llvm-readobj: Add support for reading relocations in the Android pack…

…ed format.

This is in preparation for testing lld's upcoming relocation packing
feature (D39152). I have verified that this implementation correctly
unpacks the relocations from a Chromium DSO built with gold and the
Android relocation packer for ARM32 and ARM64.

Differential Revision: https://reviews.llvm.org/D39272

llvm-svn: 316543

llvm/include/llvm/BinaryFormat/ELF.h

@@ -730,6 +730,10 @@ enum : unsigned {
   SHT_GROUP = 17,                  // Section group.
   SHT_SYMTAB_SHNDX = 18,           // Indices for SHN_XINDEX entries.
   SHT_LOOS = 0x60000000,           // Lowest operating system-specific type.
+  // Android packed relocation section types.
+  // https://android.googlesource.com/platform/bionic/+/6f12bfece5dcc01325e0abba56a46b1bcf991c69/tools/relocation_packer/src/elf_file.cc#37
+  SHT_ANDROID_REL = 0x60000001,
+  SHT_ANDROID_RELA = 0x60000002,
   SHT_LLVM_ODRTAB = 0x6fff4c00,    // LLVM ODR table.
   SHT_GNU_ATTRIBUTES = 0x6ffffff5, // Object attributes.
   SHT_GNU_HASH = 0x6ffffff6,       // GNU-style hash table.
@@ -1166,6 +1170,13 @@ enum {
   DT_LOPROC = 0x70000000, // Start of processor specific tags.
   DT_HIPROC = 0x7FFFFFFF, // End of processor specific tags.
 
+  // Android packed relocation section tags.
+  // https://android.googlesource.com/platform/bionic/+/6f12bfece5dcc01325e0abba56a46b1bcf991c69/tools/relocation_packer/src/elf_file.cc#31
+  DT_ANDROID_REL = 0x6000000F,
+  DT_ANDROID_RELSZ = 0x60000010,
+  DT_ANDROID_RELA = 0x60000011,
+  DT_ANDROID_RELASZ = 