Configuring for bare hw ia32 PC's

[Joel Sherrill]

Luke A. Guest wrote:
> On Mon, 2008-05-12 at 14:17 -0400, Jonathan S. Shapiro wrote:
>   
>>> This is problematic with Ada as the language is huge and the compiler
>>> adds some stuff into the code which references the runtime. Now, what
>>> this stuff is, depends on what features you have available.
>>>       
>> Then either the Ada compiler is busted or there is some command line
>> option that you need to add.
>>     
>
> Er, no. This is the way that Ada works. There are parts of the language
> which when compiled, the compiler adds in extra bits of support.
>
>   
Right.  It assumes a lot of things exist.  For the tasking to
work, you need a lot.  RTEMS uses the POSIX threads port
which by default assumes pthreads, mutexes, condition
variables and keys.   The GNAT run-time also includes
a socket binding.  The Ada run-time has a lot of nice
formatted IO support which I have no idea how it is
implemented in GNAT. 

FWIW GNAT/RTEMS supports the full Ada tasking model
on a bare PC including file IO and sockets.  I posted
ACATS results for i386, powerpc, sparc, and mips last week
to gcc-testresults.  All looked very good.  The i386 was on
qemu booting a raw elf image.  The main issues there are
that qemu doesn't have accurate enough floating point to
make the tests happy.

If you disable the filesystem, about 300 of the ACATS tests
fail if I remember things right.  They assume a filesystem.
>> Back up a second. You are, in effect, compiling Ada code to run on a
>> bare board. The "hosted" specification of the standard C library assumes
>> that you are running on top of an operating system. The "freestanding"
>> version does not.
>>
>> It is okay if the Ada compiler emits things that rely on the
>> freestanding version of libc. Pragmatically, it is also okay if it
>>     
>
> Do you mean, "is it?" I would say, no that's fine. I want a basic
> runtime, just not the extra bits. Unfortunately, the way the GNAT source
> is built, there doesn't seem (I could be wrong) to be a way to say, I
> only want this and this and this, not that.
>
>   
They used to and may still have a bare non-tasking configuration.
>> relies on a few additional, commonly provided OS procedures such as
>> memcpy. But if it relies on much more than that you have a fairly
>> fundamental disconnect in compilation models, and you need to consider
>> whether the Ada compiler is generating code for the appropriate model.
>>
>> Given what you say above, I suspect that you need to start by turning
>> off every Ada feature that you can, and then see what is happening.
>>
>> Can you give an example of what the Ada compiler is referencing that is
>> causing a problem? If possible, also state why the Ada compiler is
>> referencing this -- that is, is it being called from user-provided
>> source code, or is it being called from within the Ada runtime library?
>>     
>
> As an example, say I have an array and I want to initialise it:
>
> package Something is
>    ...
> private
>    type My_Array(1 .. 3) of Integer;
>
>    My_Instance : My_Array := (3, 5, 2);
> end Something;
>
> The initialisation code will generate a call to memcpy. This is
> something I will most probably want to include in *my runtime*.
>   
And it is not uncommon to find it automatically generating
calls to lock a run-time structure either. 
> Also, to actually get the gnat tools (e.g. gnatmake, gnatclean, etc) you
> have to build the runtime. Also, I suspect that to get ASIS (which may
> be necessary) you also need the runtime and the tools. :(
>   
You can cross compile.  That's what we do.
> Thanks,
> Luke.
>
>
>   


-- 
Joel Sherrill, Ph.D.             Director of Research & Development
joel.sherrill@OARcorp.com        On-Line Applications Research
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