[Bug]: Trap redirection ignores vectored stvec and vstvec modes

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
55/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Tech stack
rust
Domain
embedded-iot, operating-systems

Research direction

Start in firmware/runtime/src/trap/redirect.rs, where frame.epc is set from the supervisor trap vector base for both the S-mode and delegated VS paths. Read the stvec and vstvec MODE field alongside BASE, and check how the cause is available at that point. Done means vectored interrupts jump to BASE + 4 * cause while direct mode and synchronous exceptions still use BASE, or vectored mode is explicitly rejected or documented.

Written by the indexing model from the issue text.

Description

C-bug help wanted

Description

firmware/runtime/src/trap/redirect.rs reads only the BASE field of stvec or vstvec when redirecting a trap. It does not inspect MODE. A payload that selects vectored mode consequently enters at the base address for every interrupt cause instead of at BASE + 4 * cause.

Steps to Reproduce

  1. Run a supervisor payload that sets stvec.MODE to Vectored and installs distinct handlers for two interrupt causes.
  2. Deliver one of the non-base interrupt causes through Runtime redirection.
  3. Observe the mepc selected for the return to the payload.

The VS path has the same issue when vstvec.MODE is Vectored.

Expected Behavior

For vectored interrupt delivery, Runtime should select BASE + 4 * cause. Direct mode and synchronous exceptions should continue to use BASE.

Actual Behavior

Both paths always assign the vector base to frame.epc:

frame.epc = supervisor::TrapVector::read()
    .get::<supervisor::BASE>()
    .address()
    .into();

The delegated VS path performs the equivalent vstvec base-only read.

RustSBI Version

main @ 721f68f7181817a727010372d9b485943a0e8242

Rust Toolchain

nightly-2026-05-11

Platform / Board

Prototyper with a supervisor payload using vectored interrupts

Execution Environment

QEMU

Additional Context

Read MODE along with BASE and apply the offset only for vectored interrupts. If vectored redirection is intentionally unsupported, reject that mode explicitly or document the limitation so the payload does not silently register handlers that cannot be reached.

Dominant language
Rust
Stars
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Forks
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Avg merge
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Merged PRs (30d)
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