Scrolling VGA terminal causing semi-null pointer dereference

[sed4906h]

Somehow, calling memmove to scroll the terminal ends up dereferencing some value in the first page of memory, which I deliberately leave unpaged. A page fault occurs.

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memmove((void*)VGA_MEMORY,(void*)(&VGA_MEMORY[VGA_WIDTH]),(VGA_WIDTH*2)*(VGA_HEIGHT-1));
memset((void*)(&VGA_MEMORY[VGA_WIDTH*VGA_HEIGHT-1]),0,VGA_WIDTH*2);

[Octocontrabass]

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VGA_WIDTH*VGA_HEIGHT-1

The multiplication operator has higher precedence than the subtraction operator. You need parentheses to perform the subtraction before the multiplication.

[sed4906h]

I didn't see that, thanks. Still, the problem occurs in the memmove. Looking at the stack trace in GDB, the parameters are clearly trashed. Perhaps improperly returning from the page fault handler messed up the stack.

[Octocontrabass]

Isn't the page fault happening after the parameters are trashed?

But you're right that your interrupt handlers don't preserve registers. That'll cause problems. They also need to clear the direction flag and set the data segment registers appropriately for your kernel's use.