541 lines
19 KiB
Ada
541 lines
19 KiB
Ada
------------------------------------------------------------------------------
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-- --
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-- GNAT COMPILER COMPONENTS --
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-- --
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-- S Y S T E M . S E C O N D A R Y _ S T A C K --
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-- --
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-- B o d y --
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-- --
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-- Copyright (C) 1992-2013, Free Software Foundation, Inc. --
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-- --
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-- GNAT is free software; you can redistribute it and/or modify it under --
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-- terms of the GNU General Public License as published by the Free Soft- --
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-- ware Foundation; either version 3, or (at your option) any later ver- --
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-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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-- or FITNESS FOR A PARTICULAR PURPOSE. --
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-- --
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-- As a special exception under Section 7 of GPL version 3, you are granted --
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-- additional permissions described in the GCC Runtime Library Exception, --
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-- version 3.1, as published by the Free Software Foundation. --
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-- --
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-- You should have received a copy of the GNU General Public License and --
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-- a copy of the GCC Runtime Library Exception along with this program; --
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-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
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-- <http://www.gnu.org/licenses/>. --
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-- --
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-- GNAT was originally developed by the GNAT team at New York University. --
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-- Extensive contributions were provided by Ada Core Technologies Inc. --
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-- --
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------------------------------------------------------------------------------
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pragma Compiler_Unit_Warning;
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with System.Soft_Links;
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with System.Parameters;
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with Ada.Unchecked_Conversion;
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with Ada.Unchecked_Deallocation;
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package body System.Secondary_Stack is
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package SSL renames System.Soft_Links;
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use type SSE.Storage_Offset;
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use type System.Parameters.Size_Type;
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SS_Ratio_Dynamic : constant Boolean :=
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Parameters.Sec_Stack_Percentage = Parameters.Dynamic;
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-- There are two entirely different implementations of the secondary
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-- stack mechanism in this unit, and this Boolean is used to select
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-- between them (at compile time, so the generated code will contain
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-- only the code for the desired variant). If SS_Ratio_Dynamic is
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-- True, then the secondary stack is dynamically allocated from the
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-- heap in a linked list of chunks. If SS_Ration_Dynamic is False,
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-- then the secondary stack is allocated statically by grabbing a
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-- section of the primary stack and using it for this purpose.
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type Memory is array (SS_Ptr range <>) of SSE.Storage_Element;
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for Memory'Alignment use Standard'Maximum_Alignment;
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-- This is the type used for actual allocation of secondary stack
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-- areas. We require maximum alignment for all such allocations.
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---------------------------------------------------------------
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-- Data Structures for Dynamically Allocated Secondary Stack --
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---------------------------------------------------------------
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-- The following is a diagram of the data structures used for the
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-- case of a dynamically allocated secondary stack, where the stack
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-- is allocated as a linked list of chunks allocated from the heap.
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-- +------------------+
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-- | Next |
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-- +------------------+
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-- | | Last (200)
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-- | |
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-- | |
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-- | |
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-- | |
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-- | |
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-- | | First (101)
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-- +------------------+
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-- +----------> | | |
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-- | +----------+-------+
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-- | | |
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-- | ^ V
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-- | | |
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-- | +-------+----------+
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-- | | | |
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-- | +------------------+
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-- | | | Last (100)
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-- | | C |
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-- | | H |
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-- +-----------------+ | +-------->| U |
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-- | Current_Chunk -|--+ | | N |
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-- +-----------------+ | | K |
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-- | Top -|-----+ | | First (1)
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-- +-----------------+ +------------------+
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-- | Default_Size | | Prev |
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-- +-----------------+ +------------------+
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--
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type Chunk_Id (First, Last : SS_Ptr);
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type Chunk_Ptr is access all Chunk_Id;
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type Chunk_Id (First, Last : SS_Ptr) is record
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Prev, Next : Chunk_Ptr;
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Mem : Memory (First .. Last);
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end record;
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type Stack_Id is record
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Top : SS_Ptr;
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Default_Size : SSE.Storage_Count;
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Current_Chunk : Chunk_Ptr;
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end record;
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type Stack_Ptr is access Stack_Id;
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-- Pointer to record used to represent a dynamically allocated secondary
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-- stack descriptor for a secondary stack chunk.
