1 | #include <stdlib.h> |
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2 | #include <stdio.h> |
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3 | #include <unwind.h> |
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4 | |
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5 | #include "lsda.h" |
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6 | |
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7 | // This macro should be the only thing that needs to change across machines. |
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8 | // struct _Unwind_Context * -> _Unwind_Reason_Code(*)() |
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9 | #define MATCHER_FROM_CONTEXT(ptr_to_context) \ |
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10 | (*(_Unwind_Reason_Code(**)())(_Unwind_GetCFA(ptr_to_context) + 8)) |
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11 | |
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12 | |
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13 | //Global which defines the current exception |
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14 | //Currently an int just to make matching easier |
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15 | int this_exception; |
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16 | |
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17 | //This is our personality routine |
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18 | //For every stack frame anotated with ".cfi_personality 0x3,__gcfa_personality_v0" |
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19 | //This function will be called twice when unwinding |
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20 | //Once in the search phased and once in the cleanup phase |
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21 | _Unwind_Reason_Code __gcfa_personality_v0 ( |
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22 | int version, _Unwind_Action actions, unsigned long long exceptionClass, |
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23 | struct _Unwind_Exception* unwind_exception, struct _Unwind_Context* context) |
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24 | { |
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25 | printf("CFA: 0x%lx\n", _Unwind_GetCFA(context)); |
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26 | |
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27 | //DEBUG |
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28 | printf("Personality function (%d, %x, %llu, %p, %p):", version, actions, exceptionClass, unwind_exception, context); |
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29 | |
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30 | //If we've reached the end of the stack then there is nothing much we can do... |
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31 | if( actions & _UA_END_OF_STACK ) return _URC_END_OF_STACK; |
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32 | |
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33 | //DEBUG |
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34 | if (actions & _UA_SEARCH_PHASE) { |
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35 | printf(" lookup phase"); |
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36 | } |
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37 | //DEBUG |
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38 | else if (actions & _UA_CLEANUP_PHASE) { |
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39 | printf(" cleanup phase"); |
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40 | } |
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41 | //Just in case, probably can't actually happen |
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42 | else { |
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43 | printf(" error\n"); |
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44 | return _URC_FATAL_PHASE1_ERROR; |
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45 | } |
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46 | |
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47 | //Get a pointer to the language specific data from which we will read what we need |
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48 | const unsigned char * lsd = (const unsigned char*) _Unwind_GetLanguageSpecificData( context ); |
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49 | |
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50 | if( !lsd ) { //Nothing to do, keep unwinding |
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51 | printf(" no LSD"); |
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52 | goto UNWIND; |
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53 | } |
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54 | |
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55 | //Get the instuction pointer and a reading pointer into the exception table |
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56 | lsda_header_info lsd_info; |
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57 | const unsigned char * cur_ptr = parse_lsda_header( context, lsd, &lsd_info); |
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58 | _Unwind_Ptr instruction_ptr = _Unwind_GetIP( context ); |
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59 | |
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60 | //Linearly search the table for stuff to do |
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61 | while( cur_ptr < lsd_info.action_table ) { |
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62 | _Unwind_Ptr callsite_start; |
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63 | _Unwind_Ptr callsite_len; |
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64 | _Unwind_Ptr callsite_landing_pad; |
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65 | _uleb128_t callsite_action; |
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66 | |
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67 | //Decode the common stuff we have in here |
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68 | cur_ptr = read_encoded_value (0, lsd_info.call_site_encoding, cur_ptr, &callsite_start); |
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69 | cur_ptr = read_encoded_value (0, lsd_info.call_site_encoding, cur_ptr, &callsite_len); |
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70 | cur_ptr = read_encoded_value (0, lsd_info.call_site_encoding, cur_ptr, &callsite_landing_pad); |
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71 | cur_ptr = read_uleb128 (cur_ptr, &callsite_action); |
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72 | |
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73 | //Have we reach the correct frame info yet? |
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74 | if( lsd_info.Start + callsite_start + callsite_len < instruction_ptr ) { |
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75 | //DEBUG BEGIN |
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76 | void * ls = (void*)lsd_info.Start; |
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77 | void * cs = (void*)callsite_start; |
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78 | void * cl = (void*)callsite_len; |
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79 | void * bp = (void*)lsd_info.Start + callsite_start; |
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80 | void * ep = (void*)lsd_info.Start + callsite_start + callsite_len; |
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81 | void * ip = (void*)instruction_ptr; |
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82 | printf("\nfound %p - %p (%p, %p, %p), looking for %p\n", bp, ep, ls, cs, cl, ip); |
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83 | //DEBUG END |
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84 | continue; |
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85 | } |
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86 | |
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87 | //Have we gone too far |
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88 | if( lsd_info.Start + callsite_start > instruction_ptr ) { |
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89 | printf(" gone too far"); |
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90 | break; |
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91 | } |
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92 | |
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93 | //Something to do? |
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94 | if( callsite_landing_pad ) { |
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95 | //Which phase are we in |
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96 | if (actions & _UA_SEARCH_PHASE) { |
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97 | //Search phase, this means we probably found a potential handler and must check if it is a match |
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98 | |
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99 | //If we have arbitrarily decided that 0 means nothing to do and 1 means there is a potential handler |
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100 | //This doesn't seem to conflict the gcc default behavior |
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101 | if (callsite_action != 0) { |
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102 | //Now we want to run some code to see if the handler matches |
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103 | //This is the tricky part where we want to the power to run arbitrary code |
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104 | //However, generating a new exception table entry and try routine every time |
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105 | //is way more expansive than we might like |
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106 | //The information we have is : |
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107 | // - The GR (Series of registers) |
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108 | // GR1=GP Global Pointer of frame ref by context |
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109 | // - The instruction pointer |
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110 | // - The instruction pointer info (???) |
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111 | // - The CFA (Canonical Frame Address) |
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112 | // - The BSP (Probably the base stack pointer) |
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113 | |
