Changeset eb46fdf for libcfa/src/exception.c

Timestamp:

Dec 12, 2019, 4:06:18 PM (5 years ago)

Author:

Andrew Beach <ajbeach@…>

Branches:

ADT, arm-eh, ast-experimental, enum, forall-pointer-decay, jacob/cs343-translation, jenkins-sandbox, master, new-ast, new-ast-unique-expr, pthread-emulation, qualifiedEnum

Children:

332bd33

Parents:

737c98a

Message:

Clean up in exception.c. Should be no changes to code.

File:

• libcfa/src/exception.c (modified) (16 diffs)

libcfa/src/exception.c

@@ -69 +69 @@
 
 
-// This macro should be the only thing that needs to change across machines.  Used in the personality function, way down
-// in termination.
+// This macro should be the only thing that needs to change across machines.
+// Used in the personality function, way down in termination.
 // struct _Unwind_Context * -> _Unwind_Reason_Code(*)(exception_t *)
 #define MATCHER_FROM_CONTEXT(ptr_to_context) \
@@ -102 +102 @@
 }
 
-// Do we control where exceptions get thrown even with concurency?  If not these are not quite thread safe, the cleanup
-// hook has to be added after the node is built but before it is made the top node.
+// Do we control where exceptions get thrown even with concurency?
+// If not these are not quite thread safe, the cleanup hook has to
+// be added after the node is built but before it is made the top node.
 
 void __cfaabi_ehm__try_resume_setup(struct __cfaabi_ehm__try_resume_node * node,
@@ -212 +213 @@
         _Unwind_Reason_Code ret = _Unwind_RaiseException( &this_exception_storage );
 
-        // If we reach here it means something happened.  For resumption to work we need to find a way to return back to
-        // here.  Most of them will probably boil down to setting a global flag and making the phase 1 either stop or
-        // fail.  Causing an error on purpose may help avoiding unnecessary work but it might have some weird side
-        // effects.  If we just pretend no handler was found that would work but may be expensive for no reason since we
-        // will always search the whole stack.
+        // If we reach here it means something happened. For resumption to work we need to find a way
+        // to return back to here. Most of them will probably boil down to setting a global flag and
+        // making the phase 1 either stop or fail. Causing an error on purpose may help avoiding
+        // unnecessary work but it might have some weird side effects. If we just pretend no handler
+        // was found that would work but may be expensive for no reason since we will always search
+        // the whole stack.
 
         if( ret == _URC_END_OF_STACK ) {
-                // No proper handler was found.  This can be handled in several way.  C++ calls std::terminate Here we
-                // force unwind the stack, basically raising a cancellation.
+                // No proper handler was found. This can be handled in many ways, C++ calls std::terminate.
+                // Here we force unwind the stack, basically raising a cancellation.
                 printf("Uncaught exception %p\n", &this_exception_storage);
 
@@ -228 +230 @@
         }
 
-        // We did not simply reach the end of the stack without finding a handler.  Something wen't wrong
+        // We did not simply reach the end of the stack without finding a handler. This is an error.
         printf("UNWIND ERROR %d after raise exception\n", ret);
         abort();
@@ -254 +256 @@
         abort();
 }
-#else
-// This is our personality routine.  For every stack frame anotated with ".cfi_personality 0x3,__gcfa_personality_v0".
-// This function will be called twice when unwinding.  Once in the search phased and once in the cleanup phase.
+#else // PIC
+// This is our personality routine. For every stack frame annotated with
+// ".cfi_personality 0x3,__gcfa_personality_v0" this function will be called twice when unwinding.
+//  Once in the search phase and once in the cleanup phase.
 _Unwind_Reason_Code __gcfa_personality_v0 (
                 int version, _Unwind_Action actions, unsigned long long exceptionClass,
@@ -264 +267 @@
 
         //__cfaabi_dbg_print_safe("CFA: 0x%lx\n", _Unwind_GetCFA(context));
-        __cfaabi_dbg_print_safe("Personality function (%d, %x, %llu, %p, %p):", version, actions, exceptionClass, unwind_exception, context);
+        __cfaabi_dbg_print_safe("Personality function (%d, %x, %llu, %p, %p):",
+                        version, actions, exceptionClass, unwind_exception, context);
 
         // If we've reached the end of the stack then there is nothing much we can do...
@@ -291 +295 @@
         // Get the instuction pointer and a reading pointer into the exception table
         lsda_header_info lsd_info;
-        const unsigned char * cur_ptr = parse_lsda_header( context, lsd, &lsd_info);
+        const unsigned char * cur_ptr = parse_lsda_header(context, lsd, &lsd_info);
         _Unwind_Ptr instruction_ptr = _Unwind_GetIP( context );
 
@@ -302 +306 @@
 
                 // Decode the common stuff we have in here
-                cur_ptr = read_encoded_value (0, lsd_info.call_site_encoding, cur_ptr, &callsite_start);
-                cur_ptr = read_encoded_value (0, lsd_info.call_site_encoding, cur_ptr, &callsite_len);
-                cur_ptr = read_encoded_value (0, lsd_info.call_site_encoding, cur_ptr, &callsite_landing_pad);
-                cur_ptr = read_uleb128 (cur_ptr, &callsite_action);
+                cur_ptr = read_encoded_value(0, lsd_info.call_site_encoding, cur_ptr, &callsite_start);
+                cur_ptr = read_encoded_value(0, lsd_info.call_site_encoding, cur_ptr, &callsite_len);
+                cur_ptr = read_encoded_value(0, lsd_info.call_site_encoding, cur_ptr, &callsite_landing_pad);
+                cur_ptr = read_uleb128(cur_ptr, &callsite_action);
 
