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* Virtual Address Space
@ 2016-09-28  5:06 Madhu K
  2016-09-28  6:05 ` Arun Sudhilal
                   ` (4 more replies)
  0 siblings, 5 replies; 17+ messages in thread
From: Madhu K @ 2016-09-28  5:06 UTC (permalink / raw)
  To: kernelnewbies

Hi All,

This is to understand the Virtual address space.Basically who generates the
virtual addresses CPU or GNU compiler?

Thanks
Madhu
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* Virtual Address Space
  2016-09-28  5:06 Virtual Address Space Madhu K
@ 2016-09-28  6:05 ` Arun Sudhilal
  2016-09-28 10:11   ` Madhu K
  2016-09-28  6:09 ` Greg KH
                   ` (3 subsequent siblings)
  4 siblings, 1 reply; 17+ messages in thread
From: Arun Sudhilal @ 2016-09-28  6:05 UTC (permalink / raw)
  To: kernelnewbies

Hello Madhu,

On Wed, Sep 28, 2016 at 10:36 AM, Madhu K <madhu.sk89@gmail.com> 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
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>

^ permalink raw reply	[flat|nested] 17+ messages in thread
* Virtual Address Space
  2016-09-28  5:06 Virtual Address Space Madhu K
  2016-09-28  6:05 ` Arun Sudhilal
@ 2016-09-28  6:09 ` Greg KH
  2016-09-28 10:14   ` Madhu K
  2016-09-28  9:14 ` Augusto Mecking Caringi
                   ` (2 subsequent siblings)
  4 siblings, 1 reply; 17+ messages in thread
From: Greg KH @ 2016-09-28  6:09 UTC (permalink / raw)
  To: kernelnewbies

On Wed, Sep 28, 2016 at 10:36:59AM +0530, Madhu K wrote:
> Hi All,
> 
> This is to understand the Virtual address space.Basically who generates the
> virtual addresses CPU or GNU compiler?

CPU.

^ permalink raw reply	[flat|nested] 17+ messages in thread
* Virtual Address Space
  2016-09-28  5:06 Virtual Address Space Madhu K
  2016-09-28  6:05 ` Arun Sudhilal
  2016-09-28  6:09 ` Greg KH
@ 2016-09-28  9:14 ` Augusto Mecking Caringi
  2016-09-28 10:21   ` Madhu K
  2016-09-28 10:37 ` Alexander Kapshuk
  2016-09-29  7:25 ` arshad hussain
  4 siblings, 1 reply; 17+ messages in thread
From: Augusto Mecking Caringi @ 2016-09-28  9:14 UTC (permalink / raw)
  To: kernelnewbies

On Wed, Sep 28, 2016 at 6:06 AM, Madhu K <madhu.sk89@gmail.com> wrote:
> Hi All,
>
> This is to understand the Virtual address space.Basically who generates the
> virtual addresses CPU or GNU compiler?

Hi,

     In my view, the linker.

     The compiler normally generates absolute addresses (starting from
0), creating object code.

     Then the linker generates an executable by combining different
object files together and assigning virtual addresses.

     Finally, is CPU (MMU) job (with the kernel helping) to translate
these virtual addresses to physical ones.

     Best regards,

-- 
Augusto Mecking Caringi

^ permalink raw reply	[flat|nested] 17+ messages in thread
* Virtual Address Space
  2016-09-28  6:05 ` Arun Sudhilal
@ 2016-09-28 10:11   ` Madhu K
  2016-09-28 10:59     ` Prabhunath G
  0 siblings, 1 reply; 17+ messages in thread
From: Madhu K @ 2016-09-28 10:11 UTC (permalink / raw)
  To: kernelnewbies

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@gmail.com> wrote:

> Hello Madhu,
>
> On Wed, Sep 28, 2016 at 10:36 AM, Madhu K <madhu.sk89@gmail.com> 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
> >
> > _______________________________________________
> > Kernelnewbies mailing list
> > Kernelnewbies at kernelnewbies.org
> > https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
> >
>
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* Virtual Address Space
  2016-09-28  6:09 ` Greg KH
@ 2016-09-28 10:14   ` Madhu K
  2016-09-28 10:29     ` Greg KH
  0 siblings, 1 reply; 17+ messages in thread
From: Madhu K @ 2016-09-28 10:14 UTC (permalink / raw)
  To: kernelnewbies

Hi Greg,

As I understand CPU's work is Fetch, Decode and Execute. How can CPU
generate virtual address.please correct me if my understanding is wrong.

