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------------------------------------------------------------------------------ -- -- -- GNAT RUN-TIME COMPONENTS -- -- -- -- T A R G P A R M -- -- -- -- S p e c -- -- -- -- Copyright (C) 1999-2011, Free Software Foundation, Inc. -- -- -- -- GNAT is free software; you can redistribute it and/or modify it under -- -- terms of the GNU General Public License as published by the Free Soft- -- -- ware Foundation; either version 3, or (at your option) any later ver- -- -- sion. GNAT is distributed in the hope that it will be useful, but WITH- -- -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY -- -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License -- -- for more details. You should have received a copy of the GNU General -- -- Public License distributed with GNAT; see file COPYING3. If not, go to -- -- http://www.gnu.org/licenses for a complete copy of the license. -- -- -- -- GNAT was originally developed by the GNAT team at New York University. -- -- Extensive contributions were provided by Ada Core Technologies Inc. -- -- -- ------------------------------------------------------------------------------ -- This package obtains parameters from the target runtime version of System, -- to indicate parameters relevant to the target environment. -- Conceptually, these parameters could be obtained using rtsfind, but -- we do not do this for four reasons: -- 1. Compiling System for every compilation wastes time -- 2. This compilation impedes debugging by adding extra compile steps -- 3. There are recursion problems coming from compiling System itself -- or any of its children. -- 4. The binder also needs the parameters, and we do not want to have -- to drag a lot of front end stuff into the binder. -- For all these reasons, we read in the source of System, and then scan -- it at the text level to extract the parameter values. -- Note however, that later on, when the ali file is written, we make sure -- that the System file is at least parsed, so that the checksum is properly -- computed and set in the ali file. This partially negates points 1 and 2 -- above although just parsing is quick and does not impact debugging much. -- The parameters acquired by this routine from system.ads fall into four -- categories: -- 1. Configuration pragmas, that must appear at the start of the file. -- Any such pragmas automatically apply to any unit compiled in the -- presence of this system file. Only a limited set of such pragmas -- may appear as documented in the corresponding section below, -- 2. Target parameters. These are boolean constants that are defined -- in the private part of the package giving fixed information -- about the target architecture, and the capabilities of the -- code generator and run-time library. -- 3. Identification information. This is an optional string constant -- that gives the name of the run-time library configuration. This -- line may be omitted for a version of system.ads to be used with -- the full Ada 95 run time. -- 4. Other characteristics of package System. At the current time the -- only item in this category is whether type Address is private. with Rident; use Rident; with Namet; use Namet; with Types; use Types; package Targparm is --------------------------- -- Configuration Pragmas -- --------------------------- -- The following switches get set if the corresponding configuration -- pragma is scanned from the source of system.ads. No other pragmas -- are permitted to appear at the start of the system.ads source file. -- If a pragma Discard_Names appears, then Opt.Global_Discard_Names is -- set to True to indicate that all units must be compiled in this mode. -- If a pragma Locking_Policy appears, then Opt.Locking_Policy is set -- to the first character of the policy name, and Opt.Locking_Policy_Sloc -- is set to System_Location. -- If a pragma Normalize_Scalars appears, then Opt.Normalize_Scalars -- is set True, as well as Opt.Init_Or_Norm_Scalars. -- If a pragma Queuing_Policy appears, then Opt.Queuing_Policy is set -- to the first character of the policy name, and Opt.Queuing_Policy_Sloc -- is set to System_Location. -- If a pragma Task_Dispatching_Policy appears, then the flag -- Opt.Task_Dispatching_Policy is set to the first character of the -- policy name, and Opt.Task_Dispatching_Policy_Sloc is set to -- System_Location. -- If a pragma Polling (On) appears, then the flag Opt.Polling_Required -- is set to True. -- If a pragma Detect_Blocking appears, then the flag Opt.Detect_Blocking -- is set to True. -- if a pragma Suppress_Exception_Locations appears, then the flag -- Opt.Exception_Locations_Suppressed is set to True. -- If a pragma Profile with a valid profile argument appears, then -- the appropriate restrictions and policy flags are set. -- The only other pragma allowed is a pragma Restrictions that specifies -- a restriction that will be imposed on all units in the partition. Note -- that in this context, only one restriction can be specified in a single -- pragma, and the pragma must appear on its own on a single source line. -- If package System contains exactly the line "type Address