disable newlib

Joel Sherrill joel.sherrill at OARcorp.com
Mon Aug 18 16:00:31 UTC 2008

Size info included.  I hope the bfin and mcf52335 persons
read this.

Manuel Coutinho wrote:
> Hi
> We are trying to make possible a configuration (using the configure script)
> where RTEMS does not have newlib (open, close, malloc, etc) and other things
> so that a minimal footprint can be achieved.
> At this stage, we are just checking how much effort is required to perform
> this. I would suggest to place #ifdef inside the RTEMS source code so that
> the unnecessary calls are not made. However, there is more work needed here.
> I've tried to take out most of the calls to libc and other things that we
> don't need from the RTEMS source code (e.g rtems_termios_init, etc) and the
> footprint has been reduced from ~70 KiB to ~37KiB, but we need to go further
> and remove all dead code. Since RTEMS itself makes calls to newlib or libc,
> if the application does not make the extra calls it is not sufficient
> because the code will still be present.
What version are you looking at?  rtems_termios_init is NOT
required at all.  Some BSPs had dependencies in old RTEMS
versions but those have long been removed.  I really hope
you guys are not hacking those old versions to this level. 

Not to be ugly but I doubt any analysis that starts with
that assertion.  termios is only used if you have a console
driver and a console driver is NOT part of the minimum
configuration.  Not even the clock tick driver is required.

I would never claim that there is no room for improvement
but I think you are barking up the wrong tree.  This is
the size of minimum.exe for arm/rtl22xx_t built from the
head with everything disabled.

 23127    2468    2512   28107    6dcb arm rtl22xx_t minimum.exe

The workspace required is only 1560 bytes.

Attached is the symbol table which only has 427 lines!!!

 I only see 4 newlib methods in this (str*, mem*) and
then some RTEMS POSIX section 2 methods to build the device
tree in the mini-IMFS.  That appears to be the only source
of calls to calloc and malloc in the executable as well.

So I have hope that GSOC project Ray has mentored
should eliminate much of that.  But memset() and memcpy()
are more than likely always going to be part of the footprint
because gcc can emit calls to them for structure operations.

For the sparc/erc32, that size changes to

  43792    2308    2204   48304    bcb0 minimum.exe

with only 430 symbols in the symbol table. Workspace
required is 3256 bytes.
> Now, we stumbled with the newlib source code that is very intertwined with
> RTEMS (mainly to make malloc reentrant, from what I can tell). This will
> need some detailed research to make sure everything works well.
I don't think you are seeing what you think you are seeing.
malloc is reentrant because it is using a mutex around a
SuperCore heap.  The RTEMS malloc_r ignores the reentrancy
parameter.  We do NOT use the code in newlib for malloc and
never have.
>> -----Original Message-----
>> From: Joel Sherrill [mailto:joel.sherrill at oarcorp.com]
>> Sent: Monday, August 18, 2008 3:38 PM
>> To: xu ray
>> Cc: Manuel Coutinho; rtems-users at rtems.com
>> Subject: Re: disable newlib
>> xu ray wrote:
>>> You can disable it with patch YanMiao is working on.
>> I don't see how you can disable the entire newlib library without
>> special tool builds.
>> You can dynamically configure where the per-task reentrancy support is
>> disabled.  That saves a fair amount of memory.
>>> But after doing this, lots of API (e.g. Posix ) and (most) C library
>>> can not be used.
>> If you build without newlib at all, this is true.  The .h files from
>> RTEMS and
>> newlib are intertwined for the C library and POSIX threading.
>>> You can use this for small footprint MCU/CPU that has limited RAM on
>> chip.
>> You can also just not call the services and not get code pulled in.
>> I will reserve judgment until I see the patch.  I tend to believe that you
>> can build everything and just not call it in your application.  If there
>> are
>> pieces of RTEMS that are required that start to pull this in, then there
>> is
>> a dependency issue.
>> 95% of the time breaking dependencies is sufficient.  Special conditional
>> builds are seldom required.
>> --joel
>>> 2008/8/18 Manuel Coutinho <manuel.coutinho at edisoft.pt
>>> <mailto:manuel.coutinho at edisoft.pt>>
>>>     Hi
>>>     Just a quick question:
>>>     How can we disable newlib (I mean, undefine RTEMS_NEWLIB)? Can
>>>     this be done in the configuration phase?
>>>     Thanks
>>>     *Manuel Coutinho
>>>     *Software Engineer - Space
>>>     *EDISOFT, S.A.*
>>>     Rua Quinta dos Medronheiros - Lazarim
>>>     Apartado 382 Monte de Caparica
>>>     2826-801 Caparica Portugal
>>>     _______________________________________________
>>>     rtems-users mailing list
>>>     rtems-users at rtems.com <mailto:rtems-users at rtems.com>
>>>     http://rtems.rtems.org/mailman/listinfo/rtems-users
>>> --
>>> Thanks & Best Regards!
>>> Ray, Xu
>> --
>> Joel Sherrill, Ph.D.             Director of Research & Development
>> joel.sherrill at OARcorp.com        On-Line Applications Research
>> Ask me about RTEMS: a free RTOS  Huntsville AL 35805
>>    Support Available             (256) 722-9985

Joel Sherrill, Ph.D.             Director of Research & Development
joel.sherrill at OARcorp.com        On-Line Applications Research
Ask me about RTEMS: a free RTOS  Huntsville AL 35805
   Support Available             (256) 722-9985

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