source: src/libcfa/exception.c @ 86d5ba7c

aaron-thesisarm-ehcleanup-dtorsdeferred_resndemanglerjacob/cs343-translationjenkins-sandboxnew-astnew-ast-unique-exprnew-envno_listpersistent-indexerresolv-newwith_gc
Last change on this file since 86d5ba7c was 86d5ba7c, checked in by Andrew Beach <ajbeach@…>, 4 years ago

Added the memory management calls to the exception control flow.

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1//
2// Cforall Version 1.0.0 Copyright (C) 2016 University of Waterloo
3//
4// The contents of this file are covered under the licence agreement in the
5// file "LICENCE" distributed with Cforall.
6//
7// exception.c --
8//
9// Author           : Andrew Beach
10// Created On       : Mon Jun 26 15:13:00 2017
11// Last Modified By : Andrew Beach
12// Last Modified On : Fri Jul 28 12:41:00 2017
13// Update Count     : 3
14//
15
16#include "exception.h"
17
18// Implementation of the secret header.
19
20#include <stdlib.h>
21#include <stdio.h>
22#include <unwind.h>
23
24// FIX ME: temporary hack to keep ARM build working
25#ifndef _URC_FATAL_PHASE1_ERROR
26#define _URC_FATAL_PHASE1_ERROR 2
27#endif // ! _URC_FATAL_PHASE1_ERROR
28#ifndef _URC_FATAL_PHASE2_ERROR
29#define _URC_FATAL_PHASE2_ERROR 2
30#endif // ! _URC_FATAL_PHASE2_ERROR
31
32#include "lsda.h"
33
34// Temperary global exception context. Does not work with concurency.
35struct exception_context_t {
36    struct __cfaehm__try_resume_node * top_resume;
37    struct __cfaehm__try_resume_node * current_resume;
38
39    exception * current_exception;
40    int current_handler_index;
41
42        // Storage to avoid using the heap for exceptions.
43        exception built_in_storage;
44} shared_stack = {NULL, NULL, 0, 0, 0};
45
46// Get the current exception context.
47// There can be a single global until multithreading occurs, then each stack
48// needs its own. It will have to be updated to handle that.
49struct exception_context_t * this_exception_context() {
50        return &shared_stack;
51}
52//#define SAVE_EXCEPTION_CONTEXT(to_name)
53//struct exception_context_t * to_name = this_exception_context();
54//exception * this_exception() {
55//    return this_exception_context()->current_exception;
56//}
57
58
59// This macro should be the only thing that needs to change across machines.  Used in the personality function, way down
60// in termination.
61// struct _Unwind_Context * -> _Unwind_Reason_Code(*)(exception *)
62#define MATCHER_FROM_CONTEXT(ptr_to_context) \
63        (*(_Unwind_Reason_Code(**)(exception*))(_Unwind_GetCFA(ptr_to_context) + 8))
64
65
66// RESUMPTION ================================================================
67
68void __cfaehm__throw_resume(exception * except) {
69
70        // DEBUG
71        printf("Throwing resumption exception %d\n", *except);
72
73        struct __cfaehm__try_resume_node * original_head = shared_stack.current_resume;
74        struct __cfaehm__try_resume_node * current =
75                (original_head) ? original_head->next : shared_stack.top_resume;
76
77        for ( ; current ; current = current->next) {
78                shared_stack.current_resume = current;
79                if (current->handler(except)) {
80                        shared_stack.current_resume = original_head;
81                        return;
82                }
83        }
84
85        printf("Unhandled exception %d\n", *except);
86        shared_stack.current_resume = original_head;
87
88        // Fall back to termination:
89        __cfaehm__throw_terminate(except);
90        // TODO: Default handler for resumption.
91}
92
93// Do we control where exceptions get thrown even with concurency?  If not these are not quite thread safe, the cleanup
94// hook has to be added after the node is built but before it is made the top node.
