link.cpp

/*
 * WDC to OMF Linker.
 *
 *
 */

#include <sysexits.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <err.h>
#include <assert.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <cctype>

#include <string>
#include <vector>
#include <algorithm>
#include <unordered_map>
#include <unordered_set>
#include <map>
#include <set>

#include <array>
#include <utility>
#include <numeric>
#include <iterator>

#include "obj816.h"
#include "expression.h"
#include "omf.h"

#include "endian.h"

#ifndef O_BINARY
#define O_BINARY 0
#endif


struct {
	bool v = false;
	bool S = false;
	std::string o;

	std::vector<std::string> l;
	std::vector<std::string> L;

	unsigned errors = 0;
	uint16_t file_type = 0;
	uint32_t aux_type = 0;

	unsigned omf_flags = 0;
} flags;



template<class T>
void swap_if(T &t, std::false_type) {}

void swap_if(uint8_t &, std::true_type) {}

void swap_if(uint16_t &value, std::true_type) {
	value = __builtin_bswap16(value);
}

void swap_if(uint32_t &value, std::true_type) {
	value = __builtin_bswap32(value);
}

void swap_if(uint64_t &value, std::true_type) {
	value = __builtin_bswap64(value);
}

template<class T>
void le_to_host(T &value) {
	swap_if(value, std::integral_constant<bool, endian::native == endian::big>{});
}


#pragma pack(push, 1)
struct Header {
	uint32_t magic;				/* magic number for detection */
	uint16_t version;			/* version number of object format */
	uint8_t filetype;			/* file type, object or library */
};

#pragma pack(pop)


struct section {
	std::string name;
	uint8_t flags = 0;
	uint32_t org = 0;
	uint32_t size = 0;

	unsigned number = -1;
	std::vector<uint8_t> data;
	std::vector<expression> expressions;

	unsigned end_symbol = 0; // auto-generated _END_{name} symbol.
};

struct symbol {
	std::string name;
	uint8_t type = 0;
	uint8_t flags = 0;
	uint32_t offset = 0;
	int section = -1;
};

template<class T>
uint8_t read_8(T &iter) {
	uint8_t tmp = *iter;
	++iter;
	return tmp;
}

template<class T>
uint16_t read_16(T &iter) {
	uint16_t tmp = 0;

	tmp |= *iter << 0;
	++iter;
	tmp |= *iter << 8;
	++iter;
	return tmp;
}

template<class T>
uint32_t read_32(T &iter) {
	uint32_t tmp = 0;

	tmp |= *iter << 0;
	++iter;
	tmp |= *iter << 8;
	++iter;
	tmp |= *iter << 16;
	++iter;
	tmp |= *iter << 24;
	++iter;


	return tmp;
}

template<class T>
std::string read_cstring(T &iter) {
	std::string s;
	for(;;) {
		uint8_t c = *iter;
		++iter;
		if (!c) break;
		s.push_back(c);
	}
	return s;
}


template<class T>
std::string read_pstring(T &iter) {
	std::string s;
	unsigned  size = *iter;
	++iter;
	s.reserve(size);
	while (size--) {
		uint8_t c = *iter;
		++iter;
		s.push_back(c);
	}
	return s;
}


std::vector<section> read_sections(const std::vector<uint8_t> &section_data) {

	std::vector<section> sections;
	auto iter = section_data.begin();
	while (iter != section_data.end()) {

		section s;

		s.number = read_8(iter);
		s.flags = read_8(iter);
		s.size = read_32(iter);
		s.org = read_32(iter);

		if (!(s.flags & SEC_NONAME)) s.name = read_cstring(iter);

		sections.emplace_back(std::move(s));
	}
	return sections;
}


std::vector<symbol> read_symbols(const std::vector<uint8_t> &symbol_data) {

	std::vector<symbol> symbols;

	auto iter = symbol_data.begin();
	while (iter != symbol_data.end()) {
		symbol s;
		s.type = read_8(iter);
		s.flags = read_8(iter);
		s.section = read_8(iter);
		s.offset = s.type == S_UND ? 0 : read_32(iter);
		s.name = read_cstring(iter);


		symbols.emplace_back(std::move(s));
	}

	return symbols;
}


std::unordered_map<std::string, int> section_map;
std::vector<section> sections;

std::unordered_map<std::string, int> symbol_map;
std::vector<symbol> symbols;

std::set<std::string> undefined_symbols;

inline std::string parenthesize(const std::string &s) {
	std::string tmp;
	tmp.push_back('(');
	tmp.append(s);
	tmp.push_back(')');
	return tmp;
}

inline void expr_error(bool fatal, const expression &e, const char *msg) {
	warnx("%s:%04x %s", sections[e.section].name.c_str(), e.offset, msg);

	// pretty-print the expression...
	bool underflow = false;

	struct pair { std::string name; int precedence = 0; };

	std::vector<pair> stack;

	int p;
	for (auto &x : e.stack) {
		auto tag = x.tag;
		switch(tag) {

			case OP_VAL: {
				p = 0;
				char buffer[6];
				snprintf(buffer, sizeof(buffer), "$%02x", x.value);
				stack.emplace_back(pair{buffer, p});
				break;
			}
			case OP_SYM: {
				p = 0;
				stack.emplace_back(pair{symbols[x.section].name, p});
				break;
			}
			case OP_LOC: {
				p = 0;
				std::string tmp = sections[x.section].name;
				if (x.value) {
					char buffer[6];
					snprintf(buffer, sizeof(buffer), "$%02x", x.value);
					tmp.push_back('+');
					tmp.append(buffer);
					p = 3;
				}
				stack.emplace_back(pair{tmp, p});
				break;
			}

