Is there a list of reserved memory addresses out there - a list of addresses that the memory of a user-space program could never be allocated to? I realize this is most likely per-OS or per-architecture, but I was hoping someone might know some of the more common OSes and Arches. I could only dig one up for a few versions of windows:
for windows NT,2k and XP that would be:
0x00000000 - 0x0000ffff -> lowest page is protected to simplify debugging
0x00001000 - 0x7ffeffff -> memory area for your application
0x7fff0000 - 0x7fffffff -> protected area to keep memory-functions from damaging the following part
0x80000000 - 0xffffffff -> memory where the system including drivers and so on is located
Anyone know about for Linux, or BSD (or anything else, for that matter)?
Linux is normally configured to own 0xC000000 to 0xFFFFFFFF by kernel. This can be changed (e.g. the infamous 4GB-4GB split that reserves none). glibc is usually loaded at 0xB000000.
Under Linux, 0x00000000 can be requested by a particular mmap() call unless blocked by a security sysctl (which turned out to be a bad idea to block).
Reguarding allocating NULL:
NULL is only explicitly allocatable so I'd assume the program that did it was prepared for the consequence of doing so. At least
-fno-delete-null-pointer-checksis required to GCC for the affected code to function. I'm told this is to emulate old BSD behavior that mapped the zero page there.