Query Regarding tohost System Call Handling in Rocket Chip

[canxin121]

Query Regarding tohost System Call Handling in Rocket Chip

Repo

For details, please see canxin121:rocket_chip_bugs

Difference Discovery

This Difference was discovered during random instruction sequence testing.

Minimized Reproduction Program

debug.s

# 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 ./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.