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 --          Copyright (C) 1999-2007, 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 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,  51  Franklin  Street,  Fifth  Floor, --
  20 -- Boston, MA 02110-1301, USA.                                              --
  21 --                                                                          --
  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.                                      --
  28 --                                                                          --
  29 -- GNAT was originally developed  by the GNAT team at  New York University. --
  30 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  31 --                                                                          --
  32 ------------------------------------------------------------------------------
  33
  34 --  This package obtains parameters from the target runtime version of System,
  35 --  to indicate parameters relevant to the target environment.
  36
  37 --  Is it right for this to be modified GPL???
  38
  39 --  Conceptually, these parameters could be obtained using rtsfind, but
  40 --  we do not do this for four reasons:
  41
  42 --    1. Compiling System for every compilation wastes time
  43
  44 --    2. This compilation impedes debugging by adding extra compile steps
  45
  46 --    3. There are recursion problems coming from compiling System itself
  47 --        or any of its children.
  48
  49 --    4. The binder also needs the parameters, and we do not want to have
  50 --        to drag a lot of front end stuff into the binder.
  51
  52 --  For all these reasons, we read in the source of System, and then scan
  53 --  it at the text level to extract the parameter values.
  54
  55 --  Note however, that later on, when the ali file is written, we make sure
  56 --  that the System file is at least parsed, so that the checksum is properly
  57 --  computed and set in the ali file. This partially negates points 1 and 2
  58 --  above although just parsing is quick and does not impact debugging much.
  59
  60 --  The parameters acquired by this routine from system.ads fall into four
  61 --  categories:
  62
  63 --     1. Configuration pragmas, that must appear at the start of the file.
  64 --        Any such pragmas automatically apply to any unit compiled in the
  65 --        presence of this system file. Only a limited set of such pragmas
  66 --        may appear as documented in the corresponding section below,
  67
  68 --     2. Target parameters. These are boolean constants that are defined
  69 --        in the private part of the package giving fixed information
  70 --        about the target architecture, and the capabilities of the
  71 --        code generator and run-time library.
  72
  73 --     3. Identification information. This is an optional string constant
  74 --        that gives the name of the run-time library configuration. This
  75 --        line may be ommitted for a version of system.ads to be used with
  76 --        the full Ada 95 run time.
  77
  78 --     4. Other characterisitics of package System. At the current time the
  79 --        only item in this category is whether type Address is private.
  80
  81 with Rident; use Rident;
  82 with Namet;  use Namet;
  83 with Types;  use Types;
  84
  85 package Targparm is
  86
  87    ---------------------------
  88    -- Configuration Pragmas --
  89    ---------------------------
  90
  91    --  The following switches get set if the corresponding configuration
  92    --  pragma is scanned from the source of system.ads. No other pragmas
  93    --  are permitted to appear at the start of the system.ads source file.
  94
  95    --  If a pragma Discard_Names appears, then Opt.Global_Discard_Names is
  96    --  set to True to indicate that all units must be compiled in this mode.
  97
  98    --  If a pragma Locking_Policy appears, then Opt.Locking_Policy is set
  99    --  to the first character of the policy name, and Opt.Locking_Policy_Sloc
 100    --  is set to System_Location.
 101
 102    --  If a pragma Normalize_Scalars appears, then Opt.Normalize_Scalars
 103    --  is set True, as well as Opt.Init_Or_Norm_Scalars.
 104
 105    --  If a pragma Queuing_Policy appears, then Opt.Queuing_Policy is set
 106    --  to the first character of the policy name, and Opt.Queuing_Policy_Sloc
 107    --  is set to System_Location.
 108
 109    --  If a pragma Task_Dispatching_Policy appears, then the flag
 110    --  Opt.Task_Dispatching_Policy is set to the first character of the
 111    --  policy name, and Opt.Task_Dispatching_Policy_Sloc is set to
 112    --  System_Location.
 113
 114    --  If a pragma Polling (On) appears, then the flag Opt.Polling_Required
 115    --  is set to True.
 116
 117    --  If a pragma Detect_Blocking appears, then the flag Opt.Detect_Blocking
 118    --  is set to True.
 119
 120    --  if a pragma Suppress_Exception_Locations appears, then the flag
 121    --  Opt.Exception_Locations_Suppressed is set to True.
 122
 123    --  If a pragma Profile with a valid profile argument appears, then
 124    --  the appropriate restrictions and policy flags are set.
