in
general (x86_64 Fedora 32 distribution has debug/ directory of 82GB
while all its other files are only 75GB). There exist several methods
how to make the *-debuginfo.rpms at least a bit smaller. Fedora 18
started using DWZ tool (from [[Features/DwarfCompressor]]) while
Google implemented] the same goal in a different way called
Almost nobody uses existing Fedora DWZ (only Fedora/CentOS/RHEL and
SuSE OSes) and so its support is missing in tools like
or binutils readelf. -fdebug-types-section is used internally by
Google (produced by clang). Debian does not store any debug info
archives. Ubuntu uses neither -fdebug-types-section nor DWZ.
* DWZ advantage: On the whole Fedora distro it saves 3.3% (5GB of the
157GB distribution size)
** If the 3.3% size increase is a concern I can implement a different
talk (2)]) as a GCC post-processing phase which would require no
changes in any DWARF consumers.
* DWZ disadvantage: DWZ has currently less support across consumers
(LLDB, llvm-dwarfdump, binutils readelf)
* DWZ disadvantage: DWZ requires 8x times more complicated (LoC count)
support in consumers than -fdebug-types-section.
* DWZ disadvantage: DWZ cannot update LLVM .debug_names index which
can be generated only by clang (it cannot be regenerated later for
* DWZ disadvantage: DWZ DWARF-5 support is a work-in-progress. DWZ has
been blocking DWARF-5 for Fedora for 3.5 years and only after I have
now proposed to drop DWZ Mark Wielaard has started porting DWZ to
DWARF-5. It can be expected next DWARF extensions will remain
unsupported again. Even currently there is no plan to support DWARF-5
features used by clang which may need -fdebug-types-section for
clang-built binaries or no size optimization of clang-built debug info
* DWZ disadvantage: Compilation (linking) requires for C++ up to 2x as
big disk space (as DWZ is processing files after linker and DWZ is
incompatible with -fdebug-types-section)
* DWZ disadvantage: Compilation (linking) is slower
This proposed DWARF format was originally submitted already for Fedora
18 as [[Features/DebugTypesSections]].
== Benefit to Fedora ==
* Better compatibility with existing debugging and tracing tools,
* Less resource-intensive rebuilds of C++ packages (in disk space,
memory requirements and compilation time).
== Scope ==
* Proposal owners: It affects all packages generating *-debuginfo.rpm,
that is compiled (not scripted) languages.
* Other developers: Report any possible debuginfo incompatibility (unexpected).
* Release engineering: [https://pagure.io/releng/issues
number] (a check of an impact with Release Engineering is needed)
* Policies and guidelines: All the needed changes should be done in
redhat-rpm-config]. The [https://src.fedoraproject.org/rpms/dwz
package] can be then retired.
* Trademark approval: N/A (not needed for this Change)
* Alignment with Objectives: The size differences are only for
*-debuginfo.rpm which is outside of scope of the listed objectives.
== Upgrade/compatibility impact ==
As *-debuginfo.rpm have to exactly match NVRA of its binary package
the compatibility is not relevant. Existing tools supporting DWZ will
still support the DWZ file format in packages which have not been
== How To Test ==
The change will update
an -fdebug-types-section patch].
Then one can use rpmbuild to rebuild a package. For mock use
-a|--addrepo with modified redhat-rpm-config.rpm (with increased
NVRA). For packages already rebuilt in Koji nothing is needed.
Test programs like lldb and gdb if they still can print source code,
function parameters, variables etc.
One should also verify integrated testsuites of tools like clang,
lldb, gcc, binutils, gdb, elfutils or rpm are not regressing with the
One can also compare *.debug files built with/without DWZ and/or
dwdiff but that will be rather done by the change owner.
== User Experience ==
No user visible change. This affects what tools can developers use.
== Dependencies ==
== Contingency Plan ==
* Contingency mechanism: Revert the change in
redhat-rpm-config]. Fedora can continue using DWZ, just some
debugging/tracing tools will stay incompatible.
* Contingency deadline: beta freeze
* Blocks release? No
* Blocks product? N/A
== Documentation ==
DWARF-5] E.2 Using Type Units
He / Him / His
Senior Program Manager, Fedora & CentOS Stream