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* arch/xtensa/kernel/vectors.S
* This file contains all exception vectors (user, kernel, and double),
* as well as the window vectors (overflow and underflow), and the debug
* vector. These are the primary vectors executed by the processor if an
* exception occurs.
* This file is subject to the terms and conditions of the GNU General
* Public License. See the file "COPYING" in the main directory of
* this archive for more details.
* Copyright (C) 2005 Tensilica, Inc.
* Chris Zankel <>
* We use a two-level table approach. The user and kernel exception vectors
* use a first-level dispatch table to dispatch the exception to a registered
* fast handler or the default handler, if no fast handler was registered.
* The default handler sets up a C-stack and dispatches the exception to a
* registerd C handler in the second-level dispatch table.
* Fast handler entry condition:
* a0: trashed, original value saved on stack (PT_AREG0)
* a1: a1
* a2: new stack pointer, original value in depc
* a3: dispatch table
* depc: a2, original value saved on stack (PT_DEPC)
* excsave_1: a3
* The value for PT_DEPC saved to stack also functions as a boolean to
* indicate that the exception is either a double or a regular exception:
* Note: Neither the kernel nor the user exception handler generate literals.
#include <linux/linkage.h>
#include <asm/ptrace.h>
#include <asm/current.h>
#include <asm/asm-offsets.h>
#include <asm/pgtable.h>
#include <asm/processor.h>
#include <asm/page.h>
#include <asm/thread_info.h>
* User exception vector. (Exceptions with PS.UM == 1, PS.EXCM == 0)
* We get here when an exception occurred while we were in userland.
* We switch to the kernel stack and jump to the first level handler
* associated to the exception cause.
* Note: the saved kernel stack pointer (EXC_TABLE_KSTK) is already
* decremented by PT_USER_SIZE.
.section .UserExceptionVector.text, "ax"
xsr a3, EXCSAVE_1 # save a3 and get dispatch table
wsr a2, DEPC # save a2
l32i a2, a3, EXC_TABLE_KSTK # load kernel stack to a2
s32i a0, a2, PT_AREG0 # save a0 to ESF
rsr a0, EXCCAUSE # retrieve exception cause
s32i a0, a2, PT_DEPC # mark it as a regular exception
addx4 a0, a0, a3 # find entry in table
l32i a0, a0, EXC_TABLE_FAST_USER # load handler
jx a0
* Kernel exception vector. (Exceptions with PS.UM == 0, PS.EXCM == 0)
* We get this exception when we were already in kernel space.
* We decrement the current stack pointer (kernel) by PT_SIZE and
* jump to the first-level handler associated with the exception cause.
* Note: we need to preserve space for the spill region.
.section .KernelExceptionVector.text, "ax"
xsr a3, EXCSAVE_1 # save a3, and get dispatch table
wsr a2, DEPC # save a2
addi a2, a1, -16-PT_SIZE # adjust stack pointer
s32i a0, a2, PT_AREG0 # save a0 to ESF
rsr a0, EXCCAUSE # retrieve exception cause
s32i a0, a2, PT_DEPC # mark it as a regular exception
addx4 a0, a0, a3 # find entry in table
l32i a0, a0, EXC_TABLE_FAST_KERNEL # load handler address
jx a0
* Double exception vector (Exceptions with PS.EXCM == 1)
* We get this exception when another exception occurs while were are
* already in an exception, such as window overflow/underflow exception,
* or 'expected' exceptions, for example memory exception when we were trying
* to read data from an invalid address in user space.
* Note that this vector is never invoked for level-1 interrupts, because such
* interrupts are disabled (masked) when PS.EXCM is set.
* We decode the exception and take the appropriate action. However, the
* double exception vector is much more careful, because a lot more error
* cases go through the double exception vector than through the user and
* kernel exception vectors.
* Occasionally, the kernel expects a double exception to occur. This usually
* happens when accessing user-space memory with the user's permissions
* (l32e/s32e instructions). The kernel state, though, is not always suitable
* for immediate transfer of control to handle_double, where "normal" exception
* processing occurs. Also in kernel mode, TLB misses can occur if accessing
* vmalloc memory, possibly requiring repair in a double exception handler.
* The variable at TABLE_FIXUP offset from the pointer in EXCSAVE_1 doubles as
* a boolean variable and a pointer to a fixup routine. If the variable
* EXC_TABLE_FIXUP is non-zero, this handler jumps to that address. A value of
* zero indicates to use the default kernel/user exception handler.
