scummvm/backends/plugins/arm-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.
 *
 * $URL$
 * $Id$
 *
 */

#if defined(DYNAMIC_MODULES) && defined(ARM_TARGET)

#include "backends/fs/ds/ds-fs.h"
#include "elf-loader.h"
#include "dsmain.h"
#include "arm-loader.h"

//#define __DEBUG_PLUGINS__

#ifdef __DEBUG_PLUGINS__
#define DBG(x,...) consolePrintf(x, ## __VA_ARGS__)
#else
#define DBG(x,...)
#endif

#define seterror(x,...) consolePrintf(x, ## __VA_ARGS__)

/**
 * Follow the instruction of a relocation section.
 *
 * @param DLFile 	 SeekableReadStream of File
 * @param offset 	 Offset into the File
 * @param size   	 Size of relocation section
 *
 */
bool ARMDLObject::relocate(Common::SeekableReadStream* DLFile, unsigned long offset, unsigned long size, void *relSegment) {
	Elf32_Rel *rel = NULL; //relocation entry

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

	// Read in our relocation table
	if (DLFile->seek(offset, SEEK_SET) < 0 ||
	        DLFile->read(rel, size) != (ssize_t)size) {
		seterror("Relocation table load failed.");
		free(rel);
		return false;
	}

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

	DBG("Loaded relocation table. %d entries. base address=%p\n", cnt, relSegment);

	int a = 0;
	unsigned int relocation = 0;

	// Loop over relocation entries
	for (int i = 0; i < cnt; i++) {

		// Get the symbol this relocation entry is referring to
		Elf32_Sym *sym = (Elf32_Sym *)(_symtab) + (REL_INDEX(rel[i].r_info));

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

		unsigned int origTarget = *target;	//Save for debugging

		// Act differently based on the type of relocation
		switch (REL_TYPE(rel[i].r_info)) {

		case R_ARM_ABS32:
			if (sym->st_shndx < SHN_LOPROC) {			// Only shift for plugin section.
				a = *target;							// Get full 32 bits of addend
				relocation = a + (Elf32_Addr)_segment;			   // Shift by main offset

				*target = relocation;

				DBG("R_ARM_ABS32: i=%d, a=%x, origTarget=%x, target=%x\n", i, a, origTarget, *target);
			}
			break;

		case R_ARM_THM_CALL:
			DBG("R_ARM_THM_CALL: PC-relative jump, ld takes care of necessary relocation work for us.\n");
			break;

		case R_ARM_CALL:
			DBG("R_ARM_CALL: PC-relative jump, ld takes care of necessary relocation work for us.\n");
			break;

		case R_ARM_JUMP24:
			DBG("R_ARM_JUMP24: PC-relative jump, ld takes care of all relocation work for us.\n");
			break;

		case R_ARM_V4BX:
			DBG("R_ARM_V4BX: No relocation calculation necessary.\n");
			break;

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

	}

	free(rel);
	return true;
}

bool ARMDLObject::relocateRels(Common::SeekableReadStream* DLFile, Elf32_Ehdr *ehdr, Elf32_Shdr *shdr) {

	// Loop over sections, finding relocation sections
	for (int i = 0; i < ehdr->e_shnum; i++) {

		Elf32_Shdr *curShdr = &(shdr[i]);

		if ((curShdr->sh_type == SHT_REL || curShdr->sh_type == SHT_RELA) &&		// Check for a relocation section
		        curShdr->sh_entsize == sizeof(Elf32_Rel) &&			// Check for proper relocation size
		        (int)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 (curShdr->sh_type == SHT_RELA) {
				seterror("RELA entries not supported yet!\n");
				return false;
			}

			if (!relocate(DLFile, curShdr->sh_offset, curShdr->sh_size, _segment)) {
				return false;
			}

		}
	}

	return true;
}

#endif /* defined(DYNAMIC_MODULES) && defined(ARM_TARGET) */