Re: [9fans] broken floating point exceptions and fpregs

[erik quanstrom <quanstro@quanstro.net>]

On Fri May 24 17:30:59 EDT 2013, cinap_lenrek@gmx.de wrote:
> the sse change broke floating point exception handling.
>
> from /sys/src/9/pc/main.c:^matherror()
> 	/*
> 	 *  save floating point state to check out error
> 	 */
> 	fpenv(&up->fpsave);
> 	mathnote();
>
> this is wrong, because fpenv() will store the enviroment
> in x87 format, but mathnote() uses mathstate() which intreprets
> the FPsave structure depending on if sse was enabled or not.
>
> a fix for this was just commited in 9front which passes the
> status word and fppc explicitely to mathnode() and uses
> mathnote(up->fpsave.status, up->fpsave.pc); in matherror()
> and the values extracted by mathstate() in mathemu().

http://ftp.9atom.org/9pccpuf-sse

this is a different implementation that steve simon used to
run linuxemu.

> the 2nd problem is how we'r going to handle the fpregs file
> in devproc. as this change changes the format. fpr() in acid
> returns garbage right now. any thoughts on it how to move
> forward on this?

why don't we just let the 386 kernel rest in peace and use
64-bit for sse?

- erik