source: mainline/kernel/arch/mips32/src/debug/stacktrace.c

/*
 * Copyright (c) 2010 Jakub Jermar
 * 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 kernel_mips32
 * @{
 */
/** @file
 */

/*
 * This stack tracing code is based on the suggested algorithm described on page
 * 3-27 and 3-28 of:
 *
 * SYSTEM V
 * APPLICATION BINARY INTERFACE
 *
 * MIPS RISC Processor
 * Supplement
 * 3rd Edition
 *
 * Unfortunately, GCC generates code which is not entirely compliant with this
 * method. For example, it places the "jr ra" instruction quite arbitrarily in
 * the middle of the function which makes the original algorithm unapplicable.
 *
 * We deal with this problem by simply not using those parts of the algorithm
 * that rely on the "jr ra" instruction occurring in the last basic block of a
 * function, which gives us still usable, but less reliable stack tracer. The
 * unreliability stems from the fact that under some circumstances it can become
 * confused and produce incorrect or incomplete stack trace. We apply extra
 * sanity checks so that the algorithm is still safe and should not crash the
 * system.
 *
 * Even though not perfect, our solution is pretty lightweight, especially when
 * compared with a prospective alternative solution based on additional
 * debugging information stored directly in the kernel image.
 */

#include <stacktrace.h>
#include <stddef.h>
#include <syscall/copy.h>
#include <typedefs.h>
#include <arch/debugger.h>

#define R0      0U
#define SP      29U
#define RA      31U

#define OP_SHIFT        26
#define RS_SHIFT        21
#define RT_SHIFT        16
#define RD_SHIFT        11

#define HINT_SHIFT      6
#define BASE_SHIFT      RS_SHIFT
#define IMM_SHIFT       0
#define OFFSET_SHIFT    IMM_SHIFT

#define RS_MASK         (0x1f << RS_SHIFT)
#define RT_MASK         (0x1f << RT_SHIFT)
#define RD_MASK         (0x1f << RD_SHIFT)
#define HINT_MASK       (0x1f << HINT_SHIFT)
#define BASE_MASK       RS_MASK
#define IMM_MASK        (0xffff << IMM_SHIFT)
#define OFFSET_MASK     IMM_MASK

#define RS_GET(inst)            (((inst) & RS_MASK) >> RS_SHIFT)
#define RD_GET(inst)            (((inst) & RD_MASK) >> RD_SHIFT)
#define IMM_GET(inst)           (int16_t)(((inst) & IMM_MASK) >> IMM_SHIFT)
#define BASE_GET(inst)          RS_GET(inst)
#define OFFSET_GET(inst)        IMM_GET(inst)

#define ADDU_R_SP_R0_TEMPL \
        ((0x0 << OP_SHIFT) | (SP << RS_SHIFT) | (R0 << RT_SHIFT) | 0x21)
#define ADDU_SP_R_R0_TEMPL \
        ((0x0 << OP_SHIFT) | (SP << RD_SHIFT) | (R0 << RT_SHIFT) | 0x21)
#define ADDI_SP_SP_IMM_TEMPL \
        ((0x8 << OP_SHIFT) | (SP << RS_SHIFT) | (SP << RT_SHIFT))
#define ADDIU_SP_SP_IMM_TEMPL \
        ((0x9 << OP_SHIFT) | (SP << RS_SHIFT) | (SP << RT_SHIFT))
#define JR_RA_TEMPL \
        ((0x0 << OP_SHIFT) | (RA << RS_SHIFT) | (0x0 << HINT_SHIFT) | 0x8)
#define SW_RA_TEMPL \
        ((0x2b << OP_SHIFT) | (RA << RT_SHIFT))

#define IS_ADDU_R_SP_R0(inst) \
        (((inst) & ~RD_MASK) == ADDU_R_SP_R0_TEMPL)
#define IS_ADDU_SP_R_R0(inst) \
        (((inst) & ~RS_MASK) == ADDU_SP_R_R0_TEMPL)
#define IS_ADDI_SP_SP_IMM(inst) \
        (((inst) & ~IMM_MASK) == ADDI_SP_SP_IMM_TEMPL)
#define IS_ADDIU_SP_SP_IMM(inst) \
        (((inst) & ~IMM_MASK) == ADDIU_SP_SP_IMM_TEMPL)
#define IS_JR_RA(inst) \
        (((inst) & ~HINT_MASK) == JR_RA_TEMPL)
#define IS_SW_RA(inst) \
        (((inst) & ~(BASE_MASK | OFFSET_MASK)) == SW_RA_TEMPL)

