source: libcfa/src/exception.c @ 851fd92

arm-ehjacob/cs343-translationnew-astnew-ast-unique-expr
Last change on this file since 851fd92 was 851fd92, checked in by Andrew Beach <ajbeach@…>, 18 months ago

The requested addition of groups to debug printing. Tested in exception.c.

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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 : Tue Apr 14 12:01:00 2020
13// Update Count     : 18
14//
15
16// Normally we would get this from the CFA prelude.
17#include <stddef.h> // for size_t
18
19#include "exception.h"
20
21// Implementation of the secret header is hardware dependent.
22#if !( defined( __x86_64 ) || defined( __i386 ) )
23#error Exception Handling: No known architecture detected.
24#endif
25
26#include <stdlib.h>
27#include <stdio.h>
28#include <unwind.h>
29#include <bits/debug.hfa>
30#include "stdhdr/assert.h"
31
32// FIX ME: temporary hack to keep ARM build working
33#ifndef _URC_FATAL_PHASE1_ERROR
34#define _URC_FATAL_PHASE1_ERROR 3
35#endif // ! _URC_FATAL_PHASE1_ERROR
36#ifndef _URC_FATAL_PHASE2_ERROR
37#define _URC_FATAL_PHASE2_ERROR 2
38#endif // ! _URC_FATAL_PHASE2_ERROR
39
40#include "lsda.h"
41
42/* The exception class for our exceptions. Because of the vendor component
43 * its value would not be standard.
44 * Vendor: UWPL
45 * Language: CFA\0
46 */
47const _Unwind_Exception_Class __cfaehm_exception_class = 0x4c50575500414643;
48
49// Base exception vtable is abstract, you should not have base exceptions.
50struct __cfaehm_base_exception_t_vtable
51                ___cfaehm_base_exception_t_vtable_instance = {
52        .parent = NULL,
53        .size = 0,
54        .copy = NULL,
55        .free = NULL,
56        .msg = NULL
57};
58
59
60// Temperary global exception context. Does not work with concurency.
61struct exception_context_t {
62        struct __cfaehm_try_resume_node * top_resume;
63
64        exception_t * current_exception;
65        int current_handler_index;
66} static shared_stack = {NULL, NULL, 0};
67
68// Get the current exception context.
69// There can be a single global until multithreading occurs, then each stack
70// needs its own. It will have to be updated to handle that.
71struct exception_context_t * this_exception_context() {
72        return &shared_stack;
73}
74
75
76// RESUMPTION ================================================================
77
78static void reset_top_resume(struct __cfaehm_try_resume_node ** store) {
79        this_exception_context()->top_resume = *store;
80}
81
82void __cfaehm_throw_resume(exception_t * except) {
83        struct exception_context_t * context = this_exception_context();
84
85        __cfadbg_print_safe(exception, "Throwing resumption exception\n");
86
87        __attribute__((cleanup(reset_top_resume)))
88        struct __cfaehm_try_resume_node * original_head = context->top_resume;
89        struct __cfaehm_try_resume_node * current = context->top_resume;
90
91        for ( ; current ; current = current->next) {
92                context->top_resume = current->next;
93                if (current->handler(except)) {
94                        return;
95                }
96        }
97
98        __cfadbg_print_safe(exception, "Unhandled exception\n");
99
100        // Fall back to termination:
101        __cfaehm_throw_terminate(except);
102        // TODO: Default handler for resumption.
103}
104
105// Do we control where exceptions get thrown even with concurency?
106// If not these are not quite thread safe, the cleanup hook has to
107// be added after the node is built but before it is made the top node.
108
109void __cfaehm_try_resume_setup(struct __cfaehm_try_resume_node * node,
110                        _Bool (*handler)(exception_t * except)) {
111        struct exception_context_t * context = this_exception_context();
112        node->next = context->top_resume;
113        node->handler = handler;
114        context->top_resume = node;
115}
116
117void __cfaehm_try_resume_cleanup(struct __cfaehm_try_resume_node * node) {
118        struct exception_context_t * context = this_exception_context();
119        context->top_resume = node->next;
120}
121
122
123// TERMINATION ===============================================================
124
125// MEMORY MANAGEMENT (still for integers)
126// May have to move to cfa for constructors and destructors (references).
