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-- --
-- --
-- --
-- B o d y --
-- (Version for x86) --
-- --
-- Copyright (C) 1999-2002 Ada Core Technologies, 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 2, 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 COPYING. If not, write --
-- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
-- MA 02111-1307, USA. --
-- --
-- As a special exception, if other files instantiate generics from this --
-- unit, or you link this unit with other files to produce an executable, --
-- this unit does not by itself cause the resulting executable to be --
-- covered by the GNU General Public License. This exception does not --
-- however invalidate any other reasons why the executable file might be --
-- covered by the GNU Public License. --
-- --
-- GNAT was originally developed by the GNAT team at New York University. --
-- Extensive contributions were provided by Ada Core Technologies Inc. --
-- --
-- Note: it is very important that this unit not generate any exception
-- tables of any kind. Otherwise we get a nasty rtsfind recursion problem.
-- This means no subprograms, including implicitly generated ones.
with Unchecked_Conversion;
with System.Storage_Elements;
with System.Machine_Code; use System.Machine_Code;
with System.Memory;
package body System.Machine_State_Operations is
use System.Exceptions;
type Uns8 is mod 2 ** 8;
type Uns32 is mod 2 ** 32;
type Bits5 is mod 2 ** 5;
type Bits6 is mod 2 ** 6;
function To_Address is new Unchecked_Conversion (Uns32, Address);
type Uns32_Ptr is access all Uns32;
function To_Uns32_Ptr is new Unchecked_Conversion (Uns32, Uns32_Ptr);
-- Note: the type Uns32 has an alignment of 4. However, in some cases
-- values of type Uns32_Ptr will not be aligned (notably in the case
-- where we get the immediate field from an instruction). However this
-- does not matter in practice, since the x86 does not require that
-- operands be aligned.
-- General Approach --
-- For the x86 version of this unit, the Subprogram_Info_Type values
-- are simply the starting code address for the subprogram. Popping
-- of stack frames works by analyzing the code in the prolog, and
-- deriving from this analysis the necessary information for restoring
-- the registers, including the return point.
-- Description of Prolog --
-- If a frame pointer is present, the prolog looks like
-- pushl %ebp
-- movl %esp,%ebp
-- subl $nnn,%esp omitted if nnn = 0
-- pushl %edi omitted if edi not used
-- pushl %esi omitted if esi not used
-- pushl %ebx omitted if ebx not used
-- If a frame pointer is not present, the prolog looks like
-- subl $nnn,%esp omitted if nnn = 0
-- pushl %ebp omitted if ebp not used
-- pushl %edi omitted if edi not used
-- pushl %esi omitted if esi not used
-- pushl %ebx omitted if ebx not used
-- Note: any or all of the save over call registers may be used and
-- if so, will be saved using pushl as shown above. The order of the
-- pushl instructions will be as shown above for gcc generated code,
-- but the code in this unit does not assume this.
-- Description of Call --
-- A call looks like:
-- pushl ... push parameters
-- pushl ...
-- call ... perform the call
-- addl $nnn,%esp omitted if no parameters
-- Note that we are not absolutely guaranteed that the call is always
-- followed by an addl operation that readjusts %esp for this particular
-- call. There are two reasons for this:
-- 1) The addl can be delayed and combined in the case where more than
-- one call appears in sequence. This can be suppressed by using the
-- switch -fno-defer-pop and for Ada code, we automatically use
-- this switch, but we could still be dealing with C code that was
-- compiled without using this switch.
-- 2) Scheduling may result in moving the addl instruction away from
-- the call. It is not clear if this actually can happen at the
-- current time, but it is certainly conceptually possible.
-- The addl after the call is important, since we need to be able to
-- restore the proper %esp value when we pop the stack. However, we do
-- not try to compensate for either of the above effects. As noted above,
-- case 1 does not occur for Ada code, and it does not appear in practice
-- that case 2 occurs with any significant frequency (we have never seen
-- an example so far for gcc generated code).
-- Furthermore, it is only in the case of -fomit-frame-pointer that we
-- really get into trouble from not properly restoring %esp. If we have
-- a frame pointer, then the worst that happens is that %esp is slightly
-- more depressed than it should be. This could waste a bit of space on
-- the stack, and even in some cases cause a storage leak on the stack,
-- but it will not affect the functional correctness of the processing.