95
96void __cfaehm__try_resume_setup(struct __cfaehm__try_resume_node * node,
97                        int (*handler)(exception * except)) {
98        node->next = shared_stack.top_resume;
99        node->handler = handler;
100        shared_stack.top_resume = node;
101}
102
103void __cfaehm__try_resume_cleanup(struct __cfaehm__try_resume_node * node) {
104        shared_stack.top_resume = node->next;
105}
106
107
108// TERMINATION ===============================================================
109
110// MEMORY MANAGEMENT (still for integers)
111// May have to move to cfa for constructors and destructors.
112
113// Creates a copy of the indicated exception and sets current_exception to it.
114static void __cfaehm__allocate_exception( exception * except ) {
115        struct exception_context_t * context = this_exception_context();
116
117        // Try to use the context's store, otherwise use the heap.
118        if ( 0 == context->built_in_storage ) {
119                context->current_exception = &context->built_in_storage;
120        } else {
121                exception * new_copy = malloc( sizeof( exception/*int*/ ) );
122                if ( ! new_copy ) {
123                        // Failure: cannot allocate exception. Terminate thread.
124                        exit(1); // <- thread or program?
125                }
126                context->current_exception = new_copy;
127        }
128
129        // Copy the exception to storage.
130        *context->current_exception = *except;
131}
132
133// Delete the provided exception, unsetting current_exception if relivant.
134static void __cfaehm__delete_exception( exception * except ) {
135        struct exception_context_t * context = this_exception_context();
136
137        // DEBUG
138        printf( "Deleting Exception %d (%s)\n", *except,
139                (&context->built_in_storage == except) ? "builtin" : "dynamic" );
140
141        if ( context->current_exception == except ) {
142                // TODO: This should restore it to the last exception.
143                context->current_exception = NULL;
144        }
145        if ( &context->built_in_storage == except ) {
146                // You can't throw the exception '0'.
147                context->built_in_storage = 0;
148        } else {
149                // Only secondary or too large exceptions are thrown.
150                free( except );
151        }
152}
153
154// If this isn't a rethrow (*except==0), delete the provided exception.
155void __cfaehm__cleanup_terminate( exception ** except ) {
156        if ( *except ) __cfaehm__delete_exception( *except );
157}
158
159
160// We need a piece of storage to raise the exception
161struct _Unwind_Exception this_exception_storage;
162
163// Function needed by force unwind
164// It basically says to unwind the whole stack and then exit when we reach the end of the stack
165static _Unwind_Reason_Code _Stop_Fn(
166                int version,
167                _Unwind_Action actions,
168                _Unwind_Exception_Class exceptionClass,
169                struct _Unwind_Exception * unwind_exception,
170                struct _Unwind_Context * context,
171                void * some_param) {
172        if( actions & _UA_END_OF_STACK  ) exit(1);
173        if( actions & _UA_CLEANUP_PHASE ) return _URC_NO_REASON;
174
175        return _URC_FATAL_PHASE2_ERROR;
176}
177
178// The exception that is being thrown must already be stored.
179__attribute__((noreturn)) void __cfaehm__begin_unwind(void) {
180        if ( ! this_exception_context()->current_exception ) {
181                printf("UNWIND ERROR missing exception in begin unwind\n");
182                abort();
183        }
184
185
186        // Call stdlibc to raise the exception
187        _Unwind_Reason_Code ret = _Unwind_RaiseException( &this_exception_storage );
188
189        // If we reach here it means something happened.  For resumption to work we need to find a way to return back to
190        // here.  Most of them will probably boil down to setting a global flag and making the phase 1 either stop or
191        // fail.  Causing an error on purpose may help avoiding unnecessary work but it might have some weird side
192        // effects.  If we just pretend no handler was found that would work but may be expensive for no reason since we
193        // will always search the whole stack.
194
195        if( ret == _URC_END_OF_STACK ) {
196                // No proper handler was found.  This can be handled in several way.  C++ calls std::terminate Here we
197                // force unwind the stack, basically raising a cancellation.
