RISC-V Registers and Calling Conventions

Use when writing or reviewing RISC-V assembly — recursion, stack frames, and register roles. Covers callee-saved s0-s11 vs caller-saved a0-a7/t0-t6, RV64 8-byte slots and 16-byte alignment, leaf functions, and argument passing. Prevents the recorded garbage-sum failures from uninitialized s0 and 4-byte frames.