-- Definitions of Instruction Formats --
type Rcode is (eax, ecx, edx, ebx, esp, ebp, esi, edi);
pragma Warnings (Off, Rcode);
-- Code indicating which register is referenced in an instruction
-- The following define the format of a pushl instruction
Op_pushl : constant Bits5 := 2#01010#;
type Ins_pushl is record
Op : Bits5 := Op_pushl;
Reg : Rcode;
end record;
for Ins_pushl use record
Op at 0 range 3 .. 7;
Reg at 0 range 0 .. 2;
end record;
Ins_pushl_ebp : constant Ins_pushl := (Op_pushl, Reg => ebp);
type Ins_pushl_Ptr is access all Ins_pushl;
-- For the movl %esp,%ebp instruction, we only need to know the length
-- because we simply skip past it when we analyze the prolog.
Ins_movl_length : constant := 2;
-- The following define the format of addl/subl esp instructions
Op_Immed : constant Bits6 := 2#100000#;
Op2_addl_Immed : constant Bits5 := 2#11100#;
pragma Unreferenced (Op2_addl_Immed);
Op2_subl_Immed : constant Bits5 := 2#11101#;
type Word_Byte is (Word, Byte);
pragma Unreferenced (Byte);
type Ins_addl_subl_byte is record
Op : Bits6; -- Set to Op_Immed
w : Word_Byte; -- Word/Byte flag (set to 1 = byte)
s : Boolean; -- Sign extension bit (1 = extend)
Op2 : Bits5; -- Secondary opcode
Reg : Rcode; -- Register
Imm8 : Uns8; -- Immediate operand
end record;
for Ins_addl_subl_byte use record
Op at 0 range 2 .. 7;
w at 0 range 1 .. 1;
s at 0 range 0 .. 0;
Op2 at 1 range 3 .. 7;
Reg at 1 range 0 .. 2;
Imm8 at 2 range 0 .. 7;
end record;
type Ins_addl_subl_word is record
Op : Bits6; -- Set to Op_Immed
w : Word_Byte; -- Word/Byte flag (set to 0 = word)
s : Boolean; -- Sign extension bit (1 = extend)
Op2 : Bits5; -- Secondary opcode
Reg : Rcode; -- Register
Imm32 : Uns32; -- Immediate operand
end record;
for Ins_addl_subl_word use record
Op at 0 range 2 .. 7;
w at 0 range 1 .. 1;
s at 0 range 0 .. 0;
Op2 at 1 range 3 .. 7;
Reg at 1 range 0 .. 2;
Imm32 at 2 range 0 .. 31;
end record;
type Ins_addl_subl_byte_Ptr is access all Ins_addl_subl_byte;
type Ins_addl_subl_word_Ptr is access all Ins_addl_subl_word;
-- Prolog Analysis --
-- The analysis of the prolog answers the following questions:
-- 1. Is %ebp used as a frame pointer?
-- 2. How far is SP depressed (i.e. what is the stack frame size)
-- 3. Which registers are saved in the prolog, and in what order
-- The following data structure stores the answers to these questions
subtype SOC is Rcode range ebx .. edi;
-- Possible save over call registers
SOC_Max : constant := 4;
-- Max number of SOC registers that can be pushed
type SOC_Push_Regs_Type is array (1 .. 4) of Rcode;
-- Used to hold the register codes of pushed SOC registers
type Prolog_Type is record
Frame_Reg : Boolean;
-- This is set to True if %ebp is used as a frame register, and
-- False otherwise (in the False case, %ebp may be saved in the
-- usual manner along with the other SOC registers).
Frame_Length : Uns32;
-- Amount by which ESP is decremented on entry, includes the effects
-- of push's of save over call registers as indicated above, e.g. if
-- the prolog of a routine is:
-- pushl %ebp
-- movl %esp,%ebp
-- subl $424,%esp
-- pushl %edi
-- pushl %esi
-- pushl %ebx
-- Then the value of Frame_Length would be 436 (424 + 3 * 4). A
-- precise definition is that it is:
-- %esp on entry minus %esp after last SOC push
-- That definition applies both in the frame pointer present and
-- the frame pointer absent cases.
Num_SOC_Push : Integer range 0 .. SOC_Max;
-- Number of save over call registers actually saved by pushl
-- instructions (other than the initial pushl to save the frame
-- pointer if a frame pointer is in use).
SOC_Push_Regs : SOC_Push_Regs_Type;
-- The First Num_SOC_Push entries of this array are used to contain
-- the codes for the SOC registers, in the order in which they were
-- pushed. Note that this array excludes %ebp if it is used as a frame
-- register, since although %ebp is still considered an SOC register
-- in this case, it is saved and restored by a separate mechanism.