198                printf("Uncaught exception %p\n", &this_exception_storage);
199
200                ret = _Unwind_ForcedUnwind( &this_exception_storage, _Stop_Fn, (void*)0x22 );
201                printf("UNWIND ERROR %d after force unwind\n", ret);
202                abort();
203        }
204
205        // We did not simply reach the end of the stack without finding a handler.  Something wen't wrong
206        printf("UNWIND ERROR %d after raise exception\n", ret);
207        abort();
208}
209
210void __cfaehm__throw_terminate( exception * val ) {
211        // DEBUG
212        printf("Throwing termination exception\n");
213
214        __cfaehm__allocate_exception( val );
215        __cfaehm__begin_unwind();
216}
217
218void __cfaehm__rethrow_terminate(void) {
219        // DEBUG
220        printf("Rethrowing termination exception\n");
221
222        __cfaehm__begin_unwind();
223}
224
225// This is our personality routine.  For every stack frame anotated with ".cfi_personality 0x3,__gcfa_personality_v0".
226// This function will be called twice when unwinding.  Once in the search phased and once in the cleanup phase.
227_Unwind_Reason_Code __gcfa_personality_v0 (
228                int version, _Unwind_Action actions, unsigned long long exceptionClass,
229                struct _Unwind_Exception* unwind_exception,
230                struct _Unwind_Context* context)
231{
232
233        // DEBUG
234        //printf("CFA: 0x%lx\n", _Unwind_GetCFA(context));
235        printf("Personality function (%d, %x, %llu, %p, %p):", version, actions, exceptionClass, unwind_exception, context);
236
237        // If we've reached the end of the stack then there is nothing much we can do...
238        if( actions & _UA_END_OF_STACK ) return _URC_END_OF_STACK;
239
240        // DEBUG
241        if (actions & _UA_SEARCH_PHASE) {
242                printf(" lookup phase");
243        }
244        // DEBUG
245        else if (actions & _UA_CLEANUP_PHASE) {
246                printf(" cleanup phase");
247        }
248        // Just in case, probably can't actually happen
249        else {
250                printf(" error\n");
251                return _URC_FATAL_PHASE1_ERROR;
252        }
253
254        // Get a pointer to the language specific data from which we will read what we need
255        const unsigned char * lsd = (const unsigned char*) _Unwind_GetLanguageSpecificData( context );
256
257        if( !lsd ) {    //Nothing to do, keep unwinding
258                printf(" no LSD");
259                goto UNWIND;
260        }
261
262        // Get the instuction pointer and a reading pointer into the exception table
263        lsda_header_info lsd_info;
264        const unsigned char * cur_ptr = parse_lsda_header( context, lsd, &lsd_info);
265        _Unwind_Ptr instruction_ptr = _Unwind_GetIP( context );
266
267        // Linearly search the table for stuff to do
268        while( cur_ptr < lsd_info.action_table ) {
269                _Unwind_Ptr callsite_start;
270                _Unwind_Ptr callsite_len;
271                _Unwind_Ptr callsite_landing_pad;
272                _uleb128_t  callsite_action;
273
274                // Decode the common stuff we have in here
275                cur_ptr = read_encoded_value (0, lsd_info.call_site_encoding, cur_ptr, &callsite_start);
276                cur_ptr = read_encoded_value (0, lsd_info.call_site_encoding, cur_ptr, &callsite_len);
277                cur_ptr = read_encoded_value (0, lsd_info.call_site_encoding, cur_ptr, &callsite_landing_pad);
278                cur_ptr = read_uleb128 (cur_ptr, &callsite_action);
279
280                // Have we reach the correct frame info yet?
