rgbds/src/link/patch.cpp

/* SPDX-License-Identifier: MIT */

#include <assert.h>
#include <deque>
#include <inttypes.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>

#include "link/object.hpp"
#include "link/patch.hpp"
#include "link/section.hpp"
#include "link/symbol.hpp"

#include "error.hpp"
#include "linkdefs.hpp"
#include "opmath.hpp"
#include "platform.hpp"

struct RPNStackEntry {
	int32_t value;
	bool errorFlag; // Whether the value is a placeholder inserted for error recovery
};

std::deque<struct RPNStackEntry> rpnStack;

static void pushRPN(int32_t value, bool comesFromError)
{
	rpnStack.push_front({ .value = value, .errorFlag = comesFromError });
}

// This flag tracks whether the RPN op that is currently being evaluated
// has popped any values with the error flag set.
static bool isError = false;

static int32_t popRPN(struct FileStackNode const *node, uint32_t lineNo)
{
	if (rpnStack.empty())
		fatal(node, lineNo, "Internal error, RPN stack empty");

	struct RPNStackEntry entry = rpnStack.front();

	rpnStack.pop_front();
	isError |= entry.errorFlag;
	return entry.value;
}

// RPN operators

static uint32_t getRPNByte(uint8_t const **expression, int32_t *size,
			   struct FileStackNode const *node, uint32_t lineNo)
{
	if (!(*size)--)
		fatal(node, lineNo, "Internal error, RPN expression overread");

	return *(*expression)++;
}

static struct Symbol const *getSymbol(std::vector<struct Symbol> const &symbolList, uint32_t index)
{
	assert(index != (uint32_t)-1); // PC needs to be handled specially, not here
	struct Symbol const &symbol = symbolList[index];

	// If the symbol is defined elsewhere...
	if (symbol.type == SYMTYPE_IMPORT)
		return sym_GetSymbol(symbol.name);

	return &symbol;
}

/*
 * Compute a patch's value from its RPN string.
 * @param patch The patch to compute the value of
 * @param section The section the patch is contained in
 * @return The patch's value
 * @return isError Set if an error occurred during evaluation, and further
 *                 errors caused by the value should be suppressed.
 */
static int32_t computeRPNExpr(struct Patch const *patch,
			      std::vector<struct Symbol> const &fileSymbols)
{
// Small shortcut to avoid a lot of repetition
#define popRPN() popRPN(patch->src, patch->lineNo)

	uint8_t const *expression = &patch->rpnExpression[0];
	int32_t size = (int32_t)patch->rpnExpression.size();

	rpnStack.clear();

	while (size > 0) {
		enum RPNCommand command = (enum RPNCommand)getRPNByte(&expression, &size,
						     patch->src, patch->lineNo);
		int32_t value;

		isError = false;

		// Be VERY careful with two `popRPN` in the same expression.
		// C++ does not guarantee order of evaluation of operands!
		// So, if there are two `popRPN` in the same expression, make
		// sure the operation is commutative.
		switch (command) {
			struct Symbol const *symbol;
			char const *name;
			struct Section const *sect;

		case RPN_ADD:
			value = popRPN() + popRPN();
			break;
		case RPN_SUB:
			value = popRPN();
			value = popRPN() - value;
			break;
		case RPN_MUL:
			value = popRPN() * popRPN();
			break;
		case RPN_DIV:
			value = popRPN();
			if (value == 0) {
				if (!isError)
					error(patch->src, patch->lineNo, "Division by 0");
				isError = true;
				popRPN();
				value = INT32_MAX;
			} else {
				value = op_divide(popRPN(), value);
			}
			break;
		case RPN_MOD:
			value = popRPN();
			if (value == 0) {
				if (!isError)
					error(patch->src, patch->lineNo, "Modulo by 0");
				isError = true;
				popRPN();
				value = 0;
			} else {
				value = op_modulo(popRPN(), value);
			}
			break;
		case RPN_NEG:
			value = -popRPN();
			break;
		case RPN_EXP:
			value = popRPN();
			if (value < 0) {
				if (!isError)
					error(patch->src, patch->lineNo, "Exponent by negative");
				isError = true;
				popRPN();
				value = 0;
			} else {
				value = op_exponent(popRPN(), value);
			}
			break;

		case RPN_OR:
			value = popRPN() | popRPN();
			break;
		case RPN_AND:
			value = popRPN() & popRPN();
			break;
		case RPN_XOR:
			value = popRPN() ^ popRPN();
			break;
		case RPN_NOT:
			value = ~popRPN();
			break;

		case RPN_LOGAND:
			value = popRPN();
			value = popRPN() && value;
			break;
		case RPN_LOGOR:
			value = popRPN();
			value = popRPN() || value;
			break;
		case RPN_LOGNOT:
			value = !popRPN();
			break;

