Re: Virtual Address Space

[Gadre Nayan <gadrenayan@xxxxxxxxx>]

Virtual addresses will be used only in case MMU is enabled, otherwise for a processor an address is something it can put on the bus, irrespective of physical or virtual.

So when your PC increments virtual address for a MMU enabled system, they will get translated to physical.

On 28 Sep 2016 4:29 p.m., "Prabhunath G" <gprabhunath@xxxxxxxxx> wrote:

The virtual addresses what you see in the output of objdump is given/associated by Linker to every instruction and data symbol in the data/bss section except for symbols in the stack section. It is wrong to use generated in the context of Linker. 

When you initiate $./a.out for execution, the kernel will take your start address from the ELF header of a.out and place it on the PC (program counter) or IP (instruction pointer) of the CPU, thereafter CPU will start incrementing or generating virtual address for every subsequent instructions. 

Regards,
Prabhu

On Wed, Sep 28, 2016 at 3:41 PM, Madhu K <madhu.sk89@xxxxxxxxx> wrote:

Hi Arun,

Thanks for your response.

I will elaborate my question.Assume I have test.c file, I compiled test.c and generated the a.out ( Executable for linux ), when I do objdump of a.out, we can see addresses( virtual address ) associated with each instruction, these instructions are generated by whom?

Thanks

On Wed, Sep 28, 2016 at 11:35 AM, Arun Sudhilal <getarunks@xxxxxxxxx> wrote:

Hello Madhu,

On Wed, Sep 28, 2016 at 10:36 AM, Madhu K <madhu.sk89@xxxxxxxxx> wrote:
> Hi All,
>
> This is to understand the Virtual address space.Basically who generates the
> virtual addresses CPU or GNU compiler?

I didn't really get your question.

Linux kernel starts at a fixed location in virtual space. This is
called PAGE_OFFSET. On a kernel split of 3GB/1GB, 32 system, its is
0xC000_0000. You can have a look at system.map file after compiling
your kernel.
When cpu runs with MMU on, your cpu generates virtual address.

Regards,
Arun

>
> Thanks
> Madhu
>
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--

Regards,
Prabhunath G
Linux Trainer
Bangalore

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