#include "exception.h"

// Implementation of the secret header.

#include <stdlib.h>
#include <stdio.h>
#include <unwind.h>

#include "lsda.h"

struct shared_stack_t shared_stack;


// 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(*)()
#define MATCHER_FROM_CONTEXT(ptr_to_context) \
	(*(_Unwind_Reason_Code(**)())(_Unwind_GetCFA(ptr_to_context) + 8))


// RESUMPTION ================================================================

void __throw_resume(exception except) {

	// DEBUG
	printf("Throwing resumption exception %d\n", except);

	struct __try_resume_node * original_head = shared_stack.current_resume;
	struct __try_resume_node * current =
		(original_head) ? original_head->next : shared_stack.top_resume;

	for ( ; current ; current = current->next) {
		shared_stack.current_resume = current;
		if (current->try_to_handle(except)) {
			shared_stack.current_resume = original_head;
			return;
		}
	}

	printf("Unhandled exception %d\n", except);
	shared_stack.current_resume = original_head;

	// Fall back to termination:
	__throw_terminate(except);
	// TODO: Default handler for resumption.
}

/* QUESTION: Could interupts interact with exception handling?
Ex. could an context switch stop execution, and we get an exception when we
come back? Is so resumption has to go:
+ create node (init next and handler)
+ prepare cleanup (add a cleanup hook with the ..._cleaup function)
  also the cleanup has to be the next node, not just a pop from the list.
+ push node on the list (change the existing node)
Which if an exception can come from anywhere, might just be required to ensure
the list is valid.

void __try_resume_setup(struct __try_resume_node * node,
                        bool (*handler)(exception except) {
	node->next = shared_stack.top_resume;
	node->try_to_handle = handler;
	shared_stack.top_resume = node;
}*/

// We have a single cleanup function
void __try_resume_cleanup(struct __try_resume_node * node) {
	shared_stack.top_resume = node->next;
}


// TERMINATION ===============================================================

// Requires -fexceptions to work.

// Global which defines the current exception
// Currently an int just to make matching easier
//int this_exception; (became shared_stack.current_exception)

// We need a piece of storage to raise the exception
struct _Unwind_Exception this_exception_storage;

// Function needed by force unwind
// It basically says to unwind the whole stack and then exit when we reach the end of the stack
static _Unwind_Reason_Code _Stop_Fn(
		int version,
		_Unwind_Action actions,
		_Unwind_Exception_Class exceptionClass,
		struct _Unwind_Exception * unwind_exception,
		struct _Unwind_Context * context,
		void * some_param) {
	if( actions & _UA_END_OF_STACK  ) exit(1);
	if( actions & _UA_CLEANUP_PHASE ) return _URC_NO_REASON;

	return _URC_FATAL_PHASE2_ERROR;
}

void __throw_terminate( int val ) {
	// Store the current exception
	shared_stack.current_exception = val;

	// DEBUG
	printf("Throwing termination exception %d\n", val);

	// Call stdlibc to raise the exception
	_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( 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
		printf("Uncaught exception %p\n", &this_exception_storage);

		ret = _Unwind_ForcedUnwind( &this_exception_storage, _Stop_Fn, (void*)0x22 );
		printf("UNWIND ERROR %d after force unwind\n", ret);
		abort();
	}

	// We did not simply reach the end of the stack without finding a handler,
	// Something wen't wrong
	printf("UNWIND ERROR %d after raise exception\n", ret);
	abort();
}

// Nesting this the other way would probably be faster.
void __rethrow_terminate(void) {
	// DEBUG
	printf("Rethrowing termination exception\n");

	__throw_terminate(shared_stack.current_exception);
}

// 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
_Unwind_Reason_Code __gcfa_personality_v0 (
		int version, _Unwind_Action actions, unsigned long long exceptionClass,
		struct _Unwind_Exception* unwind_exception,
		struct _Unwind_Context* context)
{

	// DEBUG
	//printf("CFA: 0x%lx\n", _Unwind_GetCFA(context));
	printf("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...
	if( actions & _UA_END_OF_STACK ) return _URC_END_OF_STACK;

