scummvm/backends/plugins/elf/mips-loader.cpp

/* ScummVM - Graphic Adventure Engine
 *
 * ScummVM is the legal property of its developers, whose names
 * are too numerous to list here. Please refer to the COPYRIGHT
 * file distributed with this source distribution.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 */

#include "common/scummsys.h"

#if defined(DYNAMIC_MODULES) && defined(USE_ELF_LOADER) && defined(MIPS_TARGET)

#include "backends/plugins/elf/mips-loader.h"
#include "backends/plugins/elf/memory-manager.h"

#include "common/debug.h"

#define DEBUG_NUM 2

bool MIPSDLObject::relocate(Elf32_Off offset, Elf32_Word size, byte *relSegment) {
	Elf32_Rel *rel = 0;	// relocation entry

	// Allocate memory for relocation table
	if (!(rel = (Elf32_Rel *)malloc(size))) {
		warning("elfloader: Out of memory.");
		return false;
	}

	// Read in our relocation table
	if (!_file->seek(offset, SEEK_SET) || _file->read(rel, size) != size) {
		warning("elfloader: Relocation table load failed.");
		free(rel);
		return false;
	}

	// Treat each relocation entry. Loop over all of them
	uint32 cnt = size / sizeof(*rel);

	debug(2, "elfloader: Loaded relocation table. %d entries. base address=%p", cnt, relSegment);

	Elf32_Addr adjustedMainSegment = Elf32_Addr(_segment) - _segmentVMA;	// adjust for VMA offset

	bool seenHi16 = false;			// For treating HI/LO16 commands
	int32 firstHi16 = -1;			// Mark the point of the first hi16 seen
	Elf32_Addr ahl = 0;				// Calculated addend
	int32 a = 0;					// Addend: taken from the target

	uint32 *lastTarget = 0;			// For processing hi16 when lo16 arrives
	uint32 relocation = 0;
	uint debugRelocs[10] = { 0 };	// For debugging
	uint extendedHi16 = 0;			// Count extended hi16 treatments
	Elf32_Addr lastHiSymVal = 0;
	bool hi16InShorts = false;

	// Loop over relocation entries
	for (uint32 i = 0; i < cnt; i++) {
		// Get the symbol this relocation entry is referring to
		Elf32_Sym *sym = _symtab + (REL_INDEX(rel[i].r_info));

		// Get the target instruction in the code.
		uint32 *target = (uint32 *)((byte *)relSegment + rel[i].r_offset);

		uint32 origTarget = *target;	// Save for debugging

		// Act differently based on the type of relocation
		switch (REL_TYPE(rel[i].r_info)) {
		case R_MIPS_HI16:							// Absolute addressing.
			if (sym->st_shndx < SHN_LOPROC &&		// Only shift for plugin section (ie. has a real section index)
				firstHi16 < 0) {					// Only process first in block of HI16s
				firstHi16 = i;						// Keep the first Hi16 we saw
				seenHi16 = true;
				ahl = (*target & 0xffff) << 16;		// Take lower 16 bits shifted up

				lastHiSymVal = sym->st_value;
				hi16InShorts = ShortsMan.inGeneralSegment((char *)sym->st_value); // Fix for problem with switching btw segments
				if (debugRelocs[0]++ < DEBUG_NUM)	// Print only a set number
					debug(8, "elfloader: R_MIPS_HI16: i=%d, offset=%x, ahl = %x, target = %x",
							i, rel[i].r_offset, ahl, *target);
			}
			break;

		case R_MIPS_LO16:							// Absolute addressing. Needs a HI16 to come before it
			if (sym->st_shndx < SHN_LOPROC) {		// Only shift for plugin section. (ie. has a real section index)
				if (!seenHi16) {					// We MUST have seen HI16 first
					debug(8, "elfloader: R_MIPS_LO16 w/o preceding R_MIPS_HI16 at relocation %d!", i);
					free(rel);
					return false;
				}

				// Fix: bug in gcc makes LO16s connect to wrong HI16s sometimes (shorts and regular segment)
				// Note that we can check the entire shorts segment because the executable's shorts don't belong to this plugin section
				// and will be screened out above
				bool lo16InShorts = ShortsMan.inGeneralSegment((char *)sym->st_value);

				// Correct the bug by getting the proper value in ahl (taken from the current symbol)
				if ((hi16InShorts && !lo16InShorts) || (!hi16InShorts && lo16InShorts)) {
					ahl -= (lastHiSymVal & 0xffff0000);		// We assume gcc meant the same offset
					ahl += (sym->st_value & 0xffff0000);
				}

				ahl &= 0xffff0000;				// Clean lower 16 bits for repeated LO16s
				a = *target & 0xffff;			// Take lower 16 bits of the target
				a = (a << 16) >> 16;			// Sign extend them
				ahl += a;						// Add lower 16 bits. AHL is now complete

