Elf32Lib.c

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#include "ElfLibInternal.h"
 
Elf32_Shdr *
GetElf32SectionByIndex (
  IN  UINT8   *ImageBase,
  IN  UINT32  Index
  )
{
  Elf32_Ehdr  *Ehdr;
 
  Ehdr = (Elf32_Ehdr *)ImageBase;
  if (Index >= Ehdr->e_shnum) {
    return NULL;
  }
 
  return (Elf32_Shdr *)(ImageBase + Ehdr->e_shoff + Index * Ehdr->e_shentsize);
}
 
Elf32_Phdr *
GetElf32SegmentByIndex (
  IN  UINT8   *ImageBase,
  IN  UINT32  Index
  )
{
  Elf32_Ehdr  *Ehdr;
 
  Ehdr = (Elf32_Ehdr *)ImageBase;
  if (Index >= Ehdr->e_phnum) {
    return NULL;
  }
 
  return (Elf32_Phdr *)(ImageBase + Ehdr->e_phoff + Index * Ehdr->e_phentsize);
}
 
Elf32_Shdr *
GetElf32SectionByRange (
  IN  UINT8   *ImageBase,
  IN  UINT32  Offset,
  IN  UINT32  Size
  )
{
  UINT32      Index;
  Elf32_Ehdr  *Ehdr;
  Elf32_Shdr  *Shdr;
 
  Ehdr = (Elf32_Ehdr *)ImageBase;
 
  Shdr = (Elf32_Shdr *)(ImageBase + Ehdr->e_shoff);
  for (Index = 0; Index < Ehdr->e_shnum; Index++) {
    if ((Shdr->sh_offset == Offset) && (Shdr->sh_size == Size)) {
      return Shdr;
    }
 
    Shdr = ELF_NEXT_ENTRY (Elf32_Shdr, Shdr, Ehdr->e_shentsize);
  }
 
  return NULL;
}
 
EFI_STATUS
ProcessRelocation32 (
  IN  Elf32_Rela  *Rela,
  IN  UINT32      RelaSize,
  IN  UINT32      RelaEntrySize,
  IN  UINT32      RelaType,
  IN  INTN        Delta,
  IN  BOOLEAN     DynamicLinking
  )
{
  UINTN   Index;
  UINT32  *Ptr;
  UINT32  Type;
 
  for ( Index = 0
        ; RelaEntrySize * Index < RelaSize
        ; Index++, Rela = ELF_NEXT_ENTRY (Elf32_Rela, Rela, RelaEntrySize)
        )
  {
    //
    // r_offset is the virtual address of the storage unit affected by the relocation.
    //
    Ptr  = (UINT32 *)(UINTN)(Rela->r_offset + Delta);
    Type = ELF32_R_TYPE (Rela->r_info);
    switch (Type) {
      case R_386_NONE:
      case R_386_PC32:
        //
        // No fixup entry required.
        //
        break;
 
      case R_386_32:
        if (DynamicLinking) {
          //
          // Dynamic section doesn't contain entries of this type.
          //
          DEBUG ((DEBUG_INFO, "Unsupported relocation type %02X\n", Type));
          ASSERT (FALSE);
        } else {
          *Ptr += (UINT32)Delta;
        }
 
        break;
 
      case R_386_RELATIVE:
        if (DynamicLinking) {
          //
          // A: Represents the addend used to compute the value of the relocatable field.
          // B: Represents the base address at which a shared object has been loaded into memory during execution.
          //    Generally, a shared object is built with a 0 base virtual address, but the execution address will be different.
          //
          // B (Base Address) in ELF spec is slightly different:
          //   An executable or shared object file's base address (on platforms that support the concept) is calculated during
          //   execution from three values: the virtual memory load address, the maximum page size, and the lowest virtual address
          //   of a program's loadable segment. To compute the base address, one determines the memory address associated with the
          //   lowest p_vaddr value for a PT_LOAD segment. This address is truncated to the nearest multiple of the maximum page size.
          //   The corresponding p_vaddr value itself is also truncated to the nearest multiple of the maximum page size.
          //
          //   *** The base address is the difference between the truncated memory address and the truncated p_vaddr value. ***
          //
          // Delta in this function is B.
          //
          // Calculation: B + A
          //
          if (RelaType == SHT_RELA) {
            *Ptr = (UINT32)Delta + Rela->r_addend;
          } else {
            //
            // A is stored in the field of relocation for REL type.
            //
            *Ptr = (UINT32)Delta + *Ptr;
          }
        } else {
          //
          // non-Dynamic section doesn't contain entries of this type.
          //
          DEBUG ((DEBUG_INFO, "Unsupported relocation type %02X\n", Type));
          ASSERT (FALSE);
        }
 
        break;
 
      default:
        DEBUG ((DEBUG_INFO, "Unsupported relocation type %02X\n", Type));
    }
  }
 
  return EFI_SUCCESS;
}
 
EFI_STATUS
RelocateElf32Dynamic (
  IN    ELF_IMAGE_CONTEXT  *ElfCt
  )
{
  UINT32      Index;
  Elf32_Phdr  *Phdr;
  Elf32_Shdr  *DynShdr;
  Elf32_Shdr  *RelShdr;
  Elf32_Dyn   *Dyn;
  UINT32      RelaAddress;
  UINT32      RelaCount;
  UINT32      RelaSize;
  UINT32      RelaEntrySize;
  UINT32      RelaType;
 
