1 | #include <stdio.h> |
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2 | #include "except.h" |
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3 | |
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4 | #define EXCEPTION 2 |
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5 | |
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6 | struct type_raii_t { |
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7 | char * msg; |
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8 | }; |
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9 | |
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10 | //Dtor function to test clean up routines |
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11 | void dtor( struct type_raii_t * this ) { |
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12 | printf("%s\n", this->msg); |
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13 | } |
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14 | |
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15 | //Type macro use to make scope unwinding easier to see. |
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16 | #define raii_t __attribute__(( cleanup(dtor) )) struct type_raii_t |
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17 | |
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18 | //Leaf functions that raises exception |
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19 | void bar() { |
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20 | raii_t a = { "Bar dtor" }; |
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21 | |
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22 | throw( EXCEPTION ); |
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23 | } |
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24 | |
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25 | //Matcher function which will check if the exception was correctly caught |
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26 | extern int this_exception; |
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27 | _Unwind_Reason_Code foo_try_match() { |
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28 | return this_exception == 2 ? _URC_HANDLER_FOUND : _URC_CONTINUE_UNWIND; |
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29 | } |
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30 | |
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31 | //Try statements are hoisted out see comments for details |
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32 | //With this could probably be unique and simply linked from |
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33 | //libcfa but there is one problem left, see the exception table |
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34 | //for details |
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35 | void try( void (*try_block)(), void (*catch_block)() ) |
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36 | { |
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37 | //Setup statments |
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38 | //These 2 statments won't actually result in any code, |
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39 | //they only setup global tables. |
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40 | //However, they clobber gcc cancellation support from gcc. |
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41 | //We can replace the personality routine but replacing the exception |
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42 | //table gcc generates is not really doable, it generates labels based |
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43 | //on how the assembly works. |
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44 | //Setup the personality routine |
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45 | asm volatile (".cfi_personality 0x3,__gcfa_personality_v0"); |
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46 | //Setup the exception table |
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47 | asm volatile (".cfi_lsda 0x3, .LLSDACFA2"); |
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48 | |
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49 | //Label which defines the start of the area for which the handler is setup |
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50 | asm volatile (".TRYSTART:"); |
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51 | |
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52 | //The actual statements of the try blocks |
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53 | try_block(); |
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54 | |
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55 | //asm statement to prevent deadcode removal |
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56 | asm volatile goto ("" : : : : CATCH ); |
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57 | |
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58 | //Normal return |
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59 | return; |
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60 | |
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61 | //Exceptionnal path |
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62 | CATCH : __attribute__(( unused )); |
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63 | //Label which defines the end of the area for which the handler is setup |
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64 | asm volatile (".TRYEND:"); |
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65 | //Label which defines the start of the exception landing pad |
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66 | //basically what will be called when the exception is caught |
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67 | //Note, if multiple handlers are given, the multiplexing should be done |
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68 | //by the generated code, not the exception runtime |
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69 | asm volatile (".CATCH:"); |
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70 | |
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71 | //Exception handler |
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72 | catch_block(); |
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73 | } |
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74 | |
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75 | //Exception table data we need to generate |
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76 | //While this is almost generic, the custom data refers to |
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77 | //foo_try_match try match, which is no way generic |
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78 | //Some more works need to be done if we want to have a single |
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79 | //call to the try routine |
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80 | asm ( |
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81 | //HEADER |
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82 | ".LFECFA1:\n" |
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83 | " .globl __gcfa_personality_v0\n" |
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84 | " .section .gcc_except_table,\"a\",@progbits\n" |
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85 | ".LLSDACFA2:\n" //TABLE header |
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86 | " .byte 0xff\n" |
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87 | " .byte 0xff\n" |
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88 | " .byte 0x1\n" |
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89 | " .uleb128 .LLSDACSECFA2-.LLSDACSBCFA2\n" //BODY length |
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90 | //Body uses language specific data and therefore could be modified arbitrarily |
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91 | ".LLSDACSBCFA2:\n" //BODY start |
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92 | " .uleb128 .TRYSTART-try\n" //Handled area start (relative to start of function) |
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93 | " .uleb128 .TRYEND-.TRYSTART\n" //Handled area length |
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94 | " .uleb128 .CATCH-try\n" //Hanlder landing pad adress (relative to start of function) |
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95 | " .uleb128 1\n" //Action code, gcc seems to use always 0 |
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96 | //Beyond this point we don't match gcc data' |
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97 | " .uleb128 foo_try_match-try\n" //Handler routine to check if the exception is matched |
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98 | ".LLSDACSECFA2:\n" //BODY end |
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99 | " .text\n" //TABLE footer |
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100 | " .size try, .-try\n" |
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101 | " .ident \"GCC: (Ubuntu 6.2.0-3ubuntu11~16.04) 6.2.0 20160901\"\n" |
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102 | " .section .note.GNU-stack,\"x\",@progbits\n" |
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103 | ); |
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104 | |
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105 | void foo() { |
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106 | raii_t a = { "Foo dtor" }; |
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107 | |
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108 | //Since try will clobber the gcc exception table assembly, |
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109 | //We need to nest this to have gcc regenerate the data |
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110 | void foo_try_block() { |
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111 | raii_t b = { "Foo try dtor" }; |
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112 | |
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113 | bar(); |
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114 | |
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115 | printf("Called bar successfully\n"); |
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116 | } |
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117 | |
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118 | void foo_catch_block() { |
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119 | printf("Exception caught\n"); |
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120 | } |
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121 | |
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122 | //Actual call to the try block |
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123 | try( foo_try_block, foo_catch_block ); |
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124 | |
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125 | printf( "Foo exited normally\n" ); |
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126 | } |
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127 | |
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128 | int main() { |
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129 | raii_t a = { "Main dtor" }; |
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130 | |
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131 | foo(); |
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132 | |
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133 | printf("End of program reached\n"); |
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134 | } |
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