[kaffe] Re: mipsel/jit3 regression test results

Kevin D. Kissell kevink at mips.com
Wed Oct 13 10:44:27 PDT 2004

> The threads about MIPS & jit with Kevin from 2002 (March-June, I 
> believe), 2003, and 2004 with him & Casey also may contain some patches 
> that haven't been applied yet. If you, or Casey are aware of patches 
> that I have let slip under the floor, please point me to URLs, and I'll 
> be very glad to merge them in. There was a lot of intersting commentary 
> on the JIT engine between Kevin, Casey and Tim that was over my head, 
> essentially, as I'm not very familiar with the core JIT engine. But I'd 
> be glad to play patch-bot :)

Alas, I never submitted any JIT patches as such, because I didn't see any point
in submitting patches that weren't against the head of the tree (or at least the
most current "stable" revision), but I couldn't even get the more recent sources
to build with JIT, and was working mostly from a patched 1.07 tree.  That
version of the JIT actually passed a lot of the regression tests, and could run
the embedded Caffeinemark. So my "patches" conisted of "I changed X to Y" 
rather than a source diff, which I know is a good deal less useful.

My recollection is that someone did indeed apply/check in a patch which
fixed the erroneous allocation of MIPS argument registers by the JIT, but I
don't think my suggestion to force the use of temp registers, rather than roll
through spilling and restoring "dead" values, was ever picked up.  The
last time I went at debugging the thing, I was able to step through a certain
amount of JITed code, walking gdb from JIT buffer to JIT buffer, up to the
point where it computed an address based on a null pointer and crashed.
My hypothesis was that there was an assumption in the high-level JIT code
that a value would have been flushed out to memory, but that in the case
of the low-level MIPS JIT code, it had not been, leaving the location as
an uninitialized deathtrap, but that's just an intuition.  I'm working on other
stuff these days, and regret that I've got no time to fire up my MIPS/Linux
box and dig into this further.  I'll just have to track these threads and offer
whatever advice comes to mind from memory.


            Kevin K.

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