Re: Porting DTrace to ARM

[Ryota Ozaki <ozaki-r%iij.ad.jp@localhost>]

Hi Christos,

Thanks for reviewing my patch.

(2014/01/22 2:56), Christos Zoulas wrote:
> In article <52DE274B.5080807%iij.ad.jp@localhost>,
> Ryota Ozaki  <ozaki-r%iij.ad.jp@localhost> wrote:
>> Hi,
>>
>> I'm working on porting DTrace to ARM.
> 
> Nicely done:
> 1. there seem to be some whitespace only changes

Sorry for the messy code. Will fix.

> 2. what's the STRONG_ALIAS to __ffssi2 about?

This is needed to modload solaris. Without the fix
I got the following error:
  # modload solaris
  kobj_checksyms, 880: [solaris]: linker error: symbol `__ffssi2' not found
  WARNING: module error: unable to affix module `solaris', error 8
  modload: Exec format error

This problem seems to be not dtrace specific. Other modules,
e.g., nand, are also encountered the error in the case of
evbarm/BEAGLEBONE.

I want someone to confirm the problem on an evbarm/BEAGLEBONE
machine (and other evbarm/arm machines).

I think this fix should be a separate patch if the fix is
correct.

> 3. what about the deleted code in dtrace_debug.c

The deletion is because of replacing dtrace_cmpset_long
with atomic_cas_ulong. Please see the reply to 5. for
more discussion.

> 4. I am torn about the cpuid -> cpu_id change. In my version of the
>     changes, I had fixed the arm code instead in sys/arch/arm. It was
>     used in very few places there.

Sure. I changed cpuid -> cpu_id because I thought I should
reduce the changes of the kernel core code. So if the change
of the arm code is acceptable, I will do it in my next patch.

> 5. I think that the dtrace_cmpset_long -> atomic_cas_ulong change is
>     questionable (because we probably want to keep the ABI's dtrace uses
>     stable; perhaps just making this a define in some header file and
>     leaving the source alone?

dtrace_cmpset_long is used only in dtrace_debug.c and
I think the change doesn't affect the dtrace ABIs.

...just now I found the change on FreeBSD
http://svnweb.freebsd.org/base/head/sys/cddl/dev/dtrace/dtrace_debug.c?r1=209059&r2=226452

  ozaki-r

> 
> christos
>