yuzu/src/core/loader/linker.cpp

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// Copyright 2017 Citra Emulator Project
// Licensed under GPLv2 or any later version
// Refer to the license.txt file included.
#include <vector>
#include "common/common_funcs.h"
#include "common/logging/log.h"
#include "common/swap.h"
#include "core/loader/linker.h"
#include "core/memory.h"
namespace Loader {
enum class RelocationType : u32 { ABS64 = 257, GLOB_DAT = 1025, JUMP_SLOT = 1026, RELATIVE = 1027 };
enum DynamicType : u32 {
DT_NULL = 0,
DT_PLTRELSZ = 2,
DT_STRTAB = 5,
DT_SYMTAB = 6,
DT_RELA = 7,
DT_RELASZ = 8,
DT_STRSZ = 10,
DT_JMPREL = 23,
};
struct Elf64_Rela {
u64_le offset;
RelocationType type;
u32_le symbol;
s64_le addend;
};
static_assert(sizeof(Elf64_Rela) == 0x18, "Elf64_Rela has incorrect size.");
struct Elf64_Dyn {
u64_le tag;
u64_le value;
};
static_assert(sizeof(Elf64_Dyn) == 0x10, "Elf64_Dyn has incorrect size.");
struct Elf64_Sym {
u32_le name;
INSERT_PADDING_BYTES(0x2);
u16_le shndx;
u64_le value;
u64_le size;
};
static_assert(sizeof(Elf64_Sym) == 0x18, "Elf64_Sym has incorrect size.");
void Linker::WriteRelocations(std::vector<u8>& program_image,
const std::vector<Symbol>& symbols, u64 relocation_offset,
u64 size, bool is_jump_relocation, VAddr load_base) {
for (u64 i = 0; i < size; i += sizeof(Elf64_Rela)) {
Elf64_Rela rela;
std::memcpy(&rela, &program_image[relocation_offset + i], sizeof(Elf64_Rela));
const Symbol& symbol = symbols[rela.symbol];
switch (rela.type) {
case RelocationType::RELATIVE: {
const u64 value = load_base + rela.addend;
if (!symbol.name.empty()) {
exports[symbol.name] = value;
}
std::memcpy(&program_image[rela.offset], &value, sizeof(u64));
break;
}
case RelocationType::JUMP_SLOT:
case RelocationType::GLOB_DAT:
if (!symbol.value) {
imports[symbol.name] = {rela.offset + load_base, 0};
} else {
exports[symbol.name] = symbol.value;
std::memcpy(&program_image[rela.offset], &symbol.value, sizeof(u64));
}
break;
case RelocationType::ABS64:
if (!symbol.value) {
imports[symbol.name] = {rela.offset + load_base, rela.addend};
} else {
const u64 value = symbol.value + rela.addend;
exports[symbol.name] = value;
std::memcpy(&program_image[rela.offset], &value, sizeof(u64));
}
break;
default:
LOG_CRITICAL(Loader, "Unknown relocation type: %d", rela.type);
break;
}
}
}
void Linker::Relocate(std::vector<u8>& program_image, u32 dynamic_section_offset,
VAddr load_base) {
std::map<u64, u64> dynamic;
while (dynamic_section_offset < program_image.size()) {
Elf64_Dyn dyn;
std::memcpy(&dyn, &program_image[dynamic_section_offset], sizeof(Elf64_Dyn));
dynamic_section_offset += sizeof(Elf64_Dyn);
if (dyn.tag == DT_NULL) {
break;
}
dynamic[dyn.tag] = dyn.value;
}
u64 offset = dynamic[DT_SYMTAB];
std::vector<Symbol> symbols;
while (offset < program_image.size()) {
Elf64_Sym sym;
std::memcpy(&sym, &program_image[offset], sizeof(Elf64_Sym));
offset += sizeof(Elf64_Sym);
if (sym.name >= dynamic[DT_STRSZ]) {
break;
}
std::string name = reinterpret_cast<char*>(&program_image[dynamic[DT_STRTAB] + sym.name]);
if (sym.value) {
exports[name] = load_base + sym.value;
symbols.emplace_back(std::move(name), load_base + sym.value);
} else {
symbols.emplace_back(std::move(name), 0);
}
}
if (dynamic.find(DT_RELA) != dynamic.end()) {
WriteRelocations(program_image, symbols, dynamic[DT_RELA], dynamic[DT_RELASZ], false,
load_base);
}
if (dynamic.find(DT_JMPREL) != dynamic.end()) {
WriteRelocations(program_image, symbols, dynamic[DT_JMPREL], dynamic[DT_PLTRELSZ], true,
load_base);
}
}
void Linker::ResolveImports() {
// Resolve imports
for (const auto& import : imports) {
const auto& search = exports.find(import.first);
if (search != exports.end()) {
Memory::Write64(import.second.ea, search->second + import.second.addend);
}
else {
LOG_ERROR(Loader, "Unresolved import: %s", import.first.c_str());
}
}
}
} // namespace Loader