 125
 126    --  The only other pragma allowed is a pragma Restrictions that specifies
 127    --  a restriction that will be imposed on all units in the partition. Note
 128    --  that in this context, only one restriction can be specified in a single
 129    --  pragma, and the pragma must appear on its own on a single source line.
 130
 131    --  If package System contains exactly the line "type Address is private;"
 132    --  then the flag Opt.Address_Is_Private is set True, otherwise this flag
 133    --  is set False.
 134
 135    Restrictions_On_Target : Restrictions_Info := No_Restrictions;
 136    --  Records restrictions specified by system.ads. Only the Set and Value
 137    --  members are modified. The Violated and Count fields are never modified.
 138    --  Note that entries can be set either by a pragma Restrictions or by
 139    --  a pragma Profile.
 140
 141    -------------------
 142    -- Run Time Name --
 143    -------------------
 144
 145    --  This parameter should be regarded as read only by all clients of
 146    --  of package. The only way they get modified is by calling the
 147    --  Get_Target_Parameters routine which reads the values from a provided
 148    --  text buffer containing the source of the system package.
 149
 150    --  The corresponding string constant is placed immediately at the start
 151    --  of the private part of system.ads if is present, e.g. in the form:
 152
 153    --    Run_Time_Name : constant String := "Zero Footprint Run Time";
 154
 155    --  the corresponding messages will look something like
 156
 157    --    xxx not supported (Zero Footprint Run Time)
 158
 159    Run_Time_Name_On_Target : Name_Id := No_Name;
 160    --  Set to appropriate names table entry Id value if a Run_Time_Name
 161    --  string constant is defined in system.ads. This name is used only
 162    --  for the configurable run-time case, and is used to parametrize
 163    --  messages that complain about non-supported run-time features.
 164    --  The name should contain only letters A-Z, digits 1-9, spaces,
 165    --  and underscores.
 166
 167    --------------------------
 168    -- Executable Extension --
 169    --------------------------
 170
 171    Executable_Extension_On_Target : Name_Id := No_Name;
 172    --  Executable extension on the target. This name is useful for setting
 173    --  the executable extension in a dynamic way, e.g. depending on the
 174    --  run time used, rather than using a configure-time macro as done by
 175    --  Get_Target_Executable_Suffix. If not set (No_Name), instead use
 176    --  System.OS_Lib.Get_Target_Executable_Suffix.
 177
 178    -----------------------
 179    -- Target Parameters --
 180    -----------------------
 181
 182    --  The following parameters correspond to the variables defined in the
 183    --  private part of System (without the terminating _On_Target). Note
 184    --  that it is required that all parameters defined here be specified
 185    --  in the target specific version of system.ads. Thus, to add a new
 186    --  parameter, add it to all system*.ads files. (There is a defaulting
 187    --  mechanism, but we don't normally take advantage of it, as explained
 188    --  below.)
 189
 190    --  The default values here are used if no value is found in system.ads.
 191    --  This should normally happen if the special version of system.ads used
 192    --  by the compiler itself is in use or if the value is only relevant to
 193    --  a particular target (e.g. OpenVMS, AAMP). The default values are
 194    --  suitable for use in normal environments. This approach allows the
 195    --  possibility of new versions of the compiler (possibly with new system
 196    --  parameters added) being used to compile older versions of the compiler
 197    --  sources, as well as avoiding duplicating values in all system-*.ads
 198    --  files for flags that are used on a few platforms only.
 199
 200    --  All these parameters should be regarded as read only by all clients
 201    --  of the package. The only way they get modified is by calling the
 202    --  Get_Target_Parameters routine which reads the values from a provided
 203    --  text buffer containing the source of the system package.
 204
 205    ----------------------------
 206    -- Special Target Control --
 207    ----------------------------
 208
 209    --  The great majority of GNAT ports are based on GCC. The switches in
 210    --  This section indicate the use of some non-standard target back end
 211    --  or other special targetting requirements.
 212
 213    AAMP_On_Target : Boolean := False;
 214    --  Set to True if target is AAMP
 215
 216    OpenVMS_On_Target : Boolean := False;
 217    --  Set to True if target is OpenVMS
 218
 219    type Virtual_Machine_Kind is (No_VM, JVM_Target, CLI_Target);
 220    VM_Target : Virtual_Machine_Kind := No_VM;
 221    --  Kind of virtual machine targetted
 222
 223    -------------------------------
 224    -- Backend Arithmetic Checks --
 225    -------------------------------
 226
 227    --  Divide and overflow checks are either done in the front end or
 228    --  back end. The front end will generate checks when required unless
 229    --  the corresponding parameter here is set to indicate that the back
 230    --  end will generate the required checks (or that the checks are
 231    --  automatically performed by the hardware in an appropriate form).
