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.
+ -- Map the corresponding C type used in Unwind_Exception below
type Unwind_Exception is record
Class : Exception_Class := GNAT_Exception_Class;
Private1 : Unwind_Word;
Private2 : Unwind_Word;
end record;
- -- Map the GCC struct used for exception handling.
+ -- 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). We need to match this because:
+ -- maximally aligned (see unwind.h). See additional comments on the
+ -- alignment below.
- -- 1/ We pass pointers to such headers down to the underlying
- -- libGCC unwinder,
-
- -- and
-
- -- 2/ The GNAT_GCC_Exception record below starts with this common
- -- common header and has a C counterpart which needs to be laid
- -- out identically in raise.c. If the alignment of the C and Ada
- -- common headers mismatch, their size may also differ, and the
- -- layouts may not match anymore.
-
- ---------------------------------------------------------------
- -- GNAT specific entities to deal with the GCC eh circuitry --
- ---------------------------------------------------------------
+ --------------------------------------------------------------
+ -- 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. This structure shall match the
- -- one in raise.c and is currently experimental as it might be merged
- -- with the GNAT runtime definition some day.
+ -- called by the GCC unwinding runtime.
type GNAT_GCC_Exception is record
Header : Unwind_Exception;
-- ABI Exception header first.
Id : Exception_Id;
- -- GNAT Exception identifier. This is used by the personality
- -- routine to determine if the context it examines contains a
- -- handler for the exception beeing propagated.
+ -- GNAT Exception identifier. This is filled by Propagate_Exception
+ -- and then used by the personality routine to determine if the context
+ -- it examines contains a handler for the exception beeing propagated.
N_Cleanups_To_Trigger : Integer;
- -- Number of cleanup only frames encountered in SEARCH phase.
- -- This is used to control the forced unwinding triggered when
- -- no handler has been found.
+ -- Number of cleanup only frames encountered in SEARCH phase. This is
+ -- initialized to 0 by Propagate_Exception and maintained by the
+ -- personality routine to control a forced unwinding phase triggering
+ -- all the cleanups before calling Unhandled_Exception_Terminate when
+ -- an exception is not handled.
Next_Exception : EOA;
-- Used to create a linked list of exception occurrences.
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 aleviate
+ -- the need for a C struct whole conterpart, both painful and errorprone
+ -- to maintain anyway.
+
type GNAT_GCC_Exception_Access is access all GNAT_GCC_Exception;
function To_GNAT_GCC_Exception is new
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 : GNAT_GCC_Exception_Access)
+ return Exception_Id;
+ pragma Export (C, EID_For, "__gnat_eid_for");
+
+ procedure Adjust_N_Cleanups_For
+ (GNAT_Exception : GNAT_GCC_Exception_Access;
+ Adjustment : Integer);
+ pragma Export (C, Adjust_N_Cleanups_For, "__gnat_adjust_n_cleanups_for");
+
------------
-- Remove --
------------
-- already been performed by Propagate_Exception. This hook remains for
-- potential future necessity in optimizing the overall scheme, as well
-- a useful debugging tool.
+
null;
end Begin_Handler;
procedure End_Handler (GCC_Exception : GNAT_GCC_Exception_Access) is
Removed : Boolean;
-
begin
Removed := Remove (Get_Current_Excep.all, GCC_Exception);
pragma Assert (Removed);
Unhandled_Exception_Terminate;
end Propagate_Exception;
+ ---------------------------
+ -- Adjust_N_Cleanups_For --
+ ---------------------------
+
+ procedure Adjust_N_Cleanups_For
+ (GNAT_Exception : GNAT_GCC_Exception_Access;
+ Adjustment : Integer)
+ is
+ begin
+ GNAT_Exception.N_Cleanups_To_Trigger :=
+ GNAT_Exception.N_Cleanups_To_Trigger + Adjustment;
+ end Adjust_N_Cleanups_For;
+
+ -------------
+ -- EID_For --
+ -------------
+
+ function EID_For
+ (GNAT_Exception : GNAT_GCC_Exception_Access) return Exception_Id
+ is
+ begin
+ return GNAT_Exception.Id;
+ end EID_For;
+
---------------------
-- Import_Code_For --
---------------------
-- An attempt was made to use the Private_Data pointer for this purpose.
-- It did not work because:
- -- 1/ The Private_Data has to be saved by Save_Occurrence to be usable
+ -- 1) The Private_Data has to be saved by Save_Occurrence to be usable
-- as a key in case of a later reraise,
- -- 2/ There is no easy way to synchronize End_Handler for an occurrence
+ -- 2) There is no easy way to synchronize End_Handler for an occurrence
-- and the data attached to potential copies, so these copies may end
-- up pointing to stale data. Moreover ...
- -- 3/ The same address may be reused for different occurrences, which
+ -- 3) The same address may be reused for different occurrences, which
-- defeats the idea of using it as a key.
-- The example below illustrates:
-- Saved_CE : Exception_Occurrence;
- --
+
-- begin
-- raise Constraint_Error;
-- exception
-- when CE: others =>
-- Save_Occurrence (Saved_CE, CE); <= Saved_CE.PDA = CE.PDA
-- end;
- --
+
-- <= Saved_CE.PDA is stale (!)
- --
+
-- begin
-- raise Program_Error; <= Saved_CE.PDA = PE.PDA (!!)
-- exception
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