1 ------------------------------------------------------------------------------
3 -- GNAT COMPILER COMPONENTS --
5 -- SYSTEM.MACHINE_STATE_OPERATIONS --
8 -- (Version for x86) --
10 -- Copyright (C) 1999-2002 Ada Core Technologies, Inc. --
12 -- GNAT is free software; you can redistribute it and/or modify it under --
13 -- terms of the GNU General Public License as published by the Free Soft- --
14 -- ware Foundation; either version 2, or (at your option) any later ver- --
15 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
16 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
17 -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
18 -- for more details. You should have received a copy of the GNU General --
19 -- Public License distributed with GNAT; see file COPYING. If not, write --
20 -- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
21 -- MA 02111-1307, USA. --
23 -- As a special exception, if other files instantiate generics from this --
24 -- unit, or you link this unit with other files to produce an executable, --
25 -- this unit does not by itself cause the resulting executable to be --
26 -- covered by the GNU General Public License. This exception does not --
27 -- however invalidate any other reasons why the executable file might be --
28 -- covered by the GNU Public License. --
30 -- GNAT was originally developed by the GNAT team at New York University. --
31 -- Extensive contributions were provided by Ada Core Technologies Inc. --
33 ------------------------------------------------------------------------------
35 -- Note: it is very important that this unit not generate any exception
36 -- tables of any kind. Otherwise we get a nasty rtsfind recursion problem.
37 -- This means no subprograms, including implicitly generated ones.
39 with Unchecked_Conversion
;
40 with System
.Storage_Elements
;
41 with System
.Machine_Code
; use System
.Machine_Code
;
44 package body System
.Machine_State_Operations
is
46 use System
.Exceptions
;
48 type Uns8
is mod 2 ** 8;
49 type Uns32
is mod 2 ** 32;
51 type Bits5
is mod 2 ** 5;
52 type Bits6
is mod 2 ** 6;
54 function To_Address
is new Unchecked_Conversion
(Uns32
, Address
);
56 type Uns32_Ptr
is access all Uns32
;
57 function To_Uns32_Ptr
is new Unchecked_Conversion
(Uns32
, Uns32_Ptr
);
59 -- Note: the type Uns32 has an alignment of 4. However, in some cases
60 -- values of type Uns32_Ptr will not be aligned (notably in the case
61 -- where we get the immediate field from an instruction). However this
62 -- does not matter in practice, since the x86 does not require that
63 -- operands be aligned.
65 ----------------------
66 -- General Approach --
67 ----------------------
69 -- For the x86 version of this unit, the Subprogram_Info_Type values
70 -- are simply the starting code address for the subprogram. Popping
71 -- of stack frames works by analyzing the code in the prolog, and
72 -- deriving from this analysis the necessary information for restoring
73 -- the registers, including the return point.
75 ---------------------------
76 -- Description of Prolog --
77 ---------------------------
79 -- If a frame pointer is present, the prolog looks like
83 -- subl $nnn,%esp omitted if nnn = 0
84 -- pushl %edi omitted if edi not used
85 -- pushl %esi omitted if esi not used
86 -- pushl %ebx omitted if ebx not used
88 -- If a frame pointer is not present, the prolog looks like
90 -- subl $nnn,%esp omitted if nnn = 0
91 -- pushl %ebp omitted if ebp not used
92 -- pushl %edi omitted if edi not used
93 -- pushl %esi omitted if esi not used
94 -- pushl %ebx omitted if ebx not used
96 -- Note: any or all of the save over call registers may be used and
97 -- if so, will be saved using pushl as shown above. The order of the
98 -- pushl instructions will be as shown above for gcc generated code,
99 -- but the code in this unit does not assume this.
