[mirror_edk2.git] / EmbeddedPkg / Library / GdbDebugAgent / Arm / ExceptionSupport.ARMv6.asm

//------------------------------------------------------------------------------\r
//\r
// Use ARMv6 instruction to operate on a single stack\r
//\r
// Copyright (c) 2008 - 2010, Apple Inc. All rights reserved.<BR>\r
//\r
// This program and the accompanying materials\r
// are licensed and made available under the terms and conditions of the BSD License\r
// which accompanies this distribution.  The full text of the license may be found at\r
// http://opensource.org/licenses/bsd-license.php\r
//\r
// THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,\r
// WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.\r
//\r
//------------------------------------------------------------------------------\r
\r
\r
\r
/*\r
\r
This is the stack constructed by the exception handler (low address to high address)\r
                # R0 - IFAR is EFI_SYSTEM_CONTEXT for ARM\r
  Reg   Offset\r
  ===   ======\r
  R0    0x00    # stmfd     SP!,{R0-R12}\r
  R1    0x04\r
  R2    0x08\r
  R3    0x0c\r
  R4    0x10\r
  R5    0x14\r
  R6    0x18\r
  R7    0x1c\r
  R8    0x20\r
  R9    0x24\r
  R10   0x28\r
  R11   0x2c\r
  R12   0x30\r
  SP    0x34    # reserved via adding 0x20 (32) to the SP\r
  LR    0x38\r
  PC    0x3c\r
  CPSR  0x40\r
  DFSR  0x44\r
  DFAR  0x48\r
  IFSR  0x4c\r
  IFAR  0x50\r
\r
  LR    0x54    # SVC Link register (we need to restore it)\r
\r
  LR    0x58    # pushed by srsfd\r
  CPSR  0x5c\r
\r
 */\r
\r
\r
  EXPORT  ExceptionHandlersStart\r
  EXPORT  ExceptionHandlersEnd\r
  EXPORT  CommonExceptionEntry\r
  EXPORT  AsmCommonExceptionEntry\r
  IMPORT  GdbExceptionHandler\r
\r
  PRESERVE8\r
  AREA  DxeExceptionHandlers, CODE, READONLY\r
\r
//\r
// This code gets copied to the ARM vector table\r
// ExceptionHandlersStart - ExceptionHandlersEnd gets copied\r
//\r
ExceptionHandlersStart\r
\r
Reset\r
  b   Reset\r
\r
UndefinedInstruction\r
  b   UndefinedInstructionEntry\r
\r
SoftwareInterrupt\r
  b   SoftwareInterruptEntry\r
\r
PrefetchAbort\r
  b   PrefetchAbortEntry\r
\r
DataAbort\r
  b   DataAbortEntry\r
\r
ReservedException\r
  b   ReservedExceptionEntry\r
\r
Irq\r
  b   Irq\r
\r
Fiq\r
  b   FiqEntry\r
\r
\r
UndefinedInstructionEntry\r
  sub       LR, LR, #4                ; Only -2 for Thumb, adjust in CommonExceptionEntry\r
  srsfd     #0x13!                    ; Store return state on SVC stack\r
  cpsid     f, #0x13                  ; Switch to SVC for common stack\r
  stmfd     SP!,{LR}                  ; Store the link register for the current mode\r
  sub       SP,SP,#0x20               ; Save space for SP, LR, PC, IFAR - CPSR\r
  stmfd     SP!,{R0-R12}              ; Store the register state\r
\r
  mov       R0,#1                     ; ExceptionType\r
  ldr       R1,CommonExceptionEntry;\r
  bx        R1\r
\r
SoftwareInterruptEntry\r
  sub       LR, LR, #4                ; Only -2 for Thumb, adjust in CommonExceptionEntry\r
  srsfd     #0x13!                    ; Store return state on SVC stack\r
  cpsid     f                         ; We are already in SVC mode\r