			case OP_NOT:
			case OP_NEG:
			case OP_FLP: {
				static const std::string ops[] = {
					".NOT.", "-", "\\"
				};
				p = 0;
				if (stack.empty()) {
					underflow = true;
				} else {
					auto &back = stack.back();
					if (p < back.precedence) {
						back.name = parenthesize(back.name);
					}
					back.name = ops[tag - OP_UNA] + back.name;
					back.precedence = p;
				}
				break;
			}

			case OP_EXP:
			case OP_MUL:
			case OP_DIV:
			case OP_MOD:
			case OP_SHR:
			case OP_SHL:
			case OP_ADD:
			case OP_SUB:
			case OP_AND:
			case OP_OR:
			case OP_XOR:
			case OP_EQ:
			case OP_GT:
			case OP_LT:
			case OP_UGT:
			case OP_ULT: {
				static const pair ops[] = {
					{ "**", 1 },
					{ "*", 2 },
					{ "/", 2 },
					{ ".MOD.", 2 },
					{ ">>", 2 },
					{ "<<", 2 },
					{ "+", 3 },
					{ "-", 3 },
					{ "&", 4 },
					{ "|", 5 },
					{ "^", 5 },
					{ "=", 6 },
					{ ">",  6},
					{ "<",  6},
					{ ".UGT.",  6},
					{ ".ULT.", 6 }
				};


				p = ops[tag - OP_BIN].precedence;
				if (stack.size() < 2) {
					underflow = true;
				} else {
					pair b = std::move(stack.back());
					stack.pop_back();
					pair &a = stack.back();

					if (p < b.precedence) b.name = parenthesize(b.name);
					if (p < a.precedence) a.name = parenthesize(a.name);

					a.name += ops[tag - OP_BIN].name + b.name;
					a.precedence = p;
				}
				break;
			}
			default:
				fprintf(stderr, "Unrecognized expression op %02x\n", tag);
				break;
		}

	}
	if (stack.size() == 1) {
		fprintf(stderr, "Expression: %s\n", stack.front().name.c_str());
	} else if (stack.empty() || underflow) {
		fprintf(stderr, "Expression underflow error.\n");
		fatal = true;
	} else {
		fprintf(stderr, "Expression overflow error.\n");
		fatal = true;
	}

	if (fatal) flags.errors++;
}



/*
 * replace undefined symbols (if possible) and simplify expressions.
 *
 */
void simplify() {
	for (auto &s : sections) {
		for (auto &e : s.expressions) {
			bool delta = false;

			// first check for undefined symbols.
			if (e.undefined) {
				e.undefined = false;
				for (auto &t : e.stack) {

					if (t.tag == OP_SYM) {
						const auto &ss = symbols[t.section];
						switch(ss.type & 0x0f) {
							case S_UND:
								e.undefined = true;
								break;
							case S_REL:
								t = expr{OP_LOC, ss.offset, (uint32_t)ss.section};
								delta = true;
								break;
							case S_ABS:
								t = expr{OP_VAL, (uint32_t)ss.offset};
								delta = true;
								break;
						}
					}
				}
			}
			if (e.stack.size() > 1) simplify_expression(e);
		}
	}
}



/*
 * read and process all sections...
 * if section > 5, remap based on name.
 *
 */

std::string &upper_case(std::string &s) {
	std::transform(s.begin(), s.end(), s.begin(), toupper);
	return s;
}

void one_module(const std::vector<uint8_t> &data, 
	const std::vector<uint8_t> &section_data, 
	const std::vector<uint8_t> &symbol_data,
	std::set<std::string> *local_undefined = nullptr) {

	std::array<int, 256> remap_section;


	std::fill(remap_section.begin(), remap_section.end(), -1);
	remap_section[SECT_PAGE0] = SECT_PAGE0;
	remap_section[SECT_CODE] = SECT_CODE;
	remap_section[SECT_KDATA] = SECT_KDATA;
	remap_section[SECT_DATA] = SECT_DATA;
	remap_section[SECT_UDATA] = SECT_UDATA;

	std::vector<section> local_sections = read_sections(section_data);
	std::vector<symbol> local_symbols = read_symbols(symbol_data);



	// convert local sections to global 
	for (auto &s : local_sections) {
		//printf("section %20s %d\n", s.name.c_str(), s.number);

		if (s.number <= SECT_UDATA) {
			sections[s.number].size += s.size; // for page0 / udata sections.
			continue;
		}


		// todo -- should install section name as global symbol?

		auto iter = section_map.find(s.name);
		if (iter == section_map.end()) {

			int virtual_section = sections.size();
			remap_section[s.number] = virtual_section;
			s.number = virtual_section;

			if (!(s.flags & SEC_NONAME)) {
				/* generate an _BEG_name_ and _END_name */

				symbol sym;

				sym.name = "_BEG_" + s.name;
				upper_case(sym.name);
				sym.section = virtual_section;
				sym.type = S_REL; // check if section has offset?
				sym.flags = SF_DEF | SF_GBL;


				auto iter = symbol_map.find(sym.name);
				if (iter == symbol_map.end()) {
					symbol_map.emplace(sym.name, symbols.size());
					symbols.emplace_back(std::move(sym));
				} else {
					// duplicate label error...
				}


/*
				// add entry for name? or handle via undefined symbol lookup below?
				handled at end if symbol undeinfed.

