1 ------------------------------------------------------------------------------
3 -- GNAT COMPILER COMPONENTS --
5 -- S Y S T E M . S E C O N D A R Y _ S T A C K --
9 -- Copyright (C) 1992-2004 Free Software Foundation, Inc. --
11 -- GNAT is free software; you can redistribute it and/or modify it under --
12 -- terms of the GNU General Public License as published by the Free Soft- --
13 -- ware Foundation; either version 2, or (at your option) any later ver- --
14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
16 -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
17 -- for more details. You should have received a copy of the GNU General --
18 -- Public License distributed with GNAT; see file COPYING. If not, write --
19 -- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
20 -- MA 02111-1307, USA. --
22 -- As a special exception, if other files instantiate generics from this --
23 -- unit, or you link this unit with other files to produce an executable, --
24 -- this unit does not by itself cause the resulting executable to be --
25 -- covered by the GNU General Public License. This exception does not --
26 -- however invalidate any other reasons why the executable file might be --
27 -- covered by the GNU Public License. --
29 -- GNAT was originally developed by the GNAT team at New York University. --
30 -- Extensive contributions were provided by Ada Core Technologies Inc. --
32 ------------------------------------------------------------------------------
34 with System.Soft_Links;
35 with System.Parameters;
36 with Unchecked_Conversion;
37 with Unchecked_Deallocation;
39 package body System.Secondary_Stack is
41 package SSL renames System.Soft_Links;
43 use type SSE.Storage_Offset;
44 use type System.Parameters.Size_Type;
46 SS_Ratio_Dynamic : constant Boolean :=
47 Parameters.Sec_Stack_Ratio = Parameters.Dynamic;
48 -- There are two entirely different implementations of the secondary
49 -- stack mechanism in this unit, and this Boolean is used to select
50 -- between them (at compile time, so the generated code will contain
51 -- only the code for the desired variant). If SS_Ratio_Dynamic is
52 -- True, then the secondary stack is dynamically allocated from the
53 -- heap in a linked list of chunks. If SS_Ration_Dynamic is False,
54 -- then the secondary stack is allocated statically by grabbing a
55 -- section of the primary stack and using it for this purpose.
57 type Memory is array (Mark_Id range <>) of SSE.Storage_Element;
58 for Memory'Alignment use Standard'Maximum_Alignment;
59 -- This is the type used for actual allocation of secondary stack
60 -- areas. We require maximum alignment for all such allocations.
62 ---------------------------------------------------------------
63 -- Data Structures for Dynamically Allocated Secondary Stack --
64 ---------------------------------------------------------------
66 -- The following is a diagram of the data structures used for the
67 -- case of a dynamically allocated secondary stack, where the stack
68 -- is allocated as a linked list of chunks allocated from the heap.
70 -- +------------------+
72 -- +------------------+
80 -- +------------------+
82 -- | +----------+-------+
86 -- | +-------+----------+
88 -- | +------------------+
92 -- +-----------------+ | +-------->| U |
93 -- | Current_Chunk -|--+ | | N |
94 -- +-----------------+ | | K |
95 -- | Top -|-----+ | | First (1)
96 -- +-----------------+ +------------------+
97 -- | Default_Size | | Prev |
98 -- +-----------------+ +------------------+
101 type Chunk_Id (First, Last : Mark_Id);
102 type Chunk_Ptr is access all Chunk_Id;
104 type Chunk_Id (First, Last : Mark_Id) is record
105 Prev, Next : Chunk_Ptr;
106 Mem : Memory (First .. Last);
109 type Stack_Id is record
111 Default_Size : SSE.Storage_Count;
112 Current_Chunk : Chunk_Ptr;
115 type Stack_Ptr is access Stack_Id;
116 -- Pointer to record used to represent a dynamically allocated secondary
117 -- stack descriptor for a secondary stack chunk.
119 procedure Free is new Unchecked_Deallocation (Chunk_Id, Chunk_Ptr);
120 -- Free a dynamically allocated chunk
122 function To_Stack_Ptr is new
123 Unchecked_Conversion (Address, Stack_Ptr);
124 function To_Addr is new
125 Unchecked_Conversion (Stack_Ptr, Address);
126 -- Convert to and from address stored in task data structures
128 --------------------------------------------------------------
129 -- Data Structures for Statically Allocated Secondary Stack --
130 --------------------------------------------------------------
132 -- For the static case, the secondary stack is a single contiguous
133 -- chunk of storage, carved out of the primary stack, and represented
134 -- by the following data strcuture
136 type Fixed_Stack_Id is record
138 -- Index of next available location in Mem. This is initialized to
139 -- 0, and then incremented on Allocate, and Decremented on Release.