Thanks
Madhu

On Wed, Sep 28, 2016 at 11:39 AM, Greg KH <greg@kroah.com> wrote:

> On Wed, Sep 28, 2016 at 10:36:59AM +0530, Madhu K wrote:
> > Hi All,
> >
> > This is to understand the Virtual address space.Basically who generates
> the
> > virtual addresses CPU or GNU compiler?
>
> CPU.
>
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* Virtual Address Space
  2016-09-28  9:14 ` Augusto Mecking Caringi
@ 2016-09-28 10:21   ` Madhu K
  0 siblings, 0 replies; 17+ messages in thread
From: Madhu K @ 2016-09-28 10:21 UTC (permalink / raw)
  To: kernelnewbies

Hi,

Even I read somewhere, during compilation, compiler will take the linker
script as input and it will generate the virtual addresses.

Thanks,
Madhu

On Wed, Sep 28, 2016 at 2:44 PM, Augusto Mecking Caringi <
augustocaringi@gmail.com> wrote:

> On Wed, Sep 28, 2016 at 6:06 AM, Madhu K <madhu.sk89@gmail.com> wrote:
> > Hi All,
> >
> > This is to understand the Virtual address space.Basically who generates
> the
> > virtual addresses CPU or GNU compiler?
>
> Hi,
>
>      In my view, the linker.
>
>      The compiler normally generates absolute addresses (starting from
> 0), creating object code.
>
>      Then the linker generates an executable by combining different
> object files together and assigning virtual addresses.
>
>      Finally, is CPU (MMU) job (with the kernel helping) to translate
> these virtual addresses to physical ones.
>
>      Best regards,
>
> --
> Augusto Mecking Caringi
>
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^ permalink raw reply	[flat|nested] 17+ messages in thread
* Virtual Address Space
  2016-09-28 10:14   ` Madhu K
@ 2016-09-28 10:29     ` Greg KH
  0 siblings, 0 replies; 17+ messages in thread
From: Greg KH @ 2016-09-28 10:29 UTC (permalink / raw)
  To: kernelnewbies

On Wed, Sep 28, 2016 at 03:44:28PM +0530, Madhu K wrote:
> Hi Greg,
> 
> As I understand CPU's work is Fetch, Decode and Execute. How can CPU generate
> virtual address.please correct me if my understanding is wrong.

What exactly do you mean by "generate virtual address"?

Is this a homework assignment?

greg k-h

^ permalink raw reply	[flat|nested] 17+ messages in thread
* Virtual Address Space
  2016-09-28  5:06 Virtual Address Space Madhu K
                   ` (2 preceding siblings ...)
  2016-09-28  9:14 ` Augusto Mecking Caringi
@ 2016-09-28 10:37 ` Alexander Kapshuk
  2016-09-29  7:25 ` arshad hussain
  4 siblings, 0 replies; 17+ messages in thread
From: Alexander Kapshuk @ 2016-09-28 10:37 UTC (permalink / raw)
  To: kernelnewbies

On Wed, Sep 28, 2016 at 8:06 AM, Madhu K <madhu.sk89@gmail.com> wrote:
> Hi All,
>
> This is to understand the Virtual address space.Basically who generates the
> virtual addresses CPU or GNU compiler?
>
> Thanks
> Madhu
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>

In no way does this response claim to be based on personal expert
knowledge, but if my understanding of Chapter 2 (Page tables) of
https://pdos.csail.mit.edu/6.828/2016/xv6/book-rev9.pdf is correct, it
is the hardware that performs the mapping of physical memory, RAM, to
virtual addresses on x86:
Quote:
As a reminder, x86 instructions (both user and kernel) manipulate
virtual addresses. The machine?s RAM, or physical memory, is indexed
with physical addresses. The x86 page table hardware connects these
two kinds of addresses, by mapping each virtual address to a physical
address.