				sym.name = s.name;
				sym.section = virtual_section;
				sym.type = S_REL;
				sym.flags = SF_DEF | SF_GBL;

				iter = symbol_map.find(sym.name);
				if (iter == symbol_map.end()) {
					symbol_map.emplace(sym.name, symbols.size());
					symbols.emplace_back(std::move(sym));
				} else {
					// duplicate label error...
				}
*/

				sym.name = "_END_" + s.name;
				upper_case(sym.name);

				sym.section = symbols.size();
				sym.type = S_UND;
				sym.flags = 0;

				iter = symbol_map.find(sym.name);
				if (iter == symbol_map.end()) {
					s.end_symbol = sym.section;
					symbol_map.emplace(sym.name, sym.section);
					symbols.emplace_back(std::move(sym));	
				} else {
					// duplicate label...
				}



			}

			sections.emplace_back(s);
			section_map.emplace(s.name, virtual_section);

		} else {
			auto &ss = sections[iter->second];
			assert(ss.flags == s.flags); // check org????
			remap_section[s.number] = iter->second;
			s.number = iter->second;

			// update size (for ref-only sections)
			ss.size += s.size;
		}
	}



	// convert local symbols to global.
	for (auto &s : local_symbols) {

		if (flags.v) {
			const char *status = "";
			if (s.type == S_UND) status = "extern";
			else if (s.flags & SF_GBL) status = "public";
			else status = "private";
			fprintf(stderr, "  %-20s [%s]\n", s.name.c_str(), status);
		}

		if (s.type == S_UND) {


			auto iter = symbol_map.find(s.name);
			if (iter == symbol_map.end()) {
				s.section = symbols.size();
				symbol_map.emplace(s.name, s.section);
				symbols.emplace_back(s);
				undefined_symbols.emplace(s.name);

				fprintf(stderr, "Adding %s to undefined symbols\n", s.name.c_str());
			}
			else {
				// already exists... 
				const auto &ss = symbols[iter->second];
				/* if (ss.type != S_UND) */
				// always copy over since s.section is a big deal.
				s = ss;
			}

			if (local_undefined) {
				if (s.type == S_UND) local_undefined->emplace(s.name);
			}
			continue;
		}

		// remap and fudge the offset.
		if ((s.type & 0x0f) == S_REL) {
			int virtual_section = remap_section[s.section];
			assert(virtual_section != -1);
			s.section = virtual_section;
			s.offset += sections[virtual_section].data.size();
		} else {
			s.section = -1;
		}



		constexpr const unsigned mask = SF_GBL | SF_DEF;
		if ((s.flags & mask) == mask) {

			auto iter = symbol_map.find(s.name);

			if (iter == symbol_map.end()) {
				unsigned tmp = symbols.size();
				symbol_map.emplace(s.name, tmp);
				symbols.emplace_back(s);
			} else {
				auto &ss = symbols[iter->second];

				// if it was undefined, define it!
				if (ss.type == S_UND) {
					ss = s;
					undefined_symbols.erase(s.name);
				}
				else {
					// ok if symbols are identical..
					if (ss.type != s.type || ss.flags != s.flags || ss.section != s.section || ss.offset != s.offset) {
						warnx("Duplicate label %s", s.name.c_str());
						flags.errors++;
					} 
				}
			}

		}

	}

	// set it here. sections may be resized above.
	int current_section = SECT_CODE;
	std::vector<uint8_t> *data_ptr = &sections[current_section].data;


	auto iter = data.begin();
	for(;;) {
		uint8_t op = read_8(iter);
		if (op == REC_END) return;

		if (op < 0xf0) {
			data_ptr->insert(data_ptr->end(), iter, iter + op);
			iter += op;
			continue;
		}

		switch(op) {
			case REC_SPACE: {
				uint16_t count = read_16(iter);
				data_ptr->insert(data_ptr->end(), count, 0);
				break;
			}

			case REC_SECT: {
				/* switch sections */
				uint8_t s = read_8(iter);
				current_section = remap_section[s];
				assert(current_section > 0 && current_section < sections.size());

				data_ptr = &sections[current_section].data;
				break;
			}

			case REC_ORG: {
				assert(!"ORG not supported.");
				break;
			}

			case REC_RELEXP:
			case REC_EXPR: {

				expression e;
				e.relative = op == REC_RELEXP;
				e.section = current_section;

				e.offset =  data_ptr->size();
				e.size = read_8(iter);


				data_ptr->insert(data_ptr->end(), e.size, 0);

				int reduced_size = 0;
				/**/
				for(;;) {
					op = read_8(iter);
					if (op == OP_END) break;

					switch(op) {
						case OP_VAL: {
							reduced_size++;
							uint32_t offset = read_32(iter);
							e.stack.emplace_back(op, offset);
							break;
						}
						case OP_SYM: {
							reduced_size++;
							uint16_t symbol = read_16(iter);
							assert(symbol < local_symbols.size());
							auto &s = local_symbols[symbol];
							switch (s.type & 0x0f) {
								case S_UND:
									// S_UND indicates it's still undefined globally.
									e.stack.emplace_back(OP_SYM, 0, s.section); /* section is actually a symbol number */
									e.undefined = true;
									break;

								case S_REL:
									e.stack.emplace_back(OP_LOC, s.offset, s.section);
									break;

								case S_ABS:
									e.stack.emplace_back(OP_VAL, s.offset);
									break;

								default:
									assert(!"unsupported symbol flags.");
							}
							break;
						}
						case OP_LOC: {
							reduced_size++;
							uint8_t section = read_8(iter);
							uint32_t offset = read_32(iter);
							int real_section = remap_section[section];
							assert(real_section >= 0);
							e.stack.emplace_back(op, offset, real_section);
							break;
						}
						// operations..
						//unary
						case OP_NOT:
						case OP_NEG:
						case OP_FLP:
							e.stack.emplace_back(op);
							break;
						// binary
						case OP_EXP:
						case OP_MUL:
						case OP_DIV:
						case OP_MOD:
						case OP_SHR:
						case OP_SHL:
						case OP_ADD:
						case OP_SUB:
						case OP_AND:
						case OP_OR:
						case OP_XOR:
						case OP_EQ:
						case OP_GT:
						case OP_LT:
						case OP_UGT:
						case OP_ULT:
							reduced_size--;
							e.stack.emplace_back(op);
							break;
						default:
							assert(!"unsupported expression opcode.");
					}
				}

				if (reduced_size != 1) {
					expr_error(true, e, "Malformed expression");
				}
				sections[current_section].expressions.emplace_back(std::move(e));
				break;
			}


			case REC_LINE: break;
			case REC_DEBUG: {
				uint16_t size = read_16(iter);
				iter += size;
				break;		
			}

