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More information on configuration files can be found in the GNAT documentation: [https://gcc.gnu.org/onlinedocs/gnat_ugn/Handling-of-Configuration-Pragmas.html]
 
The GNAT Reference Manual and the Ada Reference Manual provide information on the various configuration pragmas.
'''Note:''' ''Do not use '''pragma No_Run_Time''' as it is obsolete and has been for a number of years now!''
See below for a list of restriction pragmas useful for a bare bones kernel and runtime:
 
<source lang="ada">
Line 96 ⟶ 97:
</source>
 
'''Note:''' ''Do not use <tt>pragma No_Run_Time</tt>. It is obsolete.''
The final version of [https://github.com/Lucretia/bare_bones/blob/master/gnat.adc gnat.adc] can be downloaded from GitHub.
By passing the '''-r''' flag to the binder (inside the bare_bones.gpr file), the binder will list further restrictions you can apply to enforce further checks.
 
Below is an explanation of these configuration pragmas:
<source lang="ada">
package Binder is
for Default_Switches ("Ada") use ("-r");
end Binder;
</source>
 
Between the GNAT Reference Manual and the Ada 2005 Reference Manual, you can find out what the various pragmas are and what they do.
 
====Discard_Names====
 
{| {{wikitable}}
The Ada compiler automatically generates strings containing the names of enumerated data types, among others. These strings can be used in I/O.
! Restriction
! Purpose
|-
| Discard_Names || The Ada compiler automatically generates strings containing the names of enumerated data types, among others. These strings can be used in I/O.
 
<source lang="ada">
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This directive instructs the compiler not to generate these strings.
|-
 
| Normalize_Scalars || Forces all scalars to be initialised. Refer to [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/Pragma-Normalize_005fScalars.html#Pragma-Normalize_005fScalars GNAT RM:Normalize_Scalars] for more information.
====Normalize_Scalars====
|-
 
Forces| allNo_Exception_Propagation scalars|| This directive forces the compiler to bedisallow initialised,any seeattempt theto latestraise an exception over a subprogram boundary. Refer to [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/Pragma-Normalize_005fScalarsNo_005fException_005fPropagation.html#Pragma-Normalize_005fScalarsNo_005fException_005fPropagation GNAT RM:Normalize_ScalarsNo_Exception_Propagation] for more information.
 
====No_Exception_Propagation====
 
This directive forces the compiler to disallow any attempt to raise an exception over a subprogram boundary. Refer to [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/No_005fException_005fPropagation.html#No_005fException_005fPropagation GNAT RM:No_Exception_Propagation] for more information.
 
Note: The [http://docs.adacore.com/gnat-hie-docs/html/gnathie_ug_3.html#SEC8 GNAT High Integrity Edition] documentation states the following:
Line 138 ⟶ 129:
 
All exceptions that are not handled with an explicit exception handler within its subprogram will be caught with the <tt>Last_Chance_Handler</tt> subprogram. This will cause a warning to be issued at compile time.
|-
| No_Exception_Registration || Ensures no stream operations are performed on types declared in Ada.Exceptions. See [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/No_005fException_005fRegistration.html#No_005fException_005fRegistration GNAT RM:No_Exception_Registration] for more information.
|-
| No_Finalization
| Restricts the use of controlled types. Refer to [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/No_005fFinalization.html#No_005fFinalization GNAT RM:No_Finalization] for more information.
|-
| No_Tasking
| This directive restricts all features related to tasking, including the use of protected objects. Refer to [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/No_005fTasking.html#No_005fTasking GNAT RM:No_Tasking] for more information.
|-
| No_Protected_Types
| This reinforces the above restriction. Refer to [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/No_005fProtected_005fTypes.html#No_005fProtected_005fTypes GNAT RM:No_Protected_Types] for more information.
|-
| No_Delay
| Restricts the use of <tt>delay</tt> statements or the calendar package. Refer to [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/No_005fDelay.html#No_005fDelay GNAT RM:No_Delay] for more information.
|-
| No_Recursion
| Restricts the use of recursion. Refer to [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/No_005fRecursion.html#No_005fRecursion GNAT RM:No_Recursion] for more information.
|-
| No_Allocators
| Restricts the use of dynamic memory. This is essential for a bare-metal application, since there is no underlying facility for allocation of dynamic memory. Refer to [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/No_005fAllocators.html#No_005fAllocators GNAT RM:No_Allocators] for more information.
|-
| No_Dispatch
| Disallows calling a subprogram using Ada's object-orientated mechanism. Refer to [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/No_005fDispatch.html#No_005fDispatch GNAT RM:No_Dispatch] for more information.
|-
| No_Implicit_Dynamic_Code
| Disallows nested subprograms or any other features that generate trampolines on the stack. Refer to [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/No_005fImplicit_005fDynamic_005fCode.html#No_005fImplicit_005fDynamic_005fCode GNAT RM:No_Implicit_Dynamic_Code] for more information.
|-
| No_Secondary_Stack
| Ada uses a ''secondary stack'' to return unconstrained types, such as arbitrary length strings or variant records. This directive instructs the compiler that there is no secondary stack present, and to restrict the use of code that requires one. Refer to [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/No_005fSecondary_005fStack.html#No_005fSecondary_005fStack GNAT RM:No_Secondary_Stack] for more information.
|}
 