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procedure Free is new Ada.Unchecked_Deallocation (Chunk_Id, Chunk_Ptr);
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-- Free a dynamically allocated chunk
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function To_Stack_Ptr is new
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Ada.Unchecked_Conversion (Address, Stack_Ptr);
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function To_Addr is new
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Ada.Unchecked_Conversion (Stack_Ptr, Address);
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-- Convert to and from address stored in task data structures
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--------------------------------------------------------------
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-- Data Structures for Statically Allocated Secondary Stack --
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--------------------------------------------------------------
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-- For the static case, the secondary stack is a single contiguous
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-- chunk of storage, carved out of the primary stack, and represented
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-- by the following data structure
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type Fixed_Stack_Id is record
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Top : SS_Ptr;
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-- Index of next available location in Mem. This is initialized to
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-- 0, and then incremented on Allocate, and Decremented on Release.
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Last : SS_Ptr;
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-- Length of usable Mem array, which is thus the index past the
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-- last available location in Mem. Mem (Last-1) can be used. This
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-- is used to check that the stack does not overflow.
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Max : SS_Ptr;
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-- Maximum value of Top. Initialized to 0, and then may be incremented
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-- on Allocate, but is never Decremented. The last used location will
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-- be Mem (Max - 1), so Max is the maximum count of used stack space.
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Mem : Memory (0 .. 0);
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-- This is the area that is actually used for the secondary stack.
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-- Note that the upper bound is a dummy value properly defined by
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-- the value of Last. We never actually allocate objects of type
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-- Fixed_Stack_Id, so the bounds declared here do not matter.
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end record;
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Dummy_Fixed_Stack : Fixed_Stack_Id;
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pragma Warnings (Off, Dummy_Fixed_Stack);
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-- Well it is not quite true that we never allocate an object of the
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-- type. This dummy object is allocated for the purpose of getting the
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-- offset of the Mem field via the 'Position attribute (such a nuisance
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-- that we cannot apply this to a field of a type).
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type Fixed_Stack_Ptr is access Fixed_Stack_Id;
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-- Pointer to record used to describe statically allocated sec stack
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function To_Fixed_Stack_Ptr is new
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Ada.Unchecked_Conversion (Address, Fixed_Stack_Ptr);
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-- Convert from address stored in task data structures
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--------------
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-- Allocate --
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--------------
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procedure SS_Allocate
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(Addr : out Address;
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Storage_Size : SSE.Storage_Count)
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is
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Max_Align : constant SS_Ptr := SS_Ptr (Standard'Maximum_Alignment);
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Max_Size : constant SS_Ptr :=
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((SS_Ptr (Storage_Size) + Max_Align - 1) / Max_Align)
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* Max_Align;
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begin
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-- Case of fixed allocation secondary stack
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if not SS_Ratio_Dynamic then
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declare
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Fixed_Stack : constant Fixed_Stack_Ptr :=
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To_Fixed_Stack_Ptr (SSL.Get_Sec_Stack_Addr.all);
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begin
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-- Check if max stack usage is increasing
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if Fixed_Stack.Top + Max_Size > Fixed_Stack.Max then
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-- If so, check if max size is exceeded
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if Fixed_Stack.Top + Max_Size > Fixed_Stack.Last then
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raise Storage_Error;
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end if;
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-- Record new max usage
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Fixed_Stack.Max := Fixed_Stack.Top + Max_Size;
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end if;
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-- Set resulting address and update top of stack pointer
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Addr := Fixed_Stack.Mem (Fixed_Stack.Top)'Address;
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Fixed_Stack.Top := Fixed_Stack.Top + Max_Size;
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end;
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-- Case of dynamically allocated secondary stack
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else
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declare
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Stack : constant Stack_Ptr :=
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To_Stack_Ptr (SSL.Get_Sec_Stack_Addr.all);
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Chunk : Chunk_Ptr;
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To_Be_Released_Chunk : Chunk_Ptr;
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begin
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Chunk := Stack.Current_Chunk;
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-- The Current_Chunk may not be the good one if a lot of release
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-- operations have taken place. So go down the stack if necessary
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while Chunk.First > Stack.Top loop
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Chunk := Chunk.Prev;
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end loop;
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-- Find out if the available memory in the current chunk is
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-- sufficient, if not, go to the next one and eventually create
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-- the necessary room.