		}
	}
}


/*
 * n.b -- UDATA and PAGE0 are ref only, therefore no data is generated.
 * as a special case for UDATA (but not PAGE0) have a flag so it will be 0-filled and generate data?
 *
 */
void init() {

	sections.resize(5);

	sections[SECT_PAGE0].number = SECT_PAGE0;
	sections[SECT_PAGE0].flags = SEC_DATA | SEC_NONAME | SEC_DIRECT | SEC_REF_ONLY;
	sections[SECT_PAGE0].name = "page0";

	sections[SECT_CODE].number = SECT_CODE;
	sections[SECT_CODE].flags = SEC_NONAME;
	sections[SECT_CODE].name = "code"; 

	sections[SECT_KDATA].number = SECT_KDATA;
	sections[SECT_KDATA].flags = SEC_DATA | SEC_NONAME;
	sections[SECT_KDATA].name = "kdata"; 

	sections[SECT_DATA].number = SECT_DATA;
	sections[SECT_DATA].flags = SEC_DATA | SEC_NONAME;
	sections[SECT_DATA].name = "data"; 

	sections[SECT_UDATA].number = SECT_UDATA;
	sections[SECT_UDATA].flags = SEC_DATA | SEC_NONAME | SEC_REF_ONLY;
	sections[SECT_UDATA].name = "udata"; 

	/*
	 * For each section, [the linker] creates three symbols, 
	 * _ROM_BEG_secname, _BEG_secname and _END_secname, which
	 * correspond to the rom location and the execution beginning
	 * and end of the section. These will be used more in the next
	 * two sections of code.
	 */

	// n.b - only for pre-defined sections [?], skip the _ROM_BEG_* symbols...

	static std::string names[] = {
			"_BEG_PAGE0", "_END_PAGE0",
			"_BEG_CODE", "_END_CODE",
			"_BEG_KDATA", "_END_KDATA",
			"_BEG_DATA", "_END_DATA",
			"_BEG_UDATA", "_END_UDATA",
	};

	for (int i = 0; i < 5; ++i) {

		// begin is 0.
		symbol s;
		s.name = names[i * 2];
		s.section = i;
		s.type = S_REL;
		s.flags = SF_DEF | SF_GBL;
		symbol_map.emplace(s.name, i * 2);
		symbols.emplace_back(s);

		// end is undefined...
		s.name = names[i * 2 + 1];
		s.section = i * 2 + 1; // symbol number.
		s.type = S_UND;
		s.flags = 0;

		sections[i].end_symbol = s.section;

		symbol_map.emplace(s.name, s.section);
		symbols.emplace_back(s);

		// even though it's undefined, don't add it to the undefined list ...
		// don't need to search libraries for it!
	}

}

/*
 * add and return an undefined symbol. if known, adds it to the missing set.
 * if symbol is already defined, returns it.
 */
symbol &reserve_symbol(const std::string &name, bool open = true) {

	auto iter = symbol_map.find(name);
	if (iter != symbol_map.end()) return symbols[iter->second];

	if (open) undefined_symbols.emplace(name);
	else undefined_symbols.erase(name);

	symbols.emplace_back();
	auto &sym = symbols.back();

	sym.name = name;
	sym.type = S_UND;
	sym.section = symbols.size() - 1;

	symbol_map.emplace(name, sym.section);

	return sym;
}

void generate_end() {

/*
	const std::string names[] = {
			"_END_PAGE0",
			"_END_CODE",
			"_END_KDATA"
			"_END_DATA"
			"_END_UDATA"	
	};
*/
	/*
	for (int i = 0; i < 5; ++i) {
		symbol s;
		s.section = i;
		s.type = S_REL;
		s.flags = SF_DEF | SF_GBL;
		s.offset = sections[i].size; // data.size() doesn't word w/ ref_only

		symbols[i * 2 + 1] = s;
	}

	*/

	for (const auto &s : sections) {

		// if there is an undefined symbol matching the section name, add it.
		if ((s.flags & SEC_NONAME) == 0) {

			auto iter = symbol_map.find(s.name);
			if (iter != symbol_map.end()) {

				symbol &sym = symbols[iter->second];
				if (sym.type == S_UND) {
					undefined_symbols.erase(s.name);
					sym.section = s.number;
					sym.type = S_REL;
					sym.flags = SF_DEF | SF_GBL;
					sym.offset = 0;
				}
			}
		}


		if (s.end_symbol) {

			symbol &sym = symbols[s.end_symbol];

			sym.section = s.number;
			sym.type = S_REL;
			sym.flags = SF_DEF | SF_GBL;
			sym.offset = s.size;
		}
	}


