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z80: implement stack overflow error condition

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Also, remove underflow checks from next: it's taxing and useless
because underflow check already takes place in each relevant native
word.
This commit is contained in:
Virgil Dupras 2020-08-08 08:08:05 -04:00
parent 78d4d15fcf
commit d1de99d8c9
4 changed files with 20 additions and 16 deletions
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17
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@ -1,6 +1,11 @@
STACK OVERFLOW PROTECTION: To avoid having to check for stack Stack underflow and overflow: In each native word involving
underflow after each pop operation (which can end up being PSP popping, we check whether the stack is big enough. If it's
prohibitive in terms of costs), PS_ADDR should be set to not we go in "uflw" (underflow) error condition, then abort.
at least 6 bytes before its actual limit. 6 bytes because we
seldom have words requiring more than 3 items from the stack. We don't check RSP for underflow because the cost of the check
Then, at each "exit" call we check for stack underflow. is significant and its usefulness is dubious: if RSP isn't
tightly in control, we're screwed anyways, and that, well
before we reach underflow.
Overflow condition happen when RSP and PSP meet somewhere in
the middle. That check is made at each "next" call.

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@ -1,5 +1,4 @@
PC ORG @ 1 + ! ( main ) PC ORG @ 1 + ! ( main )
( STACK OVERFLOW PROTECTION: See B76 )
SP PS_ADDR LDdn, IX RS_ADDR LDdn, SP PS_ADDR LDdn, IX RS_ADDR LDdn,
( LATEST is a label to the latest entry of the dict. It is ( LATEST is a label to the latest entry of the dict. It is
written at offset 0x08 by the process or person building written at offset 0x08 by the process or person building

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@ -2,14 +2,14 @@ lblnext BSET PC ORG @ 0x1b + ! ( next )
( This routine is jumped to at the end of every word. In it, ( This routine is jumped to at the end of every word. In it,
we jump to current IP, but we also take care of increasing we jump to current IP, but we also take care of increasing
it by 2 before jumping. ) it by 2 before jumping. )
( Before we continue: are stacks within bounds? ) ( Before we continue: are we overflowing? )
( PS ) HL PS_ADDR LDdn, IX PUSH, EX(SP)HL, ( do EX to count the IX push in SP )
SP SUBHLd, SP SUBHLd, HL POP,
JRC, lblofl BWR ( abortUnderflow-B285 ) IFNC, ( SP <= IX? overflow )
( RS ) IX PUSH, HL POP, SP PS_ADDR LDdn, IX RS_ADDR LDdn,
DE RS_ADDR LDdn, DE BIN( @ 0x13 ( oflw ) + LDdd(n),
DE SUBHLd, JR, L3 FWR ( execute, B287 )
JRC, lblofl BWR ( IX < RS_ADDR? abortUnderflow-B285 ) THEN,
LDA(BC), E A LDrr, BC INCd, LDA(BC), E A LDrr, BC INCd,
LDA(BC), D A LDrr, BC INCd, LDA(BC), D A LDrr, BC INCd,
( continue to execute ) ( continue to execute )

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@ -1,4 +1,4 @@
lblexec BSET L1 FSET ( B284 ) L2 FSET ( B285 ) lblexec BSET L1 FSET ( B284 ) L2 FSET ( B285 ) L3 FSET ( B286 )
( DE -> wordref ) ( DE -> wordref )
( When we have a BIN( offset, we need to adjust stable ( When we have a BIN( offset, we need to adjust stable
ABI offsets. ) ABI offsets. )