* There is only one exception, when the value is identical to the exc_table
* label, the kernel is in trouble. This mechanism is used to protect critical
* sections, mainly when the handler writes to the stack to assert the stack
* pointer is valid. Once the fixup/default handler leaves that area, the
* EXC_TABLE_FIXUP variable is reset to the fixup handler or zero.
* Procedures wishing to use this mechanism should set EXC_TABLE_FIXUP to the
* nonzero address of a fixup routine before it could cause a double exception
* and reset it before it returns.
* Some other things to take care of when a fast exception handler doesn't
* specify a particular fixup handler but wants to use the default handlers:
* - The original stack pointer (in a1) must not be modified. The fast
* exception handler should only use a2 as the stack pointer.
* - If the fast handler manipulates the stack pointer (in a2), it has to
* register a valid fixup handler and cannot use the default handlers.
* - The handler can use any other generic register from a3 to a15, but it
* must save the content of these registers to stack (PT_AREG3...PT_AREGx)
* - These registers must be saved before a double exception can occur.
* - If we ever implement handling signals while in double exceptions, the
* number of registers a fast handler has saved (excluding a0 and a1) must
* be written to PT_AREG1. (1 if only a3 is used, 2 for a3 and a4, etc. )
* The fixup handlers are special handlers:
* - Fixup entry conditions differ from regular exceptions:
* a0: DEPC
* a1: a1
* a2: trashed, original value in EXC_TABLE_DOUBLE_A2
* a3: exctable
* depc: a0
* excsave_1: a3
* - When the kernel enters the fixup handler, it still assumes it is in a
* critical section, so EXC_TABLE_FIXUP variable is set to exc_table.
* The fixup handler, therefore, has to re-register itself as the fixup
* handler before it returns from the double exception.
* - Fixup handler can share the same exception frame with the fast handler.
* The kernel stack pointer is not changed when entering the fixup handler.
* - Fixup handlers can jump to the default kernel and user exception
* handlers. Before it jumps, though, it has to setup a exception frame
* on stack. Because the default handler resets the register fixup handler
* the fixup handler must make sure that the default handler returns to
* it instead of the exception address, so it can re-register itself as
* the fixup handler.
* In case of a critical condition where the kernel cannot recover, we jump
* to unrecoverable_exception with the following entry conditions.
* All registers a0...a15 are unchanged from the last exception, except:
* a0: last address before we jumped to the unrecoverable_exception.
* excsave_1: a0
* See the handle_alloca_user and spill_registers routines for example clients.
* FIXME: Note: we currently don't allow signal handling coming from a double
* exception, so the item markt with (*) is not required.
.section .DoubleExceptionVector.text, "ax"
.begin literal_prefix .DoubleExceptionVector
/* Deliberately destroy excsave (don't assume it's value was valid). */
wsr a3, EXCSAVE_1 # save a3
/* Check for kernel double exception (usually fatal). */
rsr a3, PS
_bbci.l a3, PS_UM_BIT, .Lksp
/* Check if we are currently handling a window exception. */
/* Note: We don't need to indicate that we enter a critical section. */
xsr a0, DEPC # get DEPC, save a0
_bltu a0, a3, .Lfixup
_bgeu a0, a3, .Lfixup
/* Window overflow/underflow exception. Get stack pointer. */
mov a3, a2
movi a2, exc_table
l32i a2, a2, EXC_TABLE_KSTK
/* Check for overflow/underflow exception, jump if overflow. */
_bbci.l a0, 6, .Lovfl
/* a0: depc, a1: a1, a2: kstk, a3: a2, depc: a0, excsave: a3 */
/* Restart window underflow exception.
* We return to the instruction in user space that caused the window
* underflow exception. Therefore, we change window base to the value
* before we entered the window underflow exception and prepare the
* registers to return as if we were coming from a regular exception
* by changing depc (in a0).
* Note: We can trash the current window frame (a0...a3) and depc!
wsr a2, DEPC # save stack pointer temporarily
rsr a0, PS
extui a0, a0, PS_OWB_SHIFT, 4
/* We are now in the previous window frame. Save registers again. */
xsr a2, DEPC # save a2 and get stack pointer
s32i a0, a2, PT_AREG0
wsr a3, EXCSAVE_1 # save a3
movi a3, exc_table
rsr a0, EXCCAUSE
s32i a0, a2, PT_DEPC # mark it as a regular exception
addx4 a0, a0, a3
l32i a0, a0, EXC_TABLE_FAST_USER
jx a0
.Lfixup:/* Check for a fixup handler or if we were in a critical section. */
/* a0: depc, a1: a1, a2: a2, a3: trashed, depc: a0, excsave1: a3 */
movi a3, exc_table
s32i a2, a3, EXC_TABLE_DOUBLE_SAVE # temporary variable
/* Enter critical section. */
l32i a2, a3, EXC_TABLE_FIXUP
s32i a3, a3, EXC_TABLE_FIXUP
beq a2, a3, .Lunrecoverable_fixup # critical!