127
128// How to clean up an exception in various situations.
129static void __cfaehm_exception_cleanup(
130                _Unwind_Reason_Code reason,
131                struct _Unwind_Exception * exception) {
132        switch (reason) {
133        case _URC_FOREIGN_EXCEPTION_CAUGHT:
134                // This one we could clean-up to allow cross-language exceptions.
135        case _URC_FATAL_PHASE1_ERROR:
136        case _URC_FATAL_PHASE2_ERROR:
137        default:
138                abort();
139        }
140}
141
142// We need a piece of storage to raise the exception, for now its a single
143// piece.
144static struct _Unwind_Exception this_exception_storage;
145
146struct __cfaehm_node {
147        struct __cfaehm_node * next;
148};
149
150#define NODE_TO_EXCEPT(node) ((exception_t *)(1 + (node)))
151#define EXCEPT_TO_NODE(except) ((struct __cfaehm_node *)(except) - 1)
152
153// Creates a copy of the indicated exception and sets current_exception to it.
154static void __cfaehm_allocate_exception( exception_t * except ) {
155        struct exception_context_t * context = this_exception_context();
156
157        // Allocate memory for the exception.
158        struct __cfaehm_node * store = malloc(
159                sizeof( struct __cfaehm_node ) + except->virtual_table->size );
160
161        if ( ! store ) {
162                // Failure: cannot allocate exception. Terminate thread.
163                abort(); // <- Although I think it might be the process.
164        }
165
166        // Add the node to the list:
167        store->next = EXCEPT_TO_NODE(context->current_exception);
168        context->current_exception = NODE_TO_EXCEPT(store);
169
170        // Copy the exception to storage.
171        except->virtual_table->copy( context->current_exception, except );
172
173        // Set up the exception storage.
174        this_exception_storage.exception_class = __cfaehm_exception_class;
175        this_exception_storage.exception_cleanup = __cfaehm_exception_cleanup;
176}
177
178// Delete the provided exception, unsetting current_exception if relivant.
179static void __cfaehm_delete_exception( exception_t * except ) {
180        struct exception_context_t * context = this_exception_context();
181
182        __cfadbg_print_safe(exception, "Deleting Exception\n");
183
184        // Remove the exception from the list.
185        struct __cfaehm_node * to_free = EXCEPT_TO_NODE(except);
186        struct __cfaehm_node * node;
187
188        if ( context->current_exception == except ) {
189                node = to_free->next;
190                context->current_exception = (node) ? NODE_TO_EXCEPT(node) : 0;
191        } else {
192                node = EXCEPT_TO_NODE(context->current_exception);
193                // It may always be in the first or second position.
194                while ( to_free != node->next ) {
195                        node = node->next;
196                }
197                node->next = to_free->next;
198        }
199
200        // Free the old exception node.
201        except->virtual_table->free( except );
202        free( to_free );
203}
204
205// If this isn't a rethrow (*except==0), delete the provided exception.
206void __cfaehm_cleanup_terminate( void * except ) {
207        if ( *(void**)except ) __cfaehm_delete_exception( *(exception_t **)except );
208}
209
210// Function needed by force unwind
211// It basically says to unwind the whole stack and then exit when we reach the end of the stack
212static _Unwind_Reason_Code _Stop_Fn(
213                int version,
214                _Unwind_Action actions,
215                _Unwind_Exception_Class exception_class,
216                struct _Unwind_Exception * unwind_exception,
217                struct _Unwind_Context * unwind_context,
218                void * stop_param) {
219        // Verify actions follow the rules we expect.
220        verify((actions & _UA_CLEANUP_PHASE) && (actions & _UA_FORCE_UNWIND));
221        verify(!(actions & (_UA_SEARCH_PHASE | _UA_HANDER_FRAME)));
222
223        if ( actions & _UA_END_OF_STACK ) {
224                exit(1);
225        } else {
226                return _URC_NO_REASON;
227        }
228}
229
230// The exception that is being thrown must already be stored.
