Messages in this thread | | | Date | Sun, 07 Mar 2010 11:00:23 +0200 | From | Avi Kivity <> | Subject | Re: use of setjmp/longjmp in x86 emulator. |
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On 03/02/2010 09:28 AM, Gleb Natapov wrote: > On Mon, Mar 01, 2010 at 02:13:32PM -0500, john cooper wrote: > >> Gleb Natapov wrote: >> >> >>> Think about what happens if in the middle of >>> instruction emulation some data from device emulated in userspace is >>> needed. Emulator should be able to tell KVM that exit to userspace is >>> needed and restart instruction emulation when data is available. >>> >> setjmp/longjmp are useful constructs in general but >> IME are better suited for infrequent exceptions vs. >> routine usage. >> > Exception condition during instruction emulation _is_ > infrequent.
Well, with mmio you'd expect it to happen every read access.
> Although setjmp/longjmp that I know about > are routine usage. See QEMU TCG main loop or userspace > thread libraries. >
Agreed, nothing magical about it.
>> If the issue is finding some clean and regular way >> to back out from (and possibly reeneter) logic >> expressed within nested function invocations, have >> you considered turning the problem inside out and >> using a state machine approach? >> > I don't see how state machine will help. But the goal > is not to rewrite emulator.c (this will no be excepted > by kvm maintainers), but improve it gradually. >
That is orthogonal. If we decide a state machine is the best implementation, then we'll find a way to move over to that. However, I don't think a state machine is a good representation considering some of the code paths are very complicated and depend on a many memory accesses (e.g. hardware task switches).
-- error compiling committee.c: too many arguments to function
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