Passing the <tt>-r</tt> flag to the binder instructs it to emit a list of further restrictions that are possible to apply to the project.
====No_Exception_Registration====
<source lang="ada">
 
package Binder is
Ensures no stream operations are performed on types declared in Ada.Exceptions, see [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/No_005fException_005fRegistration.html#No_005fException_005fRegistration GNAT RM:No_Exception_Registration] for more information.
for Default_Switches ("Ada") use ("-r");
 
end Binder;
====No_Finalization====
</source>
 
Controlled types cannot be used, see [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/No_005fFinalization.html#No_005fFinalization GNAT RM:No_Finalization] for more information.
 
====No_Tasking====
 
Turns off tasking, so you cannot define tasks or protected objects or do anything related to tasking, see [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/No_005fTasking.html#No_005fTasking GNAT RM:No_Tasking] for more information.
 
====No_Protected_Types====
 
This is pretty much here for reinforcement of the above restriction. See [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/No_005fProtected_005fTypes.html#No_005fProtected_005fTypes GNAT RM:No_Protected_Types] for more information.
 
====No_Delay====
 
You cannot use delay statements or the calendar package, see [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/No_005fDelay.html#No_005fDelay GNAT RM:No_Delay] for more information.
 
====No_Recursion====
 
Should be self evident, see [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/No_005fRecursion.html#No_005fRecursion GNAT RM:No_Recursion] for more information.
 
====No_Allocators====
 
You cannot use dynamic memory, see [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/No_005fAllocators.html#No_005fAllocators GNAT RM:No_Allocators] for more information.
 
====No_Dispatch====
 
You cannot call a subprogram using Ada's object-orientated mechanism, see [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/No_005fDispatch.html#No_005fDispatch GNAT RM:No_Dispatch] for more information.
 
====No_Implicit_Dynamic_Code====
 
You cannot use nested subprograms or any other features that generate trampolines on the stack, see [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/No_005fImplicit_005fDynamic_005fCode.html#No_005fImplicit_005fDynamic_005fCode GNAT RM:No_Implicit_Dynamic_Code] for more information.
 
====No_Secondary_Stack====
 
Without a secondary stack, you cannot return unconstrained types, such as arbitrary length strings, or variant records, see [http://gcc.gnu.org/onlinedocs/gcc-4.7.0/gnat_rm/No_005fSecondary_005fStack.html#No_005fSecondary_005fStack GNAT RM:No_Secondary_Stack] for more information.
 
What this also means is you cannot use the runtime features 'Image and 'Val on any types, this would be useful for sending debugging info to the console, i.e. means you don't have to write your own code for converting strings to/from numbers.
 
I believe that it would be a good idea to have a small secondary stack defined in the assembler startup code, but define your own System.Secondary_Stack (s-secsta.ad[sb]) package which provides the correct API. Inside this package in it's executable part, you could then import the secondary stack from the assembly code, this would then be executed on elaboration of the package at the start of the kernel's execution.
 
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