Re: GSoC 2012 - 32 bit API for 64 bit kernel

[Ivan Sichmann Freitas <ivansichfreitas@xxxxxxxxx>]

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On Thu, Mar 22, 2012 at 12:40:07AM -0300, Ivan Sichmann Freitas wrote:
> Hi,
>=20
> I'm a computer engineering student at Unicamp (brazilian university),
> interested in compilers and computer architecture (and most low level
> stuff), and the idea of implementing the ABI for running 32 bit
> applications on a 64 bit kernel seems interesting and challenging.
>=20
> I have moderated knowledge of C, OS principles and Linux systems, some
> experience with FreeBSD, I've already cloned dragonfly's git repository
> and I'm studying the code to come with a planned roadmap of what would
> be my work in gsoc. You can find me with the username ISF in github and
> IRC networks (efnet, freenode and oftc).

So, as far as I understood the idea and dragonfly's code:
    - since the current code was created to be of only one architecture,
      I would need to create a set of *_32 syscalls (will they maintain
      the same numeric value in syscalls.master in relation of its 64
      bits counterparts?).
    - it's not clear to me how I will implement the control bits to
      indicate 32 bit execution.
    - I'm thinking in a way to implement this without breaking the
      current 64 bit abi for existing applications, any thoughts on
      that?

As a draft of my planned roadmap:
    - completely understand the syscalls' handling in the kernel
    - analyze the difference of 32 and 64 elf formats and how it affects
      the loader
    - plan the implementation (try to avoid abi breakage and pitfalls)
    - do it

(not sure how much time for each step, but the 2 firsts should be quick)

I would appreciate any feedback on this.

--=20
Ivan Sichmann Freitas
GNU/Linux user #509059

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