		case RPN_LOGEQ:
			value = popRPN() == popRPN();
			break;
		case RPN_LOGNE:
			value = popRPN() != popRPN();
			break;
		case RPN_LOGGT:
			value = popRPN();
			value = popRPN() > value;
			break;
		case RPN_LOGLT:
			value = popRPN();
			value = popRPN() < value;
			break;
		case RPN_LOGGE:
			value = popRPN();
			value = popRPN() >= value;
			break;
		case RPN_LOGLE:
			value = popRPN();
			value = popRPN() <= value;
			break;

		case RPN_SHL:
			value = popRPN();
			value = op_shift_left(popRPN(), value);
			break;
		case RPN_SHR:
			value = popRPN();
			value = op_shift_right(popRPN(), value);
			break;
		case RPN_USHR:
			value = popRPN();
			value = op_shift_right_unsigned(popRPN(), value);
			break;

		case RPN_BANK_SYM:
			value = 0;
			for (uint8_t shift = 0; shift < 32; shift += 8)
				value |= getRPNByte(&expression, &size,
						    patch->src, patch->lineNo) << shift;
			symbol = getSymbol(fileSymbols, value);

			if (!symbol) {
				error(patch->src, patch->lineNo,
				      "Requested BANK() of symbol \"%s\", which was not found",
				      fileSymbols[value].name);
				isError = true;
				value = 1;
			} else if (!symbol->section) {
				error(patch->src, patch->lineNo,
				      "Requested BANK() of non-label symbol \"%s\"",
				      fileSymbols[value].name);
				isError = true;
				value = 1;
			} else {
				value = symbol->section->bank;
			}
			break;

		case RPN_BANK_SECT:
			// `expression` is not guaranteed to be '\0'-terminated. If it is not,
			// `getRPNByte` will have a fatal internal error.
			// In either case, `getRPNByte` will not free `expression`.
			name = (char const *)expression;
			while (getRPNByte(&expression, &size, patch->src, patch->lineNo))
				;

			sect = sect_GetSection(name);

			if (!sect) {
				error(patch->src, patch->lineNo,
				      "Requested BANK() of section \"%s\", which was not found",
				      name);
				isError = true;
				value = 1;
			} else {
				value = sect->bank;
			}
			break;

		case RPN_BANK_SELF:
			if (!patch->pcSection) {
				error(patch->src, patch->lineNo,
				      "PC has no bank outside a section");
				isError = true;
				value = 1;
			} else {
				value = patch->pcSection->bank;
			}
			break;

		case RPN_SIZEOF_SECT:
			// This has assumptions commented in the `RPN_BANK_SECT` case above.
			name = (char const *)expression;
			while (getRPNByte(&expression, &size, patch->src, patch->lineNo))
				;

			sect = sect_GetSection(name);

			if (!sect) {
				error(patch->src, patch->lineNo,
				      "Requested SIZEOF() of section \"%s\", which was not found",
				      name);
				isError = true;
				value = 1;
			} else {
				value = sect->size;
			}
			break;

		case RPN_STARTOF_SECT:
			// This has assumptions commented in the `RPN_BANK_SECT` case above.
			name = (char const *)expression;
			while (getRPNByte(&expression, &size, patch->src, patch->lineNo))
				;

			sect = sect_GetSection(name);
			assert(sect->offset == 0);

			if (!sect) {
				error(patch->src, patch->lineNo,
				      "Requested STARTOF() of section \"%s\", which was not found",
				      name);
				isError = true;
				value = 1;
			} else {
				value = sect->org;
			}
			break;

		case RPN_SIZEOF_SECTTYPE:
			value = getRPNByte(&expression, &size, patch->src, patch->lineNo);
			if (value < 0 || value >= SECTTYPE_INVALID) {
				error(patch->src, patch->lineNo,
				      "Requested SIZEOF() an invalid section type");
				isError = true;
				value = 0;
			} else {
				value = sectionTypeInfo[value].size;
			}
			break;

		case RPN_STARTOF_SECTTYPE:
			value = getRPNByte(&expression, &size, patch->src, patch->lineNo);
			if (value < 0 || value >= SECTTYPE_INVALID) {
				error(patch->src, patch->lineNo,
				      "Requested STARTOF() an invalid section type");
				isError = true;
				value = 0;
			} else {
				value = sectionTypeInfo[value].startAddr;
			}
			break;

		case RPN_HRAM:
			value = popRPN();
			if (!isError && (value < 0
				     || (value > 0xFF && value < 0xFF00)
				     || value > 0xFFFF)) {
				error(patch->src, patch->lineNo,
				      "Value %" PRId32 " is not in HRAM range", value);
				isError = true;
			}
			value &= 0xFF;
			break;

		case RPN_RST:
			value = popRPN();
			// Acceptable values are 0x00, 0x08, 0x10, ..., 0x38
			// They can be easily checked with a bitmask
			if (value & ~0x38) {
				if (!isError)
					error(patch->src, patch->lineNo,
					      "Value %" PRId32 " is not a RST vector", value);
				isError = true;
			}
			value |= 0xC7;
			break;

