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------------------------------------------------------------------------------ -- -- -- GNAT COMPILER COMPONENTS -- -- -- -- A D A . E X C E P T I O N S . E X C E P T I O N _ P R O P A G A T I O N -- -- -- -- B o d y -- -- -- -- Copyright (C) 1992-2011, 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. -- -- -- -- As a special exception under Section 7 of GPL version 3, you are granted -- -- additional permissions described in the GCC Runtime Library Exception, -- -- version 3.1, as published by the Free Software Foundation. -- -- -- -- You should have received a copy of the GNU General Public License and -- -- a copy of the GCC Runtime Library Exception along with this program; -- -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see -- -- <http://www.gnu.org/licenses/>. -- -- -- -- GNAT was originally developed by the GNAT team at New York University. -- -- Extensive contributions were provided by Ada Core Technologies Inc. -- -- -- ------------------------------------------------------------------------------ -- This is the version using the GCC EH mechanism with Ada.Unchecked_Conversion; with Ada.Unchecked_Deallocation; with System.Storage_Elements; use System.Storage_Elements; separate (Ada.Exceptions) package body Exception_Propagation is ------------------------------------------------ -- Entities to interface with the GCC runtime -- ------------------------------------------------ -- These come from "C++ ABI for Itanium: Exception handling", which is -- the reference for GCC. They are used only when we are relying on -- back-end tables for exception propagation, which in turn is currently -- only the case for Zero_Cost_Exceptions in GNAT5. -- Return codes from the GCC runtime functions used to propagate -- an exception. type Unwind_Reason_Code is (URC_NO_REASON, URC_FOREIGN_EXCEPTION_CAUGHT, URC_PHASE2_ERROR, URC_PHASE1_ERROR, URC_NORMAL_STOP, URC_END_OF_STACK, URC_HANDLER_FOUND, URC_INSTALL_CONTEXT, URC_CONTINUE_UNWIND); pragma Unreferenced (URC_FOREIGN_EXCEPTION_CAUGHT, URC_PHASE2_ERROR, URC_PHASE1_ERROR, URC_NORMAL_STOP, URC_END_OF_STACK, URC_HANDLER_FOUND, URC_INSTALL_CONTEXT, URC_CONTINUE_UNWIND); pragma Convention (C, Unwind_Reason_Code); -- Phase identifiers type Unwind_Action is new Integer; pragma Convention (C, Unwind_Action); UA_SEARCH_PHASE : constant Unwind_Action := 1; UA_CLEANUP_PHASE : constant Unwind_Action := 2; UA_HANDLER_FRAME : constant Unwind_Action := 4; UA_FORCE_UNWIND : constant Unwind_Action := 8; UA_END_OF_STACK : constant Unwind_Action := 16; -- GCC extension ? pragma Unreferenced (UA_SEARCH_PHASE, UA_CLEANUP_PHASE, UA_HANDLER_FRAME, UA_FORCE_UNWIND); -- Mandatory common header for any exception object handled by the -- GCC unwinding runtime. type Exception_Class is mod 2 ** 64; GNAT_Exception_Class : constant Exception_Class := 16#474e552d41646100#; -- "GNU-Ada\0" type Unwind_Word is mod 2 ** System.Word_Size; for Unwind_Word'Size use System.Word_Size; -- Map the corresponding C type used in Unwind_Exception below type Unwind_Exception is record Class : Exception_Class; Cleanup : System.Address; Private1 : Unwind_Word; Private2 : Unwind_Word; end record; pragma Convention (C, Unwind_Exception); -- Map the GCC struct used for exception handling for Unwind_Exception'Alignment use Standard'Maximum_Alignment; -- The C++ ABI mandates the common exception header to be at least -- doubleword aligned, and the libGCC implementation actually makes it -- maximally aligned (see unwind.h). See additional comments on the -- alignment below. type GCC_Exception_Access is access all Unwind_Exception; -- Pointer to a GCC exception. Do not use convention C as on VMS this -- would imply the use of 32-bits pointers. procedure Unwind_DeleteException (Excp : not null GCC_Exception_Access); pragma Import (C, Unwind_DeleteException, "_Unwind_DeleteException"); -- Procedure to free any GCC exception Foreign_Exception : aliased System.Standard_Library.Exception_Data; pragma Import (Ada, Foreign_Exception, "system__exceptions__foreign_exception"); -- Id for foreign