This is the mail archive of the ecos-discuss@sourceware.org mailing list for the eCos project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: strange size issue (i386 vs ARM)


On Thu, Oct 1, 2009 at 7:56 PM, Bart Veer <bartv@ecoscentric.com> wrote:
>>>>>> "Mandeep" == Mandeep Sandhu <mandeepsandhu.chd@gmail.com> writes:
>
> ? ?Mandeep> Look at the size output for the _same_ app compiled with
> ? ?Mandeep> the Linux Synthetic target:
>
> ? ?Mandeep> $ i386-elf-size myapp
> ? ?Mandeep> ? ?text ? ? ? data ? ? bss ? ? dec ? ? hex filename
> ? ?Mandeep> ?103690 ? ? ? 7328 8381268 8492286 ?8194fe myapp
>
> ? ?Mandeep> The text size of the ARM binary (~127KB) is
> ? ?Mandeep> understandably larger than the i386 one (~102 KB).
>
> ? ?Mandeep> But how come the data+bss value is so different!?!? The
> ? ?Mandeep> i386 one is more than 8MB!
>
> ? ?Mandeep> Is this expected? I'm still googling to find the answer.
>
> On real embedded targets the memory is physical. Not so on the
> synthetic target. Somehow or other the executable's ELF header info
> must tell the Linux OS to allocate 8MB of memory for the emulated
> target's RAM. Without that things like malloc() would not work, at
> least not without playing nasty games with mmap() at run-time. The
> easiest way to make things work is to make it seem like data+bss
> occupy all of 8MB, irrespective of the application's actual static
> data requirements. The surplus over 8MB reported by size is likely to
> be const data and the like which the linker script places in the
> read-only code region.
>
> This could probably be fixed if it was really necessary, but it would
> be non-trivial and I don't recall anybody reporting the issue in the
> past. Generally memory usage on the synthetic target will not give an
> accurate indication of memory usage on real targets because of the
> need for much larger stack sizes etc. - I won't go into all the
> unpleasant details.

Thanks Bart. This explains it. It's not an issue for me, was just
curious to know.

Regards,
-mandeep

>
> Bart
>
> --
> Bart Veer ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? eCos Configuration Architect
> eCosCentric Limited ? ?The eCos experts ? ? ?http://www.ecoscentric.com/
> Barnwell House, Barnwell Drive, Cambridge, UK. ? ? ?Tel: +44 1223 245571
> Registered in England and Wales: Reg No 4422071.
> ? ? ? >>>> Visit us at ESC-UK ?http://www.embedded.co.uk <<<<
> ? ? ? >>>> Oct 7-8 on Stand 433 at FIVE ISC, Farnborough <<<<
>

--
Before posting, please read the FAQ: http://ecos.sourceware.org/fom/ecos
and search the list archive: http://ecos.sourceware.org/ml/ecos-discuss


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]