  //
  // 1. Locate the dynamic section.
  //
  // If an object file participates in dynamic linking, its program header table
  // will have an element of type PT_DYNAMIC.
  // This ``segment'' contains the .dynamic section. A special symbol, _DYNAMIC,
  // labels the section, which contains an array of Elf32_Dyn or Elf64_Dyn.
  //
  DynShdr = NULL;
  for (Index = 0; Index < ElfCt->PhNum; Index++) {
    Phdr = GetElf32SegmentByIndex (ElfCt->FileBase, Index);
    ASSERT (Phdr != NULL);
    if (Phdr->p_type == PT_DYNAMIC) {
      //
      // Verify the existence of the dynamic section.
      //
      DynShdr = GetElf32SectionByRange (ElfCt->FileBase, Phdr->p_offset, Phdr->p_filesz);
      break;
    }
  }
 
  //
  // It's abnormal a DYN ELF doesn't contain a dynamic section.
  //
  ASSERT (DynShdr != NULL);
  if (DynShdr == NULL) {
    return EFI_UNSUPPORTED;
  }
 
  ASSERT (DynShdr->sh_type == SHT_DYNAMIC);
  ASSERT (DynShdr->sh_entsize >= sizeof (*Dyn));
 
  //
  // 2. Locate the relocation section from the dynamic section.
  //
  RelaAddress   = MAX_UINT32;
  RelaSize      = 0;
  RelaCount     = 0;
  RelaEntrySize = 0;
  RelaType      = 0;
  for ( Index = 0, Dyn = (Elf32_Dyn *)(ElfCt->FileBase + DynShdr->sh_offset)
        ; Index < DynShdr->sh_size / DynShdr->sh_entsize
        ; Index++, Dyn = ELF_NEXT_ENTRY (Elf32_Dyn, Dyn, DynShdr->sh_entsize)
        )
  {
    switch (Dyn->d_tag) {
      case DT_RELA:
      case DT_REL:
        //
        // DT_REL represent program virtual addresses.
        // A file's virtual addresses might not match the memory virtual addresses during execution.
        // When interpreting addresses contained in the dynamic structure, the dynamic linker computes actual addresses,
        // based on the original file value and the memory base address.
        // For consistency, files do not contain relocation entries to ``correct'' addresses in the dynamic structure.
        //
        RelaAddress = Dyn->d_un.d_ptr;
        RelaType    = (Dyn->d_tag == DT_RELA) ? SHT_RELA : SHT_REL;
        break;
      case DT_RELACOUNT:
      case DT_RELCOUNT:
        RelaCount = Dyn->d_un.d_val;
        break;
      case DT_RELENT:
      case DT_RELAENT:
        RelaEntrySize = Dyn->d_un.d_val;
        break;
      case DT_RELSZ:
      case DT_RELASZ:
        RelaSize = Dyn->d_un.d_val;
        break;
      default:
        break;
    }
  }
 
  if (RelaAddress == MAX_UINT32) {
    ASSERT (RelaCount     == 0);
    ASSERT (RelaEntrySize == 0);
    ASSERT (RelaSize      == 0);
    //
    // It's fine that a DYN ELF doesn't contain relocation section.
    //
    return EFI_SUCCESS;
  }
 
  //
  // Verify the existence of the relocation section.
  //
  RelShdr = NULL;
  for (Index = 0; Index < ElfCt->ShNum; Index++) {
    RelShdr = GetElf32SectionByIndex (ElfCt->FileBase, Index);
    ASSERT (RelShdr != NULL);
    if ((RelShdr->sh_addr == RelaAddress) && (RelShdr->sh_size == RelaSize)) {
      break;
    }
 
    RelShdr = NULL;
  }
 
  if (RelShdr == NULL) {
    return EFI_UNSUPPORTED;
  }
 
  ASSERT (RelShdr->sh_type == RelaType);
  ASSERT (RelShdr->sh_entsize == RelaEntrySize);
 
  //
  // 3. Process the relocation section.
  //
  ProcessRelocation32 (
    (Elf32_Rela *)(ElfCt->FileBase + RelShdr->sh_offset),
    RelShdr->sh_size,
    RelShdr->sh_entsize,
    RelShdr->sh_type,
    (UINTN)ElfCt->ImageAddress - (UINTN)ElfCt->PreferredImageAddress,
    TRUE
    );
  return EFI_SUCCESS;
}
 
