[RFC] how to call host-side stuff from -tdep code?

[Joel Brobecker <brobecker@adacore.com>]

Hello,

I am about 75% through porting FSF HEAD to ia64-hpux, and I have
a question:

I'm inside ia64-tdep.c, and I need to determine whether we're inside
a system call or not.  Apparently, the way to do that is to perform
a call to ttrace (I'm planning on wrapping this inside a -nat.c file).
But of course, you are not supposed to do that, since the -nat module
is not available in the case of a cross debugger.

To be more precise, the ttrace request is a TT_LWP_RUREGS, using
an offset set to __reason.  If the returned value is zero, then
we're in a syscall.  Otherwise, we're not.  In a way, this could
be thought of as a special register.

I don't think that adding a raw register would be really be all
that appealing, since it'd be accessible to the user.

I thought about a pseudo register, but this seems awkward, if possible
at all.  My understanding is that pseudo-registers are really a thing
of the target, which cannot depend on native stuff.

It seems to me that the easiest solution right now is to add a new
xfer object (say TARGET_OBJECT_IA64/"ia64.in_syscall"), and then
use target_xfer_partial to get the information I needed. Is that
what these objects were meant for?

I considered adding a new target method, but that seems way overkill,
just for one platform.

Any other suggestion?

-- 
Joel