source: mainline/kernel/arch/arm32/src/exception.c@ 9cc0d7c

/*
 * Copyright (c) 2007 Petr Stepan
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup arm32
 * @{
 */
/** @file
 *  @brief Exception handlers and exception initialization routines.
 */

#include <arch/exception.h>
#include <arch/debug/print.h>
#include <arch/memstr.h>
#include <arch/regutils.h>
#include <interrupt.h>
#include <arch/machine.h>
#include <arch/mm/page_fault.h>
#include <print.h>
#include <syscall/syscall.h>

/** Offset used in calculation of exception handler's relative address.
 *
 * @see install_handler()
 */
#define PREFETCH_OFFSET      0x8

/** LDR instruction's code */
#define LDR_OPCODE           0xe59ff000

/** Number of exception vectors. */
#define EXC_VECTORS          8

/** Size of memory block occupied by exception vectors. */
#define EXC_VECTORS_SIZE     (EXC_VECTORS * 4)

/** Switches to kernel stack and saves all registers there.
 *
 * Temporary exception stack is used to save a few registers
 * before stack switch takes place.
 */
inline static void setup_stack_and_save_regs()
{
        asm volatile(
                "ldr r13, =exc_stack            \n"
                "stmfd r13!, {r0}               \n"
                "mrs r0, spsr                   \n"
                "and r0, r0, #0x1f              \n"
                "cmp r0, #0x10                  \n"
                "bne 1f                         \n"

                /* prev mode was usermode */
                "ldmfd r13!, {r0}               \n"
                "ldr r13, =supervisor_sp        \n"
                "ldr r13, [r13]                 \n"
                "stmfd r13!, {lr}               \n"
                "stmfd r13!, {r0-r12}           \n"
                "stmfd r13!, {r13, lr}^         \n"
                "mrs r0, spsr                   \n"
                "stmfd r13!, {r0}               \n"
                "b 2f                           \n"

                /* mode was not usermode */
        "1:\n"
                "stmfd r13!, {r1, r2, r3}       \n"
                "mrs r1, cpsr                   \n"
                "mov r2, lr                     \n"
                "bic r1, r1, #0x1f              \n"
                "orr r1, r1, r0                 \n"
                "mrs r0, cpsr                   \n"
                "msr cpsr_c, r1                 \n"

                "mov r3, r13                    \n"
                "stmfd r13!, {r2}               \n"
                "mov r2, lr                     \n"
                "stmfd r13!, {r4-r12}           \n"
                "mov r1, r13                    \n"
                /* the following two lines are for debugging */
                "mov sp, #0                     \n"
                "mov lr, #0                     \n"
                "msr cpsr_c, r0                 \n"

                "ldmfd r13!, {r4, r5, r6, r7}   \n"
                "stmfd r1!, {r4, r5, r6}        \n"
                "stmfd r1!, {r7}                \n"
                "stmfd r1!, {r2}                \n"
                "stmfd r1!, {r3}                \n"
                "mrs r0, spsr                   \n"
                "stmfd r1!, {r0}                \n"
                "mov r13, r1                    \n"
        "2:\n"
        );
}

/** Returns from exception mode.
 * 
 * Previously saved state of registers (including control register)
 * is restored from the stack.
 */
inline static void load_regs()
{
        asm volatile(
                "ldmfd r13!, {r0}               \n"
                "msr spsr, r0                   \n"
                "and r0, r0, #0x1f              \n"
                "cmp r0, #0x10                  \n"
                "bne 1f                         \n"

                /* return to user mode */
                "ldmfd r13!, {r13, lr}^         \n"
                "b 2f                           \n"

                /* return to non-user mode */
        "1:\n"
                "ldmfd r13!, {r1, r2}           \n"
                "mrs r3, cpsr                   \n"
                "bic r3, r3, #0x1f              \n"
                "orr r3, r3, r0                 \n"
                "mrs r0, cpsr                   \n"
                "msr cpsr_c, r3                 \n"

                "mov r13, r1                    \n"
                "mov lr, r2                     \n"
                "msr cpsr_c, r0                 \n"

                /* actual return */
        "2:\n"
                "ldmfd r13, {r0-r12, pc}^\n"
        );
}


/** Switch CPU to mode in which interrupts are serviced (currently it 
 * is Undefined mode).
 *
 * The default mode for interrupt servicing (Interrupt Mode)
 * can not be used because of nested interrupts (which can occur
 * because interrupts are enabled in higher levels of interrupt handler).
 */
inline static void switch_to_irq_servicing_mode()
{
        /* switch to Undefined mode */
        asm volatile(
                /* save regs used during switching */
                "stmfd sp!, {r0-r3}             \n"

                /* save stack pointer and link register to r1, r2 */
                "mov r1, sp                     \n"
                "mov r2, lr                     \n"

                /* mode switch */
                "mrs r0, cpsr                   \n"
                "bic r0, r0, #0x1f              \n"
                "orr r0, r0, #0x1b              \n"
                "msr cpsr_c, r0                 \n"

                /* restore saved sp and lr */
                "mov sp, r1                     \n"
                "mov lr, r2                     \n"

                /* restore original regs */
                "ldmfd sp!, {r0-r3}             \n"
        );
}

/** Calls exception dispatch routine. */
#define CALL_EXC_DISPATCH(exception)            \
        asm("mov r0, %0" : : "i" (exception));  \
        asm("mov r1, r13");                     \
        asm("bl exc_dispatch");         

/** General exception handler.
 *
 *  Stores registers, dispatches the exception,
 *  and finally restores registers and returns from exception processing.
 *
 *  @param exception Exception number.
 */
#define PROCESS_EXCEPTION(exception)            \
        setup_stack_and_save_regs();            \
        CALL_EXC_DISPATCH(exception)            \
        load_regs();

