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Invalid Opcode... bug?

6 posts

Comperio#

Invalid Opcode... bug?

I discovered a problem that I'm not sure is a bug or not. Maybe someone can help me understand this:

Look at this very simplified script:
name "My Test"
outfile "blah.exe"
ShowInstDetails show
Section
SectionEnd
Function .onInit
  exch $0
  pop $R0
  MessageBox MB_OK "here it is:[$R0]"
FunctionEnd
If I compile this script, I get no errors. But, when I run the resulting EXE, I get an invalid Opcode error.

By making changing the .onInit function to push $0 (instead of exch $0), then it runs fine.

I've tried assigning values to $0, using $1 instead of $0, and even using my own variable, but each time, I get the Opcode error when I use the Exch call.

ideas?
Takhir#
Stack is empty on both exch and pop commands. Please read Manual 4.9.9.1, 4.9.9.2. Push copies your variable to stack so you can read it later using Pop.
Joel#
Function .onInit
  exch $0
  pop $R0
  MessageBox MB_OK "here it is:[$R0]"
FunctionEnd
a) 
exch $0
$0 is "empty", what are you exchanging from?
b) 
Pop $R0
$R0 is "empty", why are you poping an empty variable?
Afrow UK#edited
Not exactly. Exch $0 replaces the item on the stack with the value of $0 and places the value of $0 in its place on the stack. $0 being empty is not the problem. It is the fact that the stack is empty so no value can be put into $0 because no value exists!

-Stu
Comperio#
In answer to Joel's question about popping an empty variable:
I was just trying to illustrate the problem using the simplist means possible. (When I originally found the problem, it was in a more complex--and more useful--function.)
😉


After re-examing the docs, I did find this:
...If there are not enough items on the stack to accomplish the exchange, a fatal error will occur...
But, oddly, no such problem is mentioned with PUSH. So, I guess I have my answer. (Thanks, Joel.)

However, I still find it a bit odd that the outcomes are not consistant. If someone out there has a more technical explanation, I'd be curious to hear it. But, at least for now I can say that I know enough to code around it.

Thanks for help--you guys are GREAT! 👍