beqz a2, .Ldflt # no handler was registered
/* a0: depc, a1: a1, a2: trash, a3: exctable, depc: a0, excsave: a3 */
jx a2
.Ldflt: /* Get stack pointer. */
addi a2, a3, -PT_USER_SIZE
.Lovfl: /* Jump to default handlers. */
/* a0: depc, a1: a1, a2: kstk, a3: a2, depc: a0, excsave: a3 */
xsr a3, DEPC
s32i a0, a2, PT_DEPC
s32i a3, a2, PT_AREG0
/* a0: avail, a1: a1, a2: kstk, a3: avail, depc: a2, excsave: a3 */
movi a3, exc_table
rsr a0, EXCCAUSE
addx4 a0, a0, a3
l32i a0, a0, EXC_TABLE_FAST_USER
jx a0
* We only allow the ITLB miss exception if we are in kernel space.
* All other exceptions are unexpected and thus unrecoverable!
.extern fast_second_level_miss_double_kernel
.Lksp: /* a0: a0, a1: a1, a2: a2, a3: trashed, depc: depc, excsave: a3 */
rsr a3, EXCCAUSE
addi a3, a3, -EXCCAUSE_DTLB_MISS
bnez a3, .Lunrecoverable
1: movi a3, fast_second_level_miss_double_kernel
jx a3
.equ .Lksp, .Lunrecoverable
/* Critical! We can't handle this situation. PANIC! */
.extern unrecoverable_exception
xsr a0, DEPC
rsr a3, EXCSAVE_1
wsr a0, EXCSAVE_1
movi a0, unrecoverable_exception
callx0 a0
.end literal_prefix
* Debug interrupt vector
* There is not much space here, so simply jump to another handler.
* EXCSAVE[DEBUGLEVEL] has been set to that handler.
.section .DebugInterruptVector.text, "ax"
jx a0
/* Window overflow and underflow handlers.
* The handlers must be 64 bytes apart, first starting with the underflow
* handlers underflow-4 to underflow-12, then the overflow handlers
* overflow-4 to overflow-12.
* Note: We rerun the underflow handlers if we hit an exception, so
* we try to access any page that would cause a page fault early.
.section .WindowVectors.text, "ax"
/* 4-Register Window Overflow Vector (Handler) */
.align 64
.global _WindowOverflow4
s32e a0, a5, -16
s32e a1, a5, -12
s32e a2, a5, -8
s32e a3, a5, -4
/* 4-Register Window Underflow Vector (Handler) */
.align 64
.global _WindowUnderflow4
l32e a0, a5, -16
l32e a1, a5, -12
l32e a2, a5, -8
l32e a3, a5, -4
/* 8-Register Window Overflow Vector (Handler) */
.align 64
.global _WindowOverflow8
s32e a0, a9, -16
l32e a0, a1, -12
s32e a2, a9, -8
s32e a1, a9, -12
s32e a3, a9, -4
s32e a4, a0, -32
s32e a5, a0, -28
s32e a6, a0, -24
s32e a7, a0, -20
/* 8-Register Window Underflow Vector (Handler) */
.align 64
.global _WindowUnderflow8
l32e a1, a9, -12
l32e a0, a9, -16
l32e a7, a1, -12
l32e a2, a9, -8
l32e a4, a7, -32
l32e a3, a9, -4
l32e a5, a7, -28
l32e a6, a7, -24
l32e a7, a7, -20
/* 12-Register Window Overflow Vector (Handler) */
.align 64
.global _WindowOverflow12
s32e a0, a13, -16
l32e a0, a1, -12
s32e a1, a13, -12
s32e a2, a13, -8
s32e a3, a13, -4
s32e a4, a0, -48
s32e a5, a0, -44
s32e a6, a0, -40
s32e a7, a0, -36
s32e a8, a0, -32
s32e a9, a0, -28
s32e a10, a0, -24
s32e a11, a0, -20
/* 12-Register Window Underflow Vector (Handler) */
.align 64
.global _WindowUnderflow12
l32e a1, a13, -12
l32e a0, a13, -16
l32e a11, a1, -12
l32e a2, a13, -8
l32e a4, a11, -48
l32e a8, a11, -32
l32e a3, a13, -4
l32e a5, a11, -44
l32e a6, a11, -40
l32e a7, a11, -36
l32e a9, a11, -28
l32e a10, a11, -24
l32e a11, a11, -20