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Document bugfix: ScriptCall can overflow wScriptStack and crash

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This commit is contained in:
Rangi 2019-01-07 18:28:16 -05:00
parent 1b1b0ac6ea
commit fe04acad7b
2 changed files with 38 additions and 35 deletions
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29
docs/bugs_and_glitches.md
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@ -1422,21 +1422,26 @@ This supports up to six entries.
## `ScriptCall` can overflow `wScriptStack` and crash
In [engine/overworld/scripting.asm](/engine/overworld/scripting.asm):
**Fix:** Edit `ScriptCall` in [engine/overworld/scripting.asm](/engine/overworld/scripting.asm):
```asm
```diff
ScriptCall:
; Bug: The script stack has a capacity of 5 scripts, yet there is
; nothing to stop you from pushing a sixth script. The high part
; of the script address can then be overwritten by modifications
; to wScriptDelay, causing the script to return to the rst/interrupt
; space.
-; Bug: The script stack has a capacity of 5 scripts, yet there is
-; nothing to stop you from pushing a sixth script. The high part
-; of the script address can then be overwritten by modifications
-; to wScriptDelay, causing the script to return to the rst/interrupt
-; space.
-
+ ld hl, wScriptStackSize
+ ld a, [hl]
+ cp 5
+ ret nc
push de
ld hl, wScriptStackSize
ld e, [hl]
- ld hl, wScriptStackSize
- ld e, [hl]
inc [hl]
ld d, $0
+ ld e, a
ld d, 0
ld hl, wScriptStack
add hl, de
add hl, de
@ -1457,8 +1462,6 @@ ScriptCall:
ret
```
*To do:* Fix this bug.
## `LoadSpriteGFX` does not limit the capacity of `UsedSprites`

2
engine/overworld/scripting.asm
View File

@ -1454,7 +1454,7 @@ ScriptCall:
ld hl, wScriptStackSize
ld e, [hl]
inc [hl]
ld d, $0
ld d, 0
ld hl, wScriptStack
add hl, de
add hl, de