  stmfd     SP!,{LR}                  ; Store the link register for the current mode\r
  sub       SP,SP,#0x20               ; Save space for SP, LR, PC, IFAR - CPSR\r
  stmfd     SP!,{R0-R12}              ; Store the register state\r
\r
  mov       R0,#2                     ; ExceptionType\r
  ldr       R1,CommonExceptionEntry\r
  bx        R1\r
\r
PrefetchAbortEntry\r
  sub       LR,LR,#4\r
  srsfd     #0x13!                    ; Store return state on SVC stack\r
  cpsid     f, #0x13                  ; Switch to SVC for common stack\r
  stmfd     SP!,{LR}                  ; Store the link register for the current mode\r
  sub       SP,SP,#0x20               ; Save space for SP, LR, PC, IFAR - CPSR\r
  stmfd     SP!,{R0-R12}              ; Store the register state\r
\r
  mov       R0,#3                     ; ExceptionType\r
  ldr       R1,CommonExceptionEntry\r
  bx        R1\r
\r
DataAbortEntry\r
  sub       LR,LR,#8\r
  srsfd     #0x13!                    ; Store return state on SVC stack\r
  cpsid     f, #0x13                  ; Switch to SVC for common stack\r
  stmfd     SP!,{LR}                  ; Store the link register for the current mode\r
  sub       SP,SP,#0x20               ; Save space for SP, LR, PC, IFAR - CPSR\r
  stmfd     SP!,{R0-R12}              ; Store the register state\r
\r
  mov       R0,#4                     ; ExceptionType\r
  ldr       R1,CommonExceptionEntry\r
  bx        R1\r
\r
ReservedExceptionEntry\r
  srsfd     #0x13!                    ; Store return state on SVC stack\r
  cpsid     f, #0x13                  ; Switch to SVC for common stack\r
  stmfd     SP!,{LR}                  ; Store the link register for the current mode\r
  sub       SP,SP,#0x20               ; Save space for SP, LR, PC, IFAR - CPSR\r
  stmfd     SP!,{R0-R12}              ; Store the register state\r
\r
  mov       R0,#5                     ; ExceptionType\r
  ldr       R1,CommonExceptionEntry\r
  bx        R1\r
\r
FiqEntry\r
  sub       LR,LR,#4\r
  srsfd     #0x13!                    ; Store return state on SVC stack\r
  cps       #0x13                     ; Switch to SVC for common stack\r
  stmfd     SP!,{LR}                  ; Store the link register for the current mode\r
  sub       SP,SP,#0x20               ; Save space for SP, LR, PC, IFAR - CPSR\r
  stmfd     SP!,{R0-R12}              ; Store the register state\r
                                      ; Since we have already switch to SVC R8_fiq - R12_fiq\r
                                      ; never get used or saved\r
  mov       R0,#7                     ; ExceptionType\r
  ldr       R1,CommonExceptionEntry\r
  bx        R1\r
\r
//\r
// This gets patched by the C code that patches in the vector table\r
//\r
CommonExceptionEntry\r
  dcd       0x12345678\r
\r
ExceptionHandlersEnd\r
\r
//\r
// This code runs from CpuDxe driver loaded address. It is patched into\r
// CommonExceptionEntry.\r
//\r
AsmCommonExceptionEntry\r
  mrc       p15, 0, R1, c6, c0, 2   ; Read IFAR\r
  str       R1, [SP, #0x50]         ; Store it in EFI_SYSTEM_CONTEXT_ARM.IFAR\r
\r
  mrc       p15, 0, R1, c5, c0, 1   ; Read IFSR\r
