To achieve a substantial reliability and safety level, it is imperative to provide electronic computing systems with appropriate mechanisms to tackle soft errors. This paper proposes a low-cost system-level soft error mitigation technique, which allocates the critical application function to a pool of specific general-purpose processor registers. Both the critical function and the register pool are automatically selected by a developed profiling tool. The proposed technique was validated through more than 400K fault injections considering a Linux kernel, different benchmarks, and two multicore Arm processor architectures (ARMv7-A and ARMv8-A). Results show that our technique significantly reduces the code size and performance overheads while providing soft error reliability improvement compared with the Triple Modular Redundancy (TMR) technique.