EFI_STATUS
RelocateElf32Sections  (
  IN    ELF_IMAGE_CONTEXT  *ElfCt
  )
{
  EFI_STATUS  Status;
  Elf32_Ehdr  *Ehdr;
  Elf32_Shdr  *RelShdr;
  Elf32_Shdr  *Shdr;
  UINT32      Index;
  UINTN       Delta;
 
  Ehdr = (Elf32_Ehdr *)ElfCt->FileBase;
  if (Ehdr->e_machine != EM_386) {
    return EFI_UNSUPPORTED;
  }
 
  Delta             = (UINTN)ElfCt->ImageAddress - (UINTN)ElfCt->PreferredImageAddress;
  ElfCt->EntryPoint = (UINTN)(Ehdr->e_entry + Delta);
 
  //
  // 1. Relocate dynamic ELF using the relocation section pointed by dynamic section
  //
  if (Ehdr->e_type == ET_DYN) {
    DEBUG ((DEBUG_INFO, "DYN ELF: Relocate using dynamic sections...\n"));
    Status = RelocateElf32Dynamic (ElfCt);
    ASSERT_EFI_ERROR (Status);
    return Status;
  }
 
  //
  // 2. Executable ELF: Fix up the delta between actual image address and preferred image address.
  //
  //  Linker already fixed up EXEC ELF based on the preferred image address.
  //  A ELF loader in modern OS only loads it into the preferred image address.
  //  The below relocation is unneeded in that case.
  //  But the ELF loader in firmware supports to load the image to a different address.
  //  The below relocation is needed in this case.
  //
  DEBUG ((DEBUG_INFO, "EXEC ELF: Fix actual/preferred base address delta ...\n"));
  for ( Index = 0, RelShdr = (Elf32_Shdr *)(ElfCt->FileBase + Ehdr->e_shoff)
        ; Index < Ehdr->e_shnum
        ; Index++, RelShdr = ELF_NEXT_ENTRY (Elf32_Shdr, RelShdr, Ehdr->e_shentsize)
        )
  {
    if ((RelShdr->sh_type != SHT_REL) && (RelShdr->sh_type != SHT_RELA)) {
      continue;
    }
 
    Shdr = GetElf32SectionByIndex (ElfCt->FileBase, RelShdr->sh_info);
    if ((Shdr->sh_flags & SHF_ALLOC) == SHF_ALLOC) {
      //
      // Only fix up sections that occupy memory during process execution.
      //
      ProcessRelocation32 (
        (Elf32_Rela *)((UINT8 *)Ehdr + RelShdr->sh_offset),
        RelShdr->sh_size,
        RelShdr->sh_entsize,
        RelShdr->sh_type,
        Delta,
        FALSE
        );
    }
  }
 
  return EFI_SUCCESS;
}
 
EFI_STATUS
LoadElf32Image (
  IN    ELF_IMAGE_CONTEXT  *ElfCt
  )
{
  Elf32_Ehdr  *Ehdr;
  Elf32_Phdr  *Phdr;
  UINT16      Index;
  UINTN       Delta;
 
  ASSERT (ElfCt != NULL);
 
  //
  // Per the sprit of ELF, loading to memory only consumes info from program headers.
  //
  Ehdr = (Elf32_Ehdr *)ElfCt->FileBase;
 
  for ( Index = 0, Phdr = (Elf32_Phdr *)(ElfCt->FileBase + Ehdr->e_phoff)
        ; Index < Ehdr->e_phnum
        ; Index++, Phdr = ELF_NEXT_ENTRY (Elf32_Phdr, Phdr, Ehdr->e_phentsize)
        )
  {
    //
    // Skip segments that don't require load (type tells, or size is 0)
    //
    if ((Phdr->p_type != PT_LOAD) ||
        (Phdr->p_memsz == 0))
    {
      continue;
    }
 
    //
    // The memory offset of segment relative to the image base
    // Note: CopyMem() does nothing when the dst equals to src.
    //
    Delta = Phdr->p_paddr - (UINT32)(UINTN)ElfCt->PreferredImageAddress;
    CopyMem (ElfCt->ImageAddress + Delta, ElfCt->FileBase + Phdr->p_offset, Phdr->p_filesz);
    ZeroMem (ElfCt->ImageAddress + Delta + Phdr->p_filesz, Phdr->p_memsz - Phdr->p_filesz);
  }
 
  //
  // Relocate when new new image base is not the preferred image base.
  //
  if (ElfCt->ImageAddress != ElfCt->PreferredImageAddress) {
    RelocateElf32Sections (ElfCt);
  }
 
  return EFI_SUCCESS;
}