}


std::vector<omf::segment> omf_segments;


template<class T>
void append(std::vector<T> &to, std::vector<T> &from) {
	// std::move(from.begin(), from.end(), std::back_inserter(to));
	to.insert(to.end(),
		std::make_move_iterator(from.begin()),
		std::make_move_iterator(from.end())
	);
}


template<class T>
void append(std::vector<T> &to, const std::vector<T> &from) {
	to.insert(to.end(),
		from.begin(),
		from.end()
	);
}

template<class T>
void append(std::vector<T> &to, unsigned count, const T& value) {
	to.insert(to.end(),
		count,
		value
	);
}

/*
 * convert a wdc expression to an omf reloc/interseg record.
 *
 */

inline bool in_range(int value, int low, int high) {
	return value >= low && value <= high;
}

void to_omf(const expression &e, omf::segment &seg) {
	if (e.stack.empty() || e.size == 0) {
		expr_error(false, e, "Expression empty");
		return;
	}

	if (e.size < 1 || e.size > 4) {
		expr_error(true, e, "Expression size must be 1-4 bytes");
	}


	if (e.stack.size() == 1) {
		auto &a = e.stack[0];

		uint32_t value = a.value;

		if (e.relative) {
			if (a.tag == OP_VAL || a.tag == OP_LOC) {

				int tmp = (int)value - (int)e.offset - (int)e.size;
				bool ok = false;

				if (e.size >= 2 && in_range(tmp, -32768, 32767)) ok = true;
				if (e.size == 1 && in_range(tmp, -128, 127)) ok = true;

				if (!ok) {
					expr_error(true, e, "Relative branch out of range");
					return;					
				}

				for (int i = 0; i < e.size; ++i, tmp >>= 8)
					seg.data[e.offset + i] = tmp & 0xff;

				return;
			}

			expr_error(true, e, "Relative expression too complex");
			return;
		}


		if (a.tag == OP_VAL) {
			for (int i = 0; i < e.size; ++i, value >>= 8)
				seg.data[e.offset + i] = value & 0xff;
			return;
		}

		if (a.tag == OP_LOC) {
			auto &loc = a;

			if (loc.section == 0) {
				expr_error(true, e, "Invalid segment");
				return;
			}

			if (loc.section == seg.segnum) {
				omf::reloc r;
				r.size = e.size;
				r.offset = e.offset;
				r.value = value;

				seg.relocs.emplace_back(r);
			} else {
				omf::interseg r;
				r.size = e.size;
				r.offset = e.offset;
				r.segment = loc.section;
				r.segment_offset = loc.value;

				seg.intersegs.emplace_back(r);

				// if generating super, store 
			}
			return;
		}

		// error handled below.
	}



	if (e.stack.size() == 3) {
		auto &loc = e.stack[0];
		auto &shift = e.stack[1];
		auto &op = e.stack[2];

		if (loc.tag == OP_LOC && shift.tag == OP_VAL && (op.tag == OP_SHL || op.tag == OP_SHR)) {


			if (shift.value > 24) {
				expr_error(false, e, "Shift too large");
				// data is already pre-zeroed.
				return;
			}

			if (loc.section == 0) {
				expr_error(true, e, "Invalid segment");
				return;
			}

			uint32_t value = loc.value;
			uint8_t shift_value = shift.value;
			if (op.tag == OP_SHR) {
				value >>= shift_value;
				shift_value = -shift_value;
			} else {
				value <<= shift_value;
			}

			if (loc.section == seg.segnum) {
				omf::reloc r;
				r.size = e.size;
				r.offset = e.offset;
				r.value = loc.value;
				r.shift = shift_value;

				#if 0
				// also store value in data
				for (int i = 0; i < e.size; ++i, value >>= 8)
					seg.data[e.offset + i] = value & 0xff;
				#endif

				seg.relocs.emplace_back(r);
			} else {
				omf::interseg r;
				r.size = e.size;
				r.offset = e.offset;
				r.segment = loc.section;
				r.segment_offset = loc.value;
				r.shift = shift_value;

				seg.intersegs.emplace_back(r);
			}
			return;
		}
	}


	expr_error(true, e, "Expression too complex");
	// should also pretty-print the expression.
	return;

}


void build_omf_segments() {


	std::vector< std::pair<unsigned, uint32_t> > remap;

	remap.resize(sections.size());


	// if data + code can fit in one bank, merge them
	// otherwise, merge all data sections and 1 omf segment
	// per code section.

	// code is next segment...
	unsigned code_segment = 0;
	unsigned data_segment = 0;
	{
		omf_segments.emplace_back();
		auto &seg = omf_segments.back();

		code_segment = data_segment = seg.segnum = omf_segments.size();
		seg.kind = 0x0000; // static code segment.

		auto &s = sections[SECT_CODE];

		remap[s.number] = std::make_pair(code_segment, 0);
		append(seg.data, s.data);
		s.data.clear();
	}
	

	uint32_t total_code_size = 0;
	uint32_t total_data_size = 0;
	for (const auto &s : sections) {
		if (s.flags & SEC_REF_ONLY) continue;
		if (s.flags & SEC_DATA) {
			total_data_size += s.size;
		} else {
			total_code_size += s.size;
		}
	}

	// add in UDATA
	total_data_size += sections[SECT_UDATA].size;

	if (total_data_size + sections[SECT_CODE].size > 0xffff) {

		omf_segments.emplace_back();
		auto &seg = omf_segments.back();
		data_segment = seg.segnum = omf_segments.size();
		seg.kind = 0x0001; // static data segment.
	}


	{
		omf::segment &data_seg = omf_segments[data_segment-1];