 232
 233    Backend_Divide_Checks_On_Target : Boolean := False;
 234    --  Set True if the back end generates divide checks, or if the hardware
 235    --  checks automatically. Set False if the front end must generate the
 236    --  required tests using explicit expanded code.
 237
 238    Backend_Overflow_Checks_On_Target : Boolean := False;
 239    --  Set True if the back end generates arithmetic overflow checks, or if
 240    --  the hardware checks automatically. Set False if the front end must
 241    --  generate the required tests using explicit expanded code.
 242
 243    -----------------------------------
 244    -- Control of Exception Handling --
 245    -----------------------------------
 246
 247    --  GNAT implements three methods of implementing exceptions:
 248
 249    --    Front-End Longjmp/Setjmp Exceptions
 250
 251    --      This approach uses longjmp/setjmp to handle exceptions. It
 252    --      uses less storage, and can often propagate exceptions faster,
 253    --      at the expense of (sometimes considerable) overhead in setting
 254    --      up an exception handler. This approach is available on all
 255    --      targets, and is the default where it is the only approach.
 256
 257    --      The generation of the setjmp and longjmp calls is handled by
 258    --      the front end of the compiler (this includes gigi in the case
 259    --      of the standard GCC back end). It does not use any back end
 260    --      suport (such as the GCC3 exception handling mechanism). When
 261    --      this approach is used, the compiler generates special exception
 262    --      handlers for handling cleanups when an exception is raised.
 263
 264    --    Front-End Zero Cost Exceptions
 265
 266    --      This approach uses separate exception tables. These use extra
 267    --      storage, and exception propagation can be quite slow, but there
 268    --      is no overhead in setting up an exception handler (it is to this
 269    --      latter operation that the phrase zero-cost refers). This approach
 270    --      is only available on some targets, and is the default where it is
 271    --      available.
 272
 273    --      The generation of the exception tables is handled by the front
 274    --      end of the compiler. It does not use any back end support (such
 275    --      as the GCC3 exception handling mechanism). When this approach
 276    --      is used, the compiler generates special exception handlers for
 277    --      handling cleanups when an exception is raised.
 278
 279    --    Back-End Zero Cost Exceptions
 280
 281    --      With this approach, the back end handles the generation and
 282    --      handling of exceptions. For example, the GCC3 exception handling
 283    --      mechanisms are used in this mode. The front end simply generates
 284    --      code for explicit exception handlers, and AT END cleanup handlers
 285    --      are simply passed unchanged to the backend for generating cleanups
 286    --      both in the exceptional and non-exceptional cases.
 287
 288    --      As the name implies, this approach generally uses a zero-cost
 289    --      mechanism with tables, but the tables are generated by the back
 290    --      end. However, since the back-end is entirely responsible for the
 291    --      handling of exceptions, another mechanism might be used. In the
 292    --      case of GCC3 for instance, it might be the case that the compiler
 293    --      is configured for setjmp/longjmp handling, then everything will
 294    --      work correctly. However, it is definitely preferred that the
 295    --      back end provide zero cost exception handling.
 296
 297    --    Controlling the selection of methods
 298
 299    --      On most implementations, back-end zero-cost exceptions are used.
 300    --      Otherwise, Front-End Longjmp/Setjmp approach is used.
 301    --      Note that there is a requirement that all Ada units in a partition
 302    --      be compiled with the same exception model.
 303
 304    --    Control of Available Methods and Defaults
 305
 306    --      The following switches specify whether ZCX is available, and
 307    --      whether it is enabled by default.
 308
 309    ZCX_By_Default_On_Target : Boolean := False;
 310    --  Indicates if zero cost exceptions are active by default. If this
 311    --  variable is False, then the only possible exception method is the
 312    --  front-end setjmp/longjmp approach, and this is the default. If
 313    --  this variable is True, then GCC ZCX is used.
