| 1 | /*
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| 2 | * Copyright (c) 2010 Jakub Jermar
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| 3 | * All rights reserved.
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| 4 | *
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| 5 | * Redistribution and use in source and binary forms, with or without
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| 6 | * modification, are permitted provided that the following conditions
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| 7 | * are met:
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| 8 | *
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| 9 | * - Redistributions of source code must retain the above copyright
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| 10 | * notice, this list of conditions and the following disclaimer.
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| 11 | * - Redistributions in binary form must reproduce the above copyright
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| 12 | * notice, this list of conditions and the following disclaimer in the
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| 13 | * documentation and/or other materials provided with the distribution.
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| 14 | * - The name of the author may not be used to endorse or promote products
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| 15 | * derived from this software without specific prior written permission.
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| 16 | *
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| 17 | * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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| 18 | * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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| 19 | * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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| 20 | * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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| 21 | * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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| 22 | * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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| 23 | * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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| 24 | * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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| 25 | * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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| 26 | * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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| 27 | */
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| 28 |
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| 29 | /** @addtogroup kernel_mips32
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| 30 | * @{
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| 31 | */
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| 32 | /** @file
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| 33 | */
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| 34 |
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| 35 | /*
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| 36 | * This stack tracing code is based on the suggested algorithm described on page
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| 37 | * 3-27 and 3-28 of:
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| 38 | *
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| 39 | * SYSTEM V
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| 40 | * APPLICATION BINARY INTERFACE
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| 41 | *
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| 42 | * MIPS RISC Processor
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| 43 | * Supplement
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| 44 | * 3rd Edition
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| 45 | *
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| 46 | * Unfortunately, GCC generates code which is not entirely compliant with this
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| 47 | * method. For example, it places the "jr ra" instruction quite arbitrarily in
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| 48 | * the middle of the function which makes the original algorithm unapplicable.
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| 49 | *
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| 50 | * We deal with this problem by simply not using those parts of the algorithm
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| 51 | * that rely on the "jr ra" instruction occurring in the last basic block of a
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| 52 | * function, which gives us still usable, but less reliable stack tracer. The
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| 53 | * unreliability stems from the fact that under some circumstances it can become
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| 54 | * confused and produce incorrect or incomplete stack trace. We apply extra
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| 55 | * sanity checks so that the algorithm is still safe and should not crash the
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| 56 | * system.
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| 57 | *
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| 58 | * Even though not perfect, our solution is pretty lightweight, especially when
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| 59 | * compared with a prospective alternative solution based on additional
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| 60 | * debugging information stored directly in the kernel image.
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| 61 | */
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| 62 |
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| 63 | #include <stacktrace.h>
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| 64 | #include <stddef.h>
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| 65 | #include <syscall/copy.h>
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| 66 | #include <typedefs.h>
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| 67 | #include <arch/debugger.h>
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| 68 |
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| 69 | #define R0 0U
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| 70 | #define SP 29U
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| 71 | #define RA 31U
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| 72 |
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| 73 | #define OP_SHIFT 26
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| 74 | #define RS_SHIFT 21
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| 75 | #define RT_SHIFT 16
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| 76 | #define RD_SHIFT 11
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| 77 |
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| 78 | #define HINT_SHIFT 6
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| 79 | #define BASE_SHIFT RS_SHIFT
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| 80 | #define IMM_SHIFT 0
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| 81 | #define OFFSET_SHIFT IMM_SHIFT
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| 82 |
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| 83 | #define RS_MASK (0x1f << RS_SHIFT)
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| 84 | #define RT_MASK (0x1f << RT_SHIFT)
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| 85 | #define RD_MASK (0x1f << RD_SHIFT)
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| 86 | #define HINT_MASK (0x1f << HINT_SHIFT)
