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Diffstat (limited to 'backends/plugins/mips-relocs.cpp')
| -rw-r--r-- | backends/plugins/mips-relocs.cpp | 259 |
1 files changed, 259 insertions, 0 deletions
diff --git a/backends/plugins/mips-relocs.cpp b/backends/plugins/mips-relocs.cpp new file mode 100644 index 0000000000..fe8fa7c1a0 --- /dev/null +++ b/backends/plugins/mips-relocs.cpp @@ -0,0 +1,259 @@ +/* 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. + * + * $URL$ + * $Id$ + * + */ + +#include "elf-loader.h" + +#define __DEBUG_PLUGINS__ + +#ifdef __DEBUG_PLUGINS__ +#define DBG(x,...) printf(x, ## __VA_ARGS__) +#else +#define DBG(x,...) +#endif + +#define seterror(x,...) printf(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 + * @param relSegment Base address of relocated segment in memory (memory offset) + * + */ +bool DLObject::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); + + bool seenHi16 = false; // For treating HI/LO16 commands + int firstHi16 = -1; // Mark the point of the first hi16 seen + Elf32_Addr ahl = 0; // Calculated addend + int a = 0; // Addend: taken from the target + + unsigned int *lastTarget = 0; // For processing hi16 when lo16 arrives + unsigned int relocation = 0; + int debugRelocs[10] = {0}; // For debugging + int extendedHi16 = 0; // Count extended hi16 treatments + Elf32_Addr lastHiSymVal = 0; + bool hi16InShorts = false; + +#define DEBUG_NUM 2 + + // 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_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 + DBG("R_MIPS_HI16: i=%d, offset=%x, ahl = %x, target = %x\n", + 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 + seterror("R_MIPS_LO16 w/o preceding R_MIPS_HI16 at relocation %d!\n", 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 + (Elf32_Addr)_segment; // Add in the new offset for the segment + + if (firstHi16 >= 0) { // We haven't treated the HI16s yet so do it now + for (int j = firstHi16; j < i; j++) { + if (REL_TYPE(rel[j].r_info) != R_MIPS_HI16) continue; // Skip over non-Hi16s + + lastTarget = (unsigned int *)((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) + DBG("R_MIPS_LO16: i=%d, offset=%x, a=%x, ahl = %x, lastTarget = %x, origt = %x, target = %x\n", + i, rel[i].r_offset, a, ahl, *lastTarget, origTarget, *target); + if (lo16InShorts && debugRelocs[2]++ < DEBUG_NUM) + DBG("R_MIPS_LO16s: i=%d, offset=%x, a=%x, ahl = %x, lastTarget = %x, origt = %x, target = %x\n", + 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) + (Elf32_Addr)_segment) >> 2; // a already points to the target. Subtract our offset + *target &= 0xfc000000; // Clean lower 26 target bits + *target |= (relocation & 0x03ffffff); + + if (debugRelocs[3]++ < DEBUG_NUM) + DBG("R_MIPS_26: i=%d, offset=%x, symbol=%d, stinfo=%x, a=%x, origTarget=%x, target=%x\n", + i, rel[i].r_offset, REL_INDEX(rel[i].r_info), sym->st_info, a, origTarget, *target); + } else { + if (debugRelocs[4]++ < DEBUG_NUM) + DBG("R_MIPS_26: i=%d, offset=%x, symbol=%d, stinfo=%x, a=%x, origTarget=%x, target=%x\n", + 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) + DBG("R_MIPS_GPREL16: i=%d, a=%x, gpVal=%x, origTarget=%x, target=%x, offset=%x\n", + 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 + (Elf32_Addr)_segment; // Shift by main offset + *target = relocation; + + if (debugRelocs[6]++ < DEBUG_NUM) + DBG("R_MIPS_32: i=%d, a=%x, origTarget=%x, target=%x\n", i, a, origTarget, *target); + } + break; + + default: + seterror("Unknown relocation type %x at relocation %d.\n", REL_TYPE(rel[i].r_info), i); + free(rel); + return false; + } + } + + DBG("Done with relocation. extendedHi16=%d\n\n", extendedHi16); + + free(rel); + return true; +} + +bool DLObject::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]); + //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 + (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 (!ShortsMan.inGeneralSegment((char *)shdr[curShdr->sh_info].sh_addr)) { // regular segment + if (!relocate(DLFile, curShdr->sh_offset, curShdr->sh_size, _segment)) { + return false; + } + } else { // In Shorts segment + if (!relocate(DLFile, curShdr->sh_offset, curShdr->sh_size, (void *)_shortsSegment->getOffset())) { + return false; + } + } + + } + } + + return true; +} + |