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NAME : HCPIASIT
DESCRIPTION: Internal-Address-Space-Identification
Token
DSECT : IASIT
FUNCTION : This DSECT maps an i-ASIT, which is CP's internal
identification of an address space.
LOCATED BY : Any task needing an identification of an address
space. Some important fields which contain i-ASITs
are:
RSANASIT i-ASIT for "null" address space.
CREATED BY : HCPSIT%I when translating various representations of
address spaces into i-ASITs.
DELETED BY : Any task which no longer needs the representation.
RELOCATION CONSIDERATIONS : None
NOTES :
An i-ASIT is an eight-byte token, doubleword aligned, and
serves as a task's internal representation of a particular
address space. An i-ASIT contains information designating
which address space, information defining the task's
"capability" to access the address space, and information
defining the method of translating addresses for that
task. Since it contains more information than just what
is necessary to identify an address space, an i-ASIT
cannot be directly compared to another i-ASIT to determine
if the same space is designated. A service routine (as
provided by the HCPCMPIA macro) must be used for i-ASIT
comparison purposes.
The capabilities represented in an i-ASIT are the
following:
- r-access vs. i-access
- Read/write vs. read/only permission
- For guest instruction-stream references, whether
guest prefixing, guest low-address protection,
and guest fetch-protection override apply.
Translation of a guest real address into a host real
address is affected by whether or not the address space is
the user's base address space, and whether or not the
user's reference is a primary-space or secondary-space
reference. Prefixing, low-address protection, and
fetch-protection override apply only when the space is the
base, and when the access is a primary-space or
secondary-space reference.
An i-ASIT must be certified before it can be used for any
purposes. A certified i-ASIT is one that meets the
following criteria:
- The ASTE sequence number in the i-ASIT matches
the ASTE sequence number in the ASTE (i- or r-access)
*or*
- ASCSEQNO <= ASITSN <= ASTSN (r-access)
The i-ASIT certification function is provided by either
the HCPASMCI entry point or the HCPACERT macro (to be used
only in cases where performance is a major concern, or the
routine cannot call another routine which uses PFXTMPSV).
Other services which process i-ASITS, such as HCPCMPIA
and HCPCHCR7, handle certification of i-ASITs internally.
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