 314
 315    GCC_ZCX_Support_On_Target  : Boolean := False;
 316    --  Indicates that the target supports GCC Exceptions
 317
 318    ------------------------------------
 319    -- Run-Time Library Configuration --
 320    ------------------------------------
 321
 322    --  In configurable run-time mode, the system run-time may not support
 323    --  the full Ada language. The effect of setting this switch is to let
 324    --  the compiler know that it is not surprising (i.e. the system is not
 325    --  misconfigured) if run-time library units or entities within units are
 326    --  not present in the run-time.
 327
 328    Configurable_Run_Time_On_Target : Boolean := False;
 329    --  Indicates that the system.ads file is for a configurable run-time
 330    --
 331    --  This has some specific effects as follows
 332    --
 333    --    The binder generates the gnat_argc/argv/envp variables in the
 334    --    binder file instead of being imported from the run-time library.
 335    --    If Command_Line_Args_On_Target is set to False, then the
 336    --    generation of these variables is suppressed completely.
 337    --
 338    --    The binder generates the gnat_exit_status variable in the binder
 339    --    file instead of being imported from the run-time library. If
 340    --    Exit_Status_Supported_On_Target is set to False, then the
 341    --    generation of this variable is suppressed entirely.
 342    --
 343    --    The routine __gnat_break_start is defined within the binder file
 344    --    instead of being imported from the run-time library.
 345    --
 346    --    The variable __gnat_exit_status is generated within the binder file
 347    --    instead of being imported from the run-time library.
 348
 349    Suppress_Standard_Library_On_Target : Boolean := False;
 350    --  If this flag is True, then the standard library is not included by
 351    --  default in the executable (see unit System.Standard_Library in file
 352    --  s-stalib.ads for details of what this includes). This is for example
 353    --  set True for the zero foot print case, where these files should not
 354    --  be included by default.
 355    --
 356    --  This flag has some other related effects:
 357    --
 358    --    The generation of global variables in the bind file is suppressed,
 359    --    with the exception of the priority of the environment task, which
 360    --    is needed by the Ravenscar run-time.
 361    --
 362    --    The calls to __gnat_initialize and __gnat_finalize are omitted
 363    --
 364    --    All finalization and initialization (controlled types) is omitted
 365    --
 366    --    The routine __gnat_handler_installed is not imported
 367
 368    Preallocated_Stacks_On_Target : Boolean := False;
 369    --  If this flag is True, then the expander preallocates all task stacks
 370    --  at compile time. If the flag is False, then task stacks are not pre-
 371    --  allocated, and task stack allocation is the responsibility of the
 372    --  run-time (which typically delegates the task to the underlying
 373    --  operating system environment).
 374
 375    ---------------------
 376    -- Duration Format --
 377    ---------------------
 378
 379    --  By default, type Duration is a 64-bit fixed-point type with a delta
 380    --  and small of 10**(-9) (i.e. it is a count in nanoseconds. This flag
 381    --  allows that standard format to be modified.
 382
 383    Duration_32_Bits_On_Target : Boolean := False;
 384    --  If True, then Duration is represented in 32 bits and the delta and
 385    --  small values are set to 20.0*(10**(-3)) (i.e. it is a count in units
 386    --  of 20 milliseconds.
 387
 388    ------------------------------------
 389    -- Back-End Code Generation Flags --
 390    ------------------------------------
 391
 392    --  These flags indicate possible limitations in what the code generator
 393    --  can handle. They will all be True for a full run-time, but one or more
 394    --  of these may be false for a configurable run-time, and if a feature is
 395    --  used at the source level, and the corresponding flag is false, then an
 396    --  error message will be issued saying the feature is not supported.
 397
 398    Support_64_Bit_Divides_On_Target : Boolean := True;
 399    --  If True, the back end supports 64-bit divide operations. If False, then
 400    --  the source program may not contain 64-bit divide operations. This is
 401    --  specifically useful in the zero foot-print case, where the issue is
 402    --  whether there is a hardware divide instruction for 64-bits so that
 403    --  no run-time support is required. It should always be set True if the
 404    --  necessary run-time support is present.
 405
 406    Support_Aggregates_On_Target : Boolean := True;
 407    --  In the general case, the use of aggregates may generate calls
 408    --  to run-time routines in the C library, including memset, memcpy,
 409    --  memmove, and bcopy. This flag is set to True if these routines
 410    --  are available. If any of these routines is not available, then
 411    --  this flag is False, and the use of aggregates is not permitted.
 412
 413    Support_Composite_Assign_On_Target : Boolean := True;
 414    --  The assignment of composite objects other than small records and
 415    --  arrays whose size is 64-bits or less and is set by an explicit
 416    --  size clause may generate calls to memcpy, memmove, and bcopy.
