[Vm-dev] VM Maker: VMMaker.oscog-nice.2574.mcz

[commits at source.squeak.org]

Nicolas Cellier uploaded a new version of VMMaker to project VM Maker:
http://source.squeak.org/VMMaker/VMMaker.oscog-nice.2574.mcz

==================== Summary ====================

Name: VMMaker.oscog-nice.2574
Author: nice
Time: 28 October 2019, 7:13:28.153845 pm
UUID: 97ff56d4-01fb-422a-8b6c-edaa2d57bbde
Ancestors: VMMaker.oscog-nice.2573

Fix issue 436 again

if msecs is usqInt, then the subtraction msecs - ioMsecs() is performed as unsigned 32bits, and can lead to high value instead of slightly negative value, which remain positive when converted to 64 bit signed long deltaMsecs...

That makes a near 48 days delay before waking up!

The expression must be evaluated with 64bits signed long arithmetic, what we obtain by declaring msecs as sqLong...

When we write C code, we must think in C language, not upper level language with exact integer arithmetic (no wrap, no overflow), that's a potential danger of Slang...

=============== Diff against VMMaker.oscog-nice.2573 ===============

Item was changed:
  ----- Method: StackInterpreterPrimitives>>primitiveSignalAtMilliseconds (in category 'system control primitives') -----
  primitiveSignalAtMilliseconds
  	"Cause the time semaphore, if one has been registered, to be
  	 signalled when the microsecond clock is greater than or equal to
  	 the given tick value. A tick value of zero turns off timer interrupts."
  	| msecsObj msecs deltaMsecs sema limit |
+ 	<var: #msecs type: #sqLong>
- 	<var: #msecs type: #usqInt>
  	<var: #deltaMsecs type: #sqLong>
  	<var: #limit type: #sqLong>
  	msecsObj := self stackTop.
  	sema := self stackValue: 1.
  	msecs := self positive32BitValueOf: msecsObj.
  	
  	self successful ifTrue:
  		[(objectMemory isSemaphoreOop: sema) ifTrue:
  			[objectMemory splObj: TheTimerSemaphore put: sema.
  			 deltaMsecs := msecs - (self ioMSecs bitAnd: MillisecondClockMask).
  			 limit := MillisecondClockMask >> 1.
  			 "Handle a roll-over that could happen in between image invocation of ioMSecs and this invocation.
  			  This will limit the maximum relative duration to MillisecondClockMask/2, about 3 days currently.
  			  Every delay longer than that limit may lead to undefined behavior (shorten delay, or no delay at all)"
  			 deltaMsecs > limit ifTrue: [deltaMsecs := deltaMsecs - MillisecondClockMask].
  			 nextWakeupUsecs := deltaMsecs > 0
  				ifTrue: [self ioUTCMicroseconds + (deltaMsecs * 1000)]
  				ifFalse: [self ioUTCMicroseconds].
  			 ^self pop: 2].
  		 sema = objectMemory nilObject ifTrue:
  			[objectMemory
  				storePointer: TheTimerSemaphore
  				ofObject: objectMemory specialObjectsOop
  				withValue: objectMemory nilObject.
  			 nextWakeupUsecs := 0.
  			 ^self pop: 2]].
  	self primitiveFailFor: PrimErrBadArgument!