x86-64: `syscall` instruction; number in RAX; args in RDI, RSI, RDX, R10, R8, R9; return in RAX - ARM64: `svc #0` instruction; number in X8; args in X0, X1, X2, X3, X4, X5; return in X0 - RISC-V: `ecall` instruction; number in a7; args in a0, a1, a2, a3, a4, a5; return in a0