[ae6f1ec] | 1 | #include <stdlib.h> |
---|
| 2 | #include <stdio.h> |
---|
| 3 | #include <unwind.h> |
---|
| 4 | |
---|
| 5 | #include "lsda.h" |
---|
| 6 | |
---|
| 7 | //Global which defines the current exception |
---|
| 8 | //Currently an int just to make matching easier |
---|
| 9 | int this_exception; |
---|
| 10 | |
---|
| 11 | //This is our personality routine |
---|
| 12 | //For every stack frame anotated with ".cfi_personality 0x3,__gcfa_personality_v0" |
---|
| 13 | //This function will be called twice when unwinding |
---|
| 14 | //Once in the search phased and once in the cleanup phase |
---|
| 15 | _Unwind_Reason_Code __gcfa_personality_v0 ( |
---|
| 16 | int version, _Unwind_Action actions, unsigned long long exceptionClass, |
---|
| 17 | struct _Unwind_Exception* unwind_exception, struct _Unwind_Context* context) |
---|
| 18 | { |
---|
| 19 | //DEBUG |
---|
| 20 | printf("Personality function (%d, %x, %llu, %p, %p):", version, actions, exceptionClass, unwind_exception, context); |
---|
| 21 | |
---|
| 22 | //If we've reached the end of the stack then there is nothing much we can do... |
---|
| 23 | if( actions & _UA_END_OF_STACK ) return _URC_END_OF_STACK; |
---|
| 24 | |
---|
| 25 | //DEBUG |
---|
| 26 | if (actions & _UA_SEARCH_PHASE) { |
---|
| 27 | printf(" lookup phase"); |
---|
| 28 | } |
---|
| 29 | //DEBUG |
---|
| 30 | else if (actions & _UA_CLEANUP_PHASE) { |
---|
| 31 | printf(" cleanup phase"); |
---|
| 32 | } |
---|
| 33 | //Just in case, probably can't actually happen |
---|
| 34 | else { |
---|
| 35 | printf(" error\n"); |
---|
| 36 | return _URC_FATAL_PHASE1_ERROR; |
---|
| 37 | } |
---|
| 38 | |
---|
| 39 | //Get a pointer to the language specific data from which we will read what we need |
---|
| 40 | const unsigned char * lsd = (const unsigned char*) _Unwind_GetLanguageSpecificData( context ); |
---|
| 41 | |
---|
| 42 | if( !lsd ) { //Nothing to do, keep unwinding |
---|
| 43 | printf(" no LSD"); |
---|
| 44 | goto UNWIND; |
---|
| 45 | } |
---|
| 46 | |
---|
| 47 | //Get the instuction pointer and a reading pointer into the exception table |
---|
| 48 | lsda_header_info lsd_info; |
---|
| 49 | const unsigned char * cur_ptr = parse_lsda_header( context, lsd, &lsd_info); |
---|
| 50 | _Unwind_Ptr instruction_ptr = _Unwind_GetIP( context ); |
---|
| 51 | |
---|
| 52 | //Linearly search the table for stuff to do |
---|
| 53 | while( cur_ptr < lsd_info.action_table ) { |
---|
| 54 | _Unwind_Ptr callsite_start; |
---|
| 55 | _Unwind_Ptr callsite_len; |
---|
| 56 | _Unwind_Ptr callsite_landing_pad; |
---|
| 57 | _uleb128_t callsite_action; |
---|
| 58 | |
---|
| 59 | //Decode the common stuff we have in here |
---|
| 60 | cur_ptr = read_encoded_value (0, lsd_info.call_site_encoding, cur_ptr, &callsite_start); |
---|
| 61 | cur_ptr = read_encoded_value (0, lsd_info.call_site_encoding, cur_ptr, &callsite_len); |
---|
| 62 | cur_ptr = read_encoded_value (0, lsd_info.call_site_encoding, cur_ptr, &callsite_landing_pad); |
---|
| 63 | cur_ptr = read_uleb128 (cur_ptr, &callsite_action); |
---|
| 64 | |
---|
| 65 | //Have we reach the correct frame info yet? |
---|
| 66 | if( lsd_info.Start + callsite_start + callsite_len < instruction_ptr ) { |
---|
| 67 | //DEBUG BEGIN |
---|
| 68 | void * ls = (void*)lsd_info.Start; |
---|
| 69 | void * cs = (void*)callsite_start; |
---|
| 70 | void * cl = (void*)callsite_len; |
---|
| 71 | void * bp = (void*)lsd_info.Start + callsite_start; |
