Re: [9fans] Go and 21-bit runes (and a bit of Go status)

[erik quanstrom <quanstro@quanstro.net>]

On Mon Jun  3 01:39:33 EDT 2013, lucio@proxima.alt.za wrote:
> > there are things that could be done.  but before getting radical in a
> > hurry, is there any place other than runtime·memmove() that
> > would use sse in a note handler?
> 
> I presumed, perhaps incorrectly, that users are allowed to write their
> own signal handlers and are not prohibited from using floating point
> instructions in them.

there are no signals in plan 9.  i assume that you mean note handlers.

note handlers may be user set but may not do floating point.
see notify(2) for documentation.

as cinap pointed out, this is because the fp save area for the process
is (potentially) busy when the note is delivered.  think of it this way
here up = user process.  this is the kernel convention.  some details
of this are slightly incorrect for clarity.

user			kernel
generates fault
			saves up registers,
			saves up floating point, sets fp state to FPillegal
				the save area is already used.
starts note handler
generates fp fault
			saves up registers,
			finds that we're in FPillegal state, and process
			becomes Broken

- erik