gcc/ada/targparm.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                        GNAT RUN-TIME COMPONENTS                          --
   4 --                                                                          --
   5 --                             T A R G P A R M                              --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --                            $Revision: 1.1 $
  10 --                                                                          --
  11 --          Copyright (C) 1999-2001 Free Software Foundation, Inc.          --
  12 --                                                                          --
  13 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  14 -- terms of the  GNU General Public License as published  by the Free Soft- --
  15 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  16 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  17 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  18 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  19 -- for  more details.  You should have  received  a copy of the GNU General --
  20 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  21 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  22 -- MA 02111-1307, USA.                                                      --
  23 --                                                                          --
  24 -- GNAT was originally developed  by the GNAT team at  New York University. --
  25 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  26 --                                                                          --
  27 ------------------------------------------------------------------------------
  28
  29 --  This package obtains parameters from the target runtime version of
  30 --  System, to indicate parameters relevant to the target environment.
  31
  32 --  Conceptually, these parameters could be obtained using rtsfind, but
  33 --  we do not do this for three reasons:
  34
  35 --    1. Compiling System for every compilation wastes time
  36 --    2. This compilation impedes debugging by adding extra compile steps
  37 --    3. There are recursion problems coming from compiling System itself
  38 --        or any of its children.
  39
  40 --  For all these reasons, we read in the source of System, and then scan
  41 --  it at the text level to extract the parameter values.
  42
  43 --  Note however, that later on, when the ali file is written, we make sure
  44 --  that the System file is at least parsed, so that the checksum is properly
  45 --  computed and set in the ali file. This partially negates points 1 and 2
  46 --  above although just parsing is quick and does not impact debugging much.
  47
  48 package Targparm is
  49
  50    --  The following parameters correspond to the variables defined in the
  51    --  private part of System (without the terminating _On_Target). Note
  52    --  that it is required that all parameters be specified in system.ads.
  53
  54    -----------------------------------
  55    -- Control of Exception Handling --
  56    -----------------------------------
  57
  58    --  GNAT provides two methods of implementing exceptions:
  59
  60    --    Longjmp/Setjmp (-gnatL)
  61
  62    --      This approach uses longjmp/setjmp to handle exceptions. It
  63    --      uses less storage, and can often propagate exceptions faster,
  64    --      at the expense of (sometimes considerable) overhead in setting
  65    --      up an exception handler. This approach is available on all
  66    --      targets, and is the default where it is the only approach.
  67
  68    --    Zero Cost (-gnatZ)
  69
  70    --      This approach uses separate exception tables. These use extra
  71    --      storage, and exception propagation can be quite slow, but there
  72    --      is no overhead in setting up an exception handler (it is to this
  73    --      latter operation that the phrase zero-cost refers). This approach
  74    --      is only available on some targets, and is the default where it is
  75    --      available.
  76
  77    ZCX_By_Default_On_Target : Boolean;
  78    --  Indicates if zero cost exceptions are active by default. Can be modified
  79    --  by the use of -gnatZ and -gnatL switches.
  80
  81    GCC_ZCX_Support_On_Target  : Boolean;
  82    --  Indicates that when ZCX is active the mechanism to be used is the
  83    --  standard GCC ZCX mechanism  (introduced in GCC 3.1)
  84
  85    Front_End_ZCX_Support_On_Target : Boolean;
  86    --  Indicates that when ZCX is active (and GCC_ZCX_Support is not set)
  87    --  the mechanism to be used is the GNAT front end specific ZCX mechanism
  88
  89    ---------------------------------------
  90    -- High_Integrity (No Run Time) Mode --
  91    ---------------------------------------
  92
  93    --  In High_Integrity mode, there is no system run-time, and the flag
  94    --  Opt.No_Run_Time is set so that the language is appropriately
  95    --  restricted to forbid construct that would generate run-time calls.
  96
  97    High_Integrity_Mode_On_Target : Boolean;
  98    --  Indicates that this build is for a high integrity mode version of
  99    --  GNAT, so that no run time is permitted.
