Re: How do I go about creating a minimal GNAT runtime?

[anon@anon.org (anon)]

Well Ada has a set of rules, for Critical Mass. that insures that the critical 
issues will be handle in a safe matter but Modula 3 and other languages are 
not force to deal with these issues.  These safety factors can cause a lot of 
dead or not used code to be included in your project which means that Ada 
may not give you a small footprint that your looking for, but Ravenscar and the 
other pragma can decrease the footprint.

As for the free GPL GNAT series using the embedded uClibc, dietlibc or 
Misra C libraries, you will have to write the links, or you can check with 
Adacore to see if the GNAT PRO series contain those libraries. If they do, 
you can look for a price tag of $15K or more per year to use them.

As for using direct C libraries, well there are many problems.  One, is the
Tasking control, Ada has a set of packages to handle tasking which standard 
C's fork routine can only wish for. 


In <%8_nl.20866$Ws1.1319@nlpi064.nbdc.sbc.com>, Dimonax <dimonax@nospam.net> writes:
>On Sat, 21 Feb 2009 16:41:27 +0000, anon wrote:
>
>> First, thing you need to do, is to decide on what you want your RTL
>> system for. That we can not help you.
>> 
>> As for the 64k RTL, Forget it.  The size depends upon what you want the
>> RTL to be able to do. And are you talking about Stand-Alone OS or using
>> limited links into the OS.
>> 
>> Well there are many ways to try to do the job. Here are a few ideas.
>> 
>>   First. Use "pagma Ravenscar ;". Limits some of the RTL. In some cases,
>>   it can reduce the dead code.
>> 
>>   Second, use "pragma Restrictions" and "pragma Suppress" to remove
>>   unused packages and checks that add a large group of routines that you
>>   may not need, such as exceptions. Which means, trap your own errors
>>   instead of letting the compiler do it.
>> 
>>   Third, use simple replacement packages like GNAT.IO instead of
>>   Ada.Text_IO which contains routines for files and stream I/O as well
>>   as exceptions. This, is not standard but it can remove alot of dead
>>   code.
>> 
>>   Fourth, you can always fall back and use mix languages, like using C
>>   for the RTL. But at some point you will use another lang. becase GNAT
>>   and other version of Ada mostly use links to the OS. for files and
>>   interrupts handling.
>> 
>>     One person, back in the late 1990s rewote the GNAT Ada RTL packages
>>     to use mostly "pragma Import" statement to the C and OS compiler
>>     libraries.  But that not true Ada it C.
>> 
>>   And then there the obsolete feature "pragma No_Run_Time ;". This
>>   statement allows the 4K footprint. Note: Will this feature be there in
>>   the next version of GNAT Ada? Only time will tell.
>
>Alright, so maybe 64k is overkill(when was the last time a 3D app ran in 
>less than 64k). I have been hacking the Critical Mass Modula 3 compiler 
>to get it up to par.(The build system sucks.) That can potentially 
>produce 64k executables.
>
>
>> 
>> Now, for simpler full feature RTL (based on RM), you might rework the
>> GNAT RTL, but there is not a lot that you can do. You might save a
>> little memory but for the amount of time you spend, it not worth it. No
>> where near the limits you are looking for.
>
>Well, the nice thing is that the runtime footprint can be as large as I 
>need it to be.(Could be gigabyte size if I were to do something that 
>absurd.) Really I just need to be able to compress the generated binaries
>(executables and object files) down to thier smallest size possible.
> 
>> The only way is to write a miminal RTL is to write a Stand-Alone OS. But
>> be prepared to spend years of research and writting code just to find
>> out your OS will no longer work on those PC at that time. Outdated
>> before you start! You need a plan wih team that can get job done within
>> a year or so. But that's a full time job.
> 
>Given that Gnat typically does a lot of calls out to C, is it possible to 
>hack Gnat to just use system calls? Also, can the RTL be linked with 
>uClibc or dietlibc to provide the requisite C API?
>
>Maybe Adacore might want to do some experimentation with some embedded C 
>libs like uClibc or a Misra C lib and tell us if they think it's 
>worthwhile. I'd pay for it. 
>
>I'm well aware of the usefullness of Pragma Restrictions in reducing 
>executable size. Also such things as Pragma Discard_Names and other nifty 
>things.
>I'll start digging into the Gnat libraries and see what those do.
>
>Thanks.
>
>Freejack
>