is private;" -- then the flag Opt.Address_Is_Private is set True, otherwise this flag -- is set False. Restrictions_On_Target : Restrictions_Info := No_Restrictions; -- Records restrictions specified by system.ads. Only the Set and Value -- members are modified. The Violated and Count fields are never modified. -- Note that entries can be set either by a pragma Restrictions or by -- a pragma Profile. ------------------- -- Run Time Name -- ------------------- -- This parameter should be regarded as read only by all clients of -- of package. The only way they get modified is by calling the -- Get_Target_Parameters routine which reads the values from a provided -- text buffer containing the source of the system package. -- The corresponding string constant is placed immediately at the start -- of the private part of system.ads if is present, e.g. in the form: -- Run_Time_Name : constant String := "Zero Footprint Run Time"; -- the corresponding messages will look something like -- xxx not supported (Zero Footprint Run Time) Run_Time_Name_On_Target : Name_Id := No_Name; -- Set to appropriate names table entry Id value if a Run_Time_Name -- string constant is defined in system.ads. This name is used only -- for the configurable run-time case, and is used to parameterize -- messages that complain about non-supported run-time features. -- The name should contain only letters A-Z, digits 1-9, spaces, -- and underscores. -------------------------- -- Executable Extension -- -------------------------- Executable_Extension_On_Target : Name_Id := No_Name; -- Executable extension on the target. This name is useful for setting -- the executable extension in a dynamic way, e.g. depending on the -- run time used, rather than using a configure-time macro as done by -- Get_Target_Executable_Suffix. If not set (No_Name), instead use -- System.OS_Lib.Get_Target_Executable_Suffix. ----------------------- -- Target Parameters -- ----------------------- -- The following parameters correspond to the variables defined in the -- private part of System (without the terminating _On_Target). Note -- that it is required that all parameters defined here be specified -- in the target specific version of system.ads. Thus, to add a new -- parameter, add it to all system*.ads files. (There is a defaulting -- mechanism, but we don't normally take advantage of it, as explained -- below.) -- The default values here are used if no value is found in system.ads. -- This should normally happen if the special version of system.ads used -- by the compiler itself is in use or if the value is only relevant to -- a particular target (e.g. OpenVMS, AAMP). The default values are -- suitable for use in normal environments. This approach allows the -- possibility of new versions of the compiler (possibly with new system -- parameters added) being used to compile older versions of the compiler -- sources, as well as avoiding duplicating values in all system-*.ads -- files for flags that are used on a few platforms only. -- All these parameters should be regarded as read only by all clients -- of the package. The only way they get modified is by calling the -- Get_Target_Parameters routine which reads the values from a provided -- text buffer containing the source of the system package. ---------------------------- -- Special Target Control -- ---------------------------- -- The great majority of GNAT ports are based on GCC. The switches in -- This section indicate the use of some non-standard target back end -- or other special targetting requirements. AAMP_On_Target : Boolean := False; -- Set to True if target is AAMP OpenVMS_On_Target : Boolean := False; -- Set to True if target is OpenVMS RTX_RTSS_Kernel_Module_On_Target : Boolean := False; -- Set to True if target is RTSS module for RTX type Virtual_Machine_Kind is (No_VM, JVM_Target, CLI_Target); VM_Target : Virtual_Machine_Kind := No_VM; -- Kind of virtual machine targetted -- No_VM: no virtual machine, default case of a standard processor -- JVM_Target: Java Virtual Machine -- CLI_Target: CLI/.NET Virtual Machine ------------------------------- -- Backend Arithmetic Checks -- ------------------------------- -- Divide and overflow checks are either done in the front end or -- back end. The front end will generate checks when required unless -- the corresponding parameter here is set to indicate that the back -- end will generate the required checks (or that the checks are -- automatically performed by the hardware in an appropriate form). Backend_Divide_Checks_On_Target : Boolean := False; -- Set True if the back end generates divide checks, or if the hardware -- checks automatically. Set False if the front end must generate the -- required tests using explicit expanded code. Backend_Overflow_Checks_On_Target : Boolean := False; -- Set True if the back end generates arithmetic overflow checks, or if -- the hardware checks automatically. Set False if the front end must -- generate the required tests using explicit expanded code. ----------------------------------- -- Control of Exception Handling -- ----------------------------------- -- GNAT implements three methods of implementing