extern char ktext_start;
extern char ktext_end;

static bool bounds_check(uintptr_t pc)
{
        return (pc >= (uintptr_t) &ktext_start) &&
            (pc < (uintptr_t) &ktext_end);
}

static bool
scan(stack_trace_context_t *ctx, uintptr_t *prev_fp, uintptr_t *prev_ra)
{
        uint32_t *inst = (void *) ctx->pc;
        bool has_fp = false;
        size_t frame_size;
        unsigned int fp = SP;

        do {
                inst--;
                if (!bounds_check((uintptr_t) inst))
                        return false;
#if 0
                /*
                 * This is one of the situations in which the theory (ABI) does
                 * not meet the practice (GCC). GCC simply does not place the
                 * JR $ra instruction as dictated by the ABI, rendering the
                 * official stack tracing algorithm somewhat unapplicable.
                 */

                if (IS_ADDU_R_SP_R0(*inst)) {
                        uint32_t *cur;
                        fp = RD_GET(*inst);
                        /*
                         * We have a candidate for frame pointer.
                         */

                        /* Seek to the end of this function. */
                        cur = inst + 1;
                        while (!IS_JR_RA(*cur))
                                cur++;

                        /* Scan the last basic block */
                        for (cur--; !is_jump(*(cur - 1)); cur--) {
                                if (IS_ADDU_SP_R_R0(*cur) &&
                                    (fp == RS_GET(*cur))) {
                                        has_fp = true;
                                }
                        }
                        continue;
                }

                if (IS_JR_RA(*inst)) {
                        if (!ctx->istate)
                                return false;
                        /*
                         * No stack frame has been allocated yet.
                         * Use the values stored in istate.
                         */
                        if (prev_fp)
                                *prev_fp = ctx->istate->sp;
                        if (prev_ra)
                                *prev_ra = ctx->istate->ra - 8;
                        ctx->istate = NULL;
                        return true;
                }
#endif

        } while ((!IS_ADDIU_SP_SP_IMM(*inst) && !IS_ADDI_SP_SP_IMM(*inst)) ||
            (IMM_GET(*inst) >= 0));

        /*
         * We are at the instruction which allocates the space for the current
         * stack frame.
         */
        frame_size = -IMM_GET(*inst);
        if (prev_fp)
                *prev_fp = ctx->fp + frame_size;

        /*
         * Scan the first basic block for the occurrence of
         * SW $ra, OFFSET($base).
         */
        for (inst++; !is_jump(*(inst - 1)) && (uintptr_t) inst < ctx->pc;
            inst++) {
                if (IS_SW_RA(*inst)) {
                        unsigned int base = BASE_GET(*inst);
                        int16_t offset = OFFSET_GET(*inst);

                        if (base == SP || (has_fp && base == fp)) {
                                uint32_t *addr = (void *) (ctx->fp + offset);

                                if (offset % 4 != 0)
                                        return false;
                                /* cannot store below current stack pointer */
                                if (offset < 0)
                                        return false;
                                /* too big offsets are suspicious */
                                if ((size_t) offset > sizeof(istate_t))
                                        return false;

                                if (prev_ra)
                                        *prev_ra = *addr;
                                return true;
                        }
                }
        }

        /*
         * The first basic block does not save the return address or saves it
         * after ctx->pc, which means that the correct value is in istate.
         */
        if (prev_ra) {
                if (!ctx->istate)
                        return false;
                *prev_ra = ctx->istate->ra - 8;
                ctx->istate = NULL;
        }
        return true;
}

bool kernel_stack_trace_context_validate(stack_trace_context_t *ctx)
{
        return !((ctx->fp == 0) || ((ctx->fp % 8) != 0) ||
            (ctx->pc % 4 != 0) || !bounds_check(ctx->pc));
}

bool kernel_frame_pointer_prev(stack_trace_context_t *ctx, uintptr_t *prev)
{
        return scan(ctx, prev, NULL);
}

bool kernel_return_address_get(stack_trace_context_t *ctx, uintptr_t *ra)
{
        return scan(ctx, NULL, ra);
}

bool uspace_stack_trace_context_validate(stack_trace_context_t *ctx)
{
        return false;
}

bool uspace_frame_pointer_prev(stack_trace_context_t *ctx, uintptr_t *prev)
{
        return false;
}

bool uspace_return_address_get(stack_trace_context_t *ctx, uintptr_t *ra)
{
        return false;
}

/** @}
 */