  str       R1, [SP, #0x4c]         ; Store it in EFI_SYSTEM_CONTEXT_ARM.IFSR\r
\r
  mrc       p15, 0, R1, c6, c0, 0   ; Read DFAR\r
  str       R1, [SP, #0x48]         ; Store it in EFI_SYSTEM_CONTEXT_ARM.DFAR\r
\r
  mrc       p15, 0, R1, c5, c0, 0   ; Read DFSR\r
  str       R1, [SP, #0x44]         ; Store it in EFI_SYSTEM_CONTEXT_ARM.DFSR\r
\r
  ldr       R1, [SP, #0x5c]         ; srsfd saved pre-exception CPSR on the stack\r
  str       R1, [SP, #0x40]         ; Store it in EFI_SYSTEM_CONTEXT_ARM.CPSR\r
\r
  add       R2, SP, #0x38           ; Make R2 point to EFI_SYSTEM_CONTEXT_ARM.LR\r
  and       R3, R1, #0x1f           ; Check CPSR to see if User or System Mode\r
  cmp       R3, #0x1f               ; if ((CPSR == 0x10) || (CPSR == 0x1df))\r
  cmpne     R3, #0x10               ;\r
  stmeqed   R2, {lr}^               ;   save unbanked lr\r
                                    ; else\r
  stmneed   R2, {lr}                ;   save SVC lr\r
\r
\r
  ldr       R5, [SP, #0x58]         ; PC is the LR pushed by srsfd\r
                                    ; Check to see if we have to adjust for Thumb entry\r
  sub       r4, r0, #1              ; if (ExceptionType == 1 || ExceptionType ==2)) {\r
  cmp       r4, #1                  ;   // UND & SVC have differnt LR adjust for Thumb\r
  bhi       NoAdjustNeeded\r
\r
  tst       r1, #0x20               ;   if ((CPSR & T)) == T) {  // Thumb Mode on entry\r
  addne     R5, R5, #2              ;     PC += 2;\r
  str       R5,[SP,#0x58]           ; Update LR value pused by srsfd\r
\r
NoAdjustNeeded\r
\r
  str       R5, [SP, #0x3c]         ; Store it in EFI_SYSTEM_CONTEXT_ARM.PC\r
\r
  sub       R1, SP, #0x60           ; We pused 0x60 bytes on the stack\r
  str       R1, [SP, #0x34]         ; Store it in EFI_SYSTEM_CONTEXT_ARM.SP\r
\r
                                    ; R0 is ExceptionType\r
  mov       R1,SP                   ; R1 is SystemContext\r
\r
/*\r
VOID\r
EFIAPI\r
GdbExceptionHandler (\r
  IN     EFI_EXCEPTION_TYPE           ExceptionType,   R0\r
  IN OUT EFI_SYSTEM_CONTEXT           SystemContext    R1\r
  )\r
\r
*/\r
  blx       GdbExceptionHandler     ; Call exception handler\r
\r
  ldr       R1,[SP,#0x3c]           ; EFI_SYSTEM_CONTEXT_ARM.PC\r
  str       R1,[SP,#0x58]           ; Store it back to srsfd stack slot so it can be restored\r
\r
  ldr       R1,[SP,#0x40]           ; EFI_SYSTEM_CONTEXT_ARM.CPSR\r
  str       R1,[SP,#0x5c]           ; Store it back to srsfd stack slot so it can be restored\r
\r
  add       R3, SP, #0x54           ; Make R3 point to SVC LR saved on entry\r
  add       R2, SP, #0x38           ; Make R2 point to EFI_SYSTEM_CONTEXT_ARM.LR\r
  and       R1, R1, #0x1f           ; Check to see if User or System Mode\r
  cmp       R1, #0x1f               ; if ((CPSR == 0x10) || (CPSR == 0x1f))\r
  cmpne     R1, #0x10               ;\r
  ldmeqed   R2, {lr}^               ;   restore unbanked lr\r
                                    ; else\r
  ldmneed   R3, {lr}                ;   restore SVC lr, via ldmfd SP!, {LR}\r
\r
  ldmfd     SP!,{R0-R12}            ; Restore general purpose registers\r
                                    ; Exception handler can not change SP\r
