User-Level Native Thread Primitives (GThread) Library White Paper (G06.26+)

User-Level Native Thread Primitives (GThread Library) 03/31/2005
Hewlett-Packard Company--540065-001 Page 29 of 46
Input:
cb - The address of the thread control block for the thread being checked.
mem_guard – The amount of mem stack space, in bytes, reserved as the guard area.
reg_guard - The amount of reg stack space, in bytes, reserved as a guard area. On platforms other
than TNS/E native, this argument is ignored.
Return: int16
Returns nonzero if:
• The thread model is swapped
• The stack space wasn’t allocated
• mem_guard is greater than allocated mem stack space
• reg_guard is greater than allocated reg stack space
• A guard area has been overwritten or was not initialized with GTS_STATIC_FILL
Returns zero if the guard area has not been overwritten.
Considerations:
For this function to work properly, the GTS_STATIC_FILL Swaptions define must have been
specified during GTHREAD_INITIATE_ for the specified thread. See Section 2.11 for more
information on this option.
The mem_guard and reg_guard values should each be less than or equal to the space the user
intended to remain as guard areas for the mem and reg stacks, respectively.
Specification of zero or a negative value for either mem_guard or reg_guard is invalid; the
consequences associated with using a negative value are undefined.
For TNS and TNS/R, the concept of a separate reg stack does not exist and the contents of
reg_guard are ignored for the aforementioned checks.
This function is subject to the same limitations described in Section 3.6.3.2 concerning using guard
areas as protection against overflows of static stacks. It is provided as a ‘built in’ for clients who use
guard areas for overflow protection. The following are some basic guidelines for usage:
- Larger guard areas increase probability of detection and of containment of corruption. However,
they take longer to check.
- Shorter guard areas take less time to check, and they can more readily be entirely overwritten.
Also, a short mem_guard can be ‘stepped over’ by large memory stack frames that are sparsely
written. (The reg stack is always written densely.)