142 -- Length of usable Mem array, which is thus the index past the
143 -- last available location in Mem. Mem (Last-1) can be used. This
144 -- is used to check that the stack does not overflow.
147 -- Maximum value of Top. Initialized to 0, and then may be incremented
148 -- on Allocate, but is never Decremented. The last used location will
149 -- be Mem (Max - 1), so Max is the maximum count of used stack space.
151 Mem : Memory (0 .. 0);
152 -- This is the area that is actually used for the secondary stack.
153 -- Note that the upper bound is a dummy value properly defined by
154 -- the value of Last. We never actually allocate objects of type
155 -- Fixed_Stack_Id, so the bounds declared here do not matter.
158 Dummy_Fixed_Stack : Fixed_Stack_Id;
159 pragma Warnings (Off, Dummy_Fixed_Stack);
160 -- Well it is not quite true that we never allocate an object of the
161 -- type. This dummy object is allocated for the purpose of getting the
162 -- offset of the Mem field via the 'Position attribute (such a nuisance
163 -- that we cannot apply this to a field of a type!)
165 type Fixed_Stack_Ptr is access Fixed_Stack_Id;
166 -- Pointer to record used to describe statically allocated sec stack
168 function To_Fixed_Stack_Ptr is new
169 Unchecked_Conversion (Address, Fixed_Stack_Ptr);
170 -- Convert from address stored in task data structures
176 procedure SS_Allocate
178 Storage_Size : SSE.Storage_Count)
180 Max_Align : constant Mark_Id := Mark_Id (Standard'Maximum_Alignment);
181 Max_Size : constant Mark_Id :=
182 ((Mark_Id (Storage_Size) + Max_Align - 1) / Max_Align)
186 -- Case of fixed allocation secondary stack
188 if not SS_Ratio_Dynamic then
190 Fixed_Stack : constant Fixed_Stack_Ptr :=
191 To_Fixed_Stack_Ptr (SSL.Get_Sec_Stack_Addr.all);
194 -- Check if max stack usage is increasing
196 if Fixed_Stack.Top + Max_Size > Fixed_Stack.Max then
198 -- If so, check if max size is exceeded
200 if Fixed_Stack.Top + Max_Size > Fixed_Stack.Last then
204 -- Record new max usage
206 Fixed_Stack.Max := Fixed_Stack.Top + Max_Size;
209 -- Set resulting address and update top of stack pointer
211 Addr := Fixed_Stack.Mem (Fixed_Stack.Top)'Address;
212 Fixed_Stack.Top := Fixed_Stack.Top + Max_Size;
215 -- Case of dynamically allocated secondary stack
219 Stack : constant Stack_Ptr :=
220 To_Stack_Ptr (SSL.Get_Sec_Stack_Addr.all);
223 To_Be_Released_Chunk : Chunk_Ptr;
226 Chunk := Stack.Current_Chunk;
228 -- The Current_Chunk may not be the good one if a lot of release
229 -- operations have taken place. So go down the stack if necessary
231 while Chunk.First > Stack.Top loop
235 -- Find out if the available memory in the current chunk is
236 -- sufficient, if not, go to the next one and eventally create
237 -- the necessary room.
239 while Chunk.Last - Stack.Top + 1 < Max_Size loop
240 if Chunk.Next /= null then
242 -- Release unused non-first empty chunk
244 if Chunk.Prev /= null and then Chunk.First = Stack.Top then
245 To_Be_Released_Chunk := Chunk;
247 Chunk.Next := To_Be_Released_Chunk.Next;
248 To_Be_Released_Chunk.Next.Prev := Chunk;
249 Free (To_Be_Released_Chunk);
252 -- Create new chunk of default size unless it is not
253 -- sufficient to satisfy the current request.
