/* * 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 - 2008 Tensilica, Inc. * * Chris Zankel <chris@zankel.net> * */ /* * 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: * * PT_DEPC >= VALID_DOUBLE_EXCEPTION_ADDRESS: double exception * < VALID_DOUBLE_EXCEPTION_ADDRESS: 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> #include <asm/vectors.h> #define WINDOW_VECTORS_SIZE 0x180 /* * 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" ENTRY(_UserExceptionVector) xsr a3, excsave1 # 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 xsr a3, excsave1 # restore a3 and dispatch table jx a0 ENDPROC(_UserExceptionVector) /* * 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" ENTRY(_KernelExceptionVector) xsr a3, excsave1 # 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 xsr a3, excsave1 # restore a3 and dispatch table jx a0 ENDPROC(_KernelExceptionVector) /* * 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_SAVE * 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 .globl _DoubleExceptionVector_WindowUnderflow .globl _DoubleExceptionVector_WindowOverflow ENTRY(_DoubleExceptionVector) xsr a3, excsave1 s32i a2, a3, EXC_TABLE_DOUBLE_SAVE /* Check for kernel double exception (usually fatal). */ rsr a2, ps _bbci.l a2, 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 movi a2, WINDOW_VECTORS_VADDR _bltu a0, a2, .Lfixup addi a2, a2, WINDOW_VECTORS_SIZE _bgeu a0, a2, .Lfixup /* Window overflow/underflow exception. Get stack pointer. */ l32i a2, a3, EXC_TABLE_KSTK /* Check for overflow/underflow exception, jump if overflow. */ bbci.l a0, 6, _DoubleExceptionVector_WindowOverflow /* * Restart window underflow exception. * Currently: * depc = orig a0, * a0 = orig DEPC, * a2 = new sp based on KSTK from exc_table * a3 = excsave_1 * excsave_1 = orig a3 * * 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! */ _DoubleExceptionVector_WindowUnderflow: xsr a3, excsave1 wsr a2, depc # save stack pointer temporarily rsr a0, ps extui a0, a0, PS_OWB_SHIFT, PS_OWB_WIDTH wsr a0, windowbase rsync /* 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 xsr a3, excsave1 rsr a0, exccause s32i a0, a2, PT_DEPC # mark it as a regular exception addx4 a0, a0, a3 xsr a3, excsave1 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! */ #ifdef CONFIG_MMU .extern fast_second_level_miss_double_kernel .Lksp: /* a0: a0, a1: a1, a2: a2, a3: trashed, depc: depc, excsave: a3 */ rsr a3, exccause beqi a3, EXCCAUSE_ITLB_MISS, 1f addi a3, a3, -EXCCAUSE_DTLB_MISS bnez a3, .Lunrecoverable 1: movi a3, fast_second_level_miss_double_kernel jx a3 #else .equ .Lksp, .Lunrecoverable #endif /* Critical! We can't handle this situation. PANIC! */ .extern unrecoverable_exception .Lunrecoverable_fixup: l32i a2, a3, EXC_TABLE_DOUBLE_SAVE xsr a0, depc .Lunrecoverable: rsr a3, excsave1 wsr a0, excsave1 movi a0, unrecoverable_exception callx0 a0 .Lfixup:/* Check for a fixup handler or if we were in a critical section. */ /* a0: depc, a1: a1, a2: trash, a3: exctable, depc: a0, excsave1: a3 */ /* Enter critical section. */ l32i a2, a3, EXC_TABLE_FIXUP s32i a3, a3, EXC_TABLE_FIXUP beq a2, a3, .Lunrecoverable_fixup # critical section 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. */ l32i a2, a3, EXC_TABLE_DOUBLE_SAVE addi a2, a2, -PT_USER_SIZE /* a0: depc, a1: a1, a2: kstk, a3: exctable, depc: a0, excsave: a3 */ s32i a0, a2, PT_DEPC l32i a0, a3, EXC_TABLE_DOUBLE_SAVE xsr a0, depc s32i a0, a2, PT_AREG0 /* a0: avail, a1: a1, a2: kstk, a3: exctable, depc: a2, excsave: a3 */ rsr a0, exccause addx4 a0, a0, a3 xsr a3, excsave1 l32i a0, a0, EXC_TABLE_FAST_USER jx a0 /* * Restart window OVERFLOW exception. * Currently: * depc = orig a0, * a0 = orig DEPC, * a2 = new sp based on KSTK from exc_table * a3 = EXCSAVE_1 * excsave_1 = orig a3 * * We return to the instruction in user space that caused the window * overflow exception. Therefore, we change window base to the value * before we entered the window overflow exception and prepare the * registers to return as if we were coming from a regular exception * by changing DEPC (in a0). * * NOTE: We CANNOT trash the current window frame (a0...a3), but we * can clobber