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Potential bug in impl of LOAD "..." CODE
Hi everyone (probably for the attention of Boriel),

My search for the source of instability in my game continues, though I no longer think it is to do with memory management, but a possible bug in the compiler, for the implementation of LOAD "..." CODE. I have noticed that part of my program gets corrupted after I use LOAD "..." CODE to load some UDGs at the top of memory. Digging in to the implementation of the function, I found the following code (sorry, I can't copy and paste code out of the emulator I am using):!Atca6hVb5b8Tp5JxCEWC...g?e=qGHdEg

At the end of the snippet, a call is made to 0xE6E1, which is a wrapper to the ROM loader routine (in this case, to load a tape header). IX points to the place in memory where the header should be loaded, which -- in this case -- is inside my program code. If I understand correctly what is going on, the snippet starts with a call to MEM_FREE (0xDB56, in this case) which returns a pointer to space in the heap (perhaps where the header can be stored?). However, the IX register is loaded with 2*SP and passed to the tape loader, which I think is a mistake.

Is that a possible bug?

If this is indeed a bug, it fits with my experience. As the size of my program grows, I need to raise the origin address to avoid random crashes. For example, if I have a 30kb program with origin address at 29,000, then the stack will reside somewhere near the start of the heap, so 2*SP will be around 58,000 which will be near the end of my program. However, if I up the origin to 31,000, then 2*SP will be more like 62,000, which will be just past the end of my program. As the size of my program increases, it will eventually grow past 2*SP and then will start to get corrupted and crash randomly, when I load from tape, so I again need to raise the origin address.

It all seems to fit, but maybe I've just convinced myself,

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Potential bug in impl of LOAD "..." CODE - by georgeo - 03-15-2021, 09:21 PM

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