/* * 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 <linux/pgtable.h>#include <asm/asmmacro.h>#include <asm/ptrace.h>#include <asm/current.h>#include <asm/asm-offsets.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_KERNEL_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_KERNEL_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" ENTRY(_DoubleExceptionVector) xsr a3, excsave1 s32i a2, a3, EXC_TABLE_DOUBLE_SAVE /* Check for kernel double exception (usually fatal). */ rsr a2, ps _bbsi.l a2, PS_UM_BIT, 1f j .Lksp .align 4 .literal_position1: /* 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 #ifdef SUPPORT_WINDOWED 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 #else j .Lfixup#endif /* * 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, .Lunrecoverable1: 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 call0 unrecoverable_exception .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 #ifdef SUPPORT_WINDOWED /* * 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 a03: xsr a3, excsave1 movi a0, 0 s32i a0, a3, EXC_TABLE_FIXUP s32i a2, a3, EXC_TABLE_DOUBLE_SAVE1: /* * 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 a02: 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#endif ENDPROC(_DoubleExceptionVector) #ifdef SUPPORT_WINDOWED /* * 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);Lines 1–500 of 805. 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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 - 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 <linux/pgtable.h> #include <asm/asmmacro.h> #include <asm/ptrace.h> #include <asm/current.h> #include <asm/asm-offsets.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_KERNEL_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_KERNEL_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" ENTRY(_DoubleExceptionVector) xsr a3, excsave1 s32i a2, a3, EXC_TABLE_DOUBLE_SAVE /* Check for kernel double exception (usually fatal). */ rsr a2, ps _bbsi.l a2, PS_UM_BIT, 1f j .Lksp .align 4 .literal_position 1: /* 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 #ifdef SUPPORT_WINDOWED 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 #else j .Lfixup #endif /* * 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 call0 unrecoverable_exception .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 #ifdef SUPPORT_WINDOWED /* * 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 #endif ENDPROC(_DoubleExceptionVector) #ifdef SUPPORT_WINDOWED /* * 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);