	// DEBUG
	if (actions & _UA_SEARCH_PHASE) {
		printf(" lookup phase");
	}
	// DEBUG
	else if (actions & _UA_CLEANUP_PHASE) {
		printf(" cleanup phase");
	}
	// Just in case, probably can't actually happen
	else {
		printf(" error\n");
		return _URC_FATAL_PHASE1_ERROR;
	}

	// Get a pointer to the language specific data from which we will read what we need
	const unsigned char * lsd = (const unsigned char*) _Unwind_GetLanguageSpecificData( context );

	if( !lsd ) {	//Nothing to do, keep unwinding
		printf(" no LSD");
		goto UNWIND;
	}

	// 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);
	_Unwind_Ptr instruction_ptr = _Unwind_GetIP( context );

	// Linearly search the table for stuff to do
	while( cur_ptr < lsd_info.action_table ) {
		_Unwind_Ptr callsite_start;
		_Unwind_Ptr callsite_len;
		_Unwind_Ptr callsite_landing_pad;
		_uleb128_t  callsite_action;

		// 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);

		// Have we reach the correct frame info yet?
		if( lsd_info.Start + callsite_start + callsite_len < instruction_ptr ) {
			//DEBUG BEGIN
			void * ls = (void*)lsd_info.Start;
			void * cs = (void*)callsite_start;
			void * cl = (void*)callsite_len;
			void * bp = (void*)lsd_info.Start + callsite_start;
			void * ep = (void*)lsd_info.Start + callsite_start + callsite_len;
			void * ip = (void*)instruction_ptr;
			printf("\nfound %p - %p (%p, %p, %p), looking for %p\n", bp, ep, ls, cs, cl, ip);
			//DEBUG END
			continue;
		}

		// Have we gone too far
		if( lsd_info.Start + callsite_start > instruction_ptr ) {
			printf(" gone too far");
			break;
		}

		// Something to do?
		if( callsite_landing_pad ) {
			// 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
				if (callsite_action != 0) {
					// Now we want to run some code to see if the handler matches
					// This is the tricky part where we want to the power to run arbitrary code
					// However, generating a new exception table entry and try routine every time
					// is way more expansive than we might like
					// The information we have is :
					//  - The GR (Series of registers)
					//    GR1=GP Global Pointer of frame ref by context
					//  - The instruction pointer
					//  - The instruction pointer info (???)
					//  - The CFA (Canonical Frame Address)
					//  - The BSP (Probably the base stack pointer)


					// 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;

					_Unwind_Reason_Code (*matcher)() =
						MATCHER_FROM_CONTEXT(context);
					int index = matcher(shared_stack.current_exception);
					_Unwind_Reason_Code ret = (0 == index)
						? _URC_CONTINUE_UNWIND : _URC_HANDLER_FOUND;
					shared_stack.current_handler_index = index;

					// Based on the return value, check if we matched the exception
					if( ret == _URC_HANDLER_FOUND) printf(" handler found\n");
					else printf(" no handler\n");
					return ret;
				}

				// This is only a cleanup handler, ignore it
				printf(" no action");
			}
			else if (actions & _UA_CLEANUP_PHASE) {

				if( (callsite_action != 0) && !(actions & _UA_HANDLER_FRAME) ){
					// If this is a potential exception handler
					// but not the one that matched the exception in the seach phase,
					// just ignore it
					goto UNWIND;
				}

				// We need to run some clean-up or a handler
				// These statment do the right thing but I don't know any specifics at all
				_Unwind_SetGR( context, __builtin_eh_return_data_regno(0), (_Unwind_Ptr) unwind_exception );
				_Unwind_SetGR( context, __builtin_eh_return_data_regno(1), 0 );

				// I assume this sets the instruction pointer to the adress of the landing pad
				// It doesn't actually set it, it only state the value that needs to be set once we return _URC_INSTALL_CONTEXT
				_Unwind_SetIP( context, lsd_info.LPStart + callsite_landing_pad );

				// DEBUG
				printf(" action\n");

				// Return have some action to run
				return _URC_INSTALL_CONTEXT;
			}
		}

		// Nothing to do, move along
		printf(" no landing pad");
	}
	// No handling found
	printf(" table end reached\n");

