dolphin/Source/Core/Core/Boot/ElfReader.cpp

// Copyright 2008 Dolphin Emulator Project
// SPDX-License-Identifier: GPL-2.0-or-later

#include "Core/Boot/ElfReader.h"

#include <cstring>
#include <string>
#include <utility>

#include "Common/CommonTypes.h"
#include "Common/IOFile.h"
#include "Common/Logging/Log.h"
#include "Common/MsgHandler.h"
#include "Common/Swap.h"

#include "Core/HW/Memmap.h"
#include "Core/PowerPC/PPCSymbolDB.h"
#include "Core/System.h"

static void bswap(u32& w)
{
  w = Common::swap32(w);
}
static void bswap(u16& w)
{
  w = Common::swap16(w);
}

static void byteswapHeader(Elf32_Ehdr& ELF_H)
{
  bswap(ELF_H.e_type);
  bswap(ELF_H.e_machine);
  bswap(ELF_H.e_ehsize);
  bswap(ELF_H.e_phentsize);
  bswap(ELF_H.e_phnum);
  bswap(ELF_H.e_shentsize);
  bswap(ELF_H.e_shnum);
  bswap(ELF_H.e_shstrndx);
  bswap(ELF_H.e_version);
  bswap(ELF_H.e_entry);
  bswap(ELF_H.e_phoff);
  bswap(ELF_H.e_shoff);
  bswap(ELF_H.e_flags);
}

static void byteswapSegment(Elf32_Phdr& sec)
{
  bswap(sec.p_align);
  bswap(sec.p_filesz);
  bswap(sec.p_flags);
  bswap(sec.p_memsz);
  bswap(sec.p_offset);
  bswap(sec.p_paddr);
  bswap(sec.p_vaddr);
  bswap(sec.p_type);
}

static void byteswapSection(Elf32_Shdr& sec)
{
  bswap(sec.sh_addr);
  bswap(sec.sh_addralign);
  bswap(sec.sh_entsize);
  bswap(sec.sh_flags);
  bswap(sec.sh_info);
  bswap(sec.sh_link);
  bswap(sec.sh_name);
  bswap(sec.sh_offset);
  bswap(sec.sh_size);
  bswap(sec.sh_type);
}

ElfReader::ElfReader(std::vector<u8> buffer) : BootExecutableReader(std::move(buffer))
{
  m_is_valid = Initialize();
}

ElfReader::ElfReader(File::IOFile file) : BootExecutableReader(std::move(file))
{
  m_is_valid = Initialize();
}

ElfReader::ElfReader(const std::string& filename) : BootExecutableReader(filename)
{
  m_is_valid = Initialize();
}

ElfReader::~ElfReader() = default;

bool ElfReader::Initialize()
{
  if (m_bytes.size() < sizeof(Elf32_Ehdr))
    return false;

  base = reinterpret_cast<char*>(m_bytes.data());
  base32 = reinterpret_cast<u32*>(m_bytes.data());
  header = reinterpret_cast<Elf32_Ehdr*>(m_bytes.data());
  if (header->e_ident[EI_MAG0] != ELFMAG0 || header->e_ident[EI_MAG1] != ELFMAG1 ||
      header->e_ident[EI_MAG2] != ELFMAG2 || header->e_ident[EI_MAG3] != ELFMAG3 ||
      header->e_ident[EI_CLASS] != ELFCLASS32 || header->e_ident[EI_DATA] != ELFDATA2MSB)
  {
    return false;
  }

  byteswapHeader(*header);

  const auto is_range_valid = [this](size_t offset, size_t size) {
    return offset <= m_bytes.size() && size <= m_bytes.size() - offset;
  };
  if (header->e_ehsize != sizeof(Elf32_Ehdr) ||
      (header->e_phnum != 0 && header->e_phentsize != sizeof(Elf32_Phdr)) ||
      (header->e_shnum != 0 && header->e_shentsize != sizeof(Elf32_Shdr)) ||
      !is_range_valid(header->e_phoff, sizeof(Elf32_Phdr) * header->e_phnum) ||
      !is_range_valid(header->e_shoff, sizeof(Elf32_Shdr) * header->e_shnum) ||
      (header->e_shstrndx != SHN_UNDEF && header->e_shstrndx >= header->e_shnum))
  {
    return false;
  }

  segments = reinterpret_cast<Elf32_Phdr*>(base + header->e_phoff);
  sections = reinterpret_cast<Elf32_Shdr*>(base + header->e_shoff);

  for (int i = 0; i < GetNumSegments(); i++)
  {
    byteswapSegment(segments[i]);
    if (!is_range_valid(segments[i].p_offset, segments[i].p_filesz) ||
        segments[i].p_filesz > segments[i].p_memsz)
    {
      return false;
    }
  }

  for (int i = 0; i < GetNumSections(); i++)
  {
    byteswapSection(sections[i]);
    if (sections[i].sh_type != SHT_NOBITS &&
        !is_range_valid(sections[i].sh_offset, sections[i].sh_size))
    {
      return false;
    }
  }
  entryPoint = header->e_entry;

  bRelocate = (header->e_type != ET_EXEC);
  return true;
}

const char* ElfReader::GetSectionName(int section) const
{
  if (!m_is_valid || section < 0 || section >= header->e_shnum ||
      sections[section].sh_type == SHT_NULL)
  {
    return nullptr;
  }

  const Elf32_Shdr& string_section = sections[header->e_shstrndx];
  const size_t name_offset = sections[section].sh_name;
  const char* const ptr = reinterpret_cast<const char*>(GetSectionDataPtr(header->e_shstrndx));

  if (!ptr || name_offset >= string_section.sh_size ||
      !std::memchr(ptr + name_offset, '\0', string_section.sh_size - name_offset))
  {
    return nullptr;
  }

  return ptr + name_offset;
}

// This is just a simple elf loader, good enough to load elfs generated by devkitPPC
bool ElfReader::LoadIntoMemory(Core::System& system, bool only_in_mem1) const
{
  if (!m_is_valid)
    return false;

