[okl4-developer] new Wombat syscall and others

[Carl van Schaik]

Hi Jorge,

Jorge Torres wrote:
> Hi okl4.org <http://okl4.org>,
>
> I have a few questions, of which probably many of you know the 
> answers, but I'm starting to feel a little lost (RTFM answers are 
> welcomed too :)
>
> *Wombat magic relies on the great work of adding arch/l4 and asm-l4 
> right?, so what are all the (asm-* and arch/*)!=l4 used for?
They are mostly not used. However a number of them are included by the 
base architecture. eg ARM on L4 includes a few files from asm-arm. This 
is mostly to avoid duplication of files.
> *If one wants to add a new wombat syscall, where is it to be 
> registered? since there is no arch/l4/kernel/entry.S, which is quite 
> obvious if architecture independent code is wanted, I believe there is 
> this  syscalls.c   instead, but I cant understand completely how it 
> works, and how  can  it match with include/asm/unistd.h? perhaps it 
> doesn't really have to.  And how does this { sys_MYINTERRUPT,    {{ 
> .args = ?(QUITE OBVIOUS), .flags = ?, .ret_type = ??? }} }, works?
There are a number of options: We can support a number of different ABIs 
from one architecture. Eg on MIPS, we used to support O32, N32 etc which 
are different syscall ABIs. So you could add a new ABI for your own 
syscalls.
Alternatively, you can add extra syscalls to the base ABI. The base ABI 
depends on the architecture, eg ARM L4 uses ARM compatible syscalls.

how syscalls work: The ABI call is converted to an L4 syscall number in:
  linux/kernel/arch/l4/kernel/main.c :
       long sys_num = l4_arch_lookup_syscall(&curinfo->regs, &abi);

then the syscall is called via:
       result = l4_arch_abi_call(&curinfo->regs, sys_num, abi);

For ARM: The lookup syscall uses the: l4_arm_abi_syscalls[] table to 
convert ARM syscall numbers to L4-Linux generic syscall numbers.
This then indexes the l4_syscall_table[] table which has function 
pointers and details on number of arguments, return type etc
The flags = L4_SYS_FLAGS_NEED_REGS, means the function expects a pointer 
to the saved register context - always the last argument in a Linux 
syscall function.
>
> *What do I have to do If I want to use iguana's libraries on wombat 
> kernel code, I've seen this #include <asm/macros.h>
> #include INC_SYSTEM2(something), but I'm not sure; there is also 
> INC_SYSTEM() so, what are they for?
Iguana libraries should just be included like:
   #include <iguana/thread.h>

> *Are wombat's user threads L4 threads too, meaning they have UTCB 
> entries on Wombat's address space?
They are L4 threads, and have different address spaces to the Wombat 
address space. So they have UTCBs yes.
> *If I add an  iguana server, how can I communicate with it from a 
> Wombat user application, naming,IPC?
You need to provide a driver in Wombat that acts as a proxy for the 
user-application. We don't support direct communication between 
user-applications and iguana applications.
>
> *Iguana naming service is restricted to threads among their specific 
> protection domain, or is it a global service, meaning  that threads  
> on different  protection domains and AS  can  communicate via  naming 
> service?
Its a global service, threads in different protection domains can use 
it. The name server provided is a very simple example that does not try 
to do security.

>
> Well thank you very much,
>
> Jorge
>   
regards,
Carl