Remote Direct Memory Access (RDMA) is a key technology in modern data centers, enabling low-latency and high-throughput communication. However, evaluating RDMA performance and validating network designs often requires costly hardware setups or simulation tools with limited performance and realism. In this work, we present P4DMA, a system that leverages programmable switch ASICs to generate realistic high-performance RDMA traffic. By implementing RDMA traffic patterns using the P4 language, P4DMA enables researchers and practitioners to generate RDMA workloads at line rate, without relying on traditional RDMA NICs (RNICS). With Tofino's traffic generation capacity of up to Tbps, P4DMA offers a novel approach to stress and evaluate RDMA-capable infrastructures, and accelerate the prototyping of new RDMA-based applications.