  INFO_LOG_FMT(BOOT, "String section: {}", header->e_shstrndx);

  if (bRelocate)
  {
    PanicAlertFmt("Error: Dolphin doesn't know how to load a relocatable elf.");
    return false;
  }

  INFO_LOG_FMT(BOOT, "{} segments:", header->e_phnum);

  auto& memory = system.GetMemory();

  // Copy segments into ram.
  for (int i = 0; i < header->e_phnum; i++)
  {
    Elf32_Phdr* p = segments + i;

    INFO_LOG_FMT(BOOT, "Type: {} Vaddr: {:08x} Filesz: {} Memsz: {}", p->p_type, p->p_vaddr,
                 p->p_filesz, p->p_memsz);

    if (p->p_type == PT_LOAD)
    {
      u32 writeAddr = p->p_vaddr;
      const u8* src = GetSegmentPtr(i);
      u32 srcSize = p->p_filesz;
      u32 dstSize = p->p_memsz;

      if (only_in_mem1 && p->p_vaddr >= memory.GetRamSizeReal())
        continue;

      memory.CopyToEmu(writeAddr, src, srcSize);
      if (srcSize < dstSize)
        memory.Memset(writeAddr + srcSize, 0, dstSize - srcSize);  // zero out bss

      INFO_LOG_FMT(BOOT, "Loadable Segment Copied to {:08x}, size {:08x}", writeAddr, p->p_memsz);
    }
  }

  INFO_LOG_FMT(BOOT, "Done loading.");
  return true;
}

SectionID ElfReader::GetSectionByName(const char* name, int firstSection) const
{
  for (int i = firstSection; i < header->e_shnum; i++)
  {
    const char* secname = GetSectionName(i);

    if (secname != nullptr && strcmp(name, secname) == 0)
      return i;
  }
  return -1;
}

bool ElfReader::LoadSymbols(const Core::CPUThreadGuard& guard, PPCSymbolDB& ppc_symbol_db,
                            const std::string& filename) const
{
  if (!m_is_valid)
    return false;

  bool hasSymbols = false;
  SectionID sec = GetSectionByName(".symtab");
  if (sec != -1)
  {
    const u32 string_section_index = sections[sec].sh_link;
    if (string_section_index >= header->e_shnum)
      return false;

    const Elf32_Shdr& string_section = sections[string_section_index];
    const char* stringBase = (const char*)GetSectionDataPtr(string_section_index);
    if (!stringBase)
      return false;

    // We have a symbol table!
    Elf32_Sym* symtab = (Elf32_Sym*)(GetSectionDataPtr(sec));
    if (!symtab)
      return false;

    int numSymbols = sections[sec].sh_size / sizeof(Elf32_Sym);
    for (int sym = 0; sym < numSymbols; sym++)
    {
      int size = Common::swap32(symtab[sym].st_size);
      if (size == 0)
        continue;

      // int bind = symtab[sym].st_info >> 4;
      int type = symtab[sym].st_info & 0xF;
      int sectionIndex = Common::swap16(symtab[sym].st_shndx);
      int value = Common::swap32(symtab[sym].st_value);
      const size_t name_offset = Common::swap32(symtab[sym].st_name);
      if (name_offset >= string_section.sh_size ||
          !std::memchr(stringBase + name_offset, '\0', string_section.sh_size - name_offset))
      {
        return false;
      }
      const char* name = stringBase + name_offset;
      if (bRelocate)
        value += sectionAddrs[sectionIndex];

      auto symtype = Common::Symbol::Type::Data;
      switch (type)
      {
      case STT_OBJECT:
        symtype = Common::Symbol::Type::Data;
        break;
      case STT_FUNC:
        symtype = Common::Symbol::Type::Function;
        break;
      default:
        continue;
      }
      ppc_symbol_db.AddKnownSymbol(guard, value, size, name, filename, symtype);
      hasSymbols = true;
    }
  }
  ppc_symbol_db.Index();
  return hasSymbols;
}

bool ElfReader::IsWii() const
{
  if (!m_is_valid)
    return false;

  // Use the same method as the DOL loader uses: search for mfspr from HID4,
  // which should only be used in Wii ELFs.
  //
  // Likely to have some false positives/negatives, patches implementing a
  // better heuristic are welcome.

  // Swap these once, instead of swapping every word in the file.
  u32 HID4_pattern = Common::swap32(0x7c13fba6);
  u32 HID4_mask = Common::swap32(0xfc1fffff);

  for (int i = 0; i < GetNumSegments(); ++i)
  {
    if (IsCodeSegment(i))
    {
      u32* code = (u32*)GetSegmentPtr(i);
      for (u32 j = 0; j < GetSegmentSize(i) / sizeof(u32); ++j)
      {
        if ((code[j] & HID4_mask) == HID4_pattern)
          return true;
      }
    }
  }

  return false;
}