-- Also we will never see %esp represented in this list. Again, it is
-- true that %esp is saved over call, but it is restored by a separate
-- mechanism.
end record;
procedure Analyze_Prolog (A : Address; Prolog : out Prolog_Type);
-- Given the address of the start of the prolog for a procedure,
-- analyze the instructions of the prolog, and set Prolog to contain
-- the information obtained from this analysis.
-- Machine_State_Representation --
-- The type Machine_State is defined in the body of Ada.Exceptions as
-- a Storage_Array of length 1 .. Machine_State_Length. But really it
-- has structure as defined here. We use the structureless declaration
-- in Ada.Exceptions to avoid this unit from being implementation
-- dependent. The actual definition of Machine_State is as follows:
type SOC_Regs_Type is array (SOC) of Uns32;
type MState is record
eip : Uns32;
-- The instruction pointer location (which is the return point
-- value from the next level down in all cases).
Regs : SOC_Regs_Type;
-- Values of the save over call registers
end record;
for MState use record
eip at 0 range 0 .. 31;
Regs at 4 range 0 .. 5 * 32 - 1;
end record;
-- Note: the routines Enter_Handler, and Set_Machine_State reference
-- the fields in this structure non-symbolically.
type MState_Ptr is access all MState;
function To_MState_Ptr is
new Unchecked_Conversion (Machine_State, MState_Ptr);
-- Allocate_Machine_State --
function Allocate_Machine_State return Machine_State is
use System.Storage_Elements;
return Machine_State
(Memory.Alloc (MState'Max_Size_In_Storage_Elements));
end Allocate_Machine_State;
-- Analyze_Prolog --
procedure Analyze_Prolog (A : Address; Prolog : out Prolog_Type) is
Ptr : Address;
Ppl : Ins_pushl_Ptr;
Pas : Ins_addl_subl_byte_Ptr;
function To_Ins_pushl_Ptr is
new Unchecked_Conversion (Address, Ins_pushl_Ptr);
function To_Ins_addl_subl_byte_Ptr is
new Unchecked_Conversion (Address, Ins_addl_subl_byte_Ptr);
function To_Ins_addl_subl_word_Ptr is
new Unchecked_Conversion (Address, Ins_addl_subl_word_Ptr);
Ptr := A;
Prolog.Frame_Length := 0;
if Ptr = Null_Address then
Prolog.Num_SOC_Push := 0;
Prolog.Frame_Reg := True;
end if;
if To_Ins_pushl_Ptr (Ptr).all = Ins_pushl_ebp then
Ptr := Ptr + 1 + Ins_movl_length;
Prolog.Frame_Reg := True;
Prolog.Frame_Reg := False;
end if;
Pas := To_Ins_addl_subl_byte_Ptr (Ptr);
if Pas.Op = Op_Immed
and then Pas.Op2 = Op2_subl_Immed
and then Pas.Reg = esp
if Pas.w = Word then
Prolog.Frame_Length := Prolog.Frame_Length +
To_Ins_addl_subl_word_Ptr (Ptr).Imm32;
Ptr := Ptr + 6;
Prolog.Frame_Length := Prolog.Frame_Length + Uns32 (Pas.Imm8);
Ptr := Ptr + 3;
-- Note: we ignore sign extension, since a sign extended
-- value that was negative would imply a ludicrous frame size.
end if;
end if;
-- Now scan push instructions for SOC registers
Prolog.Num_SOC_Push := 0;
Ppl := To_Ins_pushl_Ptr (Ptr);
if Ppl.Op = Op_pushl and then Ppl.Reg in SOC then
Prolog.Num_SOC_Push := Prolog.Num_SOC_Push + 1;
Prolog.SOC_Push_Regs (Prolog.Num_SOC_Push) := Ppl.Reg;
Prolog.Frame_Length := Prolog.Frame_Length + 4;
Ptr := Ptr + 1;
end if;
end loop;
end Analyze_Prolog;
-- Enter_Handler --
procedure Enter_Handler (M : Machine_State; Handler : Handler_Loc) is
Asm ("mov %0,%%edx", Inputs => Machine_State'Asm_Input ("r", M));
Asm ("mov %0,%%eax", Inputs => Handler_Loc'Asm_Input ("r", Handler));
Asm ("mov 4(%%edx),%%ebx"); -- M.Regs (ebx)
Asm ("mov 12(%%edx),%%ebp"); -- M.Regs (ebp)
Asm ("mov 16(%%edx),%%esi"); -- M.Regs (esi)
Asm ("mov 20(%%edx),%%edi"); -- M.Regs (edi)
Asm ("mov 8(%%edx),%%esp"); -- M.Regs (esp)
Asm ("jmp %*%%eax");
end Enter_Handler;
-- Fetch_Code --
function Fetch_Code (Loc : Code_Loc) return Code_Loc is
return Loc;
end Fetch_Code;
-- Free_Machine_State --
procedure Free_Machine_State (M : in out Machine_State) is
Memory.Free (Address (M));
M := Machine_State (Null_Address);
end Free_Machine_State;
-- Get_Code_Loc --
function Get_Code_Loc (M : Machine_State) return Code_Loc is
Asm_Call_Size : constant := 2;
-- Minimum size for a call instruction under ix86. Using the minimum
-- size is safe here as the call point computed from the return point
-- will always be inside the call instruction.