\r
  add       SP,SP,#0x20             ; Clear out the remaining stack space\r
  ldmfd     SP!,{LR}                ; restore the link register for this context\r
  rfefd     SP!                     ; return from exception via srsfd stack slot\r
\r
  END\r
\r
\r
Commit	Line	Data
3402aac7	1	//------------------------------------------------------------------------------\r
1e57a462	2	//\r
	3	// Use ARMv6 instruction to operate on a single stack\r
	4	//\r
	5	// Copyright (c) 2008 - 2010, Apple Inc. All rights reserved.<BR>\r
	6	//\r
	7	// This program and the accompanying materials\r
	8	// are licensed and made available under the terms and conditions of the BSD License\r
	9	// which accompanies this distribution. The full text of the license may be found at\r
	10	// http://opensource.org/licenses/bsd-license.php\r
	11	//\r
	12	// THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,\r
	13	// WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.\r
	14	//\r
	15	//------------------------------------------------------------------------------\r
	16	\r
	17	\r
	18	\r
	19	/*\r
	20	\r
	21	This is the stack constructed by the exception handler (low address to high address)\r
	22	# R0 - IFAR is EFI_SYSTEM_CONTEXT for ARM\r
	23	Reg Offset\r
3402aac7	24	=== ======\r
1e57a462	25	R0 0x00 # stmfd SP!,{R0-R12}\r
	26	R1 0x04\r
	27	R2 0x08\r
	28	R3 0x0c\r
	29	R4 0x10\r
	30	R5 0x14\r
	31	R6 0x18\r
	32	R7 0x1c\r
	33	R8 0x20\r
	34	R9 0x24\r
	35	R10 0x28\r
	36	R11 0x2c\r
	37	R12 0x30\r
	38	SP 0x34 # reserved via adding 0x20 (32) to the SP\r
	39	LR 0x38\r
	40	PC 0x3c\r
	41	CPSR 0x40\r
	42	DFSR 0x44\r
	43	DFAR 0x48\r
	44	IFSR 0x4c\r
	45	IFAR 0x50\r
3402aac7	46	\r
1e57a462	47	LR 0x54 # SVC Link register (we need to restore it)\r
3402aac7 RC	48	\r
	49	LR 0x58 # pushed by srsfd\r
	50	CPSR 0x5c\r
1e57a462	51	\r
1e57a462	52	*/\r
3402aac7 RC	53	\r
3402aac7 RC	54	\r
1e57a462	55	EXPORT ExceptionHandlersStart\r
	56	EXPORT ExceptionHandlersEnd\r
	57	EXPORT CommonExceptionEntry\r
	58	EXPORT AsmCommonExceptionEntry\r
	59	IMPORT GdbExceptionHandler\r
	60	\r
	61	PRESERVE8\r
	62	AREA DxeExceptionHandlers, CODE, READONLY\r
3402aac7	63	\r
1e57a462	64	//\r
	65	// This code gets copied to the ARM vector table\r
	66	// ExceptionHandlersStart - ExceptionHandlersEnd gets copied\r
	67	//\r
	68	ExceptionHandlersStart\r
	69	\r
	70	Reset\r
	71	b Reset\r
	72	\r
	73	UndefinedInstruction\r
	74	b UndefinedInstructionEntry\r
	75	\r
	76	SoftwareInterrupt\r
	77	b SoftwareInterruptEntry\r
	78	\r
	79	PrefetchAbort\r
	80	b PrefetchAbortEntry\r
	81	\r
	82	DataAbort\r
	83	b DataAbortEntry\r
	84	\r
	85	ReservedException\r
	86	b ReservedExceptionEntry\r
	87	\r
	88	Irq\r
	89	b Irq\r
	90	\r
	91	Fiq\r
	92	b FiqEntry\r
	93	\r
	94	\r
	95	UndefinedInstructionEntry\r
	96	sub LR, LR, #4 ; Only -2 for Thumb, adjust in CommonExceptionEntry\r
	97	srsfd #0x13! ; Store return state on SVC stack\r
	98	cpsid f, #0x13 ; Switch to SVC for common stack\r
	99	stmfd SP!,{LR} ; Store the link register for the current mode\r
	100	sub SP,SP,#0x20 ; Save space for SP, LR, PC, IFAR - CPSR\r
	101	stmfd SP!,{R0-R12} ; Store the register state\r
