[minicoredumper] Handling of unavailable bytes in minicoredumps by GDB

[John Ogness]

Hi Simon,

On 2015-10-23, Simon Marchi <simon.marchi at ericsson.com> wrote:
> I'd like to show you a prototype of GDB that handles the bytes that
> are unavailable in the minicoredump (which are read as zeros
> currently).
>
> The principle is very similar to the GDB tracepoints, where you also
> have the concept of unavailable bytes.  Since a lot of work has been
> done to put the infrastructure in place for tracepoints, it's not so
> bad to do it now for the minicoredumps.
>
> I made some minimal modifications to minicoredumper, in order to save
> what memory was collected as part of the minicoredump.  I am saving
> the data in a file called "dumped" which is next to the core dump.
> Having this data directly in the core dump, in a section of its own,
> would be much better.

I recently completed this work from the minicoredumper side. A new ELF
section note ".note.minicoredumper.dumplist" is added to the core
file. This provides the same information that your "dumped" file
provided.

Because of a bug in libelf, using this feature currently requires HEAD
of the elfutils repository. In particular this patch [0] is
needed. Minicoredumper checks for version 0.167 of libelf, which should
be the next released version.

> To get a feel of it, I invite you to build the following branch of
> gdb:
>
>   https://github.com/simark/binutils-gdb/tree/minicore-for-linutronix
>
> It's a simple ./configure && make.  The gdb binary will be in the gdb
> directory.
>
> You can then find the modified version of minicoredumper in the
> following branch:
>
>   https://github.com/simark/minicoredumper/tree/collected-for-linutronix

I will modify your test to support retrieving the data from the ELF
section. The change should be relatively simple.

John Ogness

[0] https://git.fedorahosted.org/cgit/elfutils.git/commit/?id=96e140f6687922606657a76f185a73cf47908ef2