Various questions

Mattia Belletti mattia.belletti at poste.it
Thu Nov 11 09:00:37 CET 2004


I try to send this message again, since it seems it has not been posted:


Hi all - I have some questions; I hope they have not already been posed!

- I'm running a bare qemu + pistachio 0.4, and its kickstart + sigma0,
with a little root server of my own, on a IA32 architecture. I ask for
bootinfo location, and I find it's 0x1000 (that's where kickstart puts
it, so it's ok). However, when I try accessing it, I obviously
pagefault, but sigma0 refuses to give me that page. Anyway, if I _force_
it it to do (I've tweaked by hand source code), everything works fine -
in fact the bootinfo is there, and it is correct. Did I get something wrong?

- Little note: looking kickstart, I found this, around
user/util/kickstart/mbi-loader.cc:486:

     if (use_bootinfo)
     {
         // Allocate and initialize a bootinfo structure.
         bi = init_bootinfo (&kip);
         rec = (L4_BootRec_t *) ((L4_Word_t) bi + bi->size);

         if (bi)
             // Record MBI modules
             rec = record_bootinfo_modules (bi, rec);
         else
             use_bootinfo = false;
     }

(I'm referring to CVS version, If I remember well 0.4 version was
exactly the same). The "rec = stuff" isn't wrong? If "bi" is set to NULL
by the init_bootinfo (in case of OOM, if I remember well), this
segfaults - well, don't know what it does exactly, since there's still
no kernel around, and I don't remember IA32 defaults ;D

- Looking L4 specs (even the latest - by the way, how come the sources
theirselves aren't published? I would have found it useful when I did
those searches about sigma0 ;D), I have found no satisfying explanation
about the kinds of memory descriptors L4 knows about. That is,
UndefinedMemoryType, BootLoaderSpecificMemoryType,
ArchitectureSpecificMemoryType are obvious, but what are the differences
between ConventionalMemoryType and SharedMemoryType? What between
ReservedMemoryType and DedicatedMemoryType? What are their exact
meanings? Not that I absolutely need to work this out now, but I would
like to know this better! :-)

- Last: what purpose sigma1 has? I remember reading something about it
in the papers about transparent checkouts of kernel state, and stuff
like that...

Thank you all for the attention! :-)

-- 
Mat/tia Belletti - Undergraduate student @ cs.unibo.it
ICQ: 33292311    - email: mbellett at cs.unibo.it
IRC: RedGlow     - site(s): http://mbellett.web.cs.unibo.it/
Jabber: RedGlow  - Linux registered user 299762 @ machine 213003






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