101 -------------------------
102 -- Description of Call --
103 -------------------------
105 -- A call looks like:
107 -- pushl ... push parameters
109 -- call ... perform the call
110 -- addl $nnn,%esp omitted if no parameters
112 -- Note that we are not absolutely guaranteed that the call is always
113 -- followed by an addl operation that readjusts %esp for this particular
114 -- call. There are two reasons for this:
116 -- 1) The addl can be delayed and combined in the case where more than
117 -- one call appears in sequence. This can be suppressed by using the
118 -- switch -fno-defer-pop and for Ada code, we automatically use
119 -- this switch, but we could still be dealing with C code that was
120 -- compiled without using this switch.
122 -- 2) Scheduling may result in moving the addl instruction away from
123 -- the call. It is not clear if this actually can happen at the
124 -- current time, but it is certainly conceptually possible.
126 -- The addl after the call is important, since we need to be able to
127 -- restore the proper %esp value when we pop the stack. However, we do
128 -- not try to compensate for either of the above effects. As noted above,
129 -- case 1 does not occur for Ada code, and it does not appear in practice
130 -- that case 2 occurs with any significant frequency (we have never seen
131 -- an example so far for gcc generated code).
133 -- Furthermore, it is only in the case of -fomit-frame-pointer that we
134 -- really get into trouble from not properly restoring %esp. If we have
135 -- a frame pointer, then the worst that happens is that %esp is slightly
136 -- more depressed than it should be. This could waste a bit of space on
137 -- the stack, and even in some cases cause a storage leak on the stack,
138 -- but it will not affect the functional correctness of the processing.
140 ----------------------------------------
141 -- Definitions of Instruction Formats --
142 ----------------------------------------
144 type Rcode
is (eax
, ecx
, edx
, ebx
, esp
, ebp
, esi
, edi
);
145 pragma Warnings
(Off
, Rcode
);
146 -- Code indicating which register is referenced in an instruction
148 -- The following define the format of a pushl instruction
150 Op_pushl
: constant Bits5
:= 2#
01010#
;
152 type Ins_pushl
is record
153 Op
: Bits5
:= Op_pushl
;
157 for Ins_pushl
use record
158 Op
at 0 range 3 .. 7;
159 Reg
at 0 range 0 .. 2;
162 Ins_pushl_ebp
: constant Ins_pushl
:= (Op_pushl
, Reg
=> ebp
);
164 type Ins_pushl_Ptr
is access all Ins_pushl
;
166 -- For the movl %esp,%ebp instruction, we only need to know the length
167 -- because we simply skip past it when we analyze the prolog.
169 Ins_movl_length
: constant := 2;
171 -- The following define the format of addl/subl esp instructions
173 Op_Immed
: constant Bits6
:= 2#
100000#
;
175 Op2_addl_Immed
: constant Bits5
:= 2#
11100#
;
176 pragma Unreferenced
(Op2_addl_Immed
);
178 Op2_subl_Immed
: constant Bits5
:= 2#
11101#
;
180 type Word_Byte
is (Word
, Byte
);
181 pragma Unreferenced
(Byte
);
183 type Ins_addl_subl_byte
is record
184 Op
: Bits6
; -- Set to Op_Immed
185 w
: Word_Byte
; -- Word/Byte flag (set to 1 = byte)
186 s
: Boolean; -- Sign extension bit (1 = extend)
187 Op2
: Bits5
; -- Secondary opcode
188 Reg
: Rcode
; -- Register
189 Imm8
: Uns8
; -- Immediate operand
192 for Ins_addl_subl_byte
use record
193 Op
at 0 range 2 .. 7;
196 Op2
at 1 range 3 .. 7;
197 Reg
at 1 range 0 .. 2;
198 Imm8
at 2 range 0 .. 7;
201 type Ins_addl_subl_word
is record
202 Op
: Bits6
; -- Set to Op_Immed
203 w
: Word_Byte
; -- Word/Byte flag (set to 0 = word)
204 s
: Boolean; -- Sign extension bit (1 = extend)
205 Op2
: Bits5
; -- Secondary opcode
206 Reg
: Rcode
; -- Register
207 Imm32
: Uns32
; -- Immediate operand
210 for Ins_addl_subl_word
use record
211 Op
at 0 range 2 .. 7;
214 Op2
at 1 range 3 .. 7;
215 Reg
at 1 range 0 .. 2;
216 Imm32
at 2 range 0 .. 31;
219 type Ins_addl_subl_byte_Ptr
is access all Ins_addl_subl_byte
;
220 type Ins_addl_subl_word_Ptr
is access all Ins_addl_subl_word
;
222 ---------------------
223 -- Prolog Analysis --
224 ---------------------
226 -- The analysis of the prolog answers the following questions:
228 -- 1. Is %ebp used as a frame pointer?
