what linear address is the virtual address 0xc000 0000 respondable to ? the highest 10 bits 0x300 is pde , which means the 0x300th entry of the page dir. As I know ,at boot stage , that pde has not been ever filles . then how does the kernel code been addressed? 2013/3/1 Prabhu nath <gprabhunath@gmail.com>:
In principle, the linker will associate the kernel code/data to the Kernel virtual address space i.e. between 0xC000_0000 to 0xFFFF_FFFF and the same linker will associate the Application's code/data to the user virtual address space i.e. between 0x0000_0000 to 0xBFFF_FFFF.
Linker itself cannot distinguish between the kernel code/data and user code/data but it is the linker script that will guide the linker to associate the code/data to the respective addresses.
What you are seeing is the linker script provided to the linker with -T option when building the kernel.
To build the user application the linker uses its default linker script which you get it by executing $ ld --verbose.
To compare between the two just juxtapose the readelf output of both kernel executable (vmlinux) and any user application executable (a.out)
$ readelf -a vmlinux $ readelf -a a.out
Just inspect the section header and program header of both the outputs you will get the difference.
Regards, Prabhu
On Fri, Mar 1, 2013 at 11:07 AM, Arun KS <getarunks@gmail.com> wrote:
Hi Horseriver,
On Sun, Feb 24, 2013 at 7:26 AM, horseriver <horserivers@gmail.com> wrote:
On Sun, Feb 24, 2013 at 04:00:37PM +0700, Mulyadi Santosa wrote:
On Sat, Feb 23, 2013 at 6:45 AM, horseriver <horserivers@gmail.com> wrote:
hi:
I have built vmlinux at the top dir of kernel source ,then I use objdump to look into its section information.I find the statup_32 which is the start routine of kernel , locats at 0xc0100000. I know the 0x100000 is the defined address for locating protect-mode code .But which I can not understand is the 0xc prefix .where does it come from?
If my guess is right, that's because kernel mode code start at 0xc000000 a.k.a a bit above 3 GiB on x86 32 bit machine
I have find this answer . It is defined in lds script file .
here is the code : SECTIONS { . = 0xC0000000 + 0x100000; /* read-only */ _text = .; /* Text and read-only data */
why use 0xC0000000 as its start ? why not just use 0x100000 only ? if use 0xC0000000,every linked symbole will be prefixed by 0xc , what is the purpose ?
Usually, user kernel space split is 3G:1G. ie 1G for kernel space. And this starts from 0xC000_0000 till 0xFFFF_FFFF
All the address below 0xC000_0000(ie 3G from 0x0 to 0xBFFF_FFFF) is used for user space.
Thanks, Arun
thanks!
--
regards,
Mulyadi Santosa Freelance Linux trainer and consultant
blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com
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