epc
epc B8
This instruction increases the privilege level. The new privilege level is given by the TLB entry for the page containing this instruction. This instruction can be used to implement calls to higher-privileged routines without the overhead of an interruption.
Before increasing the privilege level, a check is performed. The PFS.ppl (previous privilege level is checked to ensure that it is not more privileged than the current privilege level. If this check fails, the instruction takes an Illegal Operation fault.
If the check succeeds, then the privilege is increased as follows:
If instruction address translation is enabled and the
page containing the epc instruction has execute-only page access rights
and the privilege level assigned to the page is higher than (numerically
less than) the current privilege level, then the current privilege level
is set to the privilege level field in the translation for the page containing
the epc instruction. This instruction can promote but cannot demote, and
the new privilege comes from the TLB entry.
If instruction address translation is disabled, then the current privilege
level is set to 0 (most privileged).
Instructions after the epc in the same instruction group may be executed
at the old privilege level or the new, higher privilege level.
Instructions in subsequent instruction groups will be executed at the
new, higher privilege level.
If the page containing the epc instruction has any other access rights besides execute-only, or if the privilege level assigned to the page is lower or equal to (numerically greater than or equal to) the current privilege level, then no action is taken (the current privilege level is unchanged).
Note that the ITLB is actually only read once, at instruction fetch. Information from the access rights and privilege level fields from the translation is then used in executing this instruction.
This instruction cannot be predicated.
Illegal Operation fault
For details, see Volume 3: Instruction Set Reference of the Intel(R) Itanium(R) Architecture Software Developer's Manual . For the latest updates on the instruction set information, go to the web site.