Pointer and binary issues

[pacman]

Hi

Im getting really annoying messages from DJGPP (gcc) concerning the following code:

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unsigned int *pageTable;
pageTable = virtualBlock.startingEntry.pageDirectory[i];
pageTable = pageTable & 0xFFFFF000;

GCC keeps throwing:

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error: invalid operands to binary &

Also, for this code...

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     void *returnAddress = (void *) virtualBlock.startingEntry.pageDirectoryEntry * 1024 * 4096;

I get...

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error: invalid operands to binary *

What am I doing wrong?

[AJ]

Hi,

You are attempting normal maths with pointers - try casting the pointers to integers before attempting the binary operations (you will, of course need to cast back to a pointer for the assignment back to the pointer variable).

Cheers,
Adam

[zerosum]

I might point out that your paging structures need to be page-aligned anyway. If they were, doing a bitwise AND with 0xFFFFF000 would have no effect at all, since the least significant 12 bits would already be zero. If they're not [page-aligned], then you're going to have problems when you try to load them into cr3.

Cheers,
Lee

[Korona]

I guess they are page aligned and the op wants to get rid of the flags by doing a binary and operation.