source: doc/working/exception/impl/main.c @ 88e0080

aaron-thesisarm-ehcleanup-dtorsdeferred_resndemanglerjacob/cs343-translationjenkins-sandboxnew-astnew-ast-unique-exprnew-envno_listpersistent-indexerresolv-newwith_gc
Last change on this file since 88e0080 was 88e0080, checked in by Andrew Beach <ajbeach@…>, 4 years ago

Added a file with notes about the new exception design.

  • Property mode set to 100644
File size: 3.9 KB
Line 
1#include <stdio.h>
2#include "except.h"
3
4#define EXCEPTION 2
5
6struct type_raii_t {
7        char * msg;
8};
9
10//Dtor function to test clean up routines
11void dtor( struct type_raii_t * this ) {
12        printf("%s\n", this->msg);
13}
14
15//Type macro use to make scope unwinding easier to see.
16#define raii_t __attribute__(( cleanup(dtor) )) struct type_raii_t
17
18//Leaf functions that raises exception
19void bar() {
20        raii_t a = { "Bar dtor" };
21
22        throw( EXCEPTION );
23}
24
25//Matcher function which will check if the exception was correctly caught
26extern int this_exception;
27_Unwind_Reason_Code foo_try_match() {
28        return this_exception == 3 ? _URC_HANDLER_FOUND : _URC_CONTINUE_UNWIND;
29}
30
31//Try statements are hoisted out see comments for details
32//With this could probably be unique and simply linked from
33//libcfa but there is one problem left, see the exception table
34//for details
35void try( void (*try_block)(), void (*catch_block)() )
36{
37        //Setup statments
38        //These 2 statments won't actually result in any code,
39        //they only setup global tables.
40        //However, they clobber gcc cancellation support from gcc.
41        //We can replace the personality routine but replacing the exception
42        //table gcc generates is not really doable, it generates labels based
43        //on how the assembly works.
44        //Setup the personality routine
45        asm volatile (".cfi_personality 0x3,__gcfa_personality_v0");
46        //Setup the exception table
47        asm volatile (".cfi_lsda 0x3, .LLSDACFA2");
48
49        //Label which defines the start of the area for which the handler is setup
50        asm volatile (".TRYSTART:");
51
52        //The actual statements of the try blocks
53        try_block();
54
55        //asm statement to prevent deadcode removal
56        asm volatile goto ("" : : : : CATCH );
57
58        //Normal return
59        return;
60
61        //Exceptionnal path
62        CATCH : __attribute__(( unused ));
63        //Label which defines the end of the area for which the handler is setup
64        asm volatile (".TRYEND:");
65        //Label which defines the start of the exception landing pad
66        //basically what will be called when the exception is caught
67        //Note, if multiple handlers are given, the multiplexing should be done
68        //by the generated code, not the exception runtime
69        asm volatile (".CATCH:");
70
71        //Exception handler
72        catch_block();
73}
74
75//Exception table data we need to generate
76//While this is almost generic, the custom data refers to
77//foo_try_match try match, which is no way generic
78//Some more works need to be done if we want to have a single
79//call to the try routine
80asm (
81        //HEADER
82        ".LFECFA1:\n"
83        "       .globl  __gcfa_personality_v0\n"
84        "       .section        .gcc_except_table,\"a\",@progbits\n"
85        ".LLSDACFA2:\n"                                                 //TABLE header
86        "       .byte   0xff\n"
87        "       .byte   0xff\n"
88        "       .byte   0x1\n"
89        "       .uleb128 .LLSDACSECFA2-.LLSDACSBCFA2\n"         //BODY length
90        //Body uses language specific data and therefore could be modified arbitrarily
91        ".LLSDACSBCFA2:\n"                                              //BODY start
92        "       .uleb128 .TRYSTART-try\n"                               //Handled area start  (relative to start of function)
93        "       .uleb128 .TRYEND-.TRYSTART\n"                           //Handled area length
94        "       .uleb128 .CATCH-try\n"                          //Hanlder landing pad adress  (relative to start of function)
95        "       .uleb128 1\n"                                           //Action code, gcc seems to use always 0
96        //Beyond this point we don't match gcc data'
97        "       .uleb128 foo_try_match-try\n"                   //Handler routine to check if the exception is matched
98        ".LLSDACSECFA2:\n"                                              //BODY end
99        "       .text\n"                                                        //TABLE footer
100        "       .size   try, .-try\n"
101        "       .ident  \"GCC: (Ubuntu 6.2.0-3ubuntu11~16.04) 6.2.0 20160901\"\n"
102        "       .section        .note.GNU-stack,\"x\",@progbits\n"
103);
104
105void foo() {
106        raii_t a = { "Foo dtor" };
107
108        //Since try will clobber the gcc exception table assembly,
109        //We need to nest this to have gcc regenerate the data
110        void foo_try_block() {
111                raii_t b = { "Foo try dtor" };
112
113                bar();
114
115                printf("Called bar successfully\n");
116        }
117
118        void foo_catch_block() {
119                printf("Exception caught\n");
120        }
121
122        //Actual call to the try block
123        try( foo_try_block, foo_catch_block );
124
125        printf( "Foo exited normally\n" );
126}
127
128int main() {
129        raii_t a = { "Main dtor" };
130
131        foo();
132
133        printf("End of program reached\n");
134}
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