231static __attribute__((noreturn)) void __cfaehm_begin_unwind(void) {
232        if ( ! this_exception_context()->current_exception ) {
233                printf("UNWIND ERROR missing exception in begin unwind\n");
234                abort();
235        }
236
237        // Call stdlibc to raise the exception
238        _Unwind_Reason_Code ret = _Unwind_RaiseException( &this_exception_storage );
239
240        // If we reach here it means something happened. For resumption to work we need to find a way
241        // to return back to here. Most of them will probably boil down to setting a global flag and
242        // making the phase 1 either stop or fail. Causing an error on purpose may help avoiding
243        // unnecessary work but it might have some weird side effects. If we just pretend no handler
244        // was found that would work but may be expensive for no reason since we will always search
245        // the whole stack.
246
247        if ( ret == _URC_END_OF_STACK ) {
248                // No proper handler was found. This can be handled in many ways, C++ calls std::terminate.
249                // Here we force unwind the stack, basically raising a cancellation.
250                printf("Uncaught exception %p\n", &this_exception_storage);
251
252                ret = _Unwind_ForcedUnwind( &this_exception_storage, _Stop_Fn, (void*)0x22 );
253                printf("UNWIND ERROR %d after force unwind\n", ret);
254                abort();
255        }
256
257        // We did not simply reach the end of the stack without finding a handler. This is an error.
258        printf("UNWIND ERROR %d after raise exception\n", ret);
259        abort();
260}
261
262void __cfaehm_throw_terminate( exception_t * val ) {
263        __cfadbg_print_safe(exception, "Throwing termination exception\n");
264
265        __cfaehm_allocate_exception( val );
266        __cfaehm_begin_unwind();
267}
268
269void __cfaehm_rethrow_terminate(void) {
270        __cfadbg_print_safe(exception, "Rethrowing termination exception\n");
271
272        __cfaehm_begin_unwind();
273}
274
275// This is our personality routine. For every stack frame annotated with
276// ".cfi_personality 0x3,__gcfa_personality_v0" this function will be called twice when unwinding.
277//  Once in the search phase and once in the cleanup phase.
278_Unwind_Reason_Code __gcfa_personality_v0(
279                int version,
280                _Unwind_Action actions,
281                unsigned long long exception_class,
282                struct _Unwind_Exception * unwind_exception,
283                struct _Unwind_Context * unwind_context)
284{
285
286        //__cfadbg_print_safe(exception, "CFA: 0x%lx\n", _Unwind_GetCFA(context));
287        __cfadbg_print_safe(exception, "Personality function (%d, %x, %llu, %p, %p):",
288                        version, actions, exception_class, unwind_exception, unwind_context);
289
290        // Verify that actions follow the rules we expect.
291        // This function should never be called at the end of the stack.
292        verify(!(actions & _UA_END_OF_STACK));
293        // Either only the search phase flag is set or...
294        if (actions & _UA_SEARCH_PHASE) {
295                verify(actions == _UA_SEARCH_PHASE);
296                __cfadbg_print_safe(exception, " lookup phase");
297        // ... we are in clean-up phase.
298        } else {
299                verify(actions & _UA_CLEANUP_PHASE);
300                __cfadbg_print_safe(exception, " cleanup phase");
301                // We shouldn't be the handler frame during forced unwind.
