260 lines
10 KiB
C++
260 lines
10 KiB
C++
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/* ScummVM - Graphic Adventure Engine
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*
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* ScummVM is the legal property of its developers, whose names
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* are too numerous to list here. Please refer to the COPYRIGHT
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* file distributed with this source distribution.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*
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* $URL$
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* $Id$
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*
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*/
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#include "elf-loader.h"
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#define __DEBUG_PLUGINS__
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#ifdef __DEBUG_PLUGINS__
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#define DBG(x,...) printf(x, ## __VA_ARGS__)
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#else
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#define DBG(x,...)
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#endif
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#define seterror(x,...) printf(x, ## __VA_ARGS__)
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/**
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* Follow the instruction of a relocation section.
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*
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* @param DLFile SeekableReadStream of File
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* @param offset Offset into the File
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* @param size Size of relocation section
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* @param relSegment Base address of relocated segment in memory (memory offset)
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*
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*/
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bool DLObject::relocate(Common::SeekableReadStream* DLFile, unsigned long offset, unsigned long size, void *relSegment) {
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Elf32_Rel *rel = NULL; // relocation entry
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// Allocate memory for relocation table
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if (!(rel = (Elf32_Rel *)malloc(size))) {
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seterror("Out of memory.");
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return false;
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}
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// Read in our relocation table
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if (DLFile->seek(offset, SEEK_SET) < 0 ||
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DLFile->read(rel, size) != (ssize_t)size) {
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seterror("Relocation table load failed.");
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free(rel);
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return false;
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}
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// Treat each relocation entry. Loop over all of them
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int cnt = size / sizeof(*rel);
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DBG("Loaded relocation table. %d entries. base address=%p\n", cnt, relSegment);
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bool seenHi16 = false; // For treating HI/LO16 commands
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int firstHi16 = -1; // Mark the point of the first hi16 seen
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Elf32_Addr ahl = 0; // Calculated addend
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int a = 0; // Addend: taken from the target
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unsigned int *lastTarget = 0; // For processing hi16 when lo16 arrives
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unsigned int relocation = 0;
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int debugRelocs[10] = {0}; // For debugging
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int extendedHi16 = 0; // Count extended hi16 treatments
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Elf32_Addr lastHiSymVal = 0;
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bool hi16InShorts = false;
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#define DEBUG_NUM 2
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// Loop over relocation entries
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for (int i = 0; i < cnt; i++) {
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// Get the symbol this relocation entry is referring to
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Elf32_Sym *sym = (Elf32_Sym *)(_symtab) + (REL_INDEX(rel[i].r_info));
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// Get the target instruction in the code
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unsigned int *target = (unsigned int *)((char *)relSegment + rel[i].r_offset);
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unsigned int origTarget = *target; // Save for debugging
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// Act differently based on the type of relocation
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switch (REL_TYPE(rel[i].r_info)) {
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case R_MIPS_HI16: // Absolute addressing.
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if (sym->st_shndx < SHN_LOPROC && // Only shift for plugin section (ie. has a real section index)
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firstHi16 < 0) { // Only process first in block of HI16s
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firstHi16 = i; // Keep the first Hi16 we saw
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seenHi16 = true;
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ahl = (*target & 0xffff) << 16; // Take lower 16 bits shifted up
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lastHiSymVal = sym->st_value;
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hi16InShorts = (ShortsMan.inGeneralSegment((char *)sym->st_value)); // Fix for problem with switching btw segments
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if (debugRelocs[0]++ < DEBUG_NUM) // Print only a set number
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DBG("R_MIPS_HI16: i=%d, offset=%x, ahl = %x, target = %x\n",
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i, rel[i].r_offset, ahl, *target);
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}
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break;
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case R_MIPS_LO16: // Absolute addressing. Needs a HI16 to come before it
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if (sym->st_shndx < SHN_LOPROC) { // Only shift for plugin section. (ie. has a real section index)
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if (!seenHi16) { // We MUST have seen HI16 first
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seterror("R_MIPS_LO16 w/o preceding R_MIPS_HI16 at relocation %d!\n", i);
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free(rel);
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return false;
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}
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// Fix: bug in gcc makes LO16s connect to wrong HI16s sometimes (shorts and regular segment)
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// Note that we can check the entire shorts segment because the executable's shorts don't belong to this plugin section
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// and will be screened out above
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bool lo16InShorts = ShortsMan.inGeneralSegment((char *)sym->st_value);
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// Correct the bug by getting the proper value in ahl (taken from the current symbol)
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if ((hi16InShorts && !lo16InShorts) || (!hi16InShorts && lo16InShorts)) {
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ahl -= (lastHiSymVal & 0xffff0000); // We assume gcc meant the same offset
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ahl += (sym->st_value & 0xffff0000);
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}
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ahl &= 0xffff0000; // Clean lower 16 bits for repeated LO16s
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a = *target & 0xffff; // Take lower 16 bits of the target
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a = (a << 16) >> 16; // Sign extend them
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ahl += a; // Add lower 16 bits. AHL is now complete
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// Fix: we can have LO16 access to the short segment sometimes
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if (lo16InShorts) {
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relocation = ahl + _shortsSegment->getOffset(); // Add in the short segment offset
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} else // It's in the regular segment
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relocation = ahl + (Elf32_Addr)_segment; // Add in the new offset for the segment