229 -- 2. How far is SP depressed (i.e. what is the stack frame size)
230 -- 3. Which registers are saved in the prolog, and in what order
232 -- The following data structure stores the answers to these questions
234 subtype SOC
is Rcode
range ebx
.. edi
;
235 -- Possible save over call registers
237 SOC_Max
: constant := 4;
238 -- Max number of SOC registers that can be pushed
240 type SOC_Push_Regs_Type
is array (1 .. 4) of Rcode
;
241 -- Used to hold the register codes of pushed SOC registers
243 type Prolog_Type
is record
246 -- This is set to True if %ebp is used as a frame register, and
247 -- False otherwise (in the False case, %ebp may be saved in the
248 -- usual manner along with the other SOC registers).
250 Frame_Length
: Uns32
;
251 -- Amount by which ESP is decremented on entry, includes the effects
252 -- of push's of save over call registers as indicated above, e.g. if
253 -- the prolog of a routine is:
262 -- Then the value of Frame_Length would be 436 (424 + 3 * 4). A
263 -- precise definition is that it is:
265 -- %esp on entry minus %esp after last SOC push
267 -- That definition applies both in the frame pointer present and
268 -- the frame pointer absent cases.
270 Num_SOC_Push
: Integer range 0 .. SOC_Max
;
271 -- Number of save over call registers actually saved by pushl
272 -- instructions (other than the initial pushl to save the frame
273 -- pointer if a frame pointer is in use).
275 SOC_Push_Regs
: SOC_Push_Regs_Type
;
276 -- The First Num_SOC_Push entries of this array are used to contain
277 -- the codes for the SOC registers, in the order in which they were
278 -- pushed. Note that this array excludes %ebp if it is used as a frame
279 -- register, since although %ebp is still considered an SOC register
280 -- in this case, it is saved and restored by a separate mechanism.
281 -- Also we will never see %esp represented in this list. Again, it is
282 -- true that %esp is saved over call, but it is restored by a separate
287 procedure Analyze_Prolog
(A
: Address
; Prolog
: out Prolog_Type
);
288 -- Given the address of the start of the prolog for a procedure,
289 -- analyze the instructions of the prolog, and set Prolog to contain
290 -- the information obtained from this analysis.
292 ----------------------------------
293 -- Machine_State_Representation --
294 ----------------------------------
296 -- The type Machine_State is defined in the body of Ada.Exceptions as
297 -- a Storage_Array of length 1 .. Machine_State_Length. But really it
298 -- has structure as defined here. We use the structureless declaration
299 -- in Ada.Exceptions to avoid this unit from being implementation
300 -- dependent. The actual definition of Machine_State is as follows:
302 type SOC_Regs_Type
is array (SOC
) of Uns32
;
304 type MState
is record
306 -- The instruction pointer location (which is the return point
307 -- value from the next level down in all cases).
309 Regs
: SOC_Regs_Type
;
310 -- Values of the save over call registers
313 for MState
use record
314 eip
at 0 range 0 .. 31;
315 Regs
at 4 range 0 .. 5 * 32 - 1;
317 -- Note: the routines Enter_Handler, and Set_Machine_State reference
318 -- the fields in this structure non-symbolically.
