Stop __set_heap_size from trashing soft stack #410
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__set_heap_limit now sanity checks against stack; users can now grab all memory for heap mos-sim flushes every output character -- no waiting for output These changes were necessary to be able to get pi.c to calculate to 50000 digits on the Commodore 64. Memory allocation had a tendency to walk all over the stack; this puts some sanity checks in place to prevent others from doing the same. Default behavior is still 4 KB for heap.
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With this change, a user can: and they will get the maximum amount of platform memory available for malloc(). |
mysterymath
approved these changes
Sep 7, 2025
| @@ -179,6 +193,7 @@ FreeChunk *find_fit(size_t size) { | |||
| return nullptr; | |||
| } | |||
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| " rts\n" | |||
| // Get current soft stack pointer value | ||
| __asm__ ( | ||
| ".text\n" | ||
| ".global __get_current_stack_top\n" |
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We can avoid making this a global symbol at all by using inline assembly in a static function. This would also allow the compiler to inline this, which would usually be beneficial.
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Okay, but inline assembly WITHIN a function is a bit of a dark art -- let me try...
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This is def optional; lemme know if you wanna take a crack at this later, and I"ll merge.
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Limit the __set_heap_size function to not trash the stack if too much memory is requested. Additionally, choose a default stack size and use it as a safety margin when increasing heap size.
The new stack size, __stack_reserve_size, is set weakly to 1024, and anyone who wants to change it can do so without recompiling.
Additionally, the simulator now flushes on stdout output. This helps establish that long-running tasks are still running on mos-sim.
These changes were necessary to be able to get pi.c to calculate to 50000 digits on the Commodore 64.