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@xxxxxxxxx>:
> 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@xxxxxxxxx> wrote:
>>
>> Hi Horseriver,
>>
>> On Sun, Feb 24, 2013 at 7:26 AM, horseriver <horserivers@xxxxxxxxx> 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@xxxxxxxxx>
>> >> 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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>>
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>
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