320 type MState_Ptr
is access all MState
;
322 function To_MState_Ptr
is
323 new Unchecked_Conversion
(Machine_State
, MState_Ptr
);
325 ----------------------------
326 -- Allocate_Machine_State --
327 ----------------------------
329 function Allocate_Machine_State
return Machine_State
is
330 use System
.Storage_Elements
;
334 (Memory
.Alloc
(MState
'Max_Size_In_Storage_Elements));
335 end Allocate_Machine_State
;
341 procedure Analyze_Prolog
(A
: Address
; Prolog
: out Prolog_Type
) is
344 Pas
: Ins_addl_subl_byte_Ptr
;
346 function To_Ins_pushl_Ptr
is
347 new Unchecked_Conversion
(Address
, Ins_pushl_Ptr
);
349 function To_Ins_addl_subl_byte_Ptr
is
350 new Unchecked_Conversion
(Address
, Ins_addl_subl_byte_Ptr
);
352 function To_Ins_addl_subl_word_Ptr
is
353 new Unchecked_Conversion
(Address
, Ins_addl_subl_word_Ptr
);
357 Prolog
.Frame_Length
:= 0;
359 if Ptr
= Null_Address
then
360 Prolog
.Num_SOC_Push
:= 0;
361 Prolog
.Frame_Reg
:= True;
365 if To_Ins_pushl_Ptr
(Ptr
).all = Ins_pushl_ebp
then
366 Ptr
:= Ptr
+ 1 + Ins_movl_length
;
367 Prolog
.Frame_Reg
:= True;
369 Prolog
.Frame_Reg
:= False;
372 Pas
:= To_Ins_addl_subl_byte_Ptr
(Ptr
);
375 and then Pas
.Op2
= Op2_subl_Immed
376 and then Pas
.Reg
= esp
379 Prolog
.Frame_Length
:= Prolog
.Frame_Length
+
380 To_Ins_addl_subl_word_Ptr
(Ptr
).Imm32
;
384 Prolog
.Frame_Length
:= Prolog
.Frame_Length
+ Uns32
(Pas
.Imm8
);
387 -- Note: we ignore sign extension, since a sign extended
388 -- value that was negative would imply a ludicrous frame size.
392 -- Now scan push instructions for SOC registers
394 Prolog
.Num_SOC_Push
:= 0;
397 Ppl
:= To_Ins_pushl_Ptr
(Ptr
);
399 if Ppl
.Op
= Op_pushl
and then Ppl
.Reg
in SOC
then
400 Prolog
.Num_SOC_Push
:= Prolog
.Num_SOC_Push
+ 1;
401 Prolog
.SOC_Push_Regs
(Prolog
.Num_SOC_Push
) := Ppl
.Reg
;
402 Prolog
.Frame_Length
:= Prolog
.Frame_Length
+ 4;
416 procedure Enter_Handler
(M
: Machine_State
; Handler
: Handler_Loc
) is
418 Asm
("mov %0,%%edx", Inputs
=> Machine_State
'Asm_Input ("r", M
));
419 Asm
("mov %0,%%eax", Inputs
=> Handler_Loc
'Asm_Input ("r", Handler
));
421 Asm
("mov 4(%%edx),%%ebx"); -- M.Regs (ebx)
422 Asm
("mov 12(%%edx),%%ebp"); -- M.Regs (ebp)
423 Asm
("mov 16(%%edx),%%esi"); -- M.Regs (esi)
424 Asm
("mov 20(%%edx),%%edi"); -- M.Regs (edi)
425 Asm
("mov 8(%%edx),%%esp"); -- M.Regs (esp)
433 function Fetch_Code
(Loc
: Code_Loc
) return Code_Loc
is
438 ------------------------
439 -- Free_Machine_State --
440 ------------------------
442 procedure Free_Machine_State
(M
: in out Machine_State
) is
444 Memory
.Free
(Address
(M
));
445 M
:= Machine_State
(Null_Address
);
446 end Free_Machine_State
;
452 function Get_Code_Loc
(M
: Machine_State
) return Code_Loc
is
454 Asm_Call_Size
: constant := 2;
455 -- Minimum size for a call instruction under ix86. Using the minimum
456 -- size is safe here as the call point computed from the return point
457 -- will always be inside the call instruction.