		// KDATA, DATA, UDATA, other segment order.
		for (auto &s : sections) {
			if (s.flags & SEC_REF_ONLY) continue;
			if ((s.flags & SEC_DATA) == 0) continue;

			remap[s.number] = std::make_pair(data_segment, data_seg.data.size());

			append(data_seg.data, s.data);
			s.data.clear();
		}

		// add in UDATA
		{
			auto &s = sections[SECT_UDATA];
			remap[s.number] = std::make_pair(data_segment, data_seg.data.size());
			append(data_seg.data, s.size, (uint8_t)0);
		}
		// data_seg no longer valid since emplace_back() may invalidate.
	}

	// for all other sections, create a new segment.
	for (auto &s : sections) {
		if (s.flags & SEC_REF_ONLY) continue;
		if (s.flags & SEC_DATA) continue;
		if (s.number == SECT_CODE) continue;


		omf_segments.emplace_back();
		auto &seg = omf_segments.back();

		seg.segnum = omf_segments.size();
		seg.kind = 0x0000; // static code.
		seg.data = std::move(s.data);
		seg.segname = s.name;
		s.data.clear();

		remap[s.number] = std::make_pair(seg.segnum, 0);
	}


	// add a stack segment at the end
	if (flags.S) {
		auto &s = sections[SECT_PAGE0];

		// create stack/dp segment.
		uint32_t size = s.size;
		if (size) {
			// ????
			size = (size + 255) & ~255;


			omf_segments.emplace_back();
			auto &seg = omf_segments.back();

			seg.segnum = omf_segments.size();
			seg.kind = 0x12; // static dp/stack segment.
			seg.data.resize(size, 0);
			seg.loadname = "~Stack";
			omf_segments.emplace_back(std::move(seg));

			// remap SECT_PAGE0...
			remap[s.number] = std::make_pair(seg.segnum, 0);

		} else {
			warnx("page0 is 0 sized. Stack/dp segment not created.");
		}
	}

	// now adjust all the expressions, simplify, and convert to reloc records.
	for (auto &s :sections) {

		auto &x = remap[s.number];

		for (auto &e : s.expressions) {

			e.offset += x.second;

			for (auto &t : e.stack) {
				if (t.tag == OP_LOC) {
					const auto &x = remap[t.section];
					t.section = x.first;
					t.value += x.second;
				}
			}
			simplify_expression(e);

			unsigned segnum = remap[s.number].first;
			to_omf(e, omf_segments.at(segnum-1));
		}
	}

	// and we're done...

}


bool one_module(const std::string &name, int fd, std::set<std::string> *local_undefined = nullptr) {
	Mod_head h;
	ssize_t ok;

	ok = read(fd, &h, sizeof(h));
	if (ok == 0) return false;

	if (ok < sizeof(h)) {
		warnx("Invalid object file: %s", name.c_str());
		return false;;
	}

	le_to_host(h.h_magic);
	le_to_host(h.h_version);
	le_to_host(h.h_filtyp);
	le_to_host(h.h_namlen);
	le_to_host(h.h_recsize);
	le_to_host(h.h_secsize);
	le_to_host(h.h_symsize);
	le_to_host(h.h_optsize);
	le_to_host(h.h_tot_secs);
	le_to_host(h.h_num_secs);
	le_to_host(h.h_num_syms);

	assert(h.h_magic == MOD_MAGIC);
	assert(h.h_version == 1);
	assert(h.h_filtyp == 1);


	std::string module_name;
	{
		// now read the name (h_namlen includes 0 terminator.)
		std::vector<char> tmp;
		tmp.resize(h.h_namlen);
		ok = read(fd, tmp.data(), h.h_namlen);
		if (ok != h.h_namlen) {
			warnx("Invalid object file: %s", name.c_str());
			return false;
		}
		module_name.assign(tmp.data());
	}

	std::vector<uint8_t> record_data;
	std::vector<uint8_t> symbol_data;
	std::vector<uint8_t> section_data;

	record_data.resize(h.h_recsize);
	ok = read(fd, record_data.data(), h.h_recsize);
	if (ok != h.h_recsize) {
		warnx("Truncated object file: %s", name.c_str());
		return false;
	}

	section_data.resize(h.h_secsize);
	ok = read(fd, section_data.data(), h.h_secsize);
	if (ok != h.h_secsize) {
		warnx("Truncated object file: %s", name.c_str());
		return false;
	}

	symbol_data.resize(h.h_symsize);
	ok = read(fd, symbol_data.data(), h.h_symsize);
	if (ok != h.h_symsize)  {
		warnx("Truncated object file: %s", name.c_str());
		return false;
	}

	if (flags.v) {
		printf("Processing %s:%s\n", name.c_str(), module_name.c_str());
	}

	// should probably pass in name and module....
	one_module(record_data, section_data, symbol_data, local_undefined);
	

	if (h.h_optsize) lseek(fd, h.h_optsize, SEEK_CUR);

	return true;
}

bool one_file(const std::string &name) {

	if (flags.v) printf("Processing %s\n", name.c_str());

	int fd = open(name.c_str(), O_RDONLY | O_BINARY);
	if (fd < 0) {
		warn("Unable to open %s", name.c_str());
		return false;
	}
	bool rv = false;

	Header h;
	ssize_t ok;

	ok = read(fd, &h, sizeof(h));
	if (ok != sizeof(h)) {
		warnx("Invalid object file: %s", name.c_str());
		close(fd);
		return false;
	}

	le_to_host(h.magic);
	le_to_host(h.version);
	le_to_host(h.filetype);

	if (h.magic != MOD_MAGIC || h.version != MOD_VERSION || h.filetype < MOD_OBJECT || h.filetype > MOD_LIBRARY) {
		warnx("Invalid object file: %s", name.c_str());
		close(fd);
		return false;
	}

	if (h.filetype == MOD_LIBRARY) {
		warnx("%s is a library", name.c_str());
		close(fd);
		// todo -- add to library list...
		return true;
	}

	lseek(fd, 0, SEEK_SET);
	while(one_module(name, fd)) ;

	close(fd);
	return true;
}


enum {
	kPending = 1,
	kProcessed = 2,
};