exceptions -------------------------------------------------------------- -- GNAT Specific Entities To Deal With The GCC EH Circuitry -- -------------------------------------------------------------- -- A GNAT exception object to be dealt with by the personality routine -- called by the GCC unwinding runtime. type GNAT_GCC_Exception is record Header : Unwind_Exception; -- ABI Exception header first Occurrence : Exception_Occurrence; -- The Ada occurrence end record; pragma Convention (C, GNAT_GCC_Exception); -- There is a subtle issue with the common header alignment, since the C -- version is aligned on BIGGEST_ALIGNMENT, the Ada version is aligned on -- Standard'Maximum_Alignment, and those two values don't quite represent -- the same concepts and so may be decoupled someday. One typical reason -- is that BIGGEST_ALIGNMENT may be larger than what the underlying system -- allocator guarantees, and there are extra costs involved in allocating -- objects aligned to such factors. -- To deal with the potential alignment differences between the C and Ada -- representations, the Ada part of the whole structure is only accessed -- by the personality routine through the accessors declared below. Ada -- specific fields are thus always accessed through consistent layout, and -- we expect the actual alignment to always be large enough to avoid traps -- from the C accesses to the common header. Besides, accessors alleviate -- the need for a C struct whole counterpart, both painful and error-prone -- to maintain anyway. type GNAT_GCC_Exception_Access is access all GNAT_GCC_Exception; function To_GCC_Exception is new Unchecked_Conversion (GNAT_GCC_Exception_Access, GCC_Exception_Access); function To_GNAT_GCC_Exception is new Unchecked_Conversion (GCC_Exception_Access, GNAT_GCC_Exception_Access); procedure GNAT_GCC_Exception_Cleanup (Reason : Unwind_Reason_Code; Excep : not null GNAT_GCC_Exception_Access); pragma Convention (C, GNAT_GCC_Exception_Cleanup); -- Procedure called when a GNAT GCC exception is free. procedure Propagate_GCC_Exception (GCC_Exception : not null GCC_Exception_Access); pragma No_Return (Propagate_GCC_Exception); -- Propagate a GCC exception procedure Reraise_GCC_Exception (GCC_Exception : not null GCC_Exception_Access); pragma No_Return (Reraise_GCC_Exception); pragma Export (C, Reraise_GCC_Exception, "__gnat_reraise_zcx"); -- Called to implement raise without exception, ie reraise. Called -- directly from gigi. procedure Setup_Current_Excep (GCC_Exception : not null GCC_Exception_Access); pragma Export (C, Setup_Current_Excep, "__gnat_setup_current_excep"); -- Write Get_Current_Excep.all from GCC_Exception function CleanupUnwind_Handler (UW_Version : Integer; UW_Phases : Unwind_Action; UW_Eclass : Exception_Class; UW_Exception : not null GCC_Exception_Access; UW_Context : System.Address; UW_Argument : System.Address) return Unwind_Reason_Code; -- Hook called at each step of the forced unwinding we perform to -- trigger cleanups found during the propagation of an unhandled -- exception. -- GCC runtime functions used. These are C non-void functions, actually, -- but we ignore the return values. See raise.c as to why we are using -- __gnat stubs for these. procedure Unwind_RaiseException (UW_Exception : not null GCC_Exception_Access); pragma Import (C, Unwind_RaiseException, "__gnat_Unwind_RaiseException"); procedure Unwind_ForcedUnwind (UW_Exception : not null GCC_Exception_Access; UW_Handler : System.Address; UW_Argument : System.Address); pragma Import (C, Unwind_ForcedUnwind, "__gnat_Unwind_ForcedUnwind"); -- Hooks called when entering/leaving an exception handler for a given -- occurrence, aimed at handling the stack of active occurrences. The -- calls are generated by gigi in tree_transform/N_Exception_Handler. procedure Begin_Handler (GCC_Exception : not null GCC_Exception_Access); pragma Export (C, Begin_Handler, "__gnat_begin_handler"); procedure End_Handler (GCC_Exception : GCC_Exception_Access); pragma Export (C, End_Handler, "__gnat_end_handler"); -------------------------------------------------------------------- -- Accessors