                 // Have we reach the correct frame info yet?
@@ -316 +320 @@
                         void * ep = (void*)lsd_info.Start + callsite_start + callsite_len;
                         void * ip = (void*)instruction_ptr;
-                        __cfaabi_dbg_print_safe("\nfound %p - %p (%p, %p, %p), looking for %p\n", bp, ep, ls, cs, cl, ip);
+                        __cfaabi_dbg_print_safe("\nfound %p - %p (%p, %p, %p), looking for %p\n",
+                                        bp, ep, ls, cs, cl, ip);
 #endif // __CFA_DEBUG_PRINT__
                         continue;
                 }
 
-                // Have we gone too far
+                // Have we gone too far?
                 if( lsd_info.Start + callsite_start > instruction_ptr ) {
                         printf(" gone too far");
@@ -331 +336 @@
                         // Which phase are we in
                         if (actions & _UA_SEARCH_PHASE) {
-                                // Search phase, this means we probably found a potential handler and must check if it is a match
-
-                                // If we have arbitrarily decided that 0 means nothing to do and 1 means there is a potential handler
-                                // This doesn't seem to conflict the gcc default behavior
+                                // In search phase, these means we found a potential handler we must check.
+
+                                // We have arbitrarily decided that 0 means nothing to do and 1 means there is
+                                // a potential handler. This doesn't seem to conflict the gcc default behavior.
                                 if (callsite_action != 0) {
                                         // Now we want to run some code to see if the handler matches
@@ -351 +356 @@
                                         // The current apprach uses one exception table entry per try block
                                         _uleb128_t imatcher;
-                                        // Get the relative offset to the
-                                        cur_ptr = read_uleb128 (cur_ptr, &imatcher);
-
-                                        // Get a function pointer from the relative offset and call it
-                                        // _Unwind_Reason_Code (*matcher)() = (_Unwind_Reason_Code (*)())lsd_info.LPStart + imatcher;
+                                        // Get the relative offset to the {...}?
+                                        cur_ptr = read_uleb128(cur_ptr, &imatcher);
 
                                         _Unwind_Reason_Code (*matcher)(exception_t *) =
@@ -414 +416 @@
 }
 
-// Try statements are hoisted out see comments for details.  With this could probably be unique and simply linked from
-// libcfa but there is one problem left, see the exception table for details
+// Try statements are hoisted out see comments for details. While this could probably be unique
+// and simply linked from libcfa but there is one problem left, see the exception table for details
 __attribute__((noinline))
 void __cfaabi_ehm__try_terminate(void (*try_block)(),
@@ -428 +430 @@
         // assembly works.
 
-        // Setup the personality routine
+        // Setup the personality routine and exception table.
         asm volatile (".cfi_personality 0x3,__gcfa_personality_v0");
-        // Setup the exception table
         asm volatile (".cfi_lsda 0x3, .LLSDACFA2");
 
@@ -442 +443 @@
         asm volatile goto ("" : : : : CATCH );
 
-        // Normal return
+        // Normal return for when there is no throw.
         return;
 
@@ -459 +460 @@
 }
 
-// Exception table data we need to generate.  While this is almost generic, the custom data refers to foo_try_match try
-// 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.
+// Exception table data we need to generate. While this is almost generic, the custom data refers
+// to {*}try_terminate, which is no way generic. Some more works need to be done if we want to
+// have a single call to the try routine.
 
 #if defined( __i386 ) || defined( __x86_64 )
 asm (
-        //HEADER
+        // HEADER
         ".LFECFA1:\n"
         "       .globl  __gcfa_personality_v0\n"
         "       .section        .gcc_except_table,\"a\",@progbits\n"
-        ".LLSDACFA2:\n"                                                 //TABLE header
+        // TABLE HEADER (important field is the BODY length at the end)
+        ".LLSDACFA2:\n"
         "       .byte   0xff\n"
         "       .byte   0xff\n"
         "       .byte   0x1\n"
-        "       .uleb128 .LLSDACSECFA2-.LLSDACSBCFA2\n"         // BODY length
-        // Body uses language specific data and therefore could be modified arbitrarily
-        ".LLSDACSBCFA2:\n"                                              // BODY start
-        "       .uleb128 .TRYSTART-__cfaabi_ehm__try_terminate\n"               // Handled area start  (relative to start of function)
-        "       .uleb128 .TRYEND-.TRYSTART\n"                           // Handled area length
-        "       .uleb128 .CATCH-__cfaabi_ehm__try_terminate\n"                          // Hanlder landing pad adress  (relative to start of function)
-        "       .uleb128 1\n"                                           // Action code, gcc seems to use always 0
-        ".LLSDACSECFA2:\n"                                              // BODY end
-        "       .text\n"                                                        // TABLE footer
+        "       .uleb128 .LLSDACSECFA2-.LLSDACSBCFA2\n"
+        // BODY (language specific data)
+        ".LLSDACSBCFA2:\n"
+        //      Handled area start (relative to start of function)
+        "       .uleb128 .TRYSTART-__cfaabi_ehm__try_terminate\n"
+        //      Handled area length
+        "       .uleb128 .TRYEND-.TRYSTART\n"
+        //      Handler landing pad address (relative to start of function)
+        "       .uleb128 .CATCH-__cfaabi_ehm__try_terminate\n"
+        //      Action code, gcc seems to always use 0.
+        "       .uleb128 1\n"
+        // TABLE FOOTER
+        ".LLSDACSECFA2:\n"
+        "       .text\n"
         "       .size   __cfaabi_ehm__try_terminate, .-__cfaabi_ehm__try_terminate\n"
         "       .ident  \"GCC: (Ubuntu 6.2.0-3ubuntu11~16.04) 6.2.0 20160901\"\n"
@@ -486 +494 @@
 );
 #endif // __i386 || __x86_64
-#endif //PIC
+#endif // PIC