---|
| 72 | void * ep = (void*)lsd_info.Start + callsite_start + callsite_len; |
---|
| 73 | void * ip = (void*)instruction_ptr; |
---|
| 74 | printf("\nfound %p - %p (%p, %p, %p), looking for %p\n", bp, ep, ls, cs, cl, ip); |
---|
| 75 | //DEBUG END |
---|
| 76 | continue; |
---|
| 77 | } |
---|
| 78 | |
---|
| 79 | //Have we gone too far |
---|
| 80 | if( lsd_info.Start + callsite_start > instruction_ptr ) { |
---|
| 81 | printf(" gone too far"); |
---|
| 82 | break; |
---|
| 83 | } |
---|
| 84 | |
---|
| 85 | //Something to do? |
---|
| 86 | if( callsite_landing_pad ) { |
---|
| 87 | //Which phase are we in |
---|
| 88 | if (actions & _UA_SEARCH_PHASE) { |
---|
| 89 | //Search phase, this means we probably found a potential handler and must check if it is a match |
---|
| 90 | |
---|
| 91 | //If we have arbitrarily decided that 0 means nothing to do and 1 means there is a potential handler |
---|
| 92 | //This doesn't seem to conflict the gcc default behavior |
---|
| 93 | if (callsite_action != 0) { |
---|
| 94 | //Now we want to run some code to see if the handler matches |
---|
| 95 | //This is the tricky part where we want to the power to run arbitrary code |
---|
| 96 | //However, generating a new exception table entry and try routine every time |
---|
| 97 | //is way more expansive than we might like |
---|
| 98 | //The information we have is : |
---|
| 99 | // - The GR (???) |
---|
| 100 | // - The instruction pointer |
---|
| 101 | // - The instruction pointer info (???) |
---|
| 102 | // - The CFA (???) |
---|
| 103 | // - The BSP (Probably the base stack pointer) |
---|
| 104 | |
---|
| 105 | |
---|
| 106 | //The current apprach uses one exception table entry per try block |
---|
| 107 | _uleb128_t imatcher; |
---|
| 108 | //Get the relative offset to the |
---|
| 109 | cur_ptr = read_uleb128 (cur_ptr, &imatcher); |
---|
| 110 | |
---|
| 111 | //Get a function pointer from the relative offset and call it |
---|
| 112 | _Unwind_Reason_Code (*matcher)() = (_Unwind_Reason_Code (*)())lsd_info.LPStart + imatcher; |
---|
| 113 | _Unwind_Reason_Code ret = matcher(); |
---|
| 114 | |
---|
| 115 | //Based on the return value, check if we matched the exception |
---|
| 116 | if( ret == _URC_HANDLER_FOUND) printf(" handler found\n"); |
---|
| 117 | else printf(" no handler\n"); |
---|
| 118 | return ret; |
---|
| 119 | } |
---|
| 120 | |
---|
| 121 | //This is only a cleanup handler, ignore it |
---|
| 122 | printf(" no action"); |
---|
| 123 | } |
---|
| 124 | else if (actions & _UA_CLEANUP_PHASE) { |
---|
| 125 | |
---|
| 126 | if( (callsite_action != 0) && !(actions & _UA_HANDLER_FRAME) ){ |
---|
| 127 | //If this is a potential exception handler |
---|
| 128 | //but not the one that matched the exception in the seach phase, |
---|
| 129 | //just ignore it |
---|
| 130 | goto UNWIND; |
---|
| 131 | } |
---|
| 132 | |
---|
| 133 | //We need to run some clean-up or a handler |
---|
| 134 | //These statment do the right thing but I don't know any specifics at all |
---|
| 135 | _Unwind_SetGR( context, __builtin_eh_return_data_regno(0), (_Unwind_Ptr) unwind_exception ); |
---|
| 136 | _Unwind_SetGR( context, __builtin_eh_return_data_regno(1), 0 ); |
---|
| 137 | |
---|
| 138 | //I assume this sets the instruction pointer to the adress of the landing pad |
---|
| 139 | //It doesn't actually set it, it only state the value that needs to be set once we return _URC_INSTALL_CONTEXT |