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| 87 | #define BASE_MASK RS_MASK
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| 88 | #define IMM_MASK (0xffff << IMM_SHIFT)
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| 89 | #define OFFSET_MASK IMM_MASK
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| 90 |
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| 91 | #define RS_GET(inst) (((inst) & RS_MASK) >> RS_SHIFT)
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| 92 | #define RD_GET(inst) (((inst) & RD_MASK) >> RD_SHIFT)
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| 93 | #define IMM_GET(inst) (int16_t)(((inst) & IMM_MASK) >> IMM_SHIFT)
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| 94 | #define BASE_GET(inst) RS_GET(inst)
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| 95 | #define OFFSET_GET(inst) IMM_GET(inst)
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| 96 |
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| 97 | #define ADDU_R_SP_R0_TEMPL \
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| 98 | ((0x0 << OP_SHIFT) | (SP << RS_SHIFT) | (R0 << RT_SHIFT) | 0x21)
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| 99 | #define ADDU_SP_R_R0_TEMPL \
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| 100 | ((0x0 << OP_SHIFT) | (SP << RD_SHIFT) | (R0 << RT_SHIFT) | 0x21)
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| 101 | #define ADDI_SP_SP_IMM_TEMPL \
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| 102 | ((0x8 << OP_SHIFT) | (SP << RS_SHIFT) | (SP << RT_SHIFT))
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| 103 | #define ADDIU_SP_SP_IMM_TEMPL \
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| 104 | ((0x9 << OP_SHIFT) | (SP << RS_SHIFT) | (SP << RT_SHIFT))
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| 105 | #define JR_RA_TEMPL \
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| 106 | ((0x0 << OP_SHIFT) | (RA << RS_SHIFT) | (0x0 << HINT_SHIFT) | 0x8)
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| 107 | #define SW_RA_TEMPL \
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| 108 | ((0x2b << OP_SHIFT) | (RA << RT_SHIFT))
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| 109 |
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| 110 | #define IS_ADDU_R_SP_R0(inst) \
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| 111 | (((inst) & ~RD_MASK) == ADDU_R_SP_R0_TEMPL)
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| 112 | #define IS_ADDU_SP_R_R0(inst) \
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| 113 | (((inst) & ~RS_MASK) == ADDU_SP_R_R0_TEMPL)
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| 114 | #define IS_ADDI_SP_SP_IMM(inst) \
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| 115 | (((inst) & ~IMM_MASK) == ADDI_SP_SP_IMM_TEMPL)
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| 116 | #define IS_ADDIU_SP_SP_IMM(inst) \
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| 117 | (((inst) & ~IMM_MASK) == ADDIU_SP_SP_IMM_TEMPL)
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| 118 | #define IS_JR_RA(inst) \
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| 119 | (((inst) & ~HINT_MASK) == JR_RA_TEMPL)
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| 120 | #define IS_SW_RA(inst) \
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| 121 | (((inst) & ~(BASE_MASK | OFFSET_MASK)) == SW_RA_TEMPL)
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| 122 |
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| 123 | extern char ktext_start;
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| 124 | extern char ktext_end;
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| 125 |
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| 126 | static bool bounds_check(uintptr_t pc)
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| 127 | {
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| 128 | return (pc >= (uintptr_t) &ktext_start) &&
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| 129 | (pc < (uintptr_t) &ktext_end);
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| 130 | }
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| 131 |
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| 132 | static bool
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| 133 | scan(stack_trace_context_t *ctx, uintptr_t *prev_fp, uintptr_t *prev_ra)
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| 134 | {
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| 135 | uint32_t *inst = (void *) ctx->pc;
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| 136 | bool has_fp = false;
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| 137 | size_t frame_size;
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| 138 | unsigned int fp = SP;
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| 139 |
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| 140 | do {
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| 141 | inst--;
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| 142 | if (!bounds_check((uintptr_t) inst))
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| 143 | return false;
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| 144 | #if 0
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| 145 | /*
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| 146 | * This is one of the situations in which the theory (ABI) does
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| 147 | * not meet the practice (GCC). GCC simply does not place the
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| 148 | * JR $ra instruction as dictated by the ABI, rendering the
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| 149 | * official stack tracing algorithm somewhat unapplicable.
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| 150 | */
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| 151 |
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| 152 | if (IS_ADDU_R_SP_R0(*inst)) {
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| 153 | uint32_t *cur;
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| 154 | fp = RD_GET(*inst);
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| 155 | /*
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| 156 | * We have a candidate for frame pointer.
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| 157 | */
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| 158 |
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| 159 | /* Seek to the end of this function. */
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| 160 | cur = inst + 1;
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| 161 | while (!IS_JR_RA(*cur))
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| 162 | cur++;
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| 163 |
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| 164 | /* Scan the last basic block */
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| 165 | for (cur--; !is_jump(*(cur - 1)); cur--) {
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| 166 | if (IS_ADDU_SP_R_R0(*cur) &&
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| 167 | (fp == RS_GET(*cur))) {
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| 168 | has_fp = true;
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| 169 | }
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| 170 | }
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| 171 | continue;
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| 172 | }
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| 173 |
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| 174 | if (IS_JR_RA(*inst)) {
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| 175 | if (!ctx->istate)
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| 176 | return false;
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| 177 | /*
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| 178 | * No stack frame has been allocated yet.