^ permalink raw reply	[flat|nested] 17+ messages in thread
* Virtual Address Space
  2016-09-28 10:11   ` Madhu K
@ 2016-09-28 10:59     ` Prabhunath G
  2016-09-28 13:32       ` Gadre Nayan
  0 siblings, 1 reply; 17+ messages in thread
From: Prabhunath G @ 2016-09-28 10:59 UTC (permalink / raw)
  To: kernelnewbies

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@gmail.com> 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@gmail.com>
> wrote:
>
>> Hello Madhu,
>>
>> On Wed, Sep 28, 2016 at 10:36 AM, Madhu K <madhu.sk89@gmail.com> 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
>> >
>> > _______________________________________________
>> > Kernelnewbies mailing list
>> > Kernelnewbies at kernelnewbies.org
>> > https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>> >
>>
>
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
>


-- 
Regards,
Prabhunath G
Linux Trainer
Bangalore
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* Virtual Address Space
  2016-09-28 10:59     ` Prabhunath G
@ 2016-09-28 13:32       ` Gadre Nayan
  2016-09-30 16:40         ` Román Martínez
  0 siblings, 1 reply; 17+ messages in thread
From: Gadre Nayan @ 2016-09-28 13:32 UTC (permalink / raw)
  To: kernelnewbies

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@gmail.com> 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@gmail.com> 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@gmail.com>
>> wrote:
>>
>>> Hello Madhu,
>>>
>>> On Wed, Sep 28, 2016 at 10:36 AM, Madhu K <madhu.sk89@gmail.com> 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
>>> >
>>> > _______________________________________________
>>> > Kernelnewbies mailing list
>>> > Kernelnewbies at kernelnewbies.org
>>> > https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>>> >
>>>
>>
>>
>> _______________________________________________
>> Kernelnewbies mailing list
>> Kernelnewbies at kernelnewbies.org
>> https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>>
>>
>
>
> --
> Regards,
> Prabhunath G
> Linux Trainer
> Bangalore
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
>
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* Virtual Address Space
  2016-09-28  5:06 Virtual Address Space Madhu K
                   ` (3 preceding siblings ...)
  2016-09-28 10:37 ` Alexander Kapshuk
@ 2016-09-29  7:25 ` arshad hussain
  2016-09-30 17:09   ` roman at mailoo.org
  4 siblings, 1 reply; 17+ messages in thread
From: arshad hussain @ 2016-09-29  7:25 UTC (permalink / raw)
  To: kernelnewbies


> On 28-Sep-2016, at 10:36 am, Madhu K <madhu.sk89@gmail.com> wrote:
> 
> Hi All,

The support comes right through from the architecture. 

Linear address: Also virtual address. This is Address CPU can address. This is 0 - 4GB under 32bit architecture.
Physical address: This are actual memory installed in your system. Linear address have to be converted to 
physical address eventually. MMU translate linear address with the help of paging to physical address.


> 
> This is to understand the Virtual address space.Basically who generates the virtual addresses CPU or GNU compiler?

A program image generated by compiler & linker uses Virtual Address . During execution of the program CPU + MMU 
translates or maps each virtual address to physical address.

Net-net this is architecture dependent and would highly recommend reading Intel?s Architecture Manual for your reference.