---|
| 140 | _Unwind_SetIP( context, lsd_info.LPStart + callsite_landing_pad ); |
---|
| 141 | |
---|
| 142 | //DEBUG |
---|
| 143 | printf(" action\n"); |
---|
| 144 | |
---|
| 145 | //Return have some action to run |
---|
| 146 | return _URC_INSTALL_CONTEXT; |
---|
| 147 | } |
---|
| 148 | } |
---|
| 149 | |
---|
| 150 | //Nothing to do, move along |
---|
| 151 | printf(" no landing pad"); |
---|
| 152 | } |
---|
| 153 | //No handling found |
---|
| 154 | printf(" table end reached\n"); |
---|
| 155 | |
---|
| 156 | //DEBUG |
---|
| 157 | UNWIND: |
---|
| 158 | printf(" unwind\n"); |
---|
| 159 | |
---|
| 160 | //Keep unwinding the stack |
---|
| 161 | return _URC_CONTINUE_UNWIND; |
---|
| 162 | } |
---|
| 163 | |
---|
| 164 | //We need a piece of storage to raise the exception |
---|
| 165 | struct _Unwind_Exception this_exception_storage; |
---|
| 166 | |
---|
| 167 | //Function needed by force unwind |
---|
| 168 | //It basically says to unwind the whole stack and then exit when we reach the end of the stack |
---|
| 169 | static _Unwind_Reason_Code _Stop_Fn( |
---|
| 170 | int version, |
---|
| 171 | _Unwind_Action actions, |
---|
| 172 | _Unwind_Exception_Class exceptionClass, |
---|
| 173 | struct _Unwind_Exception * unwind_exception, |
---|
| 174 | struct _Unwind_Context * context, |
---|
| 175 | void * some_param |
---|
| 176 | ) { |
---|
| 177 | if( actions & _UA_END_OF_STACK ) exit(1); |
---|
| 178 | if( actions & _UA_CLEANUP_PHASE ) return _URC_NO_REASON; |
---|
| 179 | |
---|
| 180 | return _URC_FATAL_PHASE2_ERROR; |
---|
| 181 | } |
---|
| 182 | |
---|
| 183 | //Example throw routine |
---|
| 184 | void throw( int val ) { |
---|
| 185 | //Store the current exception |
---|
| 186 | this_exception = val; |
---|
| 187 | |
---|
| 188 | //DEBUG |
---|
| 189 | printf("Throwing exception %d\n", this_exception); |
---|
| 190 | |
---|
| 191 | //Call stdlibc to raise the exception |
---|
| 192 | _Unwind_Reason_Code ret = _Unwind_RaiseException( &this_exception_storage ); |
---|
| 193 | |
---|
| 194 | //If we reach here it means something happened |
---|
| 195 | //For resumption to work we need to find a way to return back to here |
---|
| 196 | //Most of them will probably boil down to setting a global flag and making the phase 1 either stop or fail. |
---|
| 197 | //Causing an error on purpose may help avoiding unnecessary work but it might have some weird side effects. |
---|
| 198 | //If we just pretend no handler was found that would work but may be expensive for no reason since we will always |
---|
| 199 | //search the whole stack |
---|
| 200 | |
---|
| 201 | if( ret == _URC_END_OF_STACK ) { |
---|
| 202 | //No proper handler was found |
---|
| 203 | //This can be handled in several way |
---|
| 204 | //C++ calls std::terminate |
---|
| 205 | //Here we force unwind the stack, basically raising a cancellation |
---|
| 206 | printf("Uncaught exception %p\n", &this_exception_storage); |
---|
| 207 | |
---|
| 208 | ret = _Unwind_ForcedUnwind( &this_exception_storage, _Stop_Fn, (void*)0x22 ); |
---|
| 209 | printf("UNWIND ERROR %d after force unwind\n", ret); |
---|
| 210 | abort(); |
---|
| 211 | } |
---|
| 212 | |
---|
| 213 | //We did not simply reach the end of the stack without finding a handler, |
---|
| 214 | //Something wen't wrong |
---|
| 215 | printf("UNWIND ERROR %d after raise exception\n", ret); |
---|
| 216 | abort(); |
---|
| 217 | } |
---|