RISC-V Design · All levels

Extension Compatibility Policy: Debug Playbook

Debug Playbook for Extension Compatibility Policy.

Debug playbook

Debug Playbook for Extension Compatibility Policy is anchored on Software portability rate across SKUs and zero-regression compliance against declared ISA profiles.. Convert observations into mechanism-backed decisions with explicit ownership.

Freeze workload seed, binary, compiler, firmware, and platform setup.
Find earliest persistent mechanism failure in the timeline.
Build one reduced reproducer for dominant hypothesis.
Patch minimal fix with explicit rollback gate.
Rerun correctness + performance + power matrix.

Decision tree

diagram

ROOT CAUSE TREE - Extension Compatibility Policy

Software portability rate across SKUs and zero-regression compliance against declared ISA profiles. regressed
          |
   reproducible on fixed seed?
      /                 \
    no                   yes
    |                     |
env/tool drift       first failing domain?
                     /        |         \
                  decode    execute    memory/MMU
                    |         |            |
               control map  bypass/FU   TLB/walk/perm
                    |
         privilege/CSR side effects checked?

Stop at first confirmed mechanism, then assign explicit owner + fix proof.

Review memo template

diagram

RISC-V REVIEW MEMO - Extensions: Vector & Crypto / Extension Compatibility Policy

1. Symptom
   - Failing metric: Software portability rate across SKUs and zero-regression compliance against declared ISA profiles.
   - Failing workload slice: <name>
   - Triggering mode: <privilege/virtualization/interrupt/cache/boot>
   - Build and runtime tags: <toolchain/firmware/RTL revision>

2. Mechanism hypothesis
   - Primary mechanism: A compatibility policy defines mandatory, optional, and forbidden extensions per product tier, then ties those contracts to toolchain defaults, ABI rules, and runtime feature discovery. Policy quality depends on deterministic multi-version dispatch, clear deprecation windows, and compatibility tests that prevent accidental reliance on unavailable extensions. Mature teams align policy with upstream profile initiatives and publish explicit migration guidance so ecosystem partners can ship one codebase across heterogeneous RISC-V deployments.
   - Competing hypotheses: <decode control / hazard / MMU / privilege / integration>
   - Missing evidence: <trace/counter/proof/report>

3. Proposed action
   - Smallest reversible change: <RTL/compiler/runtime/config>
   - Expected movement: <throughput/latency/tail/perf-per-watt>
   - Regression risk: correctness, security, power, timing, software compatibility

4. Signoff
   - Required artifact: ISA policy document with profile tables, ABI commitments, compiler flags, and conformance regression gates.
   - Required owners: platform architecture lead, toolchain and SDK owner, firmware and OS owner, ecosystem enablement lead
   - Final decision: ship, bounded rollout, rollback, or escalate

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