1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT RUN-TIME COMPONENTS                         --
4--                                                                          --
5--                         S Y S T E M . M E M O R Y                        --
6--                                                                          --
7--                                 B o d y                                  --
8--                                                                          --
9--          Copyright (C) 2001-2020, Free Software Foundation, Inc.         --
10--                                                                          --
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 3,  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.                                     --
17--                                                                          --
18-- As a special exception under Section 7 of GPL version 3, you are granted --
19-- additional permissions described in the GCC Runtime Library Exception,   --
20-- version 3.1, as published by the Free Software Foundation.               --
21--                                                                          --
22-- You should have received a copy of the GNU General Public License and    --
23-- a copy of the GCC Runtime Library Exception along with this program;     --
24-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
25-- <http://www.gnu.org/licenses/>.                                          --
26--                                                                          --
27-- GNAT was originally developed  by the GNAT team at  New York University. --
28-- Extensive contributions were provided by Ada Core Technologies Inc.      --
29--                                                                          --
30------------------------------------------------------------------------------
31
32--  This is the default implementation of this package
33
34--  This implementation assumes that the underlying malloc/free/realloc
35--  implementation is thread safe, and thus, no additional lock is required.
36--  Note that when using sjlj exception handling, we still need to defer abort
37--  because an asynchronous signal (as used for implementing asynchronous abort
38--  of task on sjlj runtimes) cannot safely be handled while malloc is
39--  executing.
40
41pragma Compiler_Unit_Warning;
42
43with System.CRTL;
44with System.Parameters;
45with System.Soft_Links;
46
47package body System.Memory is
48
49   use System.Soft_Links;
50
51   function c_malloc (Size : System.CRTL.size_t) return System.Address
52     renames System.CRTL.malloc;
53
54   procedure c_free (Ptr : System.Address)
55     renames System.CRTL.free;
56
57   function c_realloc
58     (Ptr : System.Address; Size : System.CRTL.size_t) return System.Address
59     renames System.CRTL.realloc;
60
61   -----------
62   -- Alloc --
63   -----------
64
65   function Alloc (Size : size_t) return System.Address is
66      Result : System.Address;
67   begin
68      --  A previous version moved the check for size_t'Last below, into the
69      --  "if Result = System.Null_Address...". So malloc(size_t'Last) should
70      --  return Null_Address, and then we can check for that special value.
71      --  However, that doesn't work on VxWorks, because malloc(size_t'Last)
72      --  prints an unwanted warning message before returning Null_Address.
73      --  Note that the branch is correctly predicted on modern hardware, so
74      --  there is negligible overhead.
75
76      if Size = size_t'Last then
77         raise Storage_Error with "object too large";
78      end if;
79
80      if ZCX_By_Default or else Parameters.No_Abort then
81         Result := c_malloc (System.CRTL.size_t (Size));
82      else
83         Abort_Defer.all;
84         Result := c_malloc (System.CRTL.size_t (Size));
85         Abort_Undefer.all;
86      end if;
87
88      if Result = System.Null_Address then
89
90         --  If Size = 0, we can't allocate 0 bytes, because then two different
91         --  allocators, one of which has Size = 0, could return pointers that
92         --  compare equal, which is wrong. (Nonnull pointers compare equal if
93         --  and only if they designate the same object, and two different
94         --  allocators allocate two different objects).
95
96         --  malloc(0) is defined to allocate a non-zero-sized object (in which
97         --  case we won't get here, and all is well) or NULL, in which case we
98         --  get here. We also get here in case of error. So check for the
99         --  zero-size case, and allocate 1 byte. Otherwise, raise
100         --  Storage_Error.
101
102         --  We check for zero size here, rather than at the start, for
103         --  efficiency.
104
105         if Size = 0 then
106            return Alloc (1);
107         end if;
108
109         raise Storage_Error with "heap exhausted";
110      end if;
111
112      return Result;
113   end Alloc;
114
115   ----------
116   -- Free --
117   ----------
118
119   procedure Free (Ptr : System.Address) is
120   begin
121      if ZCX_By_Default or else Parameters.No_Abort then
122         c_free (Ptr);
123      else
124         Abort_Defer.all;
125         c_free (Ptr);
126         Abort_Undefer.all;
127      end if;
128   end Free;
129
130   -------------
131   -- Realloc --
132   -------------
133
134   function Realloc
135     (Ptr  : System.Address;
136      Size : size_t)
137      return System.Address
138   is
139      Result      : System.Address;
140   begin
141      if Size = size_t'Last then
142         raise Storage_Error with "object too large";
143      end if;
144
145      if ZCX_By_Default or else Parameters.No_Abort then
146         Result := c_realloc (Ptr, System.CRTL.size_t (Size));
147      else
148         Abort_Defer.all;
149         Result := c_realloc (Ptr, System.CRTL.size_t (Size));
150         Abort_Undefer.all;
151      end if;
152
153      if Result = System.Null_Address then
154         raise Storage_Error with "heap exhausted";
155      end if;
156
157      return Result;
158   end Realloc;
159
160end System.Memory;
161