302                if (actions & _UA_HANDLER_FRAME) {
303                        verify(!(actions & _UA_FORCE_UNWIND));
304                        __cfadbg_print_safe(exception, " (handler frame)");
305                } else if (actions & _UA_FORCE_UNWIND) {
306                        __cfadbg_print_safe(exception, " (force unwind)");
307                }
308        }
309
310        // Get a pointer to the language specific data from which we will read what we need
311        const unsigned char * lsd = _Unwind_GetLanguageSpecificData( unwind_context );
312
313        if ( !lsd ) {   //Nothing to do, keep unwinding
314                printf(" no LSD");
315                goto UNWIND;
316        }
317
318        // Get the instuction pointer and a reading pointer into the exception table
319        lsda_header_info lsd_info;
320        const unsigned char * cur_ptr = parse_lsda_header(unwind_context, lsd, &lsd_info);
321        _Unwind_Ptr instruction_ptr = _Unwind_GetIP(unwind_context);
322
323        struct exception_context_t * context = this_exception_context();
324
325        // Linearly search the table for stuff to do
326        while ( cur_ptr < lsd_info.action_table ) {
327                _Unwind_Ptr callsite_start;
328                _Unwind_Ptr callsite_len;
329                _Unwind_Ptr callsite_landing_pad;
330                _uleb128_t  callsite_action;
331
332                // Decode the common stuff we have in here
333                cur_ptr = read_encoded_value(0, lsd_info.call_site_encoding, cur_ptr, &callsite_start);
334                cur_ptr = read_encoded_value(0, lsd_info.call_site_encoding, cur_ptr, &callsite_len);
335                cur_ptr = read_encoded_value(0, lsd_info.call_site_encoding, cur_ptr, &callsite_landing_pad);
336                cur_ptr = read_uleb128(cur_ptr, &callsite_action);
337
338                // Have we reach the correct frame info yet?
339                if ( lsd_info.Start + callsite_start + callsite_len < instruction_ptr ) {
340#ifdef __CFA_DEBUG_PRINT__
341                        void * ls = (void*)lsd_info.Start;
342                        void * cs = (void*)callsite_start;
343                        void * cl = (void*)callsite_len;
344                        void * bp = (void*)lsd_info.Start + callsite_start;
345                        void * ep = (void*)lsd_info.Start + callsite_start + callsite_len;
346                        void * ip = (void*)instruction_ptr;
347                        __cfadbg_print_safe(exception, "\nfound %p - %p (%p, %p, %p), looking for %p\n",
348                                        bp, ep, ls, cs, cl, ip);
349#endif // __CFA_DEBUG_PRINT__
350                        continue;
351                }
352
353                // Have we gone too far?
354                if ( lsd_info.Start + callsite_start > instruction_ptr ) {
355                        printf(" gone too far");
356                        break;
357                }
358
359                // Check for what we must do:
360                if ( 0 == callsite_landing_pad ) {
361                        // Nothing to do, move along
362                        __cfadbg_print_safe(exception, " no landing pad");
363                } else if (actions & _UA_SEARCH_PHASE) {
364                        // In search phase, these means we found a potential handler we must check.
365
366                        // We have arbitrarily decided that 0 means nothing to do and 1 means there is
367                        // a potential handler. This doesn't seem to conflict the gcc default behavior.
368                        if (callsite_action != 0) {
369                                // Now we want to run some code to see if the handler matches
370                                // This is the tricky part where we want to the power to run arbitrary code
371                                // However, generating a new exception table entry and try routine every time
372                                // is way more expansive than we might like
373                                // The information we have is :
374                                //  - The GR (Series of registers)
375                                //    GR1=GP Global Pointer of frame ref by context
376                                //  - The instruction pointer
377                                //  - The instruction pointer info (???)
378                                //  - The CFA (Canonical Frame Address)
379                                //  - The BSP (Probably the base stack pointer)
380
381                                // The current apprach uses one exception table entry per try block
382                                _uleb128_t imatcher;
383                                // Get the relative offset to the {...}?
384                                cur_ptr = read_uleb128(cur_ptr, &imatcher);
385
386#                               if defined( __x86_64 )
387                                _Unwind_Word match_pos = _Unwind_GetCFA(unwind_context) + 8;
388#                               elif defined( __i386 )
389                                _Unwind_Word match_pos = _Unwind_GetCFA(unwind_context) + 24;
390#                               endif
391                                int (*matcher)(exception_t *) = *(int(**)(exception_t *))match_pos;
392
393                                int index = matcher(context->current_exception);
394                                _Unwind_Reason_Code ret = (0 == index)
395                                        ? _URC_CONTINUE_UNWIND : _URC_HANDLER_FOUND;
396                                context->current_handler_index = index;
397
398                                // Based on the return value, check if we matched the exception
399                                if (ret == _URC_HANDLER_FOUND) {
400                                        __cfadbg_print_safe(exception, " handler found\n");
401                                } else {
402                                        __cfadbg_print_safe(exception, " no handler\n");
403                                }
404                                return ret;
405                        }
406
407                        // This is only a cleanup handler, ignore it
408                        __cfadbg_print_safe(exception, " no action");
409                } else {
410                        // In clean-up phase, no destructors here but this could be the handler.