/** Updates specified exception vector to jump to given handler.
 *
 *  Addresses of handlers are stored in memory following exception vectors.
 */
static void install_handler (unsigned handler_addr, unsigned* vector)
{
        /* relative address (related to exc. vector) of the word
         * where handler's address is stored
        */
        volatile uint32_t handler_address_ptr = EXC_VECTORS_SIZE -
            PREFETCH_OFFSET;
        
        /* make it LDR instruction and store at exception vector */
        *vector = handler_address_ptr | LDR_OPCODE;
        
        /* store handler's address */
        *(vector + EXC_VECTORS) = handler_addr;

}

/** Low-level Reset Exception handler. */
static void reset_exception_entry()
{
        PROCESS_EXCEPTION(EXC_RESET);
}

/** Low-level Software Interrupt Exception handler. */
static void swi_exception_entry()
{
        PROCESS_EXCEPTION(EXC_SWI);
}

/** Low-level Undefined Instruction Exception handler. */
static void undef_instr_exception_entry()
{
        PROCESS_EXCEPTION(EXC_UNDEF_INSTR);
}

/** Low-level Fast Interrupt Exception handler. */
static void fiq_exception_entry()
{
        PROCESS_EXCEPTION(EXC_FIQ);
}

/** Low-level Prefetch Abort Exception handler. */
static void prefetch_abort_exception_entry()
{
        asm("sub lr, lr, #4");
        PROCESS_EXCEPTION(EXC_PREFETCH_ABORT);
} 

/** Low-level Data Abort Exception handler. */
static void data_abort_exception_entry()
{
        asm("sub lr, lr, #8");
        PROCESS_EXCEPTION(EXC_DATA_ABORT);
}

/** Low-level Interrupt Exception handler.
 *
 * CPU is switched to Undefined mode before further interrupt processing
 * because of possible occurence of nested interrupt exception, which
 * would overwrite (and thus spoil) stack pointer.
 */
static void irq_exception_entry()
{
        asm("sub lr, lr, #4");
        setup_stack_and_save_regs();
        
        switch_to_irq_servicing_mode();
        
        CALL_EXC_DISPATCH(EXC_IRQ)

        load_regs();
}

/** Software Interrupt handler.
 *
 * Dispatches the syscall.
 */
static void swi_exception(int exc_no, istate_t *istate)
{
        istate->r0 = syscall_handler(istate->r0, istate->r1, istate->r2,
            istate->r3, istate->r4, istate->r5, istate->r6);
}

/** Interrupt Exception handler.
 *
 * Determines the sources of interrupt and calls their handlers.
 */
static void irq_exception(int exc_no, istate_t *istate)
{
        machine_irq_exception(exc_no, istate);
}

/** Fills exception vectors with appropriate exception handlers. */
void install_exception_handlers(void)
{
        install_handler((unsigned) reset_exception_entry,
            (unsigned *) EXC_RESET_VEC);
        
        install_handler((unsigned) undef_instr_exception_entry,
            (unsigned *) EXC_UNDEF_INSTR_VEC);
        
        install_handler((unsigned) swi_exception_entry,
            (unsigned *) EXC_SWI_VEC);
        
        install_handler((unsigned) prefetch_abort_exception_entry,
            (unsigned *) EXC_PREFETCH_ABORT_VEC);
        
        install_handler((unsigned) data_abort_exception_entry,
            (unsigned *) EXC_DATA_ABORT_VEC);
        
        install_handler((unsigned) irq_exception_entry,
            (unsigned *) EXC_IRQ_VEC);
        
        install_handler((unsigned)fiq_exception_entry,
            (unsigned *) EXC_FIQ_VEC);
}

#ifdef HIGH_EXCEPTION_VECTORS
/** Activates use of high exception vectors addresses. */
static void high_vectors(void)
{
        uint32_t control_reg;
        
        asm volatile("mrc p15, 0, %0, c1, c1" : "=r" (control_reg));
        
        /* switch on the high vectors bit */
        control_reg |= CP15_R1_HIGH_VECTORS_BIT;
        
        asm volatile("mcr p15, 0, %0, c1, c1" : : "r" (control_reg));
}
#endif

/** Initializes exception handling.
 * 
 * Installs low-level exception handlers and then registers
 * exceptions and their handlers to kernel exception dispatcher.
 */
void exception_init(void)
{
#ifdef HIGH_EXCEPTION_VECTORS
        high_vectors();
#endif
        install_exception_handlers();
        
        exc_register(EXC_IRQ, "interrupt", (iroutine) irq_exception);
        exc_register(EXC_PREFETCH_ABORT, "prefetch abort",
            (iroutine) prefetch_abort);
        exc_register(EXC_DATA_ABORT, "data abort", (iroutine) data_abort);
        exc_register(EXC_SWI, "software interrupt", (iroutine) swi_exception);
}

/** Prints #istate_t structure content.
 *
 * @param istate Structure to be printed.
 */
void print_istate(istate_t *istate)
{
        dprintf("istate dump:\n");

        dprintf(" r0: %x    r1: %x    r2: %x    r3: %x\n",
            istate->r0, istate->r1, istate->r2, istate->r3);
        dprintf(" r4: %x    r5: %x    r6: %x    r7: %x\n", 
            istate->r4, istate->r5, istate->r6, istate->r7);
        dprintf(" r8: %x    r8: %x   r10: %x   r11: %x\n", 
            istate->r8, istate->r9, istate->r10, istate->r11);
        dprintf(" r12: %x    sp: %x    lr: %x  spsr: %x\n",
            istate->r12, istate->sp, istate->lr, istate->spsr);

        dprintf(" pc: %x\n", istate->pc);
}

/** @}
 */