Re: Porting DTrace to ARM

[Matt Thomas <matt%3am-software.com@localhost>]

On Mar 7, 2014, at 2:27 AM, Ryota Ozaki <ozaki-r%NetBSD.org@localhost> wrote:

> Hi Matt,
> 
> So my patch for sys/arch/arm is now rather small than
> so far (just two files); it's minimum code for the core part
> to run DTrace on ARM.
> 
> Can you please check it?
> 
> The patch for sys/arch/arm is
> http://www.netbsd.org/~ozaki-r/dtrace-arm-sys.patch
> The full patch is available at the usual place:
> https://gist.github.com/ozaki-r/8535846
> 
> Best regards,
>  ozaki-r

In undefined_init, the KDTRACE_HOOK should be after und_ev.ev_count++.

Digression ahead.

I wonder if it wouldn't be better to use a BKPT instruction on armv5t
and later and avoid the undefined trap, and use a prefetch abort with
a known FSR code.  For pre-armv5t, we'd need a undefined handler but
we have one of those now.  BKPT instructions have either a 16-bit (ARM)
or 8-bit (thumb) value encoded within.  

But that can be tackled later.