Re: how to tell if a process is 64-bit

[Eduardo Horvath <eeh%NetBSD.org@localhost>]

On Thu, 14 Sep 2017, Martin Husemann wrote:

> On Thu, Sep 14, 2017 at 02:31:29PM +0200, Thomas Klausner wrote:
> > 	kp = kvm_getproc2(kvmp, KERN_PROC_PID, pid, sizeof(*kp), &res);
> > 	if (res != 1)
> > 		exit(1);
> 
> 	if (kp->p_flag & P_32)
> 		printf("it is a 32bit process\n");
> 
> Unless you are running with a 32bit kernel, then you'll never see that
> flag (but also the question does not make sense).

In theory you could run 64-bit processes on a 32-bit kernel on CPUs that 
have disjoint user and kernel address spaces, like sparcv9.  In that case 
it would make sense to use the P_32 flag to distinguish processes with 
32-bit address spaces from those with 64-bit address spaces.

However, it would be a lot of work and probably not worth the effort since 
the kernel would be limited to 32-bits of data structures such as file 
descriptors and uvm spaces and be hard pressed to keep up with the demands 
of 64-bit address spaces.  (And implementing copyin/copyout routines would 
be fun.)

So yes, at the moment setting the P_32 flag on every process running on a 
32-bit kernel seems like a waste of CPU cycles.

Eduardo