255 elsif SSE.Storage_Count (Max_Size) <= Stack.Default_Size then
258 (First => Chunk.Last + 1,
259 Last => Chunk.Last + Mark_Id (Stack.Default_Size));
261 Chunk.Next.Prev := Chunk;
263 -- Otherwise create new chunk of requested size
268 (First => Chunk.Last + 1,
269 Last => Chunk.Last + Max_Size);
271 Chunk.Next.Prev := Chunk;
275 Stack.Top := Chunk.First;
278 -- Resulting address is the address pointed by Stack.Top
280 Addr := Chunk.Mem (Stack.Top)'Address;
281 Stack.Top := Stack.Top + Max_Size;
282 Stack.Current_Chunk := Chunk;
291 procedure SS_Free (Stk : in out Address) is
293 -- Case of statically allocated secondary stack, nothing to free
295 if not SS_Ratio_Dynamic then
298 -- Case of dynamically allocated secondary stack
302 Stack : Stack_Ptr := To_Stack_Ptr (Stk);
305 procedure Free is new Unchecked_Deallocation (Stack_Id, Stack_Ptr);
308 Chunk := Stack.Current_Chunk;
310 while Chunk.Prev /= null loop
314 while Chunk.Next /= null loop
330 function SS_Get_Max return Long_Long_Integer is
332 if SS_Ratio_Dynamic then
336 Fixed_Stack : constant Fixed_Stack_Ptr :=
337 To_Fixed_Stack_Ptr (SSL.Get_Sec_Stack_Addr.all);
339 return Long_Long_Integer (Fixed_Stack.Max);
350 Put_Line ("Secondary Stack information:");
352 -- Case of fixed secondary stack
354 if not SS_Ratio_Dynamic then
356 Fixed_Stack : constant Fixed_Stack_Ptr :=
357 To_Fixed_Stack_Ptr (SSL.Get_Sec_Stack_Addr.all);
362 & Mark_Id'Image (Fixed_Stack.Last)
366 " Current allocated space : "
367 & Mark_Id'Image (Fixed_Stack.Top - 1)
371 -- Case of dynamically allocated secondary stack
375 Stack : constant Stack_Ptr :=
376 To_Stack_Ptr (SSL.Get_Sec_Stack_Addr.all);
377 Nb_Chunks : Integer := 1;
378 Chunk : Chunk_Ptr := Stack.Current_Chunk;
381 while Chunk.Prev /= null loop
385 while Chunk.Next /= null loop
386 Nb_Chunks := Nb_Chunks + 1;
390 -- Current Chunk information
394 & Mark_Id'Image (Chunk.Last)
398 " Current allocated space : "
399 & Mark_Id'Image (Stack.Top - 1)
403 " Number of Chunks : "
404 & Integer'Image (Nb_Chunks));
407 " Default size of Chunks : "
408 & SSE.Storage_Count'Image (Stack.Default_Size));
418 (Stk : in out Address;
419 Size : Natural := Default_Secondary_Stack_Size)
422 -- Case of fixed size secondary stack
424 if not SS_Ratio_Dynamic then
426 Fixed_Stack : Fixed_Stack_Ptr := To_Fixed_Stack_Ptr (Stk);
429 Fixed_Stack.Top := 0;
430 Fixed_Stack.Max := 0;
432 if Size < Dummy_Fixed_Stack.Mem'Position then
433 Fixed_Stack.Last := 0;
436 Mark_Id (Size) - Dummy_Fixed_Stack.Mem'Position;
440 -- Case of dynamically allocated secondary stack
446 Stack := new Stack_Id;
447 Stack.Current_Chunk := new Chunk_Id (1, Mark_Id (Size));
449 Stack.Default_Size := SSE.Storage_Count (Size);
450 Stk := To_Addr (Stack);
459 function SS_Mark return Mark_Id is
461 if SS_Ratio_Dynamic then
462 return To_Stack_Ptr (SSL.Get_Sec_Stack_Addr.all).Top;
464 return To_Fixed_Stack_Ptr (SSL.Get_Sec_Stack_Addr.all).Top;
472 procedure SS_Release (M : Mark_Id) is
474 if SS_Ratio_Dynamic then
475 To_Stack_Ptr (SSL.Get_Sec_Stack_Addr.all).Top := M;
477 To_Fixed_Stack_Ptr (SSL.Get_Sec_Stack_Addr.all).Top := M;
481 -------------------------
482 -- Package Elaboration --
483 -------------------------
485 -- Allocate a secondary stack for the main program to use
487 -- We make sure that the stack has maximum alignment. Some systems require
488 -- this (e.g. Sun), and in any case it is a good idea for efficiency.
490 Stack : aliased Stack_Id;
491 for Stack'Alignment use Standard'Maximum_Alignment;
493 Chunk : aliased Chunk_Id (1, Mark_Id (Default_Secondary_Stack_Size));
494 for Chunk'Alignment use Standard'Maximum_Alignment;
496 Chunk_Address : Address;
499 if SS_Ratio_Dynamic then
501 Stack.Current_Chunk := Chunk'Access;
502 Stack.Default_Size := SSE.Storage_Offset (Default_Secondary_Stack_Size);
503 System.Soft_Links.Set_Sec_Stack_Addr_NT (Stack'Address);
506 Chunk_Address := Chunk'Address;
507 SS_Init (Chunk_Address, Default_Secondary_Stack_Size);
508 System.Soft_Links.Set_Sec_Stack_Addr_NT (Chunk_Address);
510 end System.Secondary_Stack;