Global array is at an offset from the top of the bss section, instead of being at the top

Global array is at an offset from the top of the bss section, instead of being at the top

[Nagaraju Mekala]

Hi,

   I want to understand why few bytes are reserved in start of the bss section

  I have an array defined on top of the source code as follow:

static int DestinationAddress[BUF_SIZE] ;

My expectation is the linker will put it on top of the .bss section.
However I notice there are always 28 bytes sitting in front of
DestinationAddress[] no matter what I do.

ffff0000 l       .bss      00000000 completed.8489
ffff0004 l       .bss      00000000 object.8494
ffff001c l     O .bss      00007000 DestinationAddress

I was hoping the linker puts DestinationAddress at 0xffff0000. It is
not clear to me what these items (completed.8489, object.8494) are.

 Can anyone please throw some light on it.

Thanks in Advance,
Nagaraju

Re: Global array is at an offset from the top of the bss section, instead of being at the top

[Senthil Kumar Selvaraj]

On Fri, Jun 20, 2014 at 11:20:49AM +0530, Nagaraju Mekala wrote:
> Hi,
> 
>    I want to understand why few bytes are reserved in start of the bss section
> 
>   I have an array defined on top of the source code as follow:
> 
> static int DestinationAddress[BUF_SIZE] ;
> 
> My expectation is the linker will put it on top of the .bss section.
> However I notice there are always 28 bytes sitting in front of
> DestinationAddress[] no matter what I do.
> 
> ffff0000 l       .bss      00000000 completed.8489
> ffff0004 l       .bss      00000000 object.8494
> ffff001c l     O .bss      00007000 DestinationAddress
> 
> I was hoping the linker puts DestinationAddress at 0xffff0000. It is
> not clear to me what these items (completed.8489, object.8494) are.
> 
>  Can anyone please throw some light on it.

Unless the linker itself put those two items, it must have come from
some object file (and eventually some source file).

If you link with -Wl,-Map=<some map filename>, the generated file will
tell you which object file the two items came from. You can then go back
to which source file from which the object file was generated.

Hope that helps.

Regards
Senthil

Re: Global array is at an offset from the top of the bss section, instead of being at the top

[Nagaraju Mekala]

Hi Senthil,

  Thanks for the reply.

On Fri, Jun 20, 2014 at 11:51 AM, Senthil Kumar Selvaraj
<senthil_kumar.selvaraj@atmel.com> wrote:
> On Fri, Jun 20, 2014 at 11:20:49AM +0530, Nagaraju Mekala wrote:
>> Hi,
>>
>>    I want to understand why few bytes are reserved in start of the bss section
>>
>>   I have an array defined on top of the source code as follow:
>>
>> static int DestinationAddress[BUF_SIZE] ;
>>
>> My expectation is the linker will put it on top of the .bss section.
>> However I notice there are always 28 bytes sitting in front of
>> DestinationAddress[] no matter what I do.
>>
>> ffff0000 l       .bss      00000000 completed.8489
>> ffff0004 l       .bss      00000000 object.8494
>> ffff001c l     O .bss      00007000 DestinationAddress
>>
>> I was hoping the linker puts DestinationAddress at 0xffff0000. It is
>> not clear to me what these items (completed.8489, object.8494) are.
>>
>>  Can anyone please throw some light on it.
>
> Unless the linker itself put those two items, it must have come from
> some object file (and eventually some source file).
>
> If you link with -Wl,-Map=<some map filename>, the generated file will
> tell you which object file the two items came from. You can then go back
> to which source file from which the object file was generated.
>
> Hope that helps.
I got the required info. These 28 bytes are from crt files.

Thanks a lot,
Nagaraju

> Regards
> Senthil