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| 179 | * Use the values stored in istate.
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| 180 | */
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| 181 | if (prev_fp)
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| 182 | *prev_fp = ctx->istate->sp;
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| 183 | if (prev_ra)
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| 184 | *prev_ra = ctx->istate->ra - 8;
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| 185 | ctx->istate = NULL;
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| 186 | return true;
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| 187 | }
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| 188 | #endif
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| 189 |
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| 190 | } while ((!IS_ADDIU_SP_SP_IMM(*inst) && !IS_ADDI_SP_SP_IMM(*inst)) ||
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| 191 | (IMM_GET(*inst) >= 0));
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| 192 |
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| 193 | /*
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| 194 | * We are at the instruction which allocates the space for the current
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| 195 | * stack frame.
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| 196 | */
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| 197 | frame_size = -IMM_GET(*inst);
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| 198 | if (prev_fp)
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| 199 | *prev_fp = ctx->fp + frame_size;
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| 200 |
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| 201 | /*
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| 202 | * Scan the first basic block for the occurrence of
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| 203 | * SW $ra, OFFSET($base).
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| 204 | */
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| 205 | for (inst++; !is_jump(*(inst - 1)) && (uintptr_t) inst < ctx->pc;
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| 206 | inst++) {
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| 207 | if (IS_SW_RA(*inst)) {
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| 208 | unsigned int base = BASE_GET(*inst);
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| 209 | int16_t offset = OFFSET_GET(*inst);
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| 210 |
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| 211 | if (base == SP || (has_fp && base == fp)) {
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| 212 | uint32_t *addr = (void *) (ctx->fp + offset);
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| 213 |
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| 214 | if (offset % 4 != 0)
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| 215 | return false;
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| 216 | /* cannot store below current stack pointer */
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| 217 | if (offset < 0)
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| 218 | return false;
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| 219 | /* too big offsets are suspicious */
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| 220 | if ((size_t) offset > sizeof(istate_t))
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| 221 | return false;
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| 222 |
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| 223 | if (prev_ra)
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| 224 | *prev_ra = *addr;
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| 225 | return true;
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| 226 | }
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| 227 | }
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| 228 | }
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| 229 |
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| 230 | /*
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| 231 | * The first basic block does not save the return address or saves it
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| 232 | * after ctx->pc, which means that the correct value is in istate.
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| 233 | */
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| 234 | if (prev_ra) {
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| 235 | if (!ctx->istate)
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| 236 | return false;
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| 237 | *prev_ra = ctx->istate->ra - 8;
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| 238 | ctx->istate = NULL;
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| 239 | }
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| 240 | return true;
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| 241 | }
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| 242 |
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| 243 | bool kernel_stack_trace_context_validate(stack_trace_context_t *ctx)
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| 244 | {
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| 245 | return !((ctx->fp == 0) || ((ctx->fp % 8) != 0) ||
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| 246 | (ctx->pc % 4 != 0) || !bounds_check(ctx->pc));
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| 247 | }
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| 248 |
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| 249 | bool kernel_frame_pointer_prev(stack_trace_context_t *ctx, uintptr_t *prev)
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| 250 | {
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| 251 | return scan(ctx, prev, NULL);
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| 252 | }
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| 253 |
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| 254 | bool kernel_return_address_get(stack_trace_context_t *ctx, uintptr_t *ra)
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| 255 | {
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| 256 | return scan(ctx, NULL, ra);
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| 257 | }
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| 258 |
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| 259 | bool uspace_stack_trace_context_validate(stack_trace_context_t *ctx)
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| 260 | {
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| 261 | return false;
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| 262 | }
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| 263 |
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| 264 | bool uspace_frame_pointer_prev(stack_trace_context_t *ctx, uintptr_t *prev)
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| 265 | {
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| 266 | return false;
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| 267 | }
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| 268 |
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| 269 | bool uspace_return_address_get(stack_trace_context_t *ctx, uintptr_t *ra)
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| 270 | {
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| 271 | return false;
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| 272 | }
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| 273 |
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| 274 | /** @}
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| 275 | */
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