Messages in this thread | | | From | (Linus Torvalds) | Subject | Re: PATCH: (on Alpha) emulating missing instructions | Date | 15 Oct 1999 16:48:11 GMT |
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In article <E11c73e-0004dD-00@the-village.bc.nu>, Alan Cox <alan@lxorguk.ukuu.org.uk> wrote: >> We already have FPU emulation in kernel, and there > >That should probably have been in userspace.
Nope.
I don't think you lived through the horror of Minix and having user-space FP emulation. It's a horrible pain - either overloading SIGFPE with all that implies, or another magic hidden signal with ld.so loading a FP library on demand etc - and then core-dumps tend to be impossible to figure out etc etc.
So it definitely was a lot better off in kernel space - the user space solution would just have made everybody go slightly mad after the five hundreth bug in some shared library configuration. With the kernel solution there were no surprising interactions, just a lot of reasonably complex code that had mostly been written earlier anyway.
HOWEVER, it may be that times have changed, and that it _now_ would be better off in user space simply because it's almost never an issue any more, and user space can do some hacks that you can't do in kernel space due to security reasons etc.
At the same time it also doesn't really matter any more. I don't think the FP emulator has been changed in the last year or so, and it works. It has some slightly painful issues with fp state saving etc, but they are at least _solved_ issues.
Linus
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