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while Chunk.Last - Stack.Top + 1 < Max_Size loop
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if Chunk.Next /= null then
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-- Release unused non-first empty chunk
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if Chunk.Prev /= null and then Chunk.First = Stack.Top then
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To_Be_Released_Chunk := Chunk;
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Chunk := Chunk.Prev;
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Chunk.Next := To_Be_Released_Chunk.Next;
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To_Be_Released_Chunk.Next.Prev := Chunk;
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Free (To_Be_Released_Chunk);
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end if;
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-- Create new chunk of default size unless it is not
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-- sufficient to satisfy the current request.
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elsif SSE.Storage_Count (Max_Size) <= Stack.Default_Size then
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Chunk.Next :=
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new Chunk_Id
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(First => Chunk.Last + 1,
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Last => Chunk.Last + SS_Ptr (Stack.Default_Size));
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Chunk.Next.Prev := Chunk;
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-- Otherwise create new chunk of requested size
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else
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Chunk.Next :=
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new Chunk_Id
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(First => Chunk.Last + 1,
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Last => Chunk.Last + Max_Size);
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Chunk.Next.Prev := Chunk;
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end if;
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Chunk := Chunk.Next;
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Stack.Top := Chunk.First;
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end loop;
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-- Resulting address is the address pointed by Stack.Top
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Addr := Chunk.Mem (Stack.Top)'Address;
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Stack.Top := Stack.Top + Max_Size;
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Stack.Current_Chunk := Chunk;
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end;
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end if;
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end SS_Allocate;
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-------------
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-- SS_Free --
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-------------
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procedure SS_Free (Stk : in out Address) is
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begin
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-- Case of statically allocated secondary stack, nothing to free
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if not SS_Ratio_Dynamic then
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return;
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-- Case of dynamically allocated secondary stack
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else
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declare
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Stack : Stack_Ptr := To_Stack_Ptr (Stk);
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Chunk : Chunk_Ptr;
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procedure Free is
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new Ada.Unchecked_Deallocation (Stack_Id, Stack_Ptr);
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begin
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Chunk := Stack.Current_Chunk;
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while Chunk.Prev /= null loop
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Chunk := Chunk.Prev;
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end loop;
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while Chunk.Next /= null loop
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Chunk := Chunk.Next;
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Free (Chunk.Prev);
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end loop;
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Free (Chunk);
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Free (Stack);
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Stk := Null_Address;
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end;
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end if;
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end SS_Free;
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----------------
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-- SS_Get_Max --
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----------------
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function SS_Get_Max return Long_Long_Integer is
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begin
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if SS_Ratio_Dynamic then
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return -1;
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else
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declare
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Fixed_Stack : constant Fixed_Stack_Ptr :=
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To_Fixed_Stack_Ptr (SSL.Get_Sec_Stack_Addr.all);
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begin
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return Long_Long_Integer (Fixed_Stack.Max);
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end;
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end if;
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end SS_Get_Max;
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-------------
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-- SS_Info --
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-------------
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procedure SS_Info is
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begin
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Put_Line ("Secondary Stack information:");
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-- Case of fixed secondary stack
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if not SS_Ratio_Dynamic then
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declare
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Fixed_Stack : constant Fixed_Stack_Ptr :=
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To_Fixed_Stack_Ptr (SSL.Get_Sec_Stack_Addr.all);
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begin
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Put_Line (
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" Total size : "
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& SS_Ptr'Image (Fixed_Stack.Last)
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& " bytes");
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Put_Line (
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" Current allocated space : "
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& SS_Ptr'Image (Fixed_Stack.Top - 1)
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& " bytes");
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end;
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-- Case of dynamically allocated secondary stack
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else
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declare
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Stack : constant Stack_Ptr :=
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To_Stack_Ptr (SSL.Get_Sec_Stack_Addr.all);
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Nb_Chunks : Integer := 1;
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Chunk : Chunk_Ptr := Stack.Current_Chunk;
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begin
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while Chunk.Prev /= null loop
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Chunk := Chunk.Prev;
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end loop;
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while Chunk.Next /= null loop
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Nb_Chunks := Nb_Chunks + 1;
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Chunk := Chunk.Next;
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end loop;
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-- Current Chunk information
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Put_Line (
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" Total size : "
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& SS_Ptr'Image (Chunk.Last)
