IAS:
Checkpoints

• Overview
• Sample Run

Overview

You can use the IAS checkpoint/restart feature to save the entire state of IAS to a file and later restore that state and restart execution from the same point in a different run. Because youcan save state just before a crash, and restart from the same point you can quickly debug long-running programs.

In the Tcl interface, the commands are:

checkpoint filename - Save the state to a file
restart filename - Initialize the IAS state to the state stored in the file

The commands are also available through the (officially unsupported) gdb interface as:

sim checkpoint filename
sim restart filename

Internal to IAS, the following modules are checkpointed:

Simulation control
Main memory
Global registers (including instruction counts)
Statistics objects
I-Cache
D-Cache
S-Cache
Simulation breakpoints module
Interrupts module

No other restrictions exist on checkpoints. The cache can be on or off; the stack cache can be on or off; the cache size can be set to one value, and the restart can resize the cache to another size if specified by the checkpoint file. Interrupts or breakpoints which you have set up should transparently come back as well.

An exception to this scenerio is that IAS reads environment variables that affect IAS (IAS_MAX_INSTRUCTIONS, DSV_HOME, PJSIM_TRACE_LIB, and so on) from the new environment so that you can change this control. IAS maintains instruction counts and other statistics from the checkpoint to the restarted run.

Checkpoint files have an embeddeed signature and version number to ensure that you use checkpoint files that are applicable for a given version of IAS only.

Sample Run

machine_name% ias
picoJava IAS version <>, built <>
SunOS machine_name 5.5.1 Generic_103640-08 sun4u sparc SUNW,Ultra-2
Simulator Configuration:
Pico breakpoints registers  : enabled
Simulator breakpoints       : enabled
Interrupt functionality     : enabled
Memory protection checks    : enabled
Tracing functionality       : disabled
 
class java/lang/Class loaded
class java/lang/Field loaded
class java/lang/Method loaded
class java/lang/ExceptionBlock loaded
class java/lang/DecafString loaded
reset class and handler loaded
invokestatic class and handler loaded
getstatic class and handler loaded
putstatic class and handler loaded
ldc class and handler loaded
ldc_w class and handler loaded
ldc2_w class and handler loaded
invokeinterface class and handler loaded
invokevirtual class and handler loaded
new class and handler loaded
newarray class and handler loaded
getfield class and handler loaded
putfield class and handler loaded
invokespecial class and handler loaded
aastore class and handler loaded
anewarray class and handler loaded
getfield_quick_w class and handler loaded
putfield_quick_w class and handler loaded
lookupswitch class and handler loaded
multianewarray class and handler loaded
checkcast class and handler loaded
instanceof class and handler loaded
athrow class and handler loaded
new_quick class and handler loaded
anewarray_quick class and handler loaded
checkcast_quick class and handler loaded
instanceof_quick class and handler loaded
multianewarray_quick class and handler loaded
invokeinterface_quick class and handler loaded
% loadClass QueensBenchmark
 inside
% steps 375000               <---||||| run for 375000 instructions
% where
PC=00051aa7 PSR=00722ef0 Optop=003ffa68 Vars=003ffa9c Frame=003ffa88 Constpool=000516B0 Trapbase=000105e0
0x00051aa7 54           bastore
% checkpoint abc <---|||||| checkpoint into file "abc" here
% cont           <---|||||| continue, checkpoint has no effect on current run
IAS: Test PASSED, 1017780 instructions, 0 interrupts taken, 187 total traps
% exit
machine_name%



machine_name% ias
picoJava IAS version <>, built <>
SunOS machine_name 5.5.1 Generic_103640-08 sun4u sparc SUNW,Ultra-2
Simulator Configuration:
Pico breakpoints registers  : enabled
Simulator breakpoints       : enabled
Interrupt functionality     : enabled
Memory protection checks    : enabled
Tracing functionality       : disabled
 
class java/lang/Class loaded
class java/lang/Field loaded
class java/lang/Method loaded
class java/lang/ExceptionBlock loaded
class java/lang/DecafString loaded
reset class and handler loaded
invokestatic class and handler loaded
getstatic class and handler loaded
putstatic class and handler loaded
ldc class and handler loaded
ldc_w class and handler loaded
ldc2_w class and handler loaded
invokeinterface class and handler loaded
invokevirtual class and handler loaded
new class and handler loaded
newarray class and handler loaded
getfield class and handler loaded
putfield class and handler loaded
invokespecial class and handler loaded
aastore class and handler loaded
anewarray class and handler loaded
getfield_quick_w class and handler loaded
putfield_quick_w class and handler loaded
lookupswitch class and handler loaded
multianewarray class and handler loaded
checkcast class and handler loaded
instanceof class and handler loaded
athrow class and handler loaded
new_quick class and handler loaded
anewarray_quick class and handler loaded
checkcast_quick class and handler loaded
instanceof_quick class and handler loaded
multianewarray_quick class and handler loaded
invokeinterface_quick class and handler loaded
% restart abc    <---|||| restart from state stored in file abc, 
                 <---|||| no need to load classes, etc.
                 <---|||| no harm if other programs are run before this,
                 <---|||| with different simulation controls, since entire 
                 <---|||| simulator is reinitialised to checkpointed values
% where
PC=00051aa7 PSR=00722ef0 Optop=003ffa68 Vars=003ffa9c Frame=003ffa88 Constpool=000516B0 Trapbase=000105e0
0x00051aa7 54           bastore
% cont          <---|||| program continues exactly like original run
IAS: Test PASSED, 1017780 instructions, 0 interrupts taken, 187 total traps
% exit