depc. * * The tricky part here is that overflow8 and overflow12 handlers * save a0, then clobber a0. To restart the handler, we have to restore * a0 if the double exception was past the point where a0 was clobbered. * * To keep things simple, we take advantage of the fact all overflow * handlers save a0 in their very first instruction. If DEPC was past * that instruction, we can safely restore a0 from where it was saved * on the stack. * * a0: depc, a1: a1, a2: kstk, a3: exc_table, depc: a0, excsave1: a3 */ _DoubleExceptionVector_WindowOverflow: extui a2, a0, 0, 6 # get offset into 64-byte vector handler beqz a2, 1f # if at start of vector, don't restore addi a0, a0, -128 bbsi.l a0, 8, 1f # don't restore except for overflow 8 and 12 /* * This fixup handler is for the extremely unlikely case where the * overflow handler's reference thru a0 gets a hardware TLB refill * that bumps out the (distinct, aliasing) TLB entry that mapped its * prior references thru a9/a13, and where our reference now thru * a9/a13 gets a 2nd-level miss exception (not hardware TLB refill). */ movi a2, window_overflow_restore_a0_fixup s32i a2, a3, EXC_TABLE_FIXUP l32i a2, a3, EXC_TABLE_DOUBLE_SAVE xsr a3, excsave1 bbsi.l a0, 7, 2f /* * Restore a0 as saved by _WindowOverflow8(). */ l32e a0, a9, -16 wsr a0, depc # replace the saved a0 j 3f 2: /* * Restore a0 as saved by _WindowOverflow12(). */ l32e a0, a13, -16 wsr a0, depc # replace the saved a0 3: xsr a3, excsave1 movi a0, 0 s32i a0, a3, EXC_TABLE_FIXUP s32i a2, a3, EXC_TABLE_DOUBLE_SAVE 1: /* * Restore WindowBase while leaving all address registers restored. * We have to use ROTW for this, because WSR.WINDOWBASE requires * an address register (which would prevent restore). * * Window Base goes from 0 ... 7 (Module 8) * Window Start is 8 bits; Ex: (0b1010 1010):0x55 from series of call4s */ rsr a0, ps extui a0, a0, PS_OWB_SHIFT, PS_OWB_WIDTH rsr a2, windowbase sub a0, a2, a0 extui a0, a0, 0, 3 l32i a2, a3, EXC_TABLE_DOUBLE_SAVE xsr a3, excsave1 beqi a0, 1, .L1pane beqi a0, 3, .L3pane rsr a0, depc rotw -2 /* * We are now in the user code's original window frame. * Process the exception as a user exception as if it was * taken by the user code. * * This is similar to the user exception vector, * except that PT_DEPC isn't set to EXCCAUSE. */ 1: xsr a3, excsave1 wsr a2, depc l32i a2, a3, EXC_TABLE_KSTK s32i a0, a2, PT_AREG0 rsr a0, exccause s32i a0, a2, PT_DEPC _DoubleExceptionVector_handle_exception: addi a0, a0, -EXCCAUSE_UNALIGNED beqz a0, 2f addx4 a0, a0, a3 l32i a0, a0, EXC_TABLE_FAST_USER + 4 * EXCCAUSE_UNALIGNED xsr a3, excsave1 jx a0 2: movi a0, user_exception xsr a3, excsave1 jx a0 .L1pane: rsr a0, depc rotw -1 j 1b .L3pane: rsr a0, depc rotw -3 j 1b ENDPROC(_DoubleExceptionVector) /* * Fixup handler for TLB miss in double exception handler for window owerflow. * We get here with windowbase set to the window that was being spilled and * a0 trashed. a0 bit 7 determines if this is a call8 (bit clear) or call12 * (bit set) window. * * We do the following here: * - go to the original window retaining a0 value; * - set up exception stack to return back to appropriate a0 restore code * (we'll need to rotate window back and there's no place to save this * information, use different return address for that); * - handle the exception; * - go to the window that was being spilled; * - set up window_overflow_restore_a0_fixup as a fixup routine; * - reload a0; * - restore the original window; * - reset the default fixup routine; * - return to user. By the time we get to this fixup handler all information * about the conditions of the original double exception that happened in * the window overflow handler is lost, so we just return to userspace to * retry overflow from start. * * a0: value of depc, original value in depc * a2: trashed, original value in EXC_TABLE_DOUBLE_SAVE * a3: exctable, original value in excsave1 */ ENTRY(window_overflow_restore_a0_fixup) rsr a0, ps extui a0, a0, PS_OWB_SHIFT, PS_OWB_WIDTH rsr a2, windowbase sub a0, a2, a0 extui a0, a0, 0, 3 l32i a2, a3, EXC_TABLE_DOUBLE_SAVE xsr a3, excsave1 _beqi a0, 1, .Lhandle_1 _beqi a0, 3, .Lhandle_3 .macro