Re: [MirageOS-devel] Mini-OS on ARM status

[Thomas Leonard <talex5@xxxxxxxxx>]

On 27 April 2014 23:02, Anil Madhavapeddy <anil@xxxxxxxxxx> wrote:
> On 22 Apr 2014, at 18:40, Thomas Leonard <talex5@xxxxxxxxx> wrote:
>
>> Hi guys,
>>
>> A quick status update on this work:
>>
>> - Output to the regular console now works (before, it could only
>> output to the emergency console, which requires Xen to be compiled in
>> debug mode).
>>
>> - I added a simple fault handler that dumps all registers if it gets
>> an error (data abort, prefetch abort, undefined instruction, etc).
>> That makes debugging easier.
>>
>> - It now gets the RAM start and size from the FDT passed in by the
>> hypervisor (before, it hard-coded the values). This means that the
>> full amount of memory assigned to the guest is available to malloc. I
>> also fixed a bug in malloc that was corrupting memory (it was
>> calculating offsets into its free map incorrectly). It now mallocs as
>> many blocks as possible on start-up, fills them with known values and
>> then tests them all (this is how I found the bug).
>>
>> - The GIC (interrupt controller) addresses are now read from the FDT
>> instead of being hard-coded, and interrupts now work. Before, it would
>> hang as soon as interrupts were enabled.
>>
>> There's currently no virtual memory support (if the memory gets
>> fragmented, malloc may fail, even if there are enough pages available
>> in total).
>
> This is something that's interesting with respect to x86_64 Xen, which
> requires paging to be turned on.  We could get pretty far with a small
> fixed-size malloc for the OCaml runtime to use, and give the majority
> of the pages to the OCaml GC in a fixed block that we register with the
> runtime system.
>
> Of course, virtual memory support may just be easier...
>
>> My next steps are to check that the rest of it is working and then try
>> enabling libc. It might also be interesting to look at debugger
>> support (e.g. getting gdbsx working), though I have no idea how hard
>> that would be.
>
> Before libc, it's also worth trying a few block device writes from the
> guest to check that the higher level ring plumbing is working.  I've
> never really used gdb to interactively debug, as printf debugging goes
> a long way once you have a working console.

OK, I'll try to get the grant tables working next.


-- 
Dr Thomas Leonard        http://0install.net/
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