SYSPROCPERM system table

CREATE TABLE SYS.SYSPROCPERM (
	proc_id	 UNSIGNED INT NOT NULL,
	grantee	 UNSIGNED INT NOT NULL,
	PRIMARY KEY ( proc_id, grantee )
	FOREIGN KEY ( grantee ) REFERENCES
	SYS.SYSUSERPERM ( user_id ),
	FOREIGN KEY REFERENCES SYS.SYSPROCEDURE
)

Only users who have been granted permission can call a procedure. Each row of the SYSPROCPERM table corresponds to one user granted permission to call one procedure.