 417    --  If versions of all these routines are available, then this flag
 418    --  is set to True. If any of these routines is not available, then
 419    --  the flag is set False, and composite assignments are not allowed.
 420
 421    Support_Composite_Compare_On_Target : Boolean := True;
 422    --  If this flag is True, then the back end supports bit-wise comparison
 423    --  of composite objects for equality, either generating inline code or
 424    --  calling appropriate (and available) run-time routines. If this flag
 425    --  is False, then the back end does not provide this support, and the
 426    --  front end uses component by component comparison for composites.
 427
 428    Support_Long_Shifts_On_Target : Boolean := True;
 429    --  If True, the back end supports 64-bit shift operations. If False, then
 430    --  the source program may not contain explicit 64-bit shifts. In addition,
 431    --  the code generated for packed arrays will avoid the use of long shifts.
 432
 433    --------------------
 434    -- Indirect Calls --
 435    --------------------
 436
 437    Always_Compatible_Rep_On_Target : Boolean := True;
 438    --  If True, the Can_Use_Internal_Rep flag (see Einfo) is set to False in
 439    --  all cases. This corresponds to the traditional code generation
 440    --  strategy. False allows the front end to choose a policy that partly or
 441    --  entirely eliminates dynamically generated trampolines.
 442
 443    -------------------------------
 444    -- Control of Stack Checking --
 445    -------------------------------
 446
 447    --  GNAT provides two methods of implementing exceptions:
 448
 449    --    GCC Probing Mechanism
 450
 451    --      This approach uses the standard GCC mechanism for
 452    --      stack checking. The method assumes that accessing
 453    --      storage immediately beyond the end of the stack
 454    --      will result in a trap that is converted to a storage
 455    --      error by the runtime system. This mechanism has
 456    --      minimal overhead, but requires complex hardware,
 457    --      operating system and run-time support. Probing is
 458    --      the default method where it is available. The stack
 459    --      size for the environment task depends on the operating
 460    --      system and cannot be set in a system-independent way.
 461
 462    --   GCC Stack-limit Mechanism
 463
 464    --      This approach uses the GCC stack limits mechanism.
 465    --      It relies on comparing the stack pointer with the
 466    --      values of a global symbol. If the check fails, a
 467    --      trap is explicitly generated. The advantage is
 468    --      that the mechanism requires no memory protection,
 469    --      but operating system and run-time support are
 470    --      needed to manage the per-task values of the symbol.
 471    --      This is the default method after probing where it
 472    --      is available.
 473
 474    --   GNAT Stack-limit Checking
 475
 476    --      This method relies on comparing the stack pointer
 477    --      with per-task stack limits. If the check fails, an
 478    --      exception is explicitly raised. The advantage is
 479    --      that the method requires no extra system dependent
 480    --      runtime support and can be used on systems without
 481    --      memory protection as well, but at the cost of more
 482    --      overhead for doing the check. This is the fallback
 483    --      method if the above two are not supported.
 484
 485    Stack_Check_Probes_On_Target : Boolean := False;
 486    --  Indicates if the GCC probing mechanism is used
 487
 488    Stack_Check_Limits_On_Target : Boolean := False;
 489    --  Indicates if the GCC stack-limit mechanism is used
 490
 491    --  Both flags cannot be simultaneously set to True. If neither
 492    --  is, the target independent fallback method is used.
 493
 494    Stack_Check_Default_On_Target : Boolean := False;
 495    --  Indicates if stack checking is on by default
 496
 497    ----------------------------
 498    -- Command Line Arguments --
 499    ----------------------------
 500
 501    --  For most ports of GNAT, command line arguments are supported. The
 502    --  following flag is set to False for targets that do not support
 503    --  command line arguments (VxWorks and AAMP). Note that support of
 504    --  command line arguments is not required on such targets (RM A.15(13)).
 505
 506    Command_Line_Args_On_Target : Boolean := True;
 507    --  Set False if no command line arguments on target. Note that if this
 508    --  is False in with Configurable_Run_Time_On_Target set to True, then
 509    --  this causes suppression of generation of the argv/argc variables
 510    --  used to record command line arguments.
 511
 512    --  Similarly, most ports support the use of an exit status, but AAMP
 513    --  is an exception (as allowed by RM A.15(18-20))
 514
 515    Exit_Status_Supported_On_Target : Boolean := True;
 516    --  Set False if returning of an exit status is not supported on target.
