+
+ "The stack pointer (SP) must at all times denote an address that has octaword
+ alignment. (This restriction has the side effect that the in-memory portion
+ of the argument list, if any, will start on an octaword boundary.) Note that
+ the stack grows toward lower addresses. During a procedure invocation, SP
+ can never be set to a value that is higher than the value of SP at entry to
+ that procedure invocation.
+
+ "The contents of the stack, located above the portion of the argument list
+ (if any) that is passed in memory, belong to the calling procedure. Because
+ they are part of the calling procedure, they should not be read or written
+ by the called procedure, except as specified by indirect arguments or
+ language-controlled up-level references.
+
+ "The SP value might be used by the hardware when raising exceptions and
+ asynchronous interrupts. It must be assumed that the contents of the stack
+ below the current SP value and within the stack for the current thread are
+ continually and unpredictably modified, as specified in the _Alpha
+ Architecture Reference Manual_, and as a result of asynchronous software
+ actions."
+
+ -- Compaq Computer Corporation, Houston. Tru64 UNIX Calling Standard for
+ Alpha Systems, 5.1 edition, August 2000, section 3.2.1. http://www.
+ tru64unix.compaq.com/docs/base_doc/DOCUMENTATION/V51_PDF/ARH9MBTE.PDF