README.md

BugFixes - Fixes for what I consider to be bugs

Description

Here are some small bugfixes.

Fix 1: Aborting when module exceeds globals size

A module may have at most 64 KB of global variables, as otherwise fixups to exported variables may fail. Enforce this in the compiler.

Fix 2: Initializing of GraphicFrames.TBuf variable

If you delete text from a Drawing, the extra letters get moved into a Texts.Buffer called Tbuf. Only that this buffer is never initialized, resulting in memory corruption if you delete enough text.

Fix 3: Avoid freelist corruption after memory allocation failure

If allocation of a small amount from a large block fails, the system will still store the "second half" of the null pointer into the free lists, resulting in memory corruption as soon as these free lists are used.

Fix 4: Avoid illegal IO access (-4) when GC encounters NIL pointers

As discussed on the mailing list (PO: Illegal memory access in GC), the garbage collector will read from IO address -4 when it encounters a NIL pointer and tries to read the metadata preceding the pointer. By construction, IO address -4 is unused and will return 0, but better to avoid these accesses if possible.

Fix 5: Fix register index for non-constant set literals

When compiling code like the following, which contains a set literal where the bounds are not constant, the compiler emitted correct code to calculate the set literal, but remembered the wrong register index, so the value was not correctly used.

MODULE Test;

  PROCEDURE Mask(a: SET; b: INTEGER): SET;
  RETURN a - {b .. b + 7}
  END Mask;

BEGIN
  ASSERT( Mask( {0..31}, 8 ) = {0..7, 16..31} )
END Test.

Fix 5: Fix scroll cursor corrupting the IO memory area

When dragging the mouse pointer to the top of the screen while scrolling, the scroll cursor was drawn partially outside the screen and could corrupt the IO memory area.

Installation

• Apply CheckGlobalsSize.patch to ORG.Mod

• Apply InitializeGraphicFramesTbuf.patch to GraphicFrames.Mod

• Apply NoMemoryCorruptionAfterMemoryAllocationFailure.patch to Kernel.Mod

• Apply IllegalAccessInGC.patch to Kernel.Mod

• Apply CompileSetLiterals.patch to ORG.Mod

• Apply FixScrollCursorCorruption.patch to TextFrames.Mod

• Recompile the changed modules and rebuild the inner core:

  ORP.Compile Kernel.Mod ~
  ORL.Link Modules ~
  ORL.Load Modules.bin ~
  
  ORP.Compile TextFrames.Mod ~
  ORP.Compile GraphicFrames.Mod ~
  ORP.Compile ORG.Mod ~
  

• Restart the system.