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Re: i386: Are we settled?


>>>>> "Jim" == Jim Blandy <jimb@cygnus.com> writes:
Jim> Are we settled on the essential contents of tm-i386.h?  

I think so.  

On the embedded side, we'll eventually need a mechanism to set the
processor type instead of using the HAVE_I387_REGS, etc. macros to
define the register set at compile time.  Also, an embedded target
may have need to get at the control and debug registers (cr0, cr2,
cr3, cr4, dr0-dr7) and the global, local, and interrupt descriptor 
table registers while these may not be available to user programs 
on other systems.

Jim> Essentially, I see two outstanding questions remaining:
Jim>
Jim> - How should i386 targets handle the x86 FPU's 80-bit float type?
Jim>   How can we make sure that hosts capable of handling it properly
Jim>   don't perform lossy conversions?

I may have mentioned this before, but I believe that in the longer
term we should move away from lossy conversions on all hosts, even
those without 80/96 bit FP support by integrating a software FP
engine/library (This might be useful for simulators as well, since
we'd be able to handle exceptional conditions, rounding flags, etc.
more precisely).  The library I'm familiar with is John Hauser's
SoftFloat:
    http://HTTP.CS.Berkeley.EDU/~jhauser/arithmetic/SoftFloat.html

Jim> - What format should the output from "info float" take?
Jim>   (Actually, it sounds like this is pretty much resolved.)

I'm more or less happy with the results, but I have no strong feelings
either.  As long as users can write user defined functions to present
the registers values in whatever format they want/need, I'm satisfied.

Jim> Notably missing from this list are any other questions about
Jim> tm-i386.h as it stands.  Am I correct in thinking that the other
Jim> x86 port maintainers think it's basically sane?

I think there are unresolved issues with MMX, but since you've started
another thread on that topic, I'll address them there.

        --jtc

-- 
J.T. Conklin
RedBack Networks

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