 517    --  Note that if this False in with Configurable_Run_Time_On_Target
 518    --  set to True, then this causes suppression of the gnat_exit_status
 519    --  variable used to record the exit status.
 520
 521    -----------------------
 522    -- Main Program Name --
 523    -----------------------
 524
 525    --  When the binder generates the main program to be used to create the
 526    --  executable, the main program name is main by default (to match the
 527    --  usual Unix practice). If this parameter is set to True, then the
 528    --  name is instead by default taken from the actual Ada main program
 529    --  name (just the name of the child if the main program is a child unit).
 530    --  In either case, this value can be overridden using -M name.
 531
 532    Use_Ada_Main_Program_Name_On_Target : Boolean := False;
 533    --  Set True to use the Ada main program name as the main name
 534
 535    ----------------------------------------------
 536    -- Boolean-Valued Floating-Point Attributes --
 537    ----------------------------------------------
 538
 539    --  The constants below give the values for representation oriented
 540    --  floating-point attributes that are the same for all float types
 541    --  on the target. These are all boolean values.
 542
 543    --  A value is only True if the target reliably supports the corresponding
 544    --  feature. Reliably here means that support is guaranteed for all
 545    --  possible settings of the relevant compiler switches (like -mieee),
 546    --  since we cannot control the user setting of those switches.
 547
 548    --  The attributes cannot dependent on the current setting of compiler
 549    --  switches, since the values must be static and consistent throughout
 550    --  the partition. We probably should add such consistency checks in future,
 551    --  but for now we don't do this.
 552
 553    --  Note: the compiler itself does not use floating-point, so the
 554    --  settings of the defaults here are not really relevant.
 555
 556    --  Note: in some cases, proper support of some of these floating point
 557    --  features may require a specific switch (e.g. -mieee on the Alpha)
 558    --  to be used to obtain full RM compliant support.
 559
 560    Denorm_On_Target : Boolean := False;
 561    --  Set to False on targets that do not reliably support denormals
 562
 563    Machine_Rounds_On_Target : Boolean := True;
 564    --  Set to False for targets where S'Machine_Rounds is False
 565
 566    Machine_Overflows_On_Target : Boolean := False;
 567    --  Set to True for targets where S'Machine_Overflows is True
 568
 569    Signed_Zeros_On_Target : Boolean := True;
 570    --  Set to False on targets that do not reliably support signed zeros
 571
 572    -------------------------------------------
 573    -- Boolean-Valued Fixed-Point Attributes --
 574    -------------------------------------------
 575
 576    Fractional_Fixed_Ops_On_Target : Boolean := False;
 577    --  Set to True for targets that support fixed-by-fixed multiplication
 578    --  and division for fixed-point types with a small value equal to
 579    --  2 ** (-(T'Object_Size - 1)) and whose values have an absolute
 580    --  value less than 1.0.
 581
 582    -----------------
 583    -- Data Layout --
 584    -----------------
 585
 586    --  Normally when using the GCC backend, Gigi and GCC perform much of the
 587    --  data layout using the standard layout capabilities of GCC. If the
 588    --  parameter Backend_Layout is set to False, then the front end must
 589    --  perform all data layout. For further details see the package Layout.
 590
 591    Frontend_Layout_On_Target : Boolean := False;
 592    --  Set True if front end does layout
 593
 594    -----------------
 595    -- Subprograms --
 596    -----------------
 597
 598    --  These subprograms are used to initialize the target parameter values
 599    --  from the system.ads file. Note that this is only done once, so if more
 600    --  than one call is made to either routine, the second and subsequent
 601    --  calls are ignored.
 602
 603    procedure Get_Target_Parameters
 604      (System_Text  : Source_Buffer_Ptr;
 605       Source_First : Source_Ptr;
 606       Source_Last  : Source_Ptr);
 607    --  Called at the start of execution to obtain target parameters from
 608    --  the source of package System. The parameters provide the source
 609    --  text to be scanned (in System_Text (Source_First .. Source_Last)).
 610
 611    procedure Get_Target_Parameters;
 612    --  This version reads in system.ads using Osint. The idea is that the
 613    --  caller uses the first version if they have to read system.ads anyway
 614    --  (e.g. the compiler) and uses this simpler interface if system.ads is
 615    --  not otherwise needed.
 616
 617 end Targparm;