Query Regarding tohost System Call Handling in Rocket Chip

# Query Regarding tohost System Call Handling in Rocket Chip

## Repo

For details, please see [canxin121:rocket_chip_bugs](https://github.com/canxin121/rocket_chip_bugs/tree/master/3)

## Difference Discovery

This Difference was discovered during random instruction sequence testing.

## Minimized Reproduction Program

### debug.s

```riscv
# existing code ...
binvi x6, x21, 31
bclr x30, x6, x14
amoand.d.rl x28, x2, (x14)
max x4, x9, x30
sh2add x1, x25, x6
amomaxu.w.rl x10, x4, (x1)
hlv.hu x7, 0(x21)
# existing code ...
```

## Reproduction Steps

```bash
bash ./run.sh
```

Check the content of the `run` script to understand the specific execution steps and parameter settings.

## Spike Execution Results

- **Normal mode**: Crashes after executing the `amomaxu.w a0, tp, (ra)` instruction (i.e., `amomaxu.w.rl x10, x4, (x1)`)
- **Debug mode**: Crashes after executing the `amomaxu.w a0, tp, (ra)` instruction (i.e., `amomaxu.w.rl x10, x4, (x1)`)

## Rocket Execution Results

*** PASSED *** Completed after 28712 cycles

## Difference Analysis

### Spike

`amomaxu.w` happened to write the wrong system call ID to tohost, causing the spike program to exit with a bad system call error. This is the expected behavior.

### Rocket

`amomaxu.w` also wrote the wrong system call ID to tohost, but rocket did not respond to the system call and exited normally with PASSED. This differs from Spike's behavior.

Start with the minimized instruction sequence in debug.s and run bash ./run.sh, then inspect the run script's Rocket and Spike execution paths. Compare how each handles the incorrect tohost system call ID after amomaxu.w.rl. Done means the discrepancy is resolved and the reproduction no longer reports different outcomes.

Written by the indexing model from the issue text.