459 MS
: constant MState_Ptr
:= To_MState_Ptr
(M
);
463 return To_Address
(MS
.eip
);
465 -- When doing a call the return address is pushed to the stack.
466 -- We want to return the call point address, so we subtract
467 -- Asm_Call_Size from the return address. This value is set
468 -- to 5 as an asm call takes 5 bytes on x86 architectures.
470 return To_Address
(MS
.eip
- Asm_Call_Size
);
474 --------------------------
475 -- Machine_State_Length --
476 --------------------------
478 function Machine_State_Length
479 return System
.Storage_Elements
.Storage_Offset
482 return MState
'Max_Size_In_Storage_Elements;
483 end Machine_State_Length
;
491 Info
: Subprogram_Info_Type
)
493 MS
: constant MState_Ptr
:= To_MState_Ptr
(M
);
497 -- Pointer to stack location after last SOC push
500 -- Pointer to stack location containing return address
503 Analyze_Prolog
(Info
, PL
);
505 -- Case of frame register, use EBP, safer than ESP
508 SOC_Ptr
:= MS
.Regs
(ebp
) - PL
.Frame_Length
;
509 Rtn_Ptr
:= MS
.Regs
(ebp
) + 4;
510 MS
.Regs
(ebp
) := To_Uns32_Ptr
(MS
.Regs
(ebp
)).all;
512 -- No frame pointer, use ESP, and hope we have it exactly right!
515 SOC_Ptr
:= MS
.Regs
(esp
);
516 Rtn_Ptr
:= SOC_Ptr
+ PL
.Frame_Length
;
519 -- Get saved values of SOC registers
521 for J
in reverse 1 .. PL
.Num_SOC_Push
loop
522 MS
.Regs
(PL
.SOC_Push_Regs
(J
)) := To_Uns32_Ptr
(SOC_Ptr
).all;
523 SOC_Ptr
:= SOC_Ptr
+ 4;
526 MS
.eip
:= To_Uns32_Ptr
(Rtn_Ptr
).all;
527 MS
.Regs
(esp
) := Rtn_Ptr
+ 4;
530 -----------------------
531 -- Set_Machine_State --
532 -----------------------
534 procedure Set_Machine_State
(M
: Machine_State
) is
535 N
: constant Asm_Output_Operand
:= No_Output_Operands
;
538 Asm
("mov %0,%%edx", N
, Machine_State
'Asm_Input ("r", M
));
540 -- At this stage, we have the following situation (note that we
541 -- are assuming that the -fomit-frame-pointer switch has not been
542 -- used in compiling this procedure.
546 -- old ebp <------ current ebp/esp value
548 -- The values of registers ebx/esi/edi are unchanged from entry
549 -- so they have the values we want, and %edx points to the parameter
550 -- value M, so we can store these values directly.
552 Asm
("mov %%ebx,4(%%edx)"); -- M.Regs (ebx)
553 Asm
("mov %%esi,16(%%edx)"); -- M.Regs (esi)
554 Asm
("mov %%edi,20(%%edx)"); -- M.Regs (edi)
556 -- The desired value of ebp is the old value
558 Asm
("mov 0(%%ebp),%%eax");
559 Asm
("mov %%eax,12(%%edx)"); -- M.Regs (ebp)
561 -- The return point is the desired eip value
563 Asm
("mov 4(%%ebp),%%eax");
564 Asm
("mov %%eax,(%%edx)"); -- M.eip
566 -- Finally, the desired %esp value is the value at the point of
567 -- call to this routine *before* pushing the parameter value.
569 Asm
("lea 12(%%ebp),%%eax");
570 Asm
("mov %%eax,8(%%edx)"); -- M.Regs (esp)
571 end Set_Machine_State
;
573 ------------------------------
574 -- Set_Signal_Machine_State --
575 ------------------------------
577 procedure Set_Signal_Machine_State
579 Context
: System
.Address
)
581 pragma Warnings
(Off
, M
);
582 pragma Warnings
(Off
, Context
);
586 end Set_Signal_Machine_State
;
588 end System
.Machine_State_Operations
;