exceptions: -- Front-End Longjmp/Setjmp Exceptions -- This approach uses longjmp/setjmp to handle exceptions. It -- uses less storage, and can often propagate exceptions faster, -- at the expense of (sometimes considerable) overhead in setting -- up an exception handler. This approach is available on all -- targets, and is the default where it is the only approach. -- The generation of the setjmp and longjmp calls is handled by -- the front end of the compiler (this includes gigi in the case -- of the standard GCC back end). It does not use any back end -- support (such as the GCC3 exception handling mechanism). When -- this approach is used, the compiler generates special exception -- handlers for handling cleanups when an exception is raised. -- Front-End Zero Cost Exceptions -- This approach uses separate exception tables. These use extra -- storage, and exception propagation can be quite slow, but there -- is no overhead in setting up an exception handler (it is to this -- latter operation that the phrase zero-cost refers). This approach -- is only available on some targets, and is the default where it is -- available. -- The generation of the exception tables is handled by the front -- end of the compiler. It does not use any back end support (such -- as the GCC3 exception handling mechanism). When this approach -- is used, the compiler generates special exception handlers for -- handling cleanups when an exception is raised. -- Back-End Zero Cost Exceptions -- With this approach, the back end handles the generation and -- handling of exceptions. For example, the GCC3 exception handling -- mechanisms are used in this mode. The front end simply generates -- code for explicit exception handlers, and AT END cleanup handlers -- are simply passed unchanged to the backend for generating cleanups -- both in the exceptional and non-exceptional cases. -- As the name implies, this approach generally uses a zero-cost -- mechanism with tables, but the tables are generated by the back -- end. However, since the back-end is entirely responsible for the -- handling of exceptions, another mechanism might be used. In the -- case of GCC3 for instance, it might be the case that the compiler -- is configured for setjmp/longjmp handling, then everything will -- work correctly. However, it is definitely preferred that the -- back end provide zero cost exception handling. -- Controlling the selection of methods -- On most implementations, back-end zero-cost exceptions are used. -- Otherwise, Front-End Longjmp/Setjmp approach is used. -- Note that there is a requirement that all Ada units in a partition -- be compiled with the same exception model. -- Control of Available Methods and Defaults -- The following switches specify whether ZCX is available, and -- whether it is enabled by default. ZCX_By_Default_On_Target : Boolean := False; -- Indicates if zero cost exceptions are active by default. If this -- variable is False, then the only possible exception method is the -- front-end setjmp/longjmp approach, and this is the default. If -- this variable is True, then GCC ZCX is used. ------------------------------------ -- Run-Time Library Configuration -- ------------------------------------ -- In configurable run-time mode, the system run-time may not support -- the full Ada language. The effect of setting this switch is to let -- the compiler know that it is not surprising (i.e. the system is not -- misconfigured) if run-time library units or entities within units are -- not present in the run-time. Configurable_Run_Time_On_Target : Boolean := False; -- Indicates that the system.ads file is for a configurable run-time -- -- This has some specific effects as follows -- -- The binder generates the gnat_argc/argv/envp variables in the -- binder file instead of being imported from the run-time library. -- If Command_Line_Args_On_Target is set to False, then the -- generation of these variables is suppressed completely. -- -- The binder generates the gnat_exit_status variable in the binder -- file instead of being imported from the run-time library. If -- Exit_Status_Supported_On_Target is set to False, then the -- generation of this variable is suppressed entirely. -- -- The routine __gnat_break_start is defined within the binder file -- instead of being imported from the run-time library. -- -- The variable __gnat_exit_status is generated within the binder file -- instead of being imported from the run-time library. Suppress_Standard_Library_On_Target : Boolean := False; -- If this flag is True, then the standard library is not included by -- default in the executable (see unit System.Standard_Library in file -- s-stalib.ads for details of what this includes). This is for example -- set True for the zero foot print case, where these files should not -- be included by default. -- -- This flag has some other related effects: -- -- The generation of global variables in the bind file is suppressed, -- with the exception of the priority of the environment task, which -- is needed by the Ravenscar run-time. -- -- The calls to __gnat_initialize and __gnat_finalize are omitted -- -- All finalization and