Sorry, I typed that in haste without testing.   I don’t have a 2.11 system to try it on.
However, reading the source code, I did that wrong.
The args go on the stack, not in line with the code.

       mov $6, -(sp)
       mov a, -(sp)
       mov $1,-(sp)
       sys 4


> On Apr 29, 2020, at 12:08 AM, Jacob Ritorto <jacob.ritorto@gmail.com> wrote:
> 
> Shoot, celebrated too soon.  I rearranged it per your tutelage, Ron, and it's still giving an  Illegal Instruction error!
> From the adb output it looks like it's balking at the "14" instruction at location 24, which, based on the BSD updates you mentioned, I thought should've been taken as an arg, not an instruction, right?
> 
> I assume this worked for you on some BSD, right?  
> If so, is it a bug in the recent 2.11BSD patch release, perhaps?  Anyone able to help me understand?
> 
> > vi hello.s
> "hello.s" 8 lines, 52 characters 
>          sys 4
>          1
>          a
>          6
>         sys 1
>         0
> a:      <Hello\n>
> 
> "hello.s" 7 lines, 78 characters 
> > as !$
> as hello.s
> > ./a.out 
> Illegal instruction (core dumped)
> > od a.out
> 0000000  000407 000022 000000 000000 000010 000000 000000 000000
> 0000020  104404 000001 000014 000006 104401 000000 062510 066154
> 0000040  005157 000000 000000 000002 000000 000000 000000 000000
> 0000060  000000 000000 000000 000004 000002 000014 000000 000006
> 0000100  000141
> 0000102
> > adb
> adb> :s
> stopped at      0:              sys     write
> adb> :s
> a.out: running
> stopped at      04:             <illegal op>    014
> adb> :s
> a.out: running
> Illegal instruction
> stopped at      06:             rtt
> adb> :s
> a.out: running
> Illegal instruction - core dumped
> process terminated
> adb> > 
> 
> On Tue, Apr 28, 2020 at 10:26 PM Noel Chiappa <jnc@mercury.lcs.mit.edu <mailto:jnc@mercury.lcs.mit.edu>> wrote:
>     > From: Jacob Ritorto
> 
>     > I wonder if the differences are written up somewhere.  I did try to look
>     > for more documentation but came up short.
> 
> Sounds like a perfect topic for a CHWiki page. :-) E.g. this one:
> 
>   http://gunkies.org/wiki/Unix_V6_internals <http://gunkies.org/wiki/Unix_V6_internals>
> 
> which I did as a bit of an addendum to Lions, to explain rsav, qsav and ssav, and
> similar topics.
> 
> 
> I noticed in the comparison of your two binary files that the instructions
> looked the same, but the a.out headers had a difference, but I didn't remember
> the fields in the a.out header enough to know what the differences meant.
> 
> I thought I remembered doing an a.out page there, but apparently not. I
> thought about doing one now, but decided it wasn't worth it; I just needed to
> spin up my V6 system and do 'man a.out'! :-)
> 
>    Noel
>