Volume 2, Part 2: Context Management
2:557
4.5
Context Switching
This section discusses context switching at the user and kernel levels.
4.5.1
User-level Context Switching
4.5.1.1
Non-local Control Transfers (setjmp/longjmp)
A non-local control transfer such as the C language
setjmp()
/
longjmp()
pair requires
software to correctly handle the register stack and the RSE. The register stack provides
the BSP application register which always contains the backing store address of the
current GR32. This permits execution of a
setjmp()
without having to manipulate any
register stack or RSE state. All register stack and RSE manipulation is postponed to the
much less frequent
longjmp()
.
In
setjmp()
only the RSC, PFS and BSP application registers have to be preserved. This
can be accomplished by reading these registers, and without having to disable the RSE.
The preserved values will be referred to as
setjmp_rsc
,
setjmp_pfs
, and
setjmp_bsp
further on.
In
longjmp()
restoration of the appropriate register stack and RSE state is more
involved, and software needs to take the following steps:
1. Stop RSE by setting RSC.mode bits to zero.
2. Read current BSPSTORE (referred to as
current_bspstore
further down).
3. Find
setjmp()
’s RNAT collection (
rnat_value
).
a. Compute the backing store location of
setjmp()
’s RNAT collection as follows:
rnat_collection_address{63:0} = setjmp_bsp{63:0} | 0x1F8
The RNAT location is computed by setting bits{8:3} of
setjmp()
’s BSP to all
ones. This is where
setjmp()
’s RNAT collection will have been spilled to
memory.
b. If
(current_bspstore > rnat_collection_address)
, then the required
RNAT collection has already been spilled to the backing store.
c. Otherwise if
(current_bspstore <= rnat_collection_address)
, the
required RNAT collection is incomplete and is still contained in the register
stack. To materialize the complete RNAT collection, flush the register stack to
the backing store using a
flushrs
instruction.
d. Finally, load
rnat_value
from
rnat_collection_address
in memory.
4. Invalidate the contents of the register stack as follows:
a. Allocate a zero size register stack frame using the
alloc
instruction.
b. Write RSC.loadrs field with all zeros and execute a
loadrs
instruction.
c. Invalidate the ALAT using the
invala
instruction.
5. Restore
setjmp()
’s register stack and RSE state as follows:
a. Write BSPSTORE with
setjmp_bsp
.
b. Write RNAT with
rnat_value
.
Summary of Contents for ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS VOLUME 3 REV 2.3
Page 1: ......
Page 11: ...x Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 13: ...1 2 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 33: ...1 22 Volume 1 Part 1 Introduction to the Intel Itanium Architecture ...
Page 57: ...1 46 Volume 1 Part 1 Execution Environment ...
Page 147: ...1 136 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 149: ...1 138 Volume 1 Part 2 About the Optimization Guide ...
Page 191: ...1 180 Volume 1 Part 2 Predication Control Flow and Instruction Stream ...
Page 230: ......
Page 248: ...236 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 250: ...2 2 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 264: ...2 16 Volume 2 Part 1 Intel Itanium System Environment ...
Page 380: ...2 132 Volume 2 Part 1 Interruptions ...
Page 398: ...2 150 Volume 2 Part 1 Register Stack Engine ...
Page 486: ...2 238 Volume 2 Part 1 IA 32 Interruption Vector Descriptions ...
Page 750: ...2 502 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 754: ...2 506 Volume 2 Part 2 About the System Programmer s Guide ...
Page 796: ...2 548 Volume 2 Part 2 Interruptions and Serialization ...
Page 808: ...2 560 Volume 2 Part 2 Context Management ...
Page 842: ...2 594 Volume 2 Part 2 Floating point System Software ...
Page 850: ...2 602 Volume 2 Part 2 IA 32 Application Support ...
Page 862: ...2 614 Volume 2 Part 2 External Interrupt Architecture ...
Page 870: ...2 622 Volume 2 Part 2 Performance Monitoring Support ...
Page 891: ......
Page 1099: ...3 200 Volume 3 Instruction Reference padd Interruptions Illegal Operation fault ...
Page 1295: ...3 396 Volume 3 Resource and Dependency Semantics ...
Page 1296: ......
Page 1302: ...402 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 1494: ...4 192 Volume 4 Base IA 32 Instruction Reference FWAIT Wait See entry for WAIT ...
Page 1647: ...Volume 4 Base IA 32 Instruction Reference 4 345 ROL ROR Rotate See entry for RCL RCR ROL ROR ...
Page 1884: ...4 582 Volume 4 IA 32 SSE Instruction Reference ...
Page 1885: ...Index Intel Itanium Architecture Software Developer s Manual Rev 2 3 Index ...
Page 1886: ...Index Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 1898: ...INDEX Index 12 Index for Volumes 1 2 3 and 4 ...