MS : constant MState_Ptr := To_MState_Ptr (M);
if MS.eip = 0 then
return To_Address (MS.eip);
-- When doing a call the return address is pushed to the stack.
-- We want to return the call point address, so we substract
-- Asm_Call_Size from the return address. This value is set
-- to 5 as an asm call takes 5 bytes on x86 architectures.
return To_Address (MS.eip - Asm_Call_Size);
end if;
end Get_Code_Loc;
-- Machine_State_Length --
function Machine_State_Length
return System.Storage_Elements.Storage_Offset
return MState'Max_Size_In_Storage_Elements;
end Machine_State_Length;
-- Pop_Frame --
procedure Pop_Frame
(M : Machine_State;
Info : Subprogram_Info_Type)
MS : constant MState_Ptr := To_MState_Ptr (M);
PL : Prolog_Type;
SOC_Ptr : Uns32;
-- Pointer to stack location after last SOC push
Rtn_Ptr : Uns32;
-- Pointer to stack location containing return address
Analyze_Prolog (Info, PL);
-- Case of frame register, use EBP, safer than ESP
if PL.Frame_Reg then
SOC_Ptr := MS.Regs (ebp) - PL.Frame_Length;
Rtn_Ptr := MS.Regs (ebp) + 4;
MS.Regs (ebp) := To_Uns32_Ptr (MS.Regs (ebp)).all;
-- No frame pointer, use ESP, and hope we have it exactly right!
SOC_Ptr := MS.Regs (esp);
Rtn_Ptr := SOC_Ptr + PL.Frame_Length;
end if;
-- Get saved values of SOC registers
for J in reverse 1 .. PL.Num_SOC_Push loop
MS.Regs (PL.SOC_Push_Regs (J)) := To_Uns32_Ptr (SOC_Ptr).all;
SOC_Ptr := SOC_Ptr + 4;
end loop;
MS.eip := To_Uns32_Ptr (Rtn_Ptr).all;
MS.Regs (esp) := Rtn_Ptr + 4;
end Pop_Frame;
-- Set_Machine_State --
procedure Set_Machine_State (M : Machine_State) is
N : constant Asm_Output_Operand := No_Output_Operands;
Asm ("mov %0,%%edx", N, Machine_State'Asm_Input ("r", M));
-- At this stage, we have the following situation (note that we
-- are assuming that the -fomit-frame-pointer switch has not been
-- used in compiling this procedure.
-- (value of M)
-- return point
-- old ebp <------ current ebp/esp value
-- The values of registers ebx/esi/edi are unchanged from entry
-- so they have the values we want, and %edx points to the parameter
-- value M, so we can store these values directly.
Asm ("mov %%ebx,4(%%edx)"); -- M.Regs (ebx)
Asm ("mov %%esi,16(%%edx)"); -- M.Regs (esi)
Asm ("mov %%edi,20(%%edx)"); -- M.Regs (edi)
-- The desired value of ebp is the old value
Asm ("mov 0(%%ebp),%%eax");
Asm ("mov %%eax,12(%%edx)"); -- M.Regs (ebp)
-- The return point is the desired eip value
Asm ("mov 4(%%ebp),%%eax");
Asm ("mov %%eax,(%%edx)"); -- M.eip
-- Finally, the desired %esp value is the value at the point of
-- call to this routine *before* pushing the parameter value.
Asm ("lea 12(%%ebp),%%eax");
Asm ("mov %%eax,8(%%edx)"); -- M.Regs (esp)
end Set_Machine_State;
-- Set_Signal_Machine_State --
procedure Set_Signal_Machine_State
(M : Machine_State;
Context : System.Address)
pragma Warnings (Off, M);
pragma Warnings (Off, Context);
end Set_Signal_Machine_State;
end System.Machine_State_Operations;