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1 ------------------------------------------------------------------------------
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2 -- --
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3 -- GNAT COMPILER COMPONENTS --
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4 -- --
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5 -- S Y S T E M . E X C E P T I O N S . M A C H I N E --
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6 -- --
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7 -- S p e c --
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8 -- --
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145
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9 -- Copyright (C) 2013-2019, Free Software Foundation, Inc. --
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111
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10 -- --
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11 -- GNAT is free software; you can redistribute it and/or modify it under --
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12 -- terms of the GNU General Public License as published by the Free Soft- --
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13 -- ware Foundation; either version 3, or (at your option) any later ver- --
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14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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16 -- or FITNESS FOR A PARTICULAR PURPOSE. --
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17 -- --
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18 -- As a special exception under Section 7 of GPL version 3, you are granted --
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19 -- additional permissions described in the GCC Runtime Library Exception, --
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20 -- version 3.1, as published by the Free Software Foundation. --
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21 -- --
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22 -- You should have received a copy of the GNU General Public License and --
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23 -- a copy of the GCC Runtime Library Exception along with this program; --
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24 -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
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25 -- <http://www.gnu.org/licenses/>. --
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26 -- --
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27 -- GNAT was originally developed by the GNAT team at New York University. --
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28 -- Extensive contributions were provided by Ada Core Technologies Inc. --
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29 -- --
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30 ------------------------------------------------------------------------------
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31
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32 -- Declaration of the machine exception and some associated facilities. The
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33 -- machine exception is the object that is propagated by low level routines
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34 -- and that contains the Ada exception occurrence.
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35
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36 -- This is the version using the GCC EH mechanism
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37
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38 with Ada.Unchecked_Conversion;
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39 with Ada.Exceptions;
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40
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41 package System.Exceptions.Machine is
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42 pragma Preelaborate;
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43
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44 ------------------------------------------------
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45 -- Entities to interface with the GCC runtime --
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46 ------------------------------------------------
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47
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48 -- These come from "C++ ABI for Itanium: Exception handling", which is
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49 -- the reference for GCC.
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50
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51 -- Return codes from the GCC runtime functions used to propagate
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52 -- an exception.
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53
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54 type Unwind_Reason_Code is
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55 (URC_NO_REASON,
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56 URC_FOREIGN_EXCEPTION_CAUGHT,
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57 URC_PHASE2_ERROR,
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58 URC_PHASE1_ERROR,
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59 URC_NORMAL_STOP,
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60 URC_END_OF_STACK,
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61 URC_HANDLER_FOUND,
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62 URC_INSTALL_CONTEXT,
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63 URC_CONTINUE_UNWIND);
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64
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65 pragma Unreferenced
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66 (URC_NO_REASON,
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67 URC_FOREIGN_EXCEPTION_CAUGHT,
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68 URC_PHASE2_ERROR,
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69 URC_PHASE1_ERROR,
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70 URC_NORMAL_STOP,
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71 URC_END_OF_STACK,
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72 URC_HANDLER_FOUND,
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73 URC_INSTALL_CONTEXT,
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74 URC_CONTINUE_UNWIND);
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75
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76 pragma Convention (C, Unwind_Reason_Code);
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77
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78 -- Mandatory common header for any exception object handled by the
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79 -- GCC unwinding runtime.
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80
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81 type Exception_Class is mod 2 ** 64;
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82
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83 GNAT_Exception_Class : constant Exception_Class := 16#474e552d41646100#;
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84 -- "GNU-Ada\0"
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85
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86 type Unwind_Word is mod 2 ** System.Word_Size;
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87 for Unwind_Word'Size use System.Word_Size;
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88 -- Map the corresponding C type used in Unwind_Exception below
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89
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90 type Unwind_Exception is record
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91 Class : Exception_Class;
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92 Cleanup : System.Address;
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93 Private1 : Unwind_Word;
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94 Private2 : Unwind_Word;
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95
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96 -- Usual exception structure has only two private fields, but the SEH
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97 -- one has six. To avoid making this file more complex, we use six
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98 -- fields on all platforms, wasting a few bytes on some.
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99
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100 Private3 : Unwind_Word;
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101 Private4 : Unwind_Word;
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102 Private5 : Unwind_Word;
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103 Private6 : Unwind_Word;
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104 end record;
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105 pragma Convention (C, Unwind_Exception);
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106 -- Map the GCC struct used for exception handling
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107
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108 for Unwind_Exception'Alignment use Standard'Maximum_Alignment;
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109 -- The C++ ABI mandates the common exception header to be at least
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110 -- doubleword aligned, and the libGCC implementation actually makes it
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111 -- maximally aligned (see unwind.h). See additional comments on the
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112 -- alignment below.
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113
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114 -- There is a subtle issue with the common header alignment, since the C
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115 -- version is aligned on BIGGEST_ALIGNMENT, the Ada version is aligned on
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116 -- Standard'Maximum_Alignment, and those two values don't quite represent
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117 -- the same concepts and so may be decoupled someday. One typical reason
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118 -- is that BIGGEST_ALIGNMENT may be larger than what the underlying system
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119 -- allocator guarantees, and there are extra costs involved in allocating
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120 -- objects aligned to such factors.
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121
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122 -- To deal with the potential alignment differences between the C and Ada
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123 -- representations, the Ada part of the whole structure is only accessed
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124 -- by the personality routine through accessors. Ada specific fields are
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125 -- thus always accessed through consistent layout, and we expect the
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126 -- actual alignment to always be large enough to avoid traps from the C
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127 -- accesses to the common header. Besides, accessors alleviate the need
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128 -- for a C struct whole counterpart, both painful and error-prone to
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129 -- maintain anyway.
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130
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131 type GCC_Exception_Access is access all Unwind_Exception;
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132 -- Pointer to a GCC exception
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133
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134 procedure Unwind_DeleteException (Excp : not null GCC_Exception_Access);
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135 pragma Import (C, Unwind_DeleteException, "_Unwind_DeleteException");
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136 -- Procedure to free any GCC exception
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137
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138 --------------------------------------------------------------
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139 -- GNAT Specific Entities To Deal With The GCC EH Circuitry --
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140 --------------------------------------------------------------
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141
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142 -- A GNAT exception object to be dealt with by the personality routine
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143 -- called by the GCC unwinding runtime.
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144
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145 type GNAT_GCC_Exception is record
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146 Header : Unwind_Exception;
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147 -- ABI Exception header first
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148
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149 Occurrence : aliased Ada.Exceptions.Exception_Occurrence;
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150 -- The Ada occurrence
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151 end record;
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152
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153 pragma Convention (C, GNAT_GCC_Exception);
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154
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155 type GNAT_GCC_Exception_Access is access all GNAT_GCC_Exception;
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156
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157 function To_GCC_Exception is new
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158 Ada.Unchecked_Conversion (System.Address, GCC_Exception_Access);
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159
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160 function To_GNAT_GCC_Exception is new
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161 Ada.Unchecked_Conversion
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162 (GCC_Exception_Access, GNAT_GCC_Exception_Access);
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163
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164 function New_Occurrence return GNAT_GCC_Exception_Access;
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165 -- Allocate and initialize a machine occurrence
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166
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167 end System.Exceptions.Machine;
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