		case RPN_CONST:
			value = 0;
			for (uint8_t shift = 0; shift < 32; shift += 8)
				value |= getRPNByte(&expression, &size,
						    patch->src, patch->lineNo) << shift;
			break;

		case RPN_SYM:
			value = 0;
			for (uint8_t shift = 0; shift < 32; shift += 8)
				value |= getRPNByte(&expression, &size,
						    patch->src, patch->lineNo) << shift;

			if (value == -1) { // PC
				if (!patch->pcSection) {
					error(patch->src, patch->lineNo,
					      "PC has no value outside a section");
					value = 0;
					isError = true;
				} else {
					value = patch->pcOffset + patch->pcSection->org;
				}
			} else {
				symbol = getSymbol(fileSymbols, value);

				if (!symbol) {
					error(patch->src, patch->lineNo,
					      "Unknown symbol \"%s\"", fileSymbols[value].name);
					isError = true;
				} else {
					value = symbol->value;
					// Symbols attached to sections have offsets
					if (symbol->section)
						value += symbol->section->org;
				}
			}
			break;
		}

		pushRPN(value, isError);
	}

	if (rpnStack.size() > 1)
		error(patch->src, patch->lineNo,
		      "RPN stack has %zu entries on exit, not 1", rpnStack.size());

	isError = false;
	return popRPN();

#undef popRPN
}

void patch_CheckAssertions(std::deque<struct Assertion> &assertions)
{
	verbosePrint("Checking assertions...\n");

	for (struct Assertion &assert : assertions) {
		int32_t value = computeRPNExpr(&assert.patch, *assert.fileSymbols);
		enum AssertionType type = (enum AssertionType)assert.patch.type;

		if (!isError && !value) {
			switch (type) {
			case ASSERT_FATAL:
				fatal(assert.patch.src, assert.patch.lineNo, "%s",
				      assert.message[0] ? assert.message
							 : "assert failure");
			case ASSERT_ERROR:
				error(assert.patch.src, assert.patch.lineNo, "%s",
				      assert.message[0] ? assert.message
							 : "assert failure");
				break;
			case ASSERT_WARN:
				warning(assert.patch.src, assert.patch.lineNo, "%s",
					assert.message[0] ? assert.message
							   : "assert failure");
				break;
			}
		} else if (isError && type == ASSERT_FATAL) {
			fatal(assert.patch.src, assert.patch.lineNo,
			      "Failed to evaluate assertion%s%s",
			      assert.message[0] ? ": " : "",
			      assert.message);
		}
	}
}

/*
 * Applies all of a section's patches
 * @param section The section component to patch
 * @param dataSection The section to patch
 */
static void applyFilePatches(struct Section *section, struct Section *dataSection)
{
	verbosePrint("Patching section \"%s\"...\n", section->name);
	for (struct Patch &patch : *section->patches) {
		int32_t value = computeRPNExpr(&patch, *section->fileSymbols);
		uint16_t offset = patch.offset + section->offset;

		// `jr` is quite unlike the others...
		if (patch.type == PATCHTYPE_JR) {
			// Offset is relative to the byte *after* the operand
			// PC as operand to `jr` is lower than reference PC by 2
			uint16_t address = patch.pcSection->org + patch.pcOffset + 2;
			int16_t jumpOffset = value - address;

			if (!isError && (jumpOffset < -128 || jumpOffset > 127))
				error(patch.src, patch.lineNo,
				      "jr target out of reach (expected -129 < %" PRId16 " < 128)",
				      jumpOffset);
			(*dataSection->data)[offset] = jumpOffset & 0xFF;
		} else {
			// Patch a certain number of bytes
			struct {
				uint8_t size;
				int32_t min;
				int32_t max;
			} const types[PATCHTYPE_INVALID] = {
				{ 1,      -128,       255 }, // PATCHTYPE_BYTE
				{ 2,    -32768,     65536 }, // PATCHTYPE_WORD
				{ 4, INT32_MIN, INT32_MAX }, // PATCHTYPE_LONG
			};

			if (!isError && (value < types[patch.type].min
				      || value > types[patch.type].max))
				error(patch.src, patch.lineNo,
				      "Value %" PRId32 "%s is not %u-bit",
				      value, value < 0 ? " (maybe negative?)" : "",
				      types[patch.type].size * 8U);
			for (uint8_t i = 0; i < types[patch.type].size; i++) {
				(*dataSection->data)[offset + i] = value & 0xFF;
				value >>= 8;
			}
		}
	}
}

/*
 * Applies all of a section's patches, iterating over "components" of unionized sections
 * @param section The section to patch
 */
static void applyPatches(struct Section *section)
{
	if (!sect_HasData(section->type))
		return;

	for (struct Section *component = section; component; component = component->nextu)
		applyFilePatches(component, section);
}

void patch_ApplyPatches(void)
{
	sect_ForEach(applyPatches);
}