 100
 101    -------------------------------
 102    -- Control of Stack Checking --
 103    -------------------------------
 104
 105    --  GNAT provides two methods of implementing exceptions:
 106
 107    --    GCC Probing Mechanism
 108
 109    --      This approach uses the standard GCC mechanism for
 110    --      stack checking. The method assumes that accessing
 111    --      storage immediately beyond the end of the stack
 112    --      will result in a trap that is converted to a storage
 113    --      error by the runtime system. This mechanism has
 114    --      minimal overhead, but requires complex hardware,
 115    --      operating system and run-time support. Probing is
 116    --      the default method where it is available. The stack
 117    --      size for the environment task depends on the operating
 118    --      system and cannot be set in a system-independent way.
 119
 120    --   GNAT Stack-limit Checking
 121
 122    --      This method relies on comparing the stack pointer
 123    --      with per-task stack limits. If the check fails, an
 124    --      exception is explicitly raised. The advantage is
 125    --      that the method requires no extra system dependent
 126    --      runtime support and can be used on systems without
 127    --      memory protection as well, but at the cost of more
 128    --      overhead for doing the check. This method is the
 129    --      default on systems that lack complete support for
 130    --      probing.
 131
 132    Stack_Check_Probes_On_Target : Boolean;
 133    --  Indicates if stack check probes are used, as opposed to the standard
 134    --  target independent comparison method.
 135
 136    Stack_Check_Default_On_Target : Boolean;
 137    --  Indicates if stack checking is on by default
 138
 139    ----------------------------
 140    -- Command Line Arguments --
 141    ----------------------------
 142
 143    --  For most ports of GNAT, command line arguments are supported. The
 144    --  following flag is set to False for targets that do not support
 145    --  command line arguments (notably VxWorks).
 146
 147    Command_Line_Args_On_Target : Boolean;
 148    --  Set False if no command line arguments on target
 149
 150    --  Note: this is prepared for future use, but not yet used, since we
 151    --  do not yet have a way of propagating Targparm params to the binder
 152
 153    -----------------------
 154    -- Main Program Name --
 155    -----------------------
 156
 157    --  When the binder generates the main program to be used to create the
 158    --  executable, the main program name is main by default (to match the
 159    --  usual Unix practice). If this parameter is set to True, then the
 160    --  name is instead by default taken from the actual Ada main program
 161    --  name (just the name of the child if the main program is a child unit).
 162    --  In either case, this value can be overridden using -M name.
 163
 164    Use_Ada_Main_Program_Name_On_Target : Boolean;
 165    --  Set True to use the Ada main program name as the main name
 166
 167    --  Note: this is prepared for future use, but not yet used, since we
 168    --  do not yet have a way of propagating Targparm params to the binder
 169
 170    ----------------------------
 171    -- Support of Long Shifts --
 172    ----------------------------
 173
 174    --  In GNORT mode, we cannot call library routines, and in particular
 175    --  we cannot call routines for long (64-bit) shifts if such routines
 176    --  are required on the target. This comes up in the context of support
 177    --  of packed arrays. We can only represent packed arrays whose length
 178    --  is in the range 33- to 64-bits as modular types if long shifts are
 179    --  done with inline code.
 180
 181    --  For the default version, for now we set long shifts inlined as True
 182    --  This may not be quite accurate, but until we get proper separate
 183    --  System's for each target, it is a safer choice.
 184
 185    Long_Shifts_Inlined_On_Target : Boolean;
 186    --  Indicates if long (double word) shifts are generated using inlined
 187    --  code (and thus are permissible in No_Run_Time mode).
 188
 189    ----------------------------------------------
 190    -- Boolean-Valued Floating-Point Attributes --
 191    ----------------------------------------------
 192
 193    --  The constants below give the values for representation oriented
 194    --  floating-point attributes that are the same for all float types
 195    --  on the target. These are all boolean values.