> 
> Thanks
> Madhu
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

^ permalink raw reply	[flat|nested] 17+ messages in thread
* Virtual Address Space
  2016-09-28 13:32       ` Gadre Nayan
@ 2016-09-30 16:40         ` Román Martínez
  2016-10-02  2:52           ` Arshad Hussain
  0 siblings, 1 reply; 17+ messages in thread
From: Román Martínez @ 2016-09-30 16:40 UTC (permalink / raw)
  To: kernelnewbies

Hi,

I compile main.s and it generates main.o. With objdump I can see:

0000000000000000 <_start>:
???0:	b8 01 00 00 00???????	mov????$0x1,%eax
???5:	bb 00 00 00 00???????	mov????$0x0,%ebx
???a:	cd 80????????????????	? ? ? ? int????$0x80

After link main.o it generates main. With objdump I now can see:

0000000000400078 <_start>:
? 400078:	b8 01 00 00 00???????	mov????$0x1,%eax
? 40007d:	bb 00 00 00 00???????	mov????$0x0,%ebx
? 400082:	cd 80????????????????	? ? ? ? int????$0x80

So, linker generates virtual address, doesn't it? But why it starts at
400078 and not in other any location? Is there any logic here? A
virtual address can start at 0?

Regards.

El mi?, 28-09-2016 a las 19:02 +0530, Gadre Nayan escribi?:
> > > 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@gmail.com>
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@gmail.com>
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@gmail.
com> wrote:
> > > > Hello Madhu,
> > > > 
> > > > 
> > > > > > > > On Wed, Sep 28, 2016 at 10:36 AM, Madhu K <madhu.sk89@gmail.com
> 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
> > > > 
> > > > >
> > > > 
> > > > > _______________________________________________
> > > > 
> > > > > Kernelnewbies mailing list
> > > > 
> > > > > Kernelnewbies at kernelnewbies.org
> > > > 
> > > > > > > > > https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbie
s
> > > > 
> > > > >
> > > > 
> > > > 
> > > 
> > > 
> > > 
> > > 
> > > 
> > > _______________________________________________
> > > 
> > > Kernelnewbies mailing list
> > > 
> > > Kernelnewbies at kernelnewbies.org
> > > 
> > > https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
> > > 
> > > 
> > 
> > 
> > 
> > --?
> > Regards,
> > Prabhunath G
> > Linux Trainer
> > Bangalore
> > 
> > 
> > 
> > 
> > 
> > 
> > _______________________________________________
> > 
> > Kernelnewbies mailing list
> > 
> > Kernelnewbies at kernelnewbies.org
> > 
> > https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
> > 
> > 
> 
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
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^ permalink raw reply	[flat|nested] 17+ messages in thread
* Virtual Address Space
  2016-09-29  7:25 ` arshad hussain
@ 2016-09-30 17:09   ` roman at mailoo.org
  2016-10-01 18:02     ` piyush moghe
  0 siblings, 1 reply; 17+ messages in thread
From: roman at mailoo.org @ 2016-09-30 17:09 UTC (permalink / raw)
  To: kernelnewbies

Hi, 

I COMPILE MAIN.S and it generates MAIN.O. With objdump I can see: 

0000000000000000 <_start>: 
   0: b8 01 00 00 00        mov    $0x1,%eax 
   5: bb 00 00 00 00        mov    $0x0,%ebx 
   a: cd 80                         int    $0x80 

After LINK MAIN.O it generates MAIN. With objdump I now can see: 

0000000000400078 <_start>: 
  400078: b8 01 00 00 00        mov    $0x1,%eax 
  40007d: bb 00 00 00 00        mov    $0x0,%ebx 
  400082: cd 80                         int    $0x80 

So, linker generates virtual address, doesn't it? But why it starts at
400078 and not in other any location? Is there any logic here? A virtual
address can start at 0? 

Regards. 