	102	\r
	103	mov R0,#1 ; ExceptionType\r
3402aac7	104	ldr R1,CommonExceptionEntry;\r
1e57a462	105	bx R1\r
	106	\r
	107	SoftwareInterruptEntry\r
	108	sub LR, LR, #4 ; Only -2 for Thumb, adjust in CommonExceptionEntry\r
	109	srsfd #0x13! ; Store return state on SVC stack\r
	110	cpsid f ; We are already in SVC mode\r
	111	stmfd SP!,{LR} ; Store the link register for the current mode\r
	112	sub SP,SP,#0x20 ; Save space for SP, LR, PC, IFAR - CPSR\r
	113	stmfd SP!,{R0-R12} ; Store the register state\r
	114	\r
	115	mov R0,#2 ; ExceptionType\r
	116	ldr R1,CommonExceptionEntry\r
	117	bx R1\r
	118	\r
	119	PrefetchAbortEntry\r
	120	sub LR,LR,#4\r
	121	srsfd #0x13! ; Store return state on SVC stack\r
	122	cpsid f, #0x13 ; Switch to SVC for common stack\r
	123	stmfd SP!,{LR} ; Store the link register for the current mode\r
	124	sub SP,SP,#0x20 ; Save space for SP, LR, PC, IFAR - CPSR\r
	125	stmfd SP!,{R0-R12} ; Store the register state\r
	126	\r
	127	mov R0,#3 ; ExceptionType\r
	128	ldr R1,CommonExceptionEntry\r
	129	bx R1\r
	130	\r
	131	DataAbortEntry\r
	132	sub LR,LR,#8\r
	133	srsfd #0x13! ; Store return state on SVC stack\r
	134	cpsid f, #0x13 ; Switch to SVC for common stack\r
	135	stmfd SP!,{LR} ; Store the link register for the current mode\r
	136	sub SP,SP,#0x20 ; Save space for SP, LR, PC, IFAR - CPSR\r
	137	stmfd SP!,{R0-R12} ; Store the register state\r
	138	\r
	139	mov R0,#4 ; ExceptionType\r
	140	ldr R1,CommonExceptionEntry\r
	141	bx R1\r
	142	\r
	143	ReservedExceptionEntry\r
	144	srsfd #0x13! ; Store return state on SVC stack\r
	145	cpsid f, #0x13 ; Switch to SVC for common stack\r
	146	stmfd SP!,{LR} ; Store the link register for the current mode\r
	147	sub SP,SP,#0x20 ; Save space for SP, LR, PC, IFAR - CPSR\r
	148	stmfd SP!,{R0-R12} ; Store the register state\r
	149	\r
	150	mov R0,#5 ; ExceptionType\r
	151	ldr R1,CommonExceptionEntry\r
	152	bx R1\r
	153	\r
	154	FiqEntry\r
	155	sub LR,LR,#4\r
	156	srsfd #0x13! ; Store return state on SVC stack\r
	157	cps #0x13 ; Switch to SVC for common stack\r
	158	stmfd SP!,{LR} ; Store the link register for the current mode\r
	159	sub SP,SP,#0x20 ; Save space for SP, LR, PC, IFAR - CPSR\r
	160	stmfd SP!,{R0-R12} ; Store the register state\r
	161	; Since we have already switch to SVC R8_fiq - R12_fiq\r
	162	; never get used or saved\r
	163	mov R0,#7 ; ExceptionType\r
	164	ldr R1,CommonExceptionEntry\r
	165	bx R1\r
	166	\r
	167	//\r
	168	// This gets patched by the C code that patches in the vector table\r
169	//\r
170	CommonExceptionEntry\r
171	dcd 0x12345678\r
172	\r
173	ExceptionHandlersEnd\r
174	\r
175	//\r
3402aac7	176	// This code runs from CpuDxe driver loaded address. It is patched into\r
1e57a462	177	// CommonExceptionEntry.\r
	178	//\r
	179	AsmCommonExceptionEntry\r
	180	mrc p15, 0, R1, c6, c0, 2 ; Read IFAR\r
3402aac7 RC	181	str R1, [SP, #0x50] ; Store it in EFI_SYSTEM_CONTEXT_ARM.IFAR\r
3402aac7 RC	182	\r
1e57a462	183	mrc p15, 0, R1, c5, c0, 1 ; Read IFSR\r
1e57a462	184	str R1, [SP, #0x4c] ; Store it in EFI_SYSTEM_CONTEXT_ARM.IFSR\r
3402aac7	185	\r
1e57a462	186	mrc p15, 0, R1, c6, c0, 0 ; Read DFAR\r
