[U-Boot-Users] Re: The i386 patch

Wolfgang Denk wd at denx.de
Wed Nov 20 15:06:47 CET 2002

In message <200211201114.gAKBEss01326 at dagobert.svc.sysgo.de> you wrote:
> > What do you mean with "stack to copy"?
> The standard method for the x86 to implement a syscall is through a 
> "gate", which is also a mechanism to switch to a higher protection level. 
> Since caller and callee run at different protection levels, they use 

OK, understood.

But this is not what U-Boot needs.

> Does that mean that the caller always runs at the same protection level as 
> U-Boot?


> If so, then I think that a syscall mechanism for the x86 through gates would 
> be overkill. But then, OTOH, why use syscalls at all ? A simple jump table 
> could do the same thing, and do it portably.

You may remember that we used a jump table  attached  to  the  global
data in early versions of PPCBoot. I didn't like this. The nice thing
about  the  syscall  trap  on  PPC is that you can easily put a "jump
table" at a well-known location, so that a standalone application can
access certain services (those explicitely exported by  U-Boot  using
the  syscall  interface)  without  depending  on  a  special software

I have to admit that I did not think about other architectures at the
time we implemented this.

Best regards,

Wolfgang Denk

Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd at denx.de
Remember that Beethoven wrote his first symphony in C ...

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