Why does the loader load any exe at a virtual address which is basically 0X10000 or, in most cases 0X400000?? Isn't it supposed to load it at address 0X00000, afterall the address is virtual and each process has its own address space?? Wouldn't this be more convenient??
How would you detect NULL pointer dereferences, if 0x00000000 were a mapped address?
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
Ok fine. But why particulaly 0X400000, what's wrong with all the addresses less than 0X400000. If 0X00000 is to be reserved for NULL references then why not start from say 0X00001..
If you have
Now p->bar is NULL, but p->baz would be 0x00004Code:struct foo { int bar; int baz; }; struct foo *p = NULL;
You can't get too close to address 0, otherwise large offsets from NULL would suddenly map to valid memory locations.
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
Can you address these other two questions..
Need for relocations in an exe
section header location in an exe
Other things are mapped into the address space besides the code in the executable. DLLs are mapped into the virtual address space too. Actually, they can be mapped into the VA space of multiple processes at once. Presumably, given the numbers you mention, statically linked DLLs are mapped into the low addresses.
The cost of software maintenance increases with the square of the programmer's creativity. - Robert D. Bliss