overflow_fixup_handle_exception_pane n rsr a0, depc rotw -\n xsr a3, excsave1 wsr a2, depc l32i a2, a3, EXC_TABLE_KSTK s32i a0, a2, PT_AREG0 movi a0, .Lrestore_\n s32i a0, a2, PT_DEPC rsr a0, exccause j _DoubleExceptionVector_handle_exception .endm overflow_fixup_handle_exception_pane 2 .Lhandle_1: overflow_fixup_handle_exception_pane 1 .Lhandle_3: overflow_fixup_handle_exception_pane 3 .macro overflow_fixup_restore_a0_pane n rotw \n /* Need to preserve a0 value here to be able to handle exception * that may occur on a0 reload from stack. It may occur because * TLB miss handler may not be atomic and pointer to page table * may be lost before we get here. There are no free registers, * so we need to use EXC_TABLE_DOUBLE_SAVE area. */ xsr a3, excsave1 s32i a2, a3, EXC_TABLE_DOUBLE_SAVE movi a2, window_overflow_restore_a0_fixup s32i a2, a3, EXC_TABLE_FIXUP l32i a2, a3, EXC_TABLE_DOUBLE_SAVE xsr a3, excsave1 bbsi.l a0, 7, 1f l32e a0, a9, -16 j 2f 1: l32e a0, a13, -16 2: rotw -\n .endm .Lrestore_2: overflow_fixup_restore_a0_pane 2 .Lset_default_fixup: xsr a3, excsave1 s32i a2, a3, EXC_TABLE_DOUBLE_SAVE movi a2, 0 s32i a2, a3, EXC_TABLE_FIXUP l32i a2, a3, EXC_TABLE_DOUBLE_SAVE xsr a3, excsave1 rfe .Lrestore_1: overflow_fixup_restore_a0_pane 1 j .Lset_default_fixup .Lrestore_3: overflow_fixup_restore_a0_pane 3 j .Lset_default_fixup ENDPROC(window_overflow_restore_a0_fixup) .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" ENTRY(_DebugInterruptVector) xsr a0, SREG_EXCSAVE + XCHAL_DEBUGLEVEL jx a0 ENDPROC(_DebugInterruptVector) /* * Medium priority level interrupt vectors * * Each takes less than 16 (0x10) bytes, no literals, by placing * the extra 8 bytes that would otherwise be required in the window * vectors area where there is space. With relocatable vectors, * all vectors are within ~ 4 kB range of each other, so we can * simply jump (J) to another vector without having to use JX. * * common_exception code gets current IRQ level in PS.INTLEVEL * and preserves it for the IRQ handling time. */ .macro irq_entry_level level .if XCHAL_EXCM_LEVEL >= \level .section .Level\level\()InterruptVector.text, "ax" ENTRY(_Level\level\()InterruptVector) wsr a0, excsave2 rsr a0, epc\level wsr a0, epc1 movi a0, EXCCAUSE_LEVEL1_INTERRUPT wsr a0, exccause rsr a0, eps\level # branch to user or kernel vector j _SimulateUserKernelVectorException .endif .endm irq_entry_level 2 irq_entry_level 3 irq_entry_level 4 irq_entry_level 5 irq_entry_level 6 /* 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. */ #define ENTRY_ALIGN64(name) \ .globl name; \ .align 64; \ name: .section .WindowVectors.text, "ax" /* 4-Register Window Overflow Vector (Handler) */ ENTRY_ALIGN64(_WindowOverflow4) s32e a0, a5, -16 s32e a1, a5, -12 s32e a2, a5, -8 s32e a3, a5, -4 rfwo ENDPROC(_WindowOverflow4) #if XCHAL_EXCM_LEVEL >= 2 /* Not a window vector - but a convenient location * (where we know there's space) for continuation of * medium priority interrupt dispatch code. * On entry here, a0 contains PS, and EPC2 contains saved a0: */ .align 4 _SimulateUserKernelVectorException: addi a0, a0, (1 << PS_EXCM_BIT) wsr a0, ps bbsi.l a0, PS_UM_BIT, 1f # branch if user mode rsr a0, excsave2 # restore a0 j _KernelExceptionVector # simulate kernel vector exception 1: rsr a0, excsave2 # restore a0 j _UserExceptionVector # simulate user vector exception #endif /* 4-Register Window Underflow Vector (Handler) */ ENTRY_ALIGN64(_WindowUnderflow4) l32e a0, a5, -16 l32e a1, a5, -12 l32e a2, a5, -8 l32e a3, a5, -4 rfwu ENDPROC(_WindowUnderflow4) /* 8-Register Window Overflow Vector (Handler) */ ENTRY_ALIGN64(_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 rfwo ENDPROC(_WindowOverflow8) /* 8-Register Window Underflow Vector (Handler) */ ENTRY_ALIGN64(_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 rfwu ENDPROC(_WindowUnderflow8) /* 12-Register Window Overflow Vector (Handler) */ ENTRY_ALIGN64(_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 rfwo ENDPROC(_WindowOverflow12) /* 12-Register Window Underflow Vector (Handler) */ ENTRY_ALIGN64(_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 rfwu ENDPROC(_WindowUnderflow12) .text