281                if( lsd_info.Start + callsite_start + callsite_len < instruction_ptr ) {
282                        //DEBUG BEGIN
283                        void * ls = (void*)lsd_info.Start;
284                        void * cs = (void*)callsite_start;
285                        void * cl = (void*)callsite_len;
286                        void * bp = (void*)lsd_info.Start + callsite_start;
287                        void * ep = (void*)lsd_info.Start + callsite_start + callsite_len;
288                        void * ip = (void*)instruction_ptr;
289                        printf("\nfound %p - %p (%p, %p, %p), looking for %p\n", bp, ep, ls, cs, cl, ip);
290                        //DEBUG END
291                        continue;
292                }
293
294                // Have we gone too far
295                if( lsd_info.Start + callsite_start > instruction_ptr ) {
296                        printf(" gone too far");
297                        break;
298                }
299
300                // Something to do?
301                if( callsite_landing_pad ) {
302                        // Which phase are we in
303                        if (actions & _UA_SEARCH_PHASE) {
304                                // Search phase, this means we probably found a potential handler and must check if it is a match
305
306                                // If we have arbitrarily decided that 0 means nothing to do and 1 means there is a potential handler
307                                // This doesn't seem to conflict the gcc default behavior
308                                if (callsite_action != 0) {
309                                        // Now we want to run some code to see if the handler matches
310                                        // This is the tricky part where we want to the power to run arbitrary code
311                                        // However, generating a new exception table entry and try routine every time
312                                        // is way more expansive than we might like
313                                        // The information we have is :
314                                        //  - The GR (Series of registers)
315                                        //    GR1=GP Global Pointer of frame ref by context
316                                        //  - The instruction pointer
317                                        //  - The instruction pointer info (???)
318                                        //  - The CFA (Canonical Frame Address)
319                                        //  - The BSP (Probably the base stack pointer)
320
321
322                                        // The current apprach uses one exception table entry per try block
323                                        _uleb128_t imatcher;
324                                        // Get the relative offset to the
325                                        cur_ptr = read_uleb128 (cur_ptr, &imatcher);
326
327                                        // Get a function pointer from the relative offset and call it
328                                        // _Unwind_Reason_Code (*matcher)() = (_Unwind_Reason_Code (*)())lsd_info.LPStart + imatcher;                                   
329
330                                        _Unwind_Reason_Code (*matcher)(exception *) =
331                                                MATCHER_FROM_CONTEXT(context);
332                                        int index = matcher(shared_stack.current_exception);
333                                        _Unwind_Reason_Code ret = (0 == index)
334                                                ? _URC_CONTINUE_UNWIND : _URC_HANDLER_FOUND;
335                                        shared_stack.current_handler_index = index;
336
337                                        // Based on the return value, check if we matched the exception
338                                        if( ret == _URC_HANDLER_FOUND) printf(" handler found\n");
339                                        else printf(" no handler\n");
340                                        return ret;
341                                }
342
343                                // This is only a cleanup handler, ignore it
344                                printf(" no action");
345                        }
346                        else if (actions & _UA_CLEANUP_PHASE) {
347
348                                if( (callsite_action != 0) && !(actions & _UA_HANDLER_FRAME) ){
349                                        // If this is a potential exception handler
350                                        // but not the one that matched the exception in the seach phase,
351                                        // just ignore it
352                                        goto UNWIND;
353                                }
354
355                                // We need to run some clean-up or a handler
356                                // These statment do the right thing but I don't know any specifics at all
357                                _Unwind_SetGR( context, __builtin_eh_return_data_regno(0), (_Unwind_Ptr) unwind_exception );
358                                _Unwind_SetGR( context, __builtin_eh_return_data_regno(1), 0 );
359
360                                // I assume this sets the instruction pointer to the adress of the landing pad
361                                // It doesn't actually set it, it only state the value that needs to be set once we return _URC_INSTALL_CONTEXT
362                                _Unwind_SetIP( context, ((lsd_info.LPStart) + (callsite_landing_pad)) );
363
364                                // DEBUG
365                                printf(" action\n");
366
367                                // Return have some action to run
368                                return _URC_INSTALL_CONTEXT;
369                        }
370                }
371
372                // Nothing to do, move along
373                printf(" no landing pad");
374        }
375        // No handling found
376        printf(" table end reached\n");
377
378        // DEBUG
379        UNWIND:
380        printf(" unwind\n");
381
382        // Keep unwinding the stack
383        return _URC_CONTINUE_UNWIND;
384}
385
386// Try statements are hoisted out see comments for details.  With this could probably be unique and simply linked from
387// libcfa but there is one problem left, see the exception table for details
388__attribute__((noinline))
389void __cfaehm__try_terminate(void (*try_block)(),
390                void (*catch_block)(int index, exception * except),
391                __attribute__((unused)) int (*match_block)(exception * except)) {
392        //! volatile int xy = 0;
393        //! printf("%p %p %p %p\n", &try_block, &catch_block, &match_block, &xy);
394
395        // Setup statments: These 2 statments won't actually result in any code, they only setup global tables.