411
412                        if ( (callsite_action != 0) && !(actions & _UA_HANDLER_FRAME) ){
413                                // If this is a potential exception handler
414                                // but not the one that matched the exception in the seach phase,
415                                // just ignore it
416                                goto UNWIND;
417                        }
418
419                        // We need to run some clean-up or a handler
420                        // These statment do the right thing but I don't know any specifics at all
421                        _Unwind_SetGR( unwind_context, __builtin_eh_return_data_regno(0),
422                                (_Unwind_Ptr)unwind_exception );
423                        _Unwind_SetGR( unwind_context, __builtin_eh_return_data_regno(1), 0 );
424
425                        // I assume this sets the instruction pointer to the adress of the landing pad
426                        // It doesn't actually set it, it only state the value that needs to be set once we
427                        // return _URC_INSTALL_CONTEXT
428                        _Unwind_SetIP( unwind_context, ((lsd_info.LPStart) + (callsite_landing_pad)) );
429
430                        __cfadbg_print_safe(exception, " action\n");
431
432                        // Return have some action to run
433                        return _URC_INSTALL_CONTEXT;
434                }
435        }
436        // No handling found
437        __cfadbg_print_safe(exception, " table end reached");
438
439        UNWIND:
440        __cfadbg_print_safe(exception, " unwind\n");
441
442        // Keep unwinding the stack
443        return _URC_CONTINUE_UNWIND;
444}
445
446#pragma GCC push_options
447#pragma GCC optimize(0)
448
449// Try statements are hoisted out see comments for details. While this could probably be unique
450// and simply linked from libcfa but there is one problem left, see the exception table for details
451__attribute__((noinline))
452void __cfaehm_try_terminate(void (*try_block)(),
453                void (*catch_block)(int index, exception_t * except),
454                __attribute__((unused)) int (*match_block)(exception_t * except)) {
455        //! volatile int xy = 0;
456        //! printf("%p %p %p %p\n", &try_block, &catch_block, &match_block, &xy);
457
458        // Setup the personality routine and exception table.
459        // Unforturnately these clobber gcc cancellation support which means we can't get access to
460        // the attribute cleanup tables at the same time. We would have to inspect the assembly to
461        // create a new set ourselves.
462#ifdef __PIC__
463        asm volatile (".cfi_personality 0x9b,CFA.ref.__gcfa_personality_v0");
464        asm volatile (".cfi_lsda 0x1b, .LLSDACFA2");
465#else
466        asm volatile (".cfi_personality 0x3,__gcfa_personality_v0");
467        asm volatile (".cfi_lsda 0x3, .LLSDACFA2");
468#endif
469
470        // Label which defines the start of the area for which the handler is setup.
471        asm volatile (".TRYSTART:");
472
473        // The actual statements of the try blocks
474        try_block();
475
476        // asm statement to prevent deadcode removal
477        asm volatile goto ("" : : : : CATCH );
478
479        // Normal return for when there is no throw.
480        return;
481
482        // Exceptionnal path
483        CATCH : __attribute__(( unused ));
484        // Label which defines the end of the area for which the handler is setup.
485        asm volatile (".TRYEND:");
486        // Label which defines the start of the exception landing pad. Basically what is called when
487        // the exception is caught. Note, if multiple handlers are given, the multiplexing should be
488        // done by the generated code, not the exception runtime.
489        asm volatile (".CATCH:");
490
491        // Exception handler
492        // Note: Saving the exception context on the stack breaks termination exceptions.