to Basic Components of a GNAT Exception Data Pointer -- -------------------------------------------------------------------- -- As of today, these are only used by the C implementation of the GCC -- propagation personality routine to avoid having to rely on a C -- counterpart of the whole exception_data structure, which is both -- painful and error prone. These subprograms could be moved to a more -- widely visible location if need be. function Is_Handled_By_Others (E : Exception_Data_Ptr) return Boolean; pragma Export (C, Is_Handled_By_Others, "__gnat_is_handled_by_others"); pragma Warnings (Off, Is_Handled_By_Others); function Language_For (E : Exception_Data_Ptr) return Character; pragma Export (C, Language_For, "__gnat_language_for"); function Import_Code_For (E : Exception_Data_Ptr) return Exception_Code; pragma Export (C, Import_Code_For, "__gnat_import_code_for"); function EID_For (GNAT_Exception : not null GNAT_GCC_Exception_Access) return Exception_Id; pragma Export (C, EID_For, "__gnat_eid_for"); --------------------------------------------------------------------------- -- Objects to materialize "others" and "all others" in the GCC EH tables -- --------------------------------------------------------------------------- -- Currently, these only have their address taken and compared so there is -- no real point having whole exception data blocks allocated. In any case -- the types should match what gigi and the personality routine expect. -- The initial value is an arbitrary value that will not exceed the range -- of Integer on 16-bit targets (such as AAMP). Others_Value : constant Integer := 16#7FFF#; pragma Export (C, Others_Value, "__gnat_others_value"); All_Others_Value : constant Integer := 16#7FFF#; pragma Export (C, All_Others_Value, "__gnat_all_others_value"); -------------------------------- -- GNAT_GCC_Exception_Cleanup -- -------------------------------- procedure GNAT_GCC_Exception_Cleanup (Reason : Unwind_Reason_Code; Excep : not null GNAT_GCC_Exception_Access) is pragma Unreferenced (Reason); procedure Free is new Unchecked_Deallocation (GNAT_GCC_Exception, GNAT_GCC_Exception_Access); Copy : GNAT_GCC_Exception_Access := Excep; begin -- Simply free the memory Free (Copy); end GNAT_GCC_Exception_Cleanup; --------------------------- -- CleanupUnwind_Handler -- --------------------------- function CleanupUnwind_Handler (UW_Version : Integer; UW_Phases : Unwind_Action; UW_Eclass : Exception_Class; UW_Exception : not null GCC_Exception_Access; UW_Context : System.Address; UW_Argument : System.Address) return Unwind_Reason_Code is pragma Unreferenced (UW_Version, UW_Eclass, UW_Context, UW_Argument); begin -- Terminate when the end of the stack is reached if UW_Phases >= UA_END_OF_STACK then Setup_Current_Excep (UW_Exception); Unhandled_Exception_Terminate; end if; -- We know there is at least one cleanup further up. Return so that it -- is searched and entered, after which Unwind_Resume will be called -- and this hook will gain control again. return URC_NO_REASON; end CleanupUnwind_Handler; ------------------------- -- Setup_Current_Excep -- ------------------------- procedure Setup_Current_Excep (GCC_Exception : not null GCC_Exception_Access) is Excep : constant EOA := Get_Current_Excep.all; begin -- Setup the exception occurrence if GCC_Exception.Class = GNAT_Exception_Class then -- From the GCC exception declare GNAT_Occurrence : constant GNAT_GCC_Exception_Access := To_GNAT_GCC_Exception (GCC_Exception); begin Excep.all := GNAT_Occurrence.Occurrence; end; else -- A default one Excep.Id := Foreign_Exception'Access; Excep.Msg_Length := 0; Excep.Exception_Raised := True; Excep.Pid := Local_Partition_ID; Excep.Num_Tracebacks := 0; end if; end Setup_Current_Excep; ------------------- -- Begin_Handler -- ------------------- procedure Begin_Handler (GCC_Exception : not null GCC_Exception_Access) is pragma Unreferenced (GCC_Exception); begin null; end Begin_Handler; ----------------- -- End_Handler -- ----------------- procedure End_Handler (GCC_Exception : GCC_Exception_Access) is begin if GCC_Exception /= null then -- The