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Delayed state updates #10

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opened 2021-07-25 08:14:07 +02:00 by numas13 · 0 comments
numas13 commented 2021-07-25 08:14:07 +02:00
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Currently in v5 branch, all checks for operations in a bundle occur in sequential order without any delayed state updates. This means that if any exception occurs, such a bundle will perform a partial state update and the correct recovery from the exception will no longer occur.

{
    addd,0 %r0, 1, %r0      ! update r0
    ldd,2 [ addr ], %r1     ! an exception may occur here
    addd,3 %r2, 1, %r2
}

In this example, the initial value of the %r0 register will be lost if ldd fails due to a page fault.

This behavior wasn't a big problem in user mode emulation, but in system mode it's no longer acceptable.

Currently in v5 branch, all checks for operations in a bundle occur in sequential order without any delayed state updates. This means that if any exception occurs, such a bundle will perform a partial state update and the correct recovery from the exception will no longer occur. ``` { addd,0 %r0, 1, %r0 ! update r0 ldd,2 [ addr ], %r1 ! an exception may occur here addd,3 %r2, 1, %r2 } ``` In this example, the initial value of the `%r0` register will be lost if `ldd` fails due to a page fault. This behavior wasn't a big problem in user mode emulation, but in system mode it's no longer acceptable.
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numas13 added this to the System Emulation project 2021-07-25 08:14:07 +02:00
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Reference: OpenE2K/qemu-e2k#10
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