Avoid overflow in checking the size of free gaps in vm_map_findspace

[dougm]

Summary

To test to see if a free space is big enough compare the required length to the difference of the two offsets that define the gap, to avoid overflow, rather that adding the length to an offset and comparing that to another offset.

This addresses an overflow issue reported by Peter Holm on i386.

[kib]

Is this a fix for the i386 wrap issue, or just a related change ?

vm_map.c

1802

(void *) space before star.

Since you are changing format, note that the length is truncated. Perhaps use %ju (I would prefer %jx) and cast to uintmax_t for length.

[dougm]

Change formatting in error log, as suggested.

[kib]

vm_map.c

1801

I suggest %#jx

[pho]

I tested this patch on i386 with all of the mmap() tests I have. I also ran the same tests on amd64 plus a buildworld.
I can run a full test if you prefer that.