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114 | |
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115 | //The current apprach uses one exception table entry per try block |
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116 | _uleb128_t imatcher; |
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117 | //Get the relative offset to the |
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118 | cur_ptr = read_uleb128 (cur_ptr, &imatcher); |
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119 | |
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120 | //Get a function pointer from the relative offset and call it |
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121 | // _Unwind_Reason_Code (*matcher)() = (_Unwind_Reason_Code (*)())lsd_info.LPStart + imatcher; |
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122 | |
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123 | _Unwind_Reason_Code (*matcher)() = |
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124 | MATCHER_FROM_CONTEXT(context); |
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125 | _Unwind_Reason_Code ret = matcher(); |
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126 | |
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127 | //Based on the return value, check if we matched the exception |
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128 | if( ret == _URC_HANDLER_FOUND) printf(" handler found\n"); |
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129 | else printf(" no handler\n"); |
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130 | return ret; |
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131 | } |
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132 | |
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133 | //This is only a cleanup handler, ignore it |
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134 | printf(" no action"); |
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135 | } |
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136 | else if (actions & _UA_CLEANUP_PHASE) { |
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137 | |
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138 | if( (callsite_action != 0) && !(actions & _UA_HANDLER_FRAME) ){ |
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139 | //If this is a potential exception handler |
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140 | //but not the one that matched the exception in the seach phase, |
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141 | //just ignore it |
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142 | goto UNWIND; |
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143 | } |
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144 | |
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145 | //We need to run some clean-up or a handler |
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146 | //These statment do the right thing but I don't know any specifics at all |
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147 | _Unwind_SetGR( context, __builtin_eh_return_data_regno(0), (_Unwind_Ptr) unwind_exception ); |
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148 | _Unwind_SetGR( context, __builtin_eh_return_data_regno(1), 0 ); |
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149 | |
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150 | //I assume this sets the instruction pointer to the adress of the landing pad |
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151 | //It doesn't actually set it, it only state the value that needs to be set once we return _URC_INSTALL_CONTEXT |
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152 | _Unwind_SetIP( context, lsd_info.LPStart + callsite_landing_pad ); |
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153 | |
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154 | //DEBUG |
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155 | printf(" action\n"); |
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156 | |
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157 | //Return have some action to run |
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158 | return _URC_INSTALL_CONTEXT; |
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159 | } |
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160 | } |
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161 | |
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162 | //Nothing to do, move along |
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163 | printf(" no landing pad"); |
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164 | } |
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165 | //No handling found |
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166 | printf(" table end reached\n"); |
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167 | |
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168 | //DEBUG |
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169 | UNWIND: |
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170 | printf(" unwind\n"); |
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171 | |
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172 | //Keep unwinding the stack |
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173 | return _URC_CONTINUE_UNWIND; |
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174 | } |
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175 | |
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176 | //We need a piece of storage to raise the exception |
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177 | struct _Unwind_Exception this_exception_storage; |
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178 | |
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179 | //Function needed by force unwind |
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180 | //It basically says to unwind the whole stack and then exit when we reach the end of the stack |
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181 | static _Unwind_Reason_Code _Stop_Fn( |
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182 | int version, |
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183 | _Unwind_Action actions, |
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184 | _Unwind_Exception_Class exceptionClass, |
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185 | struct _Unwind_Exception * unwind_exception, |
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186 | struct _Unwind_Context * context, |
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187 | void * some_param |
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188 | ) { |
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189 | if( actions & _UA_END_OF_STACK ) exit(1); |
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190 | if( actions & _UA_CLEANUP_PHASE ) return _URC_NO_REASON; |
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191 | |
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192 | return _URC_FATAL_PHASE2_ERROR; |
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193 | } |
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194 | |
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195 | //Example throw routine |
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196 | void throw( int val ) { |
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197 | //Store the current exception |
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198 | this_exception = val; |
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199 | |
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200 | //DEBUG |
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201 | printf("Throwing exception %d\n", this_exception); |
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202 | |
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203 | //Call stdlibc to raise the exception |
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204 | _Unwind_Reason_Code ret = _Unwind_RaiseException( &this_exception_storage ); |
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205 | |
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206 | //If we reach here it means something happened |
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207 | //For resumption to work we need to find a way to return back to here |
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208 | //Most of them will probably boil down to setting a global flag and making the phase 1 either stop or fail. |
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209 | //Causing an error on purpose may help avoiding unnecessary work but it might have some weird side effects. |
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210 | //If we just pretend no handler was found that would work but may be expensive for no reason since we will always |
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211 | //search the whole stack |
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212 | |
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213 | if( ret == _URC_END_OF_STACK ) { |
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214 | //No proper handler was found |
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215 | //This can be handled in several way |
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216 | //C++ calls std::terminate |
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217 | //Here we force unwind the stack, basically raising a cancellation |
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218 | printf("Uncaught exception %p\n", &this_exception_storage); |
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219 | |
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220 | ret = _Unwind_ForcedUnwind( &this_exception_storage, _Stop_Fn, (void*)0x22 ); |
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221 | printf("UNWIND ERROR %d after force unwind\n", ret); |
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222 | abort(); |
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223 | } |
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224 | |
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225 | //We did not simply reach the end of the stack without finding a handler, |
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226 | //Something wen't wrong |
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227 | printf("UNWIND ERROR %d after raise exception\n", ret); |
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228 | abort(); |
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229 | } |
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