396        // However, they clobber gcc cancellation support from gcc.  We can replace the personality routine but
397        // replacing the exception table gcc generates is not really doable, it generates labels based on how the
398        // assembly works.
399
400        // Setup the personality routine
401        asm volatile (".cfi_personality 0x3,__gcfa_personality_v0");
402        // Setup the exception table
403        asm volatile (".cfi_lsda 0x3, .LLSDACFA2");
404
405        // Label which defines the start of the area for which the handler is setup.
406        asm volatile (".TRYSTART:");
407
408        // The actual statements of the try blocks
409        try_block();
410
411        // asm statement to prevent deadcode removal
412        asm volatile goto ("" : : : : CATCH );
413
414        // Normal return
415        return;
416
417        // Exceptionnal path
418        CATCH : __attribute__(( unused ));
419        // Label which defines the end of the area for which the handler is setup.
420        asm volatile (".TRYEND:");
421        // Label which defines the start of the exception landing pad.  Basically what is called when the exception is
422        // caught.  Note, if multiple handlers are given, the multiplexing should be done by the generated code, not the
423        // exception runtime.
424        asm volatile (".CATCH:");
425
426        // Exception handler
427        catch_block( shared_stack.current_handler_index,
428                     shared_stack.current_exception );
429}
430
431// Exception table data we need to generate.  While this is almost generic, the custom data refers to foo_try_match try
432// match, which is no way generic.  Some more works need to be done if we want to have a single call to the try routine.
433
434#if defined( __x86_64__ ) || defined( __i386__ )
435asm (
436        //HEADER
437        ".LFECFA1:\n"
438        "       .globl  __gcfa_personality_v0\n"
439        "       .section        .gcc_except_table,\"a\",@progbits\n"
440        ".LLSDACFA2:\n"                                                 //TABLE header
441        "       .byte   0xff\n"
442        "       .byte   0xff\n"
443        "       .byte   0x1\n"
444        "       .uleb128 .LLSDACSECFA2-.LLSDACSBCFA2\n"         // BODY length
445        // Body uses language specific data and therefore could be modified arbitrarily
446        ".LLSDACSBCFA2:\n"                                              // BODY start
447        "       .uleb128 .TRYSTART-__cfaehm__try_terminate\n"           // Handled area start  (relative to start of function)
448        "       .uleb128 .TRYEND-.TRYSTART\n"                           // Handled area length
449        "       .uleb128 .CATCH-__cfaehm__try_terminate\n"                              // Hanlder landing pad adress  (relative to start of function)
450        "       .uleb128 1\n"                                           // Action code, gcc seems to use always 0
451        ".LLSDACSECFA2:\n"                                              // BODY end
452        "       .text\n"                                                        // TABLE footer
453        "       .size   __cfaehm__try_terminate, .-__cfaehm__try_terminate\n"
454        "       .ident  \"GCC: (Ubuntu 6.2.0-3ubuntu11~16.04) 6.2.0 20160901\"\n"
455//      "       .section        .note.GNU-stack,\"x\",@progbits\n"
456);
457#endif // __x86_64__ || __i386__
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