Re: [Qemu-devel] I want to add the ARMv6 instructions, who can give some advices?

[Laurent DESNOGUES]

> > All the information used to implement the current qemu Arm support is 
> > available from other sources not covered by this licence. I'm confident I 
> > could prove this if necessary.

True for ARMv6, probably not for ARMv7, be it -A, -R or -M.

> In the thread you cited earlier, Wolfgang Schildbach refers to "ARM
> System Developer's Guide", by Sloss, Symes, and Wright, Elsevier 2004
> as documentation that may be sufficient for Qemu ARMv6 support, and
> which is not covered by the license.

Yes.  But you would need instruction encoding that are not in the
book.  You will find them in binutils (opcode directory).

> If ARMv6 support were developed by someone else, using only that book,
> and maybe looking at other code (GCC, Linux etc.), that would prove
> that all the information used is from other sources not covered by the
> license, wouldn't it?

Linux uses a small subset of the System Coprocessor.  If you want
information about ARMv6 cp15, look in ARM TRM (arm11), I don't think
they have any restriction such as ARMv7-M.

> The support might be missing a few features, if the other information
> sources are incomplete, but even incomplete support that can be
> deduced from those sources would be good enough for most purposes.

Certainly yes.  But that's not a small effort :)

But bear in mind a few things:  for instance supersection,
that are ARMv6 specific, were added to Linux kernel in 2.6.13
which is kind of recent;  so if you omit some features, you
might have to add them in one day.

> If that were done, you could prove that the resulting feature in Qemu
> was written using sources not covered by the license.
> 
> So would you have any problem contributing to Qemu after ARMv6 support
> was integrated, if the person who contributes ARMv6 support states
> that they have never seen the ARM document and refers to the sources
> they have used instead?

I think that it could be very difficult to prove you did not
use any official NDA document.  I am doing simulator development
at ARM and would certainly never approach anything v6 or v7
related until information is publically available with no
restriction.

Anyway I am not speaking for ARM :)


Laurent