MulDiv module

Concept

The MulDiv module is described in the ProcessorFuzz paper as the multiplication unit of the RISC-V Rocket Core. It is notable in that study because its `remainder` register caused a large share of DIFUZZRTL register-coverage feedback, illustrating how datapath-heavy registers can mislead hardware fuzzers.

First seen 5/28/2026

Last seen 6/8/2026

Evidence 7 chunks

Wiki v1

WIKI

Overview

The MulDiv module is identified in the ProcessorFuzz paper as the multiplication unit of the open-source, RISC-V-based Rocket Core. In the paper, it is used as a concrete example of how register-coverage feedback in RTL processor fuzzing can be misleading when datapath registers dominate the coverage signal.

Role in DIFUZZRTL coverage feedback

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NEIGHBORHOOD

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RELATIONSHIPS

2 connections

Rocket Core part of → 100% 2e

Rocket Core contains the MulDiv module.

RISC-V Rocket Core part of → 100% 2e

The MulDiv module is the multiplication unit within the Rocket Core.

CITATIONS

5 sources

5 citations — click to expand

[1] The MulDiv module is the multiplication unit of the open-source, RISC-V-based Rocket Core. ProcessorFuzz: Processor Fuzzing with Control and

[2] DIFUZZRTL monitors registers whose values are directly or indirectly used to control multiplexer selection signals and hashes monitored register values during RTL simulation to compute register coverage. ProcessorFuzz: Processor Fuzzing with Control and

[3] In Rocket Core's MulDiv module, a 130-bit remainder register indirectly controls 98 mux selection signals, causing DIFUZZRTL to identify it for monitoring; after optimizations, 98 bits of the remainder register are tracked. ProcessorFuzz: Processor Fuzzing with Control and

[4] In a 24-hour Rocket Core fuzzing session, 62% of overall register coverage came from the MulDiv module, and the remainder register was the major contributor to coverage increase within MulDiv. ProcessorFuzz: Processor Fuzzing with Control and

[5] The ProcessorFuzz paper argues that datapath registers such as remainder can significantly increase the fuzzing search space while providing little meaningful information about the current hardware FSM state. ProcessorFuzz: Processor Fuzzing with Control and