1e57a462	187	str R1, [SP, #0x48] ; Store it in EFI_SYSTEM_CONTEXT_ARM.DFAR\r
3402aac7	188	\r
1e57a462	189	mrc p15, 0, R1, c5, c0, 0 ; Read DFSR\r
1e57a462	190	str R1, [SP, #0x44] ; Store it in EFI_SYSTEM_CONTEXT_ARM.DFSR\r
3402aac7 RC	191	\r
3402aac7 RC	192	ldr R1, [SP, #0x5c] ; srsfd saved pre-exception CPSR on the stack\r
1e57a462	193	str R1, [SP, #0x40] ; Store it in EFI_SYSTEM_CONTEXT_ARM.CPSR\r
	194	\r
	195	add R2, SP, #0x38 ; Make R2 point to EFI_SYSTEM_CONTEXT_ARM.LR\r
	196	and R3, R1, #0x1f ; Check CPSR to see if User or System Mode\r
	197	cmp R3, #0x1f ; if ((CPSR == 0x10) \|\| (CPSR == 0x1df))\r
3402aac7	198	cmpne R3, #0x10 ;\r
1e57a462	199	stmeqed R2, {lr}^ ; save unbanked lr\r
3402aac7	200	; else\r
1e57a462	201	stmneed R2, {lr} ; save SVC lr\r
	202	\r
	203	\r
3402aac7	204	ldr R5, [SP, #0x58] ; PC is the LR pushed by srsfd\r
1e57a462	205	; Check to see if we have to adjust for Thumb entry\r
1e57a462	206	sub r4, r0, #1 ; if (ExceptionType == 1 \|\| ExceptionType ==2)) {\r
3402aac7	207	cmp r4, #1 ; // UND & SVC have differnt LR adjust for Thumb\r
1e57a462	208	bhi NoAdjustNeeded\r
3402aac7 RC	209	\r
3402aac7 RC	210	tst r1, #0x20 ; if ((CPSR & T)) == T) { // Thumb Mode on entry\r
1e57a462	211	addne R5, R5, #2 ; PC += 2;\r
3402aac7 RC	212	str R5,[SP,#0x58] ; Update LR value pused by srsfd\r
3402aac7 RC	213	\r
1e57a462	214	NoAdjustNeeded\r
	215	\r
	216	str R5, [SP, #0x3c] ; Store it in EFI_SYSTEM_CONTEXT_ARM.PC\r
3402aac7 RC	217	\r
3402aac7 RC	218	sub R1, SP, #0x60 ; We pused 0x60 bytes on the stack\r
1e57a462	219	str R1, [SP, #0x34] ; Store it in EFI_SYSTEM_CONTEXT_ARM.SP\r
1e57a462	220	\r
3402aac7 RC	221	; R0 is ExceptionType\r
	222	mov R1,SP ; R1 is SystemContext\r
	223	\r
	224	/*\r
1e57a462	225	VOID\r
	226	EFIAPI\r
	227	GdbExceptionHandler (\r
	228	IN EFI_EXCEPTION_TYPE ExceptionType, R0\r
	229	IN OUT EFI_SYSTEM_CONTEXT SystemContext R1\r
	230	)\r
	231	\r
	232	*/\r
	233	blx GdbExceptionHandler ; Call exception handler\r
3402aac7	234	\r
1e57a462	235	ldr R1,[SP,#0x3c] ; EFI_SYSTEM_CONTEXT_ARM.PC\r
3402aac7	236	str R1,[SP,#0x58] ; Store it back to srsfd stack slot so it can be restored\r
1e57a462	237	\r
1e57a462	238	ldr R1,[SP,#0x40] ; EFI_SYSTEM_CONTEXT_ARM.CPSR\r
3402aac7 RC	239	str R1,[SP,#0x5c] ; Store it back to srsfd stack slot so it can be restored\r
3402aac7 RC	240	\r
1e57a462	241	add R3, SP, #0x54 ; Make R3 point to SVC LR saved on entry\r
	242	add R2, SP, #0x38 ; Make R2 point to EFI_SYSTEM_CONTEXT_ARM.LR\r
	243	and R1, R1, #0x1f ; Check to see if User or System Mode\r
	244	cmp R1, #0x1f ; if ((CPSR == 0x10) \|\| (CPSR == 0x1f))\r
3402aac7	245	cmpne R1, #0x10 ;\r
1e57a462	246	ldmeqed R2, {lr}^ ; restore unbanked lr\r
	247	; else\r
	248	ldmneed R3, {lr} ; restore SVC lr, via ldmfd SP!, {LR}\r
3402aac7	249	\r
1e57a462	250	ldmfd SP!,{R0-R12} ; Restore general purpose registers\r
1e57a462	251	; Exception handler can not change SP\r
3402aac7	252	\r
1e57a462	253	add SP,SP,#0x20 ; Clear out the remaining stack space\r
	254	ldmfd SP!,{LR} ; restore the link register for this context\r
	255	rfefd SP! ; return from exception via srsfd stack slot\r
3402aac7	256	\r
1e57a462	257	END\r
	258	\r
	259	\r