				// Fix: we can have LO16 access to the short segment sometimes
				if (lo16InShorts)
					relocation = ahl + _shortsSegment->getOffset();		// Add in the short segment offset
				else	// It's in the regular segment
					relocation = ahl + adjustedMainSegment;				// Add in the new offset for the segment

				if (firstHi16 >= 0) {					// We haven't treated the HI16s yet so do it now
					for (uint32 j = firstHi16; j < i; j++) {
						if (REL_TYPE(rel[j].r_info) != R_MIPS_HI16)
							continue;	// Skip over non-Hi16s

						lastTarget = (uint32 *)((char *)relSegment + rel[j].r_offset);	// get hi16 target
						*lastTarget &= 0xffff0000;		// Clear the lower 16 bits of the last target
						*lastTarget |= (relocation >> 16) & 0xffff;	// Take the upper 16 bits of the relocation
						if (relocation & 0x8000)
							(*lastTarget)++;	// Subtle: we need to add 1 to the HI16 in this case
					}

					firstHi16 = -1;						// Reset so we'll know we treated it
				} else {
					extendedHi16++;
				}

				*target &= 0xffff0000;						// Clear the lower 16 bits of current target
				*target |= relocation & 0xffff;				// Take the lower 16 bits of the relocation

				if (debugRelocs[1]++ < DEBUG_NUM)
					debug(8, "elfloader: R_MIPS_LO16: i=%d, offset=%x, a=%x, ahl = %x, "
							"lastTarget = %x, origt = %x, target = %x",
							i, rel[i].r_offset, a, ahl, *lastTarget, origTarget, *target);

				if (lo16InShorts && debugRelocs[2]++ < DEBUG_NUM)
					debug(8, "elfloader: R_MIPS_LO16s: i=%d, offset=%x, a=%x, ahl = %x, "
							"lastTarget = %x, origt = %x, target = %x",
							i, rel[i].r_offset, a, ahl, *lastTarget, origTarget, *target);
			}
			break;

		case R_MIPS_26:													// Absolute addressing (for jumps and branches only)
			if (sym->st_shndx < SHN_LOPROC) {							// Only relocate for main segment
				a = *target & 0x03ffffff;								// Get 26 bits' worth of the addend
				a = (a << 6) >> 6; 										// Sign extend a
				relocation = ((a << 2) + adjustedMainSegment) >> 2;		// a already points to the target. Add our offset
				*target &= 0xfc000000;									// Clean lower 26 target bits
				*target |= (relocation & 0x03ffffff);

				if (debugRelocs[3]++ < DEBUG_NUM)
					debug(8, "elfloader: R_MIPS_26: i=%d, offset=%x, symbol=%d, stinfo=%x, "
							"a=%x, origTarget=%x, target=%x",
							i, rel[i].r_offset, REL_INDEX(rel[i].r_info), sym->st_info, a, origTarget, *target);
			} else {
				if (debugRelocs[4]++ < DEBUG_NUM)
					debug(8, "elfloader: R_MIPS_26: i=%d, offset=%x, symbol=%d, stinfo=%x, "
							"a=%x, origTarget=%x, target=%x",
							i, rel[i].r_offset, REL_INDEX(rel[i].r_info), sym->st_info, a, origTarget, *target);
			}
			break;

		case R_MIPS_GPREL16:												// GP Relative addressing
			if (_shortsSegment->getOffset() != 0 &&							// Only relocate if we shift the shorts section
					ShortsMan.inGeneralSegment((char *) sym->st_value)) {	// Only relocate things in the plugin hole
				a = *target & 0xffff;										// Get 16 bits' worth of the addend
				a = (a << 16) >> 16;										// Sign extend it

				relocation = a + _shortsSegment->getOffset();

				*target &= 0xffff0000;					// Clear the lower 16 bits of the target
				*target |= relocation & 0xffff;

				if (debugRelocs[5]++ < DEBUG_NUM)
					debug(8, "elfloader: R_MIPS_GPREL16: i=%d, a=%x, gpVal=%x, origTarget=%x, "
							"target=%x, offset=%x",
							i, a, _gpVal, origTarget, *target, _shortsSegment->getOffset());
			}

			break;

		case R_MIPS_32:									// Absolute addressing
			if (sym->st_shndx < SHN_LOPROC) {			// Only shift for plugin section.
				a = *target;							// Get full 32 bits of addend

				if (ShortsMan.inGeneralSegment((char *)sym->st_value))	// Check if we're in the shorts segment
					relocation = a + _shortsSegment->getOffset();		// Shift by shorts offset
				else													// We're in the main section
					relocation = a + adjustedMainSegment;				// Shift by main offset

