factor/vm/callstack.cpp

#include "master.hpp"

namespace factor
{

void factor_vm::check_frame(stack_frame *frame)
{
#ifdef FACTOR_DEBUG
	check_code_pointer((cell)frame->entry_point);
	assert(frame->size != 0);
#endif
}

callstack *factor_vm::allot_callstack(cell size)
{
	callstack *stack = allot<callstack>(callstack_object_size(size));
	stack->length = tag_fixnum(size);
	return stack;
}

/* If 'stack' points into the middle of the frame, find the nearest valid stack
pointer where we can resume execution and hope to capture the call trace without
crashing. Also, make sure we have at least 'stack_reserved' bytes available so
that we don't run out of callstack space while handling the error. */
stack_frame *factor_vm::fix_callstack_top(stack_frame *stack)
{
	stack_frame *frame = ctx->callstack_bottom - 1;

	while(frame >= stack
		&& frame >= ctx->callstack_top
		&& (cell)frame >= ctx->callstack_seg->start + stack_reserved)
		frame = frame_successor(frame);

	return frame + 1;
}

/* We ignore the two topmost frames, the 'callstack' primitive
frame itself, and the frame calling the 'callstack' primitive,
so that set-callstack doesn't get stuck in an infinite loop.

This means that if 'callstack' is called in tail position, we
will have popped a necessary frame... however this word is only
called by continuation implementation, and user code shouldn't
be calling it at all, so we leave it as it is for now. */
stack_frame *factor_vm::second_from_top_stack_frame(context *ctx)
{
	stack_frame *frame = ctx->callstack_bottom - 1;
	while(frame >= ctx->callstack_top
		&& frame_successor(frame) >= ctx->callstack_top
		&& frame_successor(frame_successor(frame)) >= ctx->callstack_top)
	{
		frame = frame_successor(frame);
	}
	return frame + 1;
}

cell factor_vm::capture_callstack(context *ctx)
{
	stack_frame *top = second_from_top_stack_frame(ctx);
	stack_frame *bottom = ctx->callstack_bottom;

	fixnum size = std::max((fixnum)0,(fixnum)bottom - (fixnum)top);

	callstack *stack = allot_callstack(size);
	memcpy(stack->top(),top,size);
	return tag<callstack>(stack);
}

void factor_vm::primitive_callstack()
{
	ctx->push(capture_callstack(ctx));
}

void factor_vm::primitive_callstack_for()
{
	context *other_ctx = (context *)pinned_alien_offset(ctx->pop());
	ctx->push(capture_callstack(other_ctx));
}

code_block *factor_vm::frame_code(stack_frame *frame)
{
	check_frame(frame);
	return (code_block *)frame->entry_point - 1;
}

code_block_type factor_vm::frame_type(stack_frame *frame)
{
	return frame_code(frame)->type();
}

cell factor_vm::frame_executing(stack_frame *frame)
{
	return frame_code(frame)->owner;
}

cell factor_vm::frame_executing_quot(stack_frame *frame)
{
	tagged<object> executing(frame_executing(frame));
	code_block *compiled = frame_code(frame);
	if(!compiled->optimized_p() && executing->type() == WORD_TYPE)
		executing = executing.as<word>()->def;
	return executing.value();
}

stack_frame *factor_vm::frame_successor(stack_frame *frame)
{
	check_frame(frame);
	return (stack_frame *)((cell)frame - frame->size);
}

/* Allocates memory */
cell factor_vm::frame_scan(stack_frame *frame)
{
	switch(frame_type(frame))
	{
	case code_block_unoptimized:
		{
			tagged<object> obj(frame_executing(frame));
			if(obj.type_p(WORD_TYPE))
				obj = obj.as<word>()->def;

			if(obj.type_p(QUOTATION_TYPE))
			{
				char *return_addr = (char *)FRAME_RETURN_ADDRESS(frame,this);
				char *quot_entry_point = (char *)(frame_code(frame) + 1);

				return tag_fixnum(quot_code_offset_to_scan(
					obj.value(),(cell)(return_addr - quot_entry_point)));
			}    
			else
				return false_object;
		}
	case code_block_optimized:
		return false_object;
	default:
		critical_error("Bad frame type",frame_type(frame));
		return false_object;
	}
}

namespace
{

struct stack_frame_accumulator {
	factor_vm *parent;
	growable_array frames;

	explicit stack_frame_accumulator(factor_vm *parent_) : parent(parent_), frames(parent_) {} 

	void operator()(stack_frame *frame)
	{
		data_root<object> executing_quot(parent->frame_executing_quot(frame),parent);
		data_root<object> executing(parent->frame_executing(frame),parent);
		data_root<object> scan(parent->frame_scan(frame),parent);

		frames.add(executing.value());
		frames.add(executing_quot.value());
		frames.add(scan.value());
	}
};

}

void factor_vm::primitive_callstack_to_array()
{
	data_root<callstack> callstack(ctx->pop(),this);

	stack_frame_accumulator accum(this);
	iterate_callstack_object(callstack.untagged(),accum);
	accum.frames.trim();

	ctx->push(accum.frames.elements.value());
}

stack_frame *factor_vm::innermost_stack_frame(callstack *stack)
{
	stack_frame *top = stack->top();
	stack_frame *bottom = stack->bottom();
	stack_frame *frame = bottom - 1;

	while(frame >= top && frame_successor(frame) >= top)
		frame = frame_successor(frame);

	return frame;
}

/* Some primitives implementing a limited form of callstack mutation.
Used by the single stepper. */
void factor_vm::primitive_innermost_stack_frame_executing()
{
	stack_frame *frame = innermost_stack_frame(untag_check<callstack>(ctx->pop()));
	ctx->push(frame_executing_quot(frame));
}

void factor_vm::primitive_innermost_stack_frame_scan()
{
	stack_frame *frame = innermost_stack_frame(untag_check<callstack>(ctx->pop()));
	ctx->push(frame_scan(frame));
}

void factor_vm::primitive_set_innermost_stack_frame_quot()
{
	data_root<callstack> callstack(ctx->pop(),this);
	data_root<quotation> quot(ctx->pop(),this);

	callstack.untag_check(this);
	quot.untag_check(this);

	jit_compile_quot(quot.value(),true);

	stack_frame *inner = innermost_stack_frame(callstack.untagged());
	cell offset = (char *)FRAME_RETURN_ADDRESS(inner,this) - (char *)inner->entry_point;
	inner->entry_point = quot->entry_point;
	FRAME_RETURN_ADDRESS(inner,this) = (char *)quot->entry_point + offset;
}

}