How is size of kernel found? What exactly do the memory numbers mean?

[Phil Frost]

I can figure out the size of the modules, but I can not find any way to 
figure out the size of the kernel. A mail on this list a bit back said 
that the _end symbol could be used; however, I could not find any 
documentation of any such symbol by any name in the documentation of 
gcc, ld, or 2 ELF specs that I looked at. An objdump -t of my kernel 
reveals that there is no _end symbol. Is it possible at all to obtain 
the size of the kernel? If not, could this functionality be added? It 
would obviously be trivial since grub had to figure this information out 
in order to load the kernel.

Also, I am unable to find the exact meaning of the mem_lower and 
mem_upper members of the multiboot info passed to the kernel in EBX. On 
a four meg system, 639KB lower and 3072KB of upper is reported. 
3072+639=3711, 3.62MB. Where did the other 385KB go? Also, I have yet to 
see a system that did not have either 640KB or 512KB of lower RAM. While 
this could be a defective BIOS, I highly doubt it. Do these memory 
numbers indicate unused RAM, after the loading of modules, excluding the 
IDT, BIOS data areas, and all else? Or, do they specify something else?

Note: I'm not subscribed to the list, so please CC replies to me.

Thanks,
Phil Frost