	// DEBUG
	UNWIND:
	printf(" unwind\n");

	// Keep unwinding the stack
	return _URC_CONTINUE_UNWIND;
}

// 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
__attribute__((noinline))
void __try_terminate(void (*try_block)(),
		void (*catch_block)(int index, exception except),
		__attribute__((unused)) int (*match_block)(exception except)) {
	//! volatile int xy = 0;
	//! printf("%p %p %p %p\n", &try_block, &catch_block, &match_block, &xy);

	// Setup statments
	// These 2 statments won't actually result in any code,
	// they only setup global tables.
	// However, they clobber gcc cancellation support from gcc.
	// We can replace the personality routine but replacing the exception
	// table gcc generates is not really doable, it generates labels based
	// on how the assembly works.
	// Setup the personality routine
	#if defined(__PIC__)
	asm volatile (".cfi_personality 0x9b,CFA.ref.__gcfa_personality_v0");
	// Setup the exception table
	asm volatile (".cfi_lsda 0x1b, .LLSDACFA2");
	#else
	asm volatile (".cfi_personality 0x3,__gcfa_personality_v0");
	// Setup the exception table
	asm volatile (".cfi_lsda 0x3, .LLSDACFA2");
	#endif

	// Label which defines the start of the area for which the handler is setup
	asm volatile (".TRYSTART:");

	// The actual statements of the try blocks
	try_block();

	// asm statement to prevent deadcode removal
	asm volatile goto ("" : : : : CATCH );

	// Normal return
	return;

	// Exceptionnal path
	CATCH : __attribute__(( unused ));
	// Label which defines the end of the area for which the handler is setup
	asm volatile (".TRYEND:");
	// Label which defines the start of the exception landing pad
	// basically what will be called when the exception is caught
	// Note, if multiple handlers are given, the multiplexing should be done
	// by the generated code, not the exception runtime
	asm volatile (".CATCH:");

	// Exception handler
	catch_block(shared_stack.current_handler_index,
	            shared_stack.current_exception);
}

// 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
#if defined(__PIC__)
asm (
	//HEADER
	".LFECFA1:\n"
	"	.globl	__gcfa_personality_v0\n"
	"	.section	.gcc_except_table,\"a\",@progbits\n"
	".LLSDACFA2:\n"							//TABLE header
	"	.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-__try_terminate\n"		// Handled area start  (relative to start of function)
	"	.uleb128 .TRYEND-.TRYSTART\n"				// Handled area length
	"	.uleb128 .CATCH-__try_terminate\n"			// Handler 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
	"	.size	__try_terminate, .-__try_terminate\n"
);

// Somehow this piece of helps with the resolution of debug symbols.
__attribute__((unused)) static const int dummy = 0;
asm (
	"	.hidden	CFA.ref.__gcfa_personality_v0\n"	// Declare an new hidden symbol
	"	.weak	CFA.ref.__gcfa_personality_v0\n"
	"	.section	.data.rel.local.CFA.ref.__gcfa_personality_v0,\"awG\",@progbits,CFA.ref.__gcfa_personality_v0,comdat\n"	// No clue what this does specifically
	"	.align 8\n"
	"	.type CFA.ref.__gcfa_personality_v0, @object\n"	// Type of our hidden symbol (it's not actually the function itself)
	"	.size CFA.ref.__gcfa_personality_v0, 8\n"		// Size of our hidden symbol
	"CFA.ref.__gcfa_personality_v0:\n"
	"	.quad __gcfa_personality_v0\n"
);
#else
asm (
	//HEADER
	".LFECFA1:\n"
	"	.globl	__gcfa_personality_v0\n"
	"	.section	.gcc_except_table,\"a\",@progbits\n"
	".LLSDACFA2:\n"							//TABLE header
	"	.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-__try_terminate\n"		// Handled area start  (relative to start of function)
	"	.uleb128 .TRYEND-.TRYSTART\n"				// Handled area length
	"	.uleb128 .CATCH-__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
	"	.size	__try_terminate, .-__try_terminate\n"
);
#endif