initialization (controlled types) is omitted -- -- The routine __gnat_handler_installed is not imported Preallocated_Stacks_On_Target : Boolean := False; -- If this flag is True, then the expander preallocates all task stacks -- at compile time. If the flag is False, then task stacks are not pre- -- allocated, and task stack allocation is the responsibility of the -- run-time (which typically delegates the task to the underlying -- operating system environment). --------------------- -- Duration Format -- --------------------- -- By default, type Duration is a 64-bit fixed-point type with a delta -- and small of 10**(-9) (i.e. it is a count in nanoseconds. This flag -- allows that standard format to be modified. Duration_32_Bits_On_Target : Boolean := False; -- If True, then Duration is represented in 32 bits and the delta and -- small values are set to 20.0*(10**(-3)) (i.e. it is a count in units -- of 20 milliseconds. ------------------------------------ -- Back-End Code Generation Flags -- ------------------------------------ -- These flags indicate possible limitations in what the code generator -- can handle. They will all be True for a full run-time, but one or more -- of these may be false for a configurable run-time, and if a feature is -- used at the source level, and the corresponding flag is false, then an -- error message will be issued saying the feature is not supported. Support_Aggregates_On_Target : Boolean := True; -- In the general case, the use of aggregates may generate calls -- to run-time routines in the C library, including memset, memcpy, -- memmove, and bcopy. This flag is set to True if these routines -- are available. If any of these routines is not available, then -- this flag is False, and the use of aggregates is not permitted. Support_Composite_Assign_On_Target : Boolean := True; -- The assignment of composite objects other than small records and -- arrays whose size is 64-bits or less and is set by an explicit -- size clause may generate calls to memcpy, memmove, and bcopy. -- If versions of all these routines are available, then this flag -- is set to True. If any of these routines is not available, then -- the flag is set False, and composite assignments are not allowed. Support_Composite_Compare_On_Target : Boolean := True; -- If this flag is True, then the back end supports bit-wise comparison -- of composite objects for equality, either generating inline code or -- calling appropriate (and available) run-time routines. If this flag -- is False, then the back end does not provide this support, and the -- front end uses component by component comparison for composites. Support_Long_Shifts_On_Target : Boolean := True; -- If True, the back end supports 64-bit shift operations. If False, then -- the source program may not contain explicit 64-bit shifts. In addition, -- the code generated for packed arrays will avoid the use of long shifts. -------------------- -- Indirect Calls -- -------------------- Always_Compatible_Rep_On_Target : Boolean := True; -- If True, the Can_Use_Internal_Rep flag (see Einfo) is set to False in -- all cases. This corresponds to the traditional code generation -- strategy. False allows the front end to choose a policy that partly or -- entirely eliminates dynamically generated trampolines. ------------------------------- -- Control of Stack Checking -- ------------------------------- -- GNAT provides three methods of implementing exceptions: -- GCC Probing Mechanism -- This approach uses the standard GCC mechanism for -- stack checking. The method assumes that accessing -- storage immediately beyond the end of the stack -- will result in a trap that is converted to a storage -- error by the runtime system. This mechanism has -- minimal overhead, but requires complex hardware, -- operating system and run-time support. Probing is -- the default method where it is available. The stack -- size for the environment task depends on the operating -- system and cannot be set in a system-independent way. -- GCC Stack-limit Mechanism -- This approach uses the GCC stack limits mechanism. -- It relies on comparing the stack pointer with the -- values of a global symbol. If the check fails, a -- trap is explicitly generated. The advantage is -- that the mechanism requires no memory protection, -- but operating system and run-time support are -- needed to manage the per-task values of the symbol. -- This is the default method after probing where it -- is available. -- GNAT Stack-limit Checking -- This method relies on comparing the stack pointer -- with per-task stack limits. If the check fails, an -- exception is explicitly raised. The advantage is -- that the method requires no extra system dependent -- runtime support and can be used on systems without -- memory protection as well, but at the cost of more -- overhead for doing the check. This is the fallback -- method if the above two are not supported. Stack_Check_Probes_On_Target : Boolean := False; -- Indicates if the GCC probing mechanism is used Stack_Check_Limits_On_Target : Boolean := False; -- Indicates if the GCC stack-limit mechanism is used -- Both flags cannot be simultaneously