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

[Phil Frost]

Yoshinori K. Okuji wrote:

> At Thu, 24 Jan 2002 22:58:08 -0600,
> Phil Frost wrote:
>
> > 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?
>
> Are you using your own linker script?


No, i'm using ld and gcc, all standard development tools. They are both 
straight from the debian packages. One thing to note is that I'm 
building a kernel, not a linux application, so I compile with -nostdinc 
which means that nothing, to my knowledge, gets defined automaticly. 
Even _start must be defined by me, as it is usually done by the default 
libraries.


> > 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?
>
> It's ROM space used by BIOS.

> > 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?
>
> They just specify RAM. That exact meaning is BIOS-specific, I think.


I don't think it is, but if so, perhaps GRUB should contain better 
memory detection code. If you give your memory allocator numbers that 
"might" be right, you will surely get trouble. Having the code in GRUB 
would simplify things a lot, because for the OS to do it would require 
that a realmode portal is set up, which isn't as simple as making the 
calls in realmode at boot.