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if (firstHi16 >= 0) { // We haven't treated the HI16s yet so do it now
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for (int j = firstHi16; j < i; j++) {
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if (REL_TYPE(rel[j].r_info) != R_MIPS_HI16) continue; // Skip over non-Hi16s
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lastTarget = (unsigned int *)((char *)relSegment + rel[j].r_offset); // get hi16 target
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*lastTarget &= 0xffff0000; // Clear the lower 16 bits of the last target
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*lastTarget |= (relocation >> 16) & 0xffff; // Take the upper 16 bits of the relocation
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if (relocation & 0x8000)(*lastTarget)++; // Subtle: we need to add 1 to the HI16 in this case
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}
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firstHi16 = -1; // Reset so we'll know we treated it
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} else {
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extendedHi16++;
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}
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*target &= 0xffff0000; // Clear the lower 16 bits of current target
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*target |= relocation & 0xffff; // Take the lower 16 bits of the relocation
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if (debugRelocs[1]++ < DEBUG_NUM)
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DBG("R_MIPS_LO16: i=%d, offset=%x, a=%x, ahl = %x, lastTarget = %x, origt = %x, target = %x\n",
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i, rel[i].r_offset, a, ahl, *lastTarget, origTarget, *target);
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if (lo16InShorts && debugRelocs[2]++ < DEBUG_NUM)
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DBG("R_MIPS_LO16s: i=%d, offset=%x, a=%x, ahl = %x, lastTarget = %x, origt = %x, target = %x\n",
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i, rel[i].r_offset, a, ahl, *lastTarget, origTarget, *target);
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}
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break;
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case R_MIPS_26: // Absolute addressing (for jumps and branches only)
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if (sym->st_shndx < SHN_LOPROC) { // Only relocate for main segment
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a = *target & 0x03ffffff; // Get 26 bits' worth of the addend
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a = (a << 6) >> 6; // Sign extend a
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relocation = ((a << 2) + (Elf32_Addr)_segment) >> 2; // a already points to the target. Subtract our offset
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*target &= 0xfc000000; // Clean lower 26 target bits
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*target |= (relocation & 0x03ffffff);
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if (debugRelocs[3]++ < DEBUG_NUM)
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DBG("R_MIPS_26: i=%d, offset=%x, symbol=%d, stinfo=%x, a=%x, origTarget=%x, target=%x\n",
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i, rel[i].r_offset, REL_INDEX(rel[i].r_info), sym->st_info, a, origTarget, *target);
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} else {
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if (debugRelocs[4]++ < DEBUG_NUM)
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DBG("R_MIPS_26: i=%d, offset=%x, symbol=%d, stinfo=%x, a=%x, origTarget=%x, target=%x\n",
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i, rel[i].r_offset, REL_INDEX(rel[i].r_info), sym->st_info, a, origTarget, *target);
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}
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break;
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case R_MIPS_GPREL16: // GP Relative addressing
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if (_shortsSegment->getOffset() != 0 && // Only relocate if we shift the shorts section
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ShortsMan.inGeneralSegment((char *)sym->st_value)) { // Only relocate things in the plugin hole
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a = *target & 0xffff; // Get 16 bits' worth of the addend
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a = (a << 16) >> 16; // Sign extend it
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relocation = a + _shortsSegment->getOffset();
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*target &= 0xffff0000; // Clear the lower 16 bits of the target
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*target |= relocation & 0xffff;
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if (debugRelocs[5]++ < DEBUG_NUM)
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DBG("R_MIPS_GPREL16: i=%d, a=%x, gpVal=%x, origTarget=%x, target=%x, offset=%x\n",
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i, a, _gpVal, origTarget, *target, _shortsSegment->getOffset());
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}
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break;
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case R_MIPS_32: // Absolute addressing
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if (sym->st_shndx < SHN_LOPROC) { // Only shift for plugin section.
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a = *target; // Get full 32 bits of addend
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if (ShortsMan.inGeneralSegment((char *)sym->st_value)) // Check if we're in the shorts segment
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relocation = a + _shortsSegment->getOffset(); // Shift by shorts offset
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else // We're in the main section
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relocation = a + (Elf32_Addr)_segment; // Shift by main offset
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*target = relocation;
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if (debugRelocs[6]++ < DEBUG_NUM)
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DBG("R_MIPS_32: i=%d, a=%x, origTarget=%x, target=%x\n", i, a, origTarget, *target);
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}
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break;
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default:
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seterror("Unknown relocation type %x at relocation %d.\n", REL_TYPE(rel[i].r_info), i);
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free(rel);
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return false;
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}
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}
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DBG("Done with relocation. extendedHi16=%d\n\n", extendedHi16);
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free(rel);
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return true;
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}
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bool DLObject::relocateRels(Common::SeekableReadStream* DLFile, Elf32_Ehdr *ehdr, Elf32_Shdr *shdr) {
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// Loop over sections, finding relocation sections
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for (int i = 0; i < ehdr->e_shnum; i++) {
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Elf32_Shdr *curShdr = &(shdr[i]);
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//Elf32_Shdr *linkShdr = &(shdr[curShdr->sh_info]);
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if (curShdr->sh_type == SHT_REL && // Check for a relocation section
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curShdr->sh_entsize == sizeof(Elf32_Rel) && // Check for proper relocation size
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(int)curShdr->sh_link == _symtab_sect && // Check that the sh_link connects to our symbol table
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curShdr->sh_info < ehdr->e_shnum && // Check that the relocated section exists
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(shdr[curShdr->sh_info].sh_flags & SHF_ALLOC)) { // Check if relocated section resides in memory
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if (!ShortsMan.inGeneralSegment((char *)shdr[curShdr->sh_info].sh_addr)) { // regular segment
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if (!relocate(DLFile, curShdr->sh_offset, curShdr->sh_size, _segment)) {
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return false;
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}
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} else { // In Shorts segment
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if (!relocate(DLFile, curShdr->sh_offset, curShdr->sh_size, (void *)_shortsSegment->getOffset())) {
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return false;
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}
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}
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}
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}
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return true;
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}
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