Re: Xoscope nuisance console messages on Pi4 running -current

On 2021-May-3, at 08:23, bob prohaska <fbsd at www.zefox.net> wrote:

> On Mon, May 03, 2021 at 01:00:03AM -0700, Mark Millard via freebsd-ports wrote:
> [detailed code tour omitted]
> 
>> 
>> My guess would be xoscope used a signed 32-bit type
>> that got a value with sign extension to 64 bits
>> before the value started being treated as unsigned.
>> If it had used an unsigned type instead, the padding
>> would have been a zero fill instead (presuming that
>> I've guessed right).
>> 
> 
> So this was an artifact of compiling a 32 program on a 64 bit machine?

I've no evidence that you were building the port for armv7
instead of aarch64. If you were, it would be good to report
that.

Otherwise, I expect the code produced was 64-bit (aarch64)
and the rest is just how the program's source code is set
up.

> And, perhaps unnecessary use of signed versus unsigned integers? 

That is what I expect is going on in the xoscope source code.
(I've not looked.)

> This begs two more questions: It is harmless (seemingly not always), 

I doubt that it is a problem (other than the messages). As I
wrote:

QUOTE
While I do not know the specifics for the command
and command group encoding, the truncated value
seems coherent with the code that is using it.
END QUOTE

> and would it go away if compiled and run on a 32 bit machine, say armv7?

"long int" and "int" are both 32-bits on armv7 (unsigned
or signed) so no extra 1-bits would be produced by sign
extension.

So I do not expect the messages would be generated when
executed via armv7 code.

As far as I can tell, the program likely works (ignoring
the messages) for aarch64. The messages are from the
FreeBSD you are using being a debug build with INVARIANTS
enabled. A non-debug FreeBSD build would not report the
messages.

(It is possible to buildworld for armv7 and install it
into a directory tree and use chroot into that directory
tree to run armv7 code on the RPi4's. This should not
produce the messages --and if it did then there would
be FreeBSD code to change for that kind of context.)

> Many thanks for the detailed explanation, but I'll admit not understanding
> much more than the quoted part above 8-(



===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)

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