El 29.09.2016 09:25, arshad hussain escribi?:

>> On 28-Sep-2016, at 10:36 am, Madhu K <madhu.sk89@gmail.com> wrote:
>> 
>> Hi All,
> 
> The support comes right through from the architecture. 
> 
> Linear address: Also virtual address. This is Address CPU can address. This is 0 - 4GB under 32bit architecture.
> Physical address: This are actual memory installed in your system. Linear address have to be converted to 
> physical address eventually. MMU translate linear address with the help of paging to physical address.
> 
>> This is to understand the Virtual address space.Basically who generates the virtual addresses CPU or GNU compiler?
> 
> A program image generated by compiler & linker uses Virtual Address . During execution of the program CPU + MMU 
> translates or maps each virtual address to physical address.
> 
> Net-net this is architecture dependent and would highly recommend reading Intel's Architecture Manual for your reference.
> 
>> Thanks
>> Madhu
>> _______________________________________________
>> Kernelnewbies mailing list
>> Kernelnewbies at kernelnewbies.org
>> https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
> 
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
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^ permalink raw reply	[flat|nested] 17+ messages in thread
* Virtual Address Space
  2016-09-30 17:09   ` roman at mailoo.org
@ 2016-10-01 18:02     ` piyush moghe
  0 siblings, 0 replies; 17+ messages in thread
From: piyush moghe @ 2016-10-01 18:02 UTC (permalink / raw)
  To: kernelnewbies

Please refer to following links, I hope this will help in
understanding of linker generated address and virtual process address
space:

http://www.linuxjournal.com/article/6463?page=0,0
http://www.tenouk.com/ModuleW.html

Regards.
Piyush

On Fri, Sep 30, 2016 at 10:39 PM,  <roman@mailoo.org> wrote:
> Hi,
>
> I compile main.s and it generates main.o. With objdump I can see:
>
> 0000000000000000 <_start>:
>    0: b8 01 00 00 00        mov    $0x1,%eax
>    5: bb 00 00 00 00        mov    $0x0,%ebx
>    a: cd 80                         int    $0x80
>
> After link main.o it generates main. With objdump I now can see:
>
> 0000000000400078 <_start>:
>   400078: b8 01 00 00 00        mov    $0x1,%eax
>   40007d: bb 00 00 00 00        mov    $0x0,%ebx
>   400082: cd 80                         int    $0x80
>
> So, linker generates virtual address, doesn't it? But why it starts at
> 400078 and not in other any location? Is there any logic here? A virtual
> address can start at 0?
>
> Regards.
>
> El 29.09.2016 09:25, arshad hussain escribi?:
>
>
> On 28-Sep-2016, at 10:36 am, Madhu K <madhu.sk89@gmail.com> wrote:
>
> Hi All,
>
>
> The support comes right through from the architecture.
>
> Linear address: Also virtual address. This is Address CPU can address. This
> is 0 - 4GB under 32bit architecture.
> Physical address: This are actual memory installed in your system. Linear
> address have to be converted to
> physical address eventually. MMU translate linear address with the help of
> paging to physical address.
>
>
>
> This is to understand the Virtual address space.Basically who generates the
> virtual addresses CPU or GNU compiler?
>
>
> A program image generated by compiler & linker uses Virtual Address . During
> execution of the program CPU + MMU
> translates or maps each virtual address to physical address.
>
> Net-net this is architecture dependent and would highly recommend reading
> Intel's Architecture Manual for your reference.
>
>
> Thanks
> Madhu
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
>
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
>
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>

^ permalink raw reply	[flat|nested] 17+ messages in thread
* Virtual Address Space
  2016-09-30 16:40         ` Román Martínez
@ 2016-10-02  2:52           ` Arshad Hussain
  2016-10-03  5:12             ` Madhu K
  0 siblings, 1 reply; 17+ messages in thread
From: Arshad Hussain @ 2016-10-02  2:52 UTC (permalink / raw)
  To: kernelnewbies


On 30-Sep-2016, at 10:10 pm, Rom?n Mart?nez <rgmf@riseup.net> wrote:

