Syscall (System Call)

The interface through which SBF programs request services from the Solana runtime, analogous to OS system calls. Syscalls provide access to operations that cannot be implemented in userspace BPF code: cryptographic functions (SHA-256, Keccak, Poseidon, secp256k1 recovery), logging (sol_log), account data access, CPI (invoke/invoke_signed), program return data, and sysvar reads. Each syscall has a defined compute unit cost.