[Bug corefiles/31635] debuginfod cannot correctly fetch shared libraries without soname from server due to inconsistency

["amerey at redhat dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=31635

Aaron Merey <amerey at redhat dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |amerey at redhat dot com

--- Comment #2 from Aaron Merey <amerey at redhat dot com> ---
(In reply to Pablo Galindo Salgado from comment #0) 
> 1) Libraries that do not have soname will never be registered in the map by
> set_cbfd_soname_build_id. This is very unfortunate because most shared
> libraries for dynamic languages such as Python do not have sonames set.
> 2) The registering into the map from library to buildid in
> set_cbfd_soname_build_id it's made by SONAME (from the dynamic table).

One challenge for getting debuginfod to work with corefiles is figuring out 
which library buildid in the corefile corresponds to a particular library
that gdb is unable to open in solib_map_sections.  Sonames are used because
we can create a soname to buildid mapping from the corefile and then use 
this mapping to get the right buildid for the debuginfod query when a shared
library can't otherwise be found by gdb in solib_map_sections.

> [...]
> Here the query is made by the basename of the *soname* argument (lbasename
> (soname)) but this function is NOT called with the soname but rather the 
> full path. Indeed, in solib_map_sections() we can observe:
> 
>   gdb::unique_xmalloc_ptr<char> build_id_hexstr
>     = get_cbfd_soname_build_id (current_program_space->cbfd,
>                               so.so_name.c_str ());
> 
> but so.so_name.c_str() is a full path from the linker map. Notice the 
> following:
> 
> 1) This full path may be different from the one in the previous section
> because one comes from the core and the other comes from the linker map. One 
> it's an absolute path and the other can be a symlink.
> 2) The query is made by full path but the map it's populate from DT_SONAME,
> which is inconsistent.

AFAIK when the library has a soname, the basename in get_cbfd_soname_build_id
should generally match a soname in the map.  If this wasn't the case then gdb 
would fail to query debuginfod for libraries associated with corefiles much 
more often.

I'll look into what paths gdb uses in solib_map_sections for libraries with
no soname.  Maybe it's possible to create a path-to-buildid map from the
corefile
that we could use instead of the the soname-to-buildid map when a soname isn't
available.

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