/*
 * observation: the library symbol size will far exceed the missing symbols size.
 * Therefore, library symbols should be an unordered_map and explicitely look up
 * each undefined symbol.
 *
 * output c is a map (and thus sorted) to guarantee reproducable builds.
 * (could use a vector then sort/unique it...)
 */
bool intersection(const std::unordered_map<std::string, uint32_t> &a,
	const std::set<std::string> &b, 
	std::map<uint32_t, int> &c)
{
	bool rv = false;

	for (const auto &name : b) {
		auto iter = a.find(name);
		if (iter == a.end()) continue;
		rv = true;
		c.emplace(iter->second, kPending);		
	}

	return rv;
}


#if 0
bool intersection(const std::map<std::string, uint32_t> &a,
	const std::set<std::string> &b, 
	std::map<uint32_t, int> &c)
{
	auto a_iter = a.begin();
	auto b_iter = b.begin();

	bool rv = false;

	while (a_iter != a.end() && b_iter != b.end()) {

		//fprintf(stderr, "comparing %s - %s\n", a_iter->first.c_str(), b_iter->c_str());
		int cmp = strcmp(a_iter->first.c_str(), b_iter->c_str());
		if (cmp < 0) a_iter++;
		else if (cmp > 0) b_iter++;
		else {
			// insert/emplace does not overwrite a previous value.
			c.emplace(a_iter->second, kPending);
			a_iter++;
			b_iter++;
			rv = true;
		}
	}


	return rv;
}
#endif


bool one_lib(const std::string &path) {

	Lib_head h;

	int fd = open(path.c_str(), O_RDONLY | O_BINARY);
	if (fd < 0) {
		if (errno == ENOENT) return false;
	}

	if (flags.v) printf("Processing library %s\n", path.c_str());

	if (fd < 0) {
		warn("Unable to open %s", path.c_str());
		return false;
	}

	ssize_t ok;

	ok = read(fd, &h, sizeof(h));
	if (ok != sizeof(h)) {
		warnx("Invalid library file: %s", path.c_str());
		close(fd);
		return false;
	}

	le_to_host(h.l_magic);
	le_to_host(h.l_version);
	le_to_host(h.l_filtyp);
	le_to_host(h.l_unused1);
	le_to_host(h.l_modstart);
	le_to_host(h.l_numsyms);
	le_to_host(h.l_symsize);
	le_to_host(h.l_numfiles);

	if (h.l_magic != MOD_MAGIC || h.l_version != MOD_VERSION || h.l_filtyp != MOD_LIBRARY) {
		warnx("Invalid library file: %s", path.c_str());
		close(fd);
		return false;
	}

	// read the symbol dictionary.

	std::vector<uint8_t> data;
	data.resize(h.l_modstart - sizeof(h));
	ok = read(fd, data.data(), data.size());
	if (ok != data.size()) {
		warnx("Invalid library file: %s", path.c_str());
		return false;
	}

	auto iter = data.begin();
	auto end = data.end();


	// files -- only reading since it's variable length.
	for (unsigned i = 0; i < h.l_numfiles; ++i) {

		// fileno, pstring file name
		uint16_t fileno = read_16(iter);
		std::string s = read_pstring(iter);
		//uint8_t size = read_8(iter);
		//iter += size; // don't care about the name.
	}

	std::unordered_map<std::string, uint32_t> lib_symbol_map;


	// map of which modules have been loaded or are pending processing.
	std::map<uint32_t, int> modules;


	auto name_iter = iter + h.l_numsyms * 8;
	for (unsigned i = 0; i < h.l_numsyms; ++i) {
		uint16_t name_offset = read_16(iter);
		uint16_t file_number = read_16(iter);
		uint32_t offset = read_32(iter) + h.l_modstart;

		auto tmp = name_iter + name_offset;
		std::string name = read_pstring(tmp);

		lib_symbol_map.emplace(std::move(name), offset);

		//modules[offset] = 0;
	}





	// find an intersection of undefined symbols and symbols defined in lib_symbol_map

	if (!intersection(lib_symbol_map, undefined_symbols, modules)) {
		close(fd);
		return true;
	}

	for(;;) {
		bool delta = false;

		std::set<std::string> local_undefined_symbols;


		for (auto &x : modules) {
			uint32_t offset = x.first;
			int status = x.second;

			if (status == kPending) {
				x.second = kProcessed;
				lseek(fd, offset, SEEK_SET);
				one_module(path, fd, &local_undefined_symbols);
				delta = true;
			}
		}
		if (!delta) break;

		delta = intersection(lib_symbol_map, local_undefined_symbols, modules);
		if (!delta) break;
	}

	close(fd);
	return true;
}

void libraries() {

	if (undefined_symbols.empty()) return;

	for (auto &l : flags.l) {
		for (auto &L : flags.L) {
			//std::string path = L + "lib" + l;
			std::string path = L + l + ".lib";

			if (one_lib(path)) break;
		}
		if (undefined_symbols.empty()) break;
	}
}

#if 0
bool parse_ft(const std::string &s) {
	// xx
	// xx:xxxx or xx,xxxx

	auto lambda = [](const optional<int> &lhs, const uint8_t rhs) {
			if (!lhs) return lhs;
			if (rhs >= '0' && rhs <= '9')
				return optional<int>((*lhs << 4) + rhs);
			if (rhs >= 'a' && rhs <= 'f')
				return optional<int>((*lhs << 4) + (rhs - 'a' + 10));
			if (rhs >= 'A' && rhs <= 'F')
				return optional<int>((*lhs << 4) + (rhs - 'A') + 10);

