[Rpm-maint] [PATCH] debugedit: Support String/Line table rewriting for larger/smaller paths.

[Thierry Vignaud]

On 4 March 2017 at 10:28, Panu Matilainen <pmatilai at laiskiainen.org> wrote:
>> From: Mark Wielaard <mark at klomp.org>
>>
>> debugedit --base to --dest rewriting of debug source file paths only
>> supported dest paths that were smaller or equal than the base path
>> (and the size should differ more than 1 character for correct debug
>> lines).
>> All paths were changed "in place". Which could in theory mess up debug str
>> sharing.
>>
>> This rewrite supports base and dest strings of any size (some limitations,
>> see below). This is done by reconstructing the debug_str and debug_line
>> tables and updating the references in the debug_info attributes pointing
>> to these tables. Plus, if necessary (only for ET_REL kernel modules),
>> updating any relocations for the debug_info and debug_line sections.
>>
>> This has the nice benefit of merging any duplicate strings in the
>> debug_str table which might resulting on slightly smaller files.
>> kernel modules are ET_REL files that often contain a lot of duplicate
>> strings.
>>
>> The rewrite uses elfutils (either libebl or libdw) to reconstruct the
>> debug_str table. Since we are changing some section sizes now we cannot
>> just use mmap and rawdata to poke the values, but need to read in and
>> write out the changed sections. This does take a bit more memory because
>> we now also need to keep track of all string/line references.
>
>
> I dont feel qualified to really review this, and perhaps others are feeling
> the same way since it's been out there for a week now with no comments at
> all.
>
> Because this seems quite awesome (even if also a bit scary), to avoid
> stalling forever with no-one to review it: if there are no objections raised
> by Monday I'm going to just apply it (and the couple of other recent
> debuginfo patches). So anybody having doubts, speak up now.

If it does fix the infamous "Dest dir longer than base dir is not
supported", the merrier.
Though that didn't impact that much users in practice (but we did get
a report in mga a long time ago from one guy who set _topdir to
/RPM...).