> Hi,
> 
> I compile main.s and it generates main.o. With objdump I can see:
> 
> 0000000000000000 <_start>:
>    0:	b8 01 00 00 00       	mov    $0x1,%eax
>    5:	bb 00 00 00 00       	mov    $0x0,%ebx
>    a:	cd 80                	        int    $0x80
> 
> After link main.o it generates main. With objdump I now can see:
> 
> 0000000000400078 <_start>:
>   400078:	b8 01 00 00 00       	mov    $0x1,%eax
>   40007d:	bb 00 00 00 00       	mov    $0x0,%ebx
>   400082:	cd 80                	        int    $0x80
> 
> So, linker generates virtual address, doesn't it? But why it starts at 400078 and not in other any location? Is there any logic here? A virtual address can start at 0?
> 
The linker script would normally leave out some area and _not_ start from 0. (although this is not
an absolute necessity ). It will pick up and valid virtual address and assign start of .text,.bss and 
.stack. This is possible because we now have virtual memory. And every program thinks that it 
has _all_ the memory for itself.  So, 400078 is perfectly valid virtual address space and linker
has chosen this for this executable.

Also note that if the address space is getting shifted by little , this is because of the KASLR
(layout randomisation) - If this is disabled then the linker would generate the same virtual 
address for all the executable every time.



<snip>

^ permalink raw reply	[flat|nested] 17+ messages in thread
* Virtual Address Space
  2016-10-02  2:52           ` Arshad Hussain
@ 2016-10-03  5:12             ` Madhu K
  0 siblings, 0 replies; 17+ messages in thread
From: Madhu K @ 2016-10-03  5:12 UTC (permalink / raw)
  To: kernelnewbies

Hi All,

Thank you so much for all your answers.

Regards,
Madhu

On Sun, Oct 2, 2016 at 8:22 AM, Arshad Hussain <arshad.super@gmail.com>
wrote:

>
> On 30-Sep-2016, at 10:10 pm, Rom?n Mart?nez <rgmf@riseup.net> wrote:
>
> > Hi,
> >
> > I compile main.s and it generates main.o. With objdump I can see:
> >
> > 0000000000000000 <_start>:
> >    0: b8 01 00 00 00          mov    $0x1,%eax
> >    5: bb 00 00 00 00          mov    $0x0,%ebx
> >    a: cd 80                           int    $0x80
> >
> > After link main.o it generates main. With objdump I now can see:
> >
> > 0000000000400078 <_start>:
> >   400078:     b8 01 00 00 00          mov    $0x1,%eax
> >   40007d:     bb 00 00 00 00          mov    $0x0,%ebx
> >   400082:     cd 80                           int    $0x80
> >
> > So, linker generates virtual address, doesn't it? But why it starts at
> 400078 and not in other any location? Is there any logic here? A virtual
> address can start at 0?
> >
> The linker script would normally leave out some area and _not_ start from
> 0. (although this is not
> an absolute necessity ). It will pick up and valid virtual address and
> assign start of .text,.bss and
> .stack. This is possible because we now have virtual memory. And every
> program thinks that it
> has _all_ the memory for itself.  So, 400078 is perfectly valid virtual
> address space and linker
> has chosen this for this executable.
>
> Also note that if the address space is getting shifted by little , this is
> because of the KASLR
> (layout randomisation) - If this is disabled then the linker would
> generate the same virtual
> address for all the executable every time.
>
>
>
> <snip>
>
>
>
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^ permalink raw reply	[flat|nested] 17+ messages in thread
end of thread, other threads:[~2016-10-03  5:12 UTC | newest]

Thread overview: 17+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-09-28  5:06 Virtual Address Space Madhu K
2016-09-28  6:05 ` Arun Sudhilal
2016-09-28 10:11   ` Madhu K
2016-09-28 10:59     ` Prabhunath G
2016-09-28 13:32       ` Gadre Nayan
2016-09-30 16:40         ` Román Martínez
2016-10-02  2:52           ` Arshad Hussain
2016-10-03  5:12             ` Madhu K
2016-09-28  6:09 ` Greg KH
2016-09-28 10:14   ` Madhu K
2016-09-28 10:29     ` Greg KH
2016-09-28  9:14 ` Augusto Mecking Caringi
2016-09-28 10:21   ` Madhu K
2016-09-28 10:37 ` Alexander Kapshuk
2016-09-29  7:25 ` arshad hussain
2016-09-30 17:09   ` roman at mailoo.org
2016-10-01 18:02     ` piyush moghe

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