[Fwd: Re: Regarding systemtap support for AArch64]

[Petr Machata]

William Cohen <wcohen@redhat.com> writes:

> On 11/04/2013 09:48 PM, Petr Machata wrote:
>> That 0x3F in x8 might be __NR_read, that might be from the syscall that
>> got us here.  So possibly makes sense.  0x112 is __NR_syscalls, I don't
>> see how that ended up there.  Maybe from a conditional?  0x2004 might
>> certainly be a length, though it's an odd one.  The two kernel-space
>> parameters have similar values, and the one user-space is quite
>> different--again, makes sense.
>
> These examples systemtap might not be the best.  It is just printing
> information for the first vfs.read or vfs.read.return encountered, so

I understand.  I was trying to figue out what's in the registers.  I can
agree that x0 to x4 hold vfs_read arguments on entry, so why doesn't, on
function return, x0 hold the return value?

> I wonder if there might be some issue with the patches implementing
> the arm64 kprobes support and that the registers are not be saved
> properly.

I was wondering about the same thing.

Thanks,
PM