493        catch_block( this_exception_context()->current_handler_index,
494                     this_exception_context()->current_exception );
495}
496
497// Exception table data we need to generate. While this is almost generic, the custom data refers
498// to {*}try_terminate, which is no way generic. Some more works need to be done if we want to
499// have a single call to the try routine.
500
501#ifdef __PIC__
502asm (
503        // HEADER
504        ".LFECFA1:\n"
505        "       .globl  __gcfa_personality_v0\n"
506        "       .section        .gcc_except_table,\"a\",@progbits\n"
507        // TABLE HEADER (important field is the BODY length at the end)
508        ".LLSDACFA2:\n"
509        "       .byte   0xff\n"
510        "       .byte   0xff\n"
511        "       .byte   0x1\n"
512        "       .uleb128 .LLSDACSECFA2-.LLSDACSBCFA2\n"
513        // BODY (language specific data)
514        // This uses language specific data and can be modified arbitrarily
515        // We use handled area offset, handled area length,
516        // handler landing pad offset and 1 (action code, gcc seems to use 0).
517        ".LLSDACSBCFA2:\n"
518        "       .uleb128 .TRYSTART-__cfaehm_try_terminate\n"
519        "       .uleb128 .TRYEND-.TRYSTART\n"
520        "       .uleb128 .CATCH-__cfaehm_try_terminate\n"
521        "       .uleb128 1\n"
522        ".LLSDACSECFA2:\n"
523        // TABLE FOOTER
524        "       .text\n"
525        "       .size   __cfaehm_try_terminate, .-__cfaehm_try_terminate\n"
526);
527
528// Somehow this piece of helps with the resolution of debug symbols.
529__attribute__((unused)) static const int dummy = 0;
530
531asm (
532        // Add a hidden symbol which points at the function.
533        "       .hidden CFA.ref.__gcfa_personality_v0\n"
534        "       .weak   CFA.ref.__gcfa_personality_v0\n"
535        // No clue what this does specifically
536        "       .section        .data.rel.local.CFA.ref.__gcfa_personality_v0,\"awG\",@progbits,CFA.ref.__gcfa_personality_v0,comdat\n"
537        "       .align 8\n"
538        "       .type CFA.ref.__gcfa_personality_v0, @object\n"
539        "       .size CFA.ref.__gcfa_personality_v0, 8\n"
540        "CFA.ref.__gcfa_personality_v0:\n"
541#if defined( __x86_64 )
542        "       .quad __gcfa_personality_v0\n"
543#else // then __i386
544        "       .long __gcfa_personality_v0\n"
545#endif
546);
547#else // __PIC__
548asm (
549        // HEADER
550        ".LFECFA1:\n"
551        "       .globl  __gcfa_personality_v0\n"
552        "       .section        .gcc_except_table,\"a\",@progbits\n"
553        // TABLE HEADER (important field is the BODY length at the end)
554        ".LLSDACFA2:\n"
555        "       .byte   0xff\n"
556        "       .byte   0xff\n"
557        "       .byte   0x1\n"
558        "       .uleb128 .LLSDACSECFA2-.LLSDACSBCFA2\n"
559        // BODY (language specific data)
560        ".LLSDACSBCFA2:\n"
561        //      Handled area start (relative to start of function)
562        "       .uleb128 .TRYSTART-__cfaehm_try_terminate\n"
563        //      Handled area length
564        "       .uleb128 .TRYEND-.TRYSTART\n"
565        //      Handler landing pad address (relative to start of function)
566        "       .uleb128 .CATCH-__cfaehm_try_terminate\n"
567        //      Action code, gcc seems to always use 0.
568        "       .uleb128 1\n"
569        // TABLE FOOTER
570        ".LLSDACSECFA2:\n"
571        "       .text\n"
572        "       .size   __cfaehm_try_terminate, .-__cfaehm_try_terminate\n"
573        "       .ident  \"GCC: (Ubuntu 6.2.0-3ubuntu11~16.04) 6.2.0 20160901\"\n"
574        "       .section        .note.GNU-stack,\"x\",@progbits\n"
575);
576#endif // __PIC__
577
578#pragma GCC pop_options
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