Lfhint Mnemonic Values - Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 3 REV 2.3 Manual

Table 2-38.
lfhint Mnemonic
A faulting lfetch to an unimplemented address results in an Unimplemented Data
Address fault. A non-faulting lfetch to an unimplemented address does not take the
fault and will not issue a prefetch request, but, if specified, will perform a register
post-increment.
Both the non-faulting and the faulting forms of lfetch can be used speculatively. The
purpose of raising faults on the faulting form is to allow the operating system to resolve
problems with the address to the extent that it can do so relatively quickly. If problems
with the address cannot be resolved quickly, the OS simply returns to the program, and
forces the data prefetch to be skipped over.
Specifically, if a faulting lfetch takes any of the listed faults (other than Illegal
Operation fault), the operating system must handle this fault to the extent that it can
do so relatively quickly and invisibly to the interrupted program. If the fault cannot be
handled quickly or cannot be handled invisibly (e.g., if handling the fault would involve
terminating the program), the OS must return to the interrupted program, skipping
over the data prefetch. This can easily be done by setting the IPSR.ed bit to 1 before
executing an rfi to go back to the process, which will allow the lfetch.fault to
perform its base register post-increment (if specified), but will suppress any prefetch
request and hence any prefetch-related fault. Note that the OS can easily identify that a
faulting lfetch was the cause of the fault by observing that ISR.na is 1, and
ISR.code{3:0} is 4. The one exception to this is the Illegal Operation fault, which can
be caused by an lfetch.fault if base register post-increment is specified, and the
base register is outside of the current stack frame, or is GR0. Since this one fault is not
related to the prefetch aspect of lfetch.fault, but rather to the base update portion,
Illegal Operation faults on lfetch.fault should be handled the same as for any other
instruction.
Volume 3: Instruction Reference

lfhint Mnemonic Values

none Temporal locality, level 1
nt1 No temporal locality, level 1
nt2 No temporal locality, level 2
nta No temporal locality, all levels
Interpretation
lfetch
3:165