exception might have been reraised, in this case the cleanup -- mustn't be called. Unwind_DeleteException (GCC_Exception); end if; end End_Handler; ----------------------------- -- Reraise_GCC_Exception -- ----------------------------- procedure Reraise_GCC_Exception (GCC_Exception : not null GCC_Exception_Access) is begin -- Simply propagate it Propagate_GCC_Exception (GCC_Exception); end Reraise_GCC_Exception; ----------------------------- -- Propagate_GCC_Exception -- ----------------------------- -- Call Unwind_RaiseException to actually throw, taking care of handling -- the two phase scheme it implements. procedure Propagate_GCC_Exception (GCC_Exception : not null GCC_Exception_Access) is begin -- Perform a standard raise first. If a regular handler is found, it -- will be entered after all the intermediate cleanups have run. If -- there is no regular handler, it will return. Unwind_RaiseException (GCC_Exception); -- If we get here we know the exception is not handled, as otherwise -- Unwind_RaiseException arranges for the handler to be entered. Take -- the necessary steps to enable the debugger to gain control while the -- stack is still intact. Setup_Current_Excep (GCC_Exception); Notify_Unhandled_Exception; -- Now, un a forced unwind to trigger cleanups. Control should not -- resume there, if there are cleanups and in any cases as the -- unwinding hook calls Unhandled_Exception_Terminate when end of -- stack is reached. Unwind_ForcedUnwind (GCC_Exception, CleanupUnwind_Handler'Address, System.Null_Address); -- We get here in case of error. The debugger has been notified before -- the second step above. Setup_Current_Excep (GCC_Exception); Unhandled_Exception_Terminate; end Propagate_GCC_Exception; ------------------------- -- Propagate_Exception -- ------------------------- -- Build an object suitable for the libgcc processing and call -- Unwind_RaiseException to actually do the raise, taking care of -- handling the two phase scheme it implements. procedure Propagate_Exception is Excep : constant EOA := Get_Current_Excep.all; GCC_Exception : GNAT_GCC_Exception_Access; begin -- Compute the backtrace for this occurrence if the corresponding -- binder option has been set. Call_Chain takes care of the reraise -- case. -- ??? Using Call_Chain here means we are going to walk up the stack -- once only for backtracing purposes before doing it again for the -- propagation per se. -- The first inspection is much lighter, though, as it only requires -- partial unwinding of each frame. Additionally, although we could use -- the personality routine to record the addresses while propagating, -- this method has two drawbacks: -- 1) the trace is incomplete if the exception is handled since we -- don't walk past the frame with the handler, -- and -- 2) we would miss the frames for which our personality routine is not -- called, e.g. if C or C++ calls are on the way. Call_Chain (Excep); -- Allocate the GCC exception GCC_Exception := new GNAT_GCC_Exception' (Header => (Class => GNAT_Exception_Class, Cleanup => GNAT_GCC_Exception_Cleanup'Address, Private1 => 0, Private2 => 0), Occurrence => Excep.all); -- Propagate it Propagate_GCC_Exception (To_GCC_Exception (GCC_Exception)); end Propagate_Exception; ------------- -- EID_For -- ------------- function EID_For (GNAT_Exception : not null GNAT_GCC_Exception_Access) return Exception_Id is begin return GNAT_Exception.Occurrence.Id; end EID_For; --------------------- -- Import_Code_For -- --------------------- function Import_Code_For (E : SSL.Exception_Data_Ptr) return Exception_Code is begin return E.all.Import_Code; end Import_Code_For; -------------------------- -- Is_Handled_By_Others -- -------------------------- function Is_Handled_By_Others (E : SSL.Exception_Data_Ptr) return Boolean is begin return not E.all.Not_Handled_By_Others; end Is_Handled_By_Others; ------------------ -- Language_For -- ------------------ function Language_For (E : SSL.Exception_Data_Ptr) return Character is begin return E.all.Lang; end Language_For; end Exception_Propagation;
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