set to True. If neither -- is, the target independent fallback method is used. Stack_Check_Default_On_Target : Boolean := False; -- Indicates if stack checking is on by default ---------------------------- -- Command Line Arguments -- ---------------------------- -- For most ports of GNAT, command line arguments are supported. The -- following flag is set to False for targets that do not support -- command line arguments (VxWorks and AAMP). Note that support of -- command line arguments is not required on such targets (RM A.15(13)). Command_Line_Args_On_Target : Boolean := True; -- Set False if no command line arguments on target. Note that if this -- is False in with Configurable_Run_Time_On_Target set to True, then -- this causes suppression of generation of the argv/argc variables -- used to record command line arguments. -- Similarly, most ports support the use of an exit status, but AAMP -- is an exception (as allowed by RM A.15(18-20)) Exit_Status_Supported_On_Target : Boolean := True; -- Set False if returning of an exit status is not supported on target. -- Note that if this False in with Configurable_Run_Time_On_Target -- set to True, then this causes suppression of the gnat_exit_status -- variable used to record the exit status. ----------------------- -- Main Program Name -- ----------------------- -- When the binder generates the main program to be used to create the -- executable, the main program name is main by default (to match the -- usual Unix practice). If this parameter is set to True, then the -- name is instead by default taken from the actual Ada main program -- name (just the name of the child if the main program is a child unit). -- In either case, this value can be overridden using -M name. Use_Ada_Main_Program_Name_On_Target : Boolean := False; -- Set True to use the Ada main program name as the main name ---------------------------------------------- -- Boolean-Valued Floating-Point Attributes -- ---------------------------------------------- -- The constants below give the values for representation oriented -- floating-point attributes that are the same for all float types -- on the target. These are all boolean values. -- A value is only True if the target reliably supports the corresponding -- feature. Reliably here means that support is guaranteed for all -- possible settings of the relevant compiler switches (like -mieee), -- since we cannot control the user setting of those switches. -- The attributes cannot dependent on the current setting of compiler -- switches, since the values must be static and consistent throughout -- the partition. We probably should add such consistency checks in future, -- but for now we don't do this. -- Note: the compiler itself does not use floating-point, so the -- settings of the defaults here are not really relevant. -- Note: in some cases, proper support of some of these floating point -- features may require a specific switch (e.g. -mieee on the Alpha) -- to be used to obtain full RM compliant support. Denorm_On_Target : Boolean := False; -- Set to False on targets that do not reliably support denormals Machine_Rounds_On_Target : Boolean := True; -- Set to False for targets where S'Machine_Rounds is False Machine_Overflows_On_Target : Boolean := False; -- Set to True for targets where S'Machine_Overflows is True Signed_Zeros_On_Target : Boolean := True; -- Set to False on targets that do not reliably support signed zeros ------------------------------------------- -- Boolean-Valued Fixed-Point Attributes -- ------------------------------------------- Fractional_Fixed_Ops_On_Target : Boolean := False; -- Set to True for targets that support fixed-by-fixed multiplication -- and division for fixed-point types with a small value equal to -- 2 ** (-(T'Object_Size - 1)) and whose values have an absolute -- value less than 1.0. ----------------- -- Data Layout -- ----------------- -- Normally when using the GCC backend, Gigi and GCC perform much of the -- data layout using the standard layout capabilities of GCC. If the -- parameter Backend_Layout is set to False, then the front end must -- perform all data layout. For further details see the package Layout. Frontend_Layout_On_Target : Boolean := False; -- Set True if front end does layout ----------------- -- Subprograms -- ----------------- -- These subprograms are used to initialize the target parameter values -- from the system.ads file. Note that this is only done once, so if more -- than one call is made to either routine, the second and subsequent -- calls are ignored. procedure Get_Target_Parameters (System_Text : Source_Buffer_Ptr; Source_First : Source_Ptr; Source_Last : Source_Ptr); -- Called at the start of execution to obtain target parameters from -- the source of package System. The parameters provide the source -- text to be scanned (in System_Text (Source_First .. Source_Last)). procedure Get_Target_Parameters; -- This version reads in system.ads using Osint. The idea is that the -- caller uses the first version if they have to read system.ads anyway -- (e.g. the compiler) and uses this simpler interface if system.ads is -- not otherwise needed. end Targparm;