[nix-shell:~/dev/zig/build]$ ./zig build-exe test.zig -target riscv32-native -mcpu=?
info: Available CPUs for architecture 'riscv32':  baseline_rv32
 baseline_rv64
 generic_rv32
 generic_rv64

error: Unknown CPU: '?'

[nix-shell:~/dev/zig/build]$ ./zig build-exe test.zig -target riscv32-native -mcpu=generic_rv32+?
info: Available CPU features for architecture 'riscv32':  64bit: Implements RV64
 a: 'A' (Atomic Instructions)
 c: 'C' (Compressed Instructions)
 d: 'D' (Double-Precision Floating-Point)
 e: Implements RV32E (provides 16 rather than 32 GPRs)
 f: 'F' (Single-Precision Floating-Point)
 m: 'M' (Integer Multiplication and Division)
 relax: Enable Linker relaxation.
 reserve_x1: Reserve X1
 reserve_x10: Reserve X10
 reserve_x11: Reserve X11
 reserve_x12: Reserve X12
 reserve_x13: Reserve X13
 reserve_x14: Reserve X14
 reserve_x15: Reserve X15
 reserve_x16: Reserve X16
 reserve_x17: Reserve X17
 reserve_x18: Reserve X18
 reserve_x19: Reserve X19
 reserve_x2: Reserve X2
 reserve_x20: Reserve X20
 reserve_x21: Reserve X21
 reserve_x22: Reserve X22
 reserve_x23: Reserve X23
 reserve_x24: Reserve X24
 reserve_x25: Reserve X25
 reserve_x26: Reserve X26
 reserve_x27: Reserve X27
 reserve_x28: Reserve X28
 reserve_x29: Reserve X29
 reserve_x3: Reserve X3
 reserve_x30: Reserve X30
 reserve_x31: Reserve X31
 reserve_x4: Reserve X4
 reserve_x5: Reserve X5
 reserve_x6: Reserve X6
 reserve_x7: Reserve X7
 reserve_x8: Reserve X8
 reserve_x9: Reserve X9
 rvc_hints: Enable RVC Hint Instructions.

error: Unknown CPU feature: '?'