Fix the riscv_dret_test
#2338
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Fix the riscv_dret_test
#2338
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rswarbrick
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Dec 2, 2025
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Thanks for the careful explanation (I'd have struggled to understand what was going on without it!). This looks good to me (modulo a nitty comment about long lines)
The test checked for the exception handler to launch and then waited for the core to flush its pipeline. However, the flush happened immediately after the exception, which led the test to miss the first exception handler and the `check_priv_mode` to fail, since the check only executed after the flush leaving the exception handlers. This also means that on later executions, we were not checking the exception handlers as we go, but instead, the exception handler from the exception before. Accordingly, this test only failed if Ibex initially started in USER mode. Otherwise, it was anyways always in MACHINE mode
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rswarbrick
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Looks great (and thanks for the explanation!)
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The test checked for the exception handler to launch and then waited for the core to flush its pipeline. However, the flush happened immediately after the exception, which led the test to miss the first exception handler and the
check_priv_modeto fail, since the check only executed after the flush leaving the exception handlers. This also means that on later executions, we were not checking the exception handlers as we go, but instead, the exception handler from the exception before. Accordingly, this test only failed if Ibex initially started in USER mode. Otherwise, it was anyway always in MACHINE mode.The failure in the nightly regression are all due to:
Alternatively, I tried using a fork/join to check for entering the exception handler and the flush independently. This also works, but is an overkill IMO, because the flush will always be instant and communicating that the exception handler starts will always take a few cycles after the flush completed.