				*target = relocation;

				if (debugRelocs[6]++ < DEBUG_NUM)
					debug(8, "elfloader: R_MIPS_32: i=%d, a=%x, origTarget=%x, target=%x",
							i, a, origTarget, *target);
			}

			break;

		default:
			warning("elfloader: Unknown relocation type %x at relocation %d.", REL_TYPE(rel[i].r_info), i);
			free(rel);
			return false;
		}
	}

	debug(2, "elfloader: Done with relocation. extendedHi16=%d", extendedHi16);

	free(rel);
	return true;
}

bool MIPSDLObject::relocateRels(Elf32_Ehdr *ehdr, Elf32_Shdr *shdr) {
	// Loop over sections, finding relocation sections
	for (uint32 i = 0; i < ehdr->e_shnum; i++) {
		Elf32_Shdr *curShdr = &(shdr[i]);
		//Elf32_Shdr *linkShdr = &(shdr[curShdr->sh_info]);

		if (curShdr->sh_type == SHT_REL &&							// Check for a relocation section
				curShdr->sh_entsize == sizeof(Elf32_Rel) &&			// Check for proper relocation size
				int32(curShdr->sh_link) == _symtab_sect &&			// Check that the sh_link connects to our symbol table
				curShdr->sh_info < ehdr->e_shnum &&					// Check that the relocated section exists
				(shdr[curShdr->sh_info].sh_flags & SHF_ALLOC)) {	// Check if relocated section resides in memory
			if (!ShortsMan.inGeneralSegment((char *)shdr[curShdr->sh_info].sh_addr)) {			// regular segment
				if (!relocate(curShdr->sh_offset, curShdr->sh_size, _segment - _segmentVMA))
					return false;
			} else {	// In Shorts segment
				if (!relocate(curShdr->sh_offset, curShdr->sh_size, (byte *)_shortsSegment->getOffset()))
					return false;
			}
		}
	}

	return true;
}

void MIPSDLObject::relocateSymbols(ptrdiff_t offset) {
	// Loop over symbols, add relocation offset
	Elf32_Sym *s = _symtab;

	for (uint32 c = _symbol_cnt; c--; s++) {
		// Make sure we don't relocate special valued symbols
		if (s->st_shndx < SHN_LOPROC) {
			if (!ShortsMan.inGeneralSegment((char *)s->st_value)) {
				if (s->st_value < _segmentVMA)
					s->st_value = _segmentVMA;	// deal with symbols referring to sections, which start before the VMA

				s->st_value += offset;

				if (s->st_value < Elf32_Addr(_segment) || s->st_value > Elf32_Addr(_segment) + _segmentSize)
					warning("elfloader: Symbol out of bounds! st_value = %x", s->st_value);
			} else {	// shorts section
				s->st_value += _shortsSegment->getOffset();
				if (!_shortsSegment->inSegment((char *)s->st_value))
					warning("elfloader: Symbol out of bounds! st_value = %x", s->st_value);
			}
		}
	}
}

bool MIPSDLObject::loadSegment(Elf32_Phdr *phdr) {
	byte *baseAddress = 0;

	// We need to take account of non-allocated segment for shorts
	if (phdr->p_flags & PF_X) {	// This is a relocated segment
		// Attempt to allocate memory for segment
		_segment = (byte *)ELFMemMan.pluginAllocate(phdr->p_align, phdr->p_memsz);

		if (!_segment) {
			warning("elfloader: Out of memory.");
			return false;
		}

		debug(2, "elfloader: Allocated segment @ %p", _segment);

		// Get offset to load segment into
		baseAddress = _segment;
		_segmentSize = phdr->p_memsz;
		_segmentVMA = phdr->p_vaddr;

	} else {						// This is a shorts section.
		_shortsSegment = ShortsMan.newSegment(phdr->p_memsz, (char *)phdr->p_vaddr);

		baseAddress = (byte *)_shortsSegment->getStart();
		debug(2, "elfloader: Shorts segment @ %p to %p. Segment wants to be at %x. Offset=%x",
				_shortsSegment->getStart(), _shortsSegment->getEnd(), phdr->p_vaddr,
				_shortsSegment->getOffset());
	}

	// Set .sbss segment to 0 if necessary
	if (phdr->p_memsz > phdr->p_filesz) {
		debug(2, "elfloader: Setting %p to %p to 0 for bss", baseAddress + phdr->p_filesz,
				baseAddress + phdr->p_memsz);
		memset(baseAddress + phdr->p_filesz, 0, phdr->p_memsz - phdr->p_filesz);
	}

	debug(2, "elfloader: Reading the segment into memory");

	// Read the segment into memory
	if (!_file->seek(phdr->p_offset, SEEK_SET) ||
			_file->read(baseAddress, phdr->p_filesz) != phdr->p_filesz) {
		warning("elfloader: Segment load failed.");
		return false;
	}

	debug(2, "elfloader: Segment has been read into memory");

	return true;
}

// Unload all objects from memory
void MIPSDLObject::unload() {
	DLObject::unload();
	freeShortsSegment();
}

void MIPSDLObject::freeShortsSegment() {
	if (_shortsSegment) {
		ShortsMan.deleteSegment(_shortsSegment);
		_shortsSegment = 0;
	}
}

#endif /* defined(DYNAMIC_MODULES) && defined(USE_ELF_LOADER) && defined(MIPS_TARGET) */