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& " bytes");
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Put_Line (
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" Current allocated space : "
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& SS_Ptr'Image (Stack.Top - 1)
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& " bytes");
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Put_Line (
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" Number of Chunks : "
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& Integer'Image (Nb_Chunks));
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Put_Line (
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" Default size of Chunks : "
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& SSE.Storage_Count'Image (Stack.Default_Size));
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end;
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end if;
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end SS_Info;
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-------------
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-- SS_Init --
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-------------
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procedure SS_Init
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(Stk : in out Address;
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Size : Natural := Default_Secondary_Stack_Size)
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is
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begin
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-- Case of fixed size secondary stack
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if not SS_Ratio_Dynamic then
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declare
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Fixed_Stack : constant Fixed_Stack_Ptr :=
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To_Fixed_Stack_Ptr (Stk);
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begin
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Fixed_Stack.Top := 0;
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Fixed_Stack.Max := 0;
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if Size < Dummy_Fixed_Stack.Mem'Position then
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Fixed_Stack.Last := 0;
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else
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Fixed_Stack.Last :=
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SS_Ptr (Size) - Dummy_Fixed_Stack.Mem'Position;
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end if;
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end;
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-- Case of dynamically allocated secondary stack
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else
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declare
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Stack : Stack_Ptr;
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begin
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Stack := new Stack_Id;
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Stack.Current_Chunk := new Chunk_Id (1, SS_Ptr (Size));
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Stack.Top := 1;
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Stack.Default_Size := SSE.Storage_Count (Size);
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Stk := To_Addr (Stack);
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end;
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end if;
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end SS_Init;
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-------------
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-- SS_Mark --
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-------------
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function SS_Mark return Mark_Id is
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Sstk : constant System.Address := SSL.Get_Sec_Stack_Addr.all;
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begin
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if SS_Ratio_Dynamic then
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return (Sstk => Sstk, Sptr => To_Stack_Ptr (Sstk).Top);
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else
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return (Sstk => Sstk, Sptr => To_Fixed_Stack_Ptr (Sstk).Top);
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end if;
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end SS_Mark;
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----------------
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-- SS_Release --
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----------------
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procedure SS_Release (M : Mark_Id) is
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begin
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if SS_Ratio_Dynamic then
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To_Stack_Ptr (M.Sstk).Top := M.Sptr;
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else
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To_Fixed_Stack_Ptr (M.Sstk).Top := M.Sptr;
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end if;
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end SS_Release;
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-------------------------
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-- Package Elaboration --
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-------------------------
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-- Allocate a secondary stack for the main program to use
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-- We make sure that the stack has maximum alignment. Some systems require
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-- this (e.g. Sparc), and in any case it is a good idea for efficiency.
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Stack : aliased Stack_Id;
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for Stack'Alignment use Standard'Maximum_Alignment;
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Static_Secondary_Stack_Size : constant := 10 * 1024;
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-- Static_Secondary_Stack_Size must be static so that Chunk is allocated
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-- statically, and not via dynamic memory allocation.
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Chunk : aliased Chunk_Id (1, Static_Secondary_Stack_Size);
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for Chunk'Alignment use Standard'Maximum_Alignment;
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-- Default chunk used, unless gnatbind -D is specified with a value
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-- greater than Static_Secondary_Stack_Size
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begin
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declare
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Chunk_Address : Address;
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Chunk_Access : Chunk_Ptr;
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begin
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if Default_Secondary_Stack_Size <= Static_Secondary_Stack_Size then
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-- Normally we allocate the secondary stack for the main program
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-- statically, using the default secondary stack size.
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Chunk_Access := Chunk'Access;
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else
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-- Default_Secondary_Stack_Size was increased via gnatbind -D, so we
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-- need to allocate a chunk dynamically.
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Chunk_Access :=
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new Chunk_Id (1, SS_Ptr (Default_Secondary_Stack_Size));
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end if;
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if SS_Ratio_Dynamic then
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Stack.Top := 1;
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Stack.Current_Chunk := Chunk_Access;
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Stack.Default_Size :=
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SSE.Storage_Offset (Default_Secondary_Stack_Size);
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System.Soft_Links.Set_Sec_Stack_Addr_NT (Stack'Address);
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else
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Chunk_Address := Chunk_Access.all'Address;
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SS_Init (Chunk_Address, Default_Secondary_Stack_Size);
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System.Soft_Links.Set_Sec_Stack_Addr_NT (Chunk_Address);
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end if;
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end;
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end System.Secondary_Stack;
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