			return optional<int>();
	};

	optional<int> ft;
	optional<int> at;

	if (s.length() == 2 || s.length() == 7) {

		ft = std::accumulate(s.begin(), s.begin() + 2, optional<int>(0), lambda);

		if (s.length() == 7) {
			ft = optional<int>();
			if (s[2] == ':' || s[2] == ',')
				at = std::accumulate(s.begin() + 3, s.end(), optional<int>(0), lambda);
		} else at = optional<int>(0);
	}

	if (at && ft) {
		flags.file_type = *ft;
		flags.aux_type = *at;
		return true;
	}
	return false;
}

#endif


bool parse_ft(const std::string &s) {

	// gcc doesn't like std::xdigit w/ std::all_of

	if (s.length() != 2 && s.length() != 7) return false;
	if (!std::all_of(s.begin(), s.begin() + 2, isxdigit)) return false;
	if (s.length() == 7) {
		if (s[2] != ',' && s[2] != ':') return false;
		if (!std::all_of(s.begin() + 3, s.end(), isxdigit)) return false;
	}

	auto lambda = [](int lhs, uint8_t rhs){
		lhs <<= 4;
		if (rhs <= '9') return lhs + rhs - '0';
		return lhs + (rhs | 0x20) - 'a' + 10;
	};

	flags.file_type = std::accumulate(s.begin(), s.begin() + 2, 0, lambda);
	flags.aux_type = 0;

	if (s.length() == 7)
		flags.aux_type = std::accumulate(s.begin() + 3, s.end(), 0, lambda);

	return true;
}




void usage(int rv) {
	fputs(
		"wdclink [flags] file ...\n\n"
		"Flags:\n"
		" -h               show usage\n"
		" -v               be verbose\n"
		" -X               inhibit ExpressLoad segment\n"
		" -C               inhibit SUPER records\n"
		" -S               add stack segment\n"
		" -1               generate version 1 OMF File\n"
		" -o file          specify outfile name\n"
		" -l library       specify library\n"
		" -L path          specify library path\n"
		" -t xx[:xxxx]     specify file type\n",
		stdout
	);
	exit(rv);
}

int main(int argc, char **argv) {


	int c;
	while ((c = getopt(argc, argv, "vCXSL:l:o:t:")) != -1) {
		switch(c) {
			case 'h': usage(0); break;

			case 'v': flags.v = true; break;
			case 'S': flags.S = true; break;

			case '1': flags.omf_flags |= OMF_V1; break;
			case 'X': flags.omf_flags |= OMF_NO_EXPRESS; break;
			case 'C': flags.omf_flags |= OMF_NO_SUPER; break;

			case 'o': flags.o = optarg; break;

			case 'l': {
				if (*optarg) flags.l.emplace_back(optarg);
				break;
			}
			case 'L': {
				std::string tmp(optarg);
				if (tmp.empty()) tmp = ".";
				if (tmp.back() != '/') tmp.push_back('/');
				flags.L.emplace_back(std::move(tmp));
				break;
			}
			case 't': {
				// -t xx[:xxxx] -- set file/auxtype.
				if (!parse_ft(optarg)) {
					errx(EX_USAGE, "Invalid -t argument: %s", optarg);
				}
				break;
			}


			case ':':
			case '?':
			default:
				usage(EX_USAGE);
				break;
		}
	}

	argc -= optind;
	argv += optind;

	if (argc == 0) usage(EX_USAGE);

	init();

	for (int i = 0 ; i < argc; ++i) {
		if (!one_file(argv[i])) flags.errors++;
	}


	if (flags.v && !undefined_symbols.empty()) {
		printf("Undefined Symbols:\n");
		for (const auto & s : undefined_symbols) {
			printf("%s\n", s.c_str());
		}
		printf("\n");
	}

	if (!undefined_symbols.empty()) libraries();
	//

	if (!undefined_symbols.empty()) {

		fprintf(stderr, "Unable to resolve the following symbols:\n");
		for (auto &s : undefined_symbols) fprintf(stderr, "%s\n", s.c_str());

		exit(EX_DATAERR);
	}

	generate_end();
	simplify();


	if (flags.v) {
		for (const auto &s : sections) {
			//if (s.flags & SEC_REF_ONLY) continue;
			printf("section %3d %-20s $%04x $%04x\n",
				s.number, s.name.c_str(), (uint32_t)s.data.size(), s.size);
		}
		fputs("\n", stdout);
	}

	build_omf_segments();

	if (flags.v) {
		for (const auto &s : omf_segments) {
			printf("segment %3d %-20s $%04x\n",
				s.segnum, s.segname.c_str(), (uint32_t)s.data.size());

			for (auto &r : s.relocs) {
				printf("  %02x %02x %06x %06x\n",
					r.size, r.shift, r.offset, r.value);
			}
			for (auto &r : s.intersegs) {
				printf("  %02x %02x %06x %02x %04x %06x\n",
					r.size, r.shift, r.offset, r.file, r.segment, r.segment_offset);
			}
		}
	}

	if (flags.o.empty()) flags.o = "out.omf";
	if (!flags.file_type) {
		flags.file_type = 0xb3;
	}

	int set_file_type(const std::string &path, uint16_t file_type, uint32_t aux_type);

	save_omf(flags.o, omf_segments, flags.omf_flags);
	set_file_type(flags.o, flags.file_type, flags.aux_type);
}