 196
 197    --  A value is only True if the target reliably supports the corresponding
 198    --  feature. Reliably here means that support is guaranteed for all
 199    --  possible settings of the relevant compiler switches (like -mieee),
 200    --  since we cannot control the user setting of those switches.
 201
 202    --  The attributes cannot dependent on the current setting of compiler
 203    --  switches, since the values must be static and consistent throughout
 204    --  the partition. We probably should add such consistency checks in future,
 205    --  but for now we don't do this.
 206
 207    AAMP_On_Target : Boolean;
 208    --  Set to True if target is AAMP.
 209
 210    Denorm_On_Target : Boolean;
 211    --  Set to False on targets that do not reliably support denormals.
 212    --  Reliably here means for all settings of the relevant -m flag, so
 213    --  for example, this is False on the Alpha where denormals are not
 214    --  supported unless -mieee is used.
 215
 216    Machine_Rounds_On_Target : Boolean;
 217    --  Set to False for targets where S'Machine_Rounds is False
 218
 219    Machine_Overflows_On_Target : Boolean;
 220    --  Set to True for targets where S'Machine_Overflows is True
 221
 222    Signed_Zeros_On_Target : Boolean;
 223    --  Set to False on targets that do not reliably support signed zeros.
 224
 225    OpenVMS_On_Target : Boolean;
 226    --  Set to True if target is OpenVMS.
 227
 228    --------------------------------------------------------------
 229    -- Handling of Unconstrained Values Returned from Functions --
 230    --------------------------------------------------------------
 231
 232    --  Functions that return variable length objects, notably unconstrained
 233    --  arrays are a special case, because there is no simple obvious way of
 234    --  implementing this feature. Furthermore, this capability is not present
 235    --  in C++ or C, so typically the system ABI does not handle this case.
 236
 237    --  GNAT uses two different approaches
 238
 239    --    The Secondary Stack
 240
 241    --      The secondary stack is a special storage pool that is used for
 242    --      this purpose. The called function places the result on the
 243    --      secondary stack, and the caller uses or copies the value from
 244    --      the secondary stack, and pops the secondary stack after the
 245    --      value is consumed. The secondary stack is outside the system
 246    --      ABI, and the important point is that although generally it is
 247    --      handled in a stack like manner corresponding to the subprogram
 248    --      call structure, a return from a function does NOT pop the stack.
 249
 250    --    DSP (Depressed Stack Pointer)
 251
 252    --      Some targets permit the implementation of a function call/return
 253    --      protocol in which the function does not pop the main stack pointer
 254    --      on return, but rather returns with the stack pointer depressed.
 255    --      This is not generally permitted by any ABI, but for at least some
 256    --      targets, the implementation of alloca provides a model for this
 257    --      approach. If return-with-DSP is implemented, then functions that
 258    --      return variable length objects do it by returning with the stack
 259    --      pointer depressed, and the returned object is a pointer to the
 260    --      area within the stack frame of the called procedure that contains
 261    --      the returned value. The caller must then pop the main stack when
 262    --      this value is consumed.
 263
 264    Functions_Return_By_DSP_On_Target : Boolean;
 265    --  Set to True if target permits functions to return with using the
 266    --  DSP (depressed stack pointer) approach.
 267
 268    -----------------
 269    -- Data Layout --
 270    -----------------
 271
 272    --  Normally when using the GCC backend, Gigi and GCC perform much of the
 273    --  data layout using the standard layout capabilities of GCC. If the
 274    --  parameter Backend_Layout is set to False, then the front end must
 275    --  perform all data layout. For further details see the package Layout.
 276
 277    Frontend_Layout_On_Target : Boolean;
 278    --  Set True if front end does layout
 279
 280    -----------------
 281    -- Subprograms --
 282    -----------------
 283
 284    procedure Get_Target_Parameters;
 285    --  Called at the start of execution to read the source of System and
 286    --  obtain and set the values of the above parameters.
 287
 288 end Targparm;