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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Packed array problem
Date: Wed, 02 Mar 2016 17:26:27 +0000
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Xref: news.eternal-september.org comp.lang.ada:29652
Date: 2016-03-02T17:26:27+00:00
List-Id: <comp.lang.ada>

Investigating the SVD2Ada program[1], for converting an ARM System View
Description[2] into bindings, I got this message when compiling against
my STM32F429I runtime:

   stm32f429x-rcc.ads:149:09: packing of 3-bit components not supported
   by configuration

which is the same as in this little example:

     1. package Checks is
     2.    type Uint3 is mod 8 with Size => 3;
     3.    type Arry is array (0 .. 1) of Uint3
                |
        >>> packing of 3-bit components not supported by configuration

     4.    with Component_Size => 3, Size => 6;
     5. end Checks;

This code compiles perfectly happily against AdaCore's ravenscar-sfp
runtime.

The error message comes from freeze.adb:2721 in the compiler:

            if Is_Constrained (Arr)
              and then Is_Bit_Packed_Array (Arr)
              and then Present (Packed_Array_Impl_Type (Arr))
              and then Is_Array_Type (Packed_Array_Impl_Type (Arr))
            then
               declare
                  CS : constant Uint  := Component_Size (Arr);
                  RE : constant RE_Id := Get_Id (UI_To_Int (CS));

               begin
                  if RE /= RE_Null
                    and then not RTE_Available (RE)
                  then
                     Error_Msg_CRT
                       ("packing of " & UI_Image (CS) & "-bit components",
                        First_Subtype (Etype (Arr)));

and it would seem after much delving that the compiler is checking (in
rtsfind) for System.Pack_03, which isn't present in my runtime. If I
copy the spec from GCC 5.2.0 (not 4.9 - the interface has changed) then
check.ads compiles OK (I should say I normally use GCC 5.2.0, but this
problem is the same with GNAT GPL 2015).

BUT there is no s-pack03.ad? in AdaCore's arm-eabi runtimes! And when
compiling against the AdaCore runtimes there's no reference in the
generated binary to s-pack03!

SO has anyone got any idea as to what the compiler could be looking for
and finding in AdaCore's RTS but not in mine?

[1] https://github.com/AdaCore/svd2ada
[2] http://www.arm.com/products/processors/cortex-m/cortex-microcontroller-software-interface-standard.php