Re: [MirageOS-devel] Mirage/ARM plans

[Thomas Leonard <talex5@xxxxxxxxx>]

On 14 May 2014 16:53, Anil Madhavapeddy <anil@xxxxxxxxxx> wrote:
> On 14 May 2014, at 15:39, Thomas Leonard <talex5@xxxxxxxxx> wrote:
>>
>> On 14 May 2014 15:26, Thomas Gazagnaire <thomas@xxxxxxxxxxxxxx> wrote:
>>>> Note that when I refer to 'libc', I'm really talking about libm (which
>>>> is essential), a printf implementation, and malloc/calloc.
>>>
>>> Do we steel need the printf stuff for ocaml 4.02 with the new printf's 
>>> GADTs implementation ?
>>
>> Good point. For now, it's using Mini-OS's printf functions. They
>> mostly work, but don't recognise %F, for example.
>>
>> For malloc, Mini-OS provides a malloc that returns contiguous regions
>> of (guest) physical memory (it just calls _xmalloc(size,
>> DEFAULT_ALIGN)). If OCaml just grabs more memory whenever the heap is
>> full, that should be fine. If people are freeing stuff, it could
>> become a problem due to fragmentation.
>
> There's very little mallocing relative to the amount of OCaml heap activity 
> (which allocates in 2MB chunks by default and could use super pages if 
> available). So sticking with the simple allocator should be fine for now.

Good news: it's already using super pages (1MB page table entries
rather than 4KB). For the 1:1 mapping, that's the easiest thing to do
anyway.

> (The exception are perhaps Io_pages which we malloc, but should draw from a 
> fixed pool to recycle them and not share them with the main heap, since they 
> can be granted to other driver domains).
>
>> For libm, does anyone have an opinion about openlibm?
>>
>>  https://github.com/JuliaLang/openlibm
>>
>
> Looks good if it works on ARM (your comment on that issue seems hopefully, 
> but it's worrying that it's been open for a year).

Looks like it's just because on ARM long double = double. Should just
be a case of deleting the extended precision section of the Makefile,
but I'll have to fix a couple of other things in mirage-platform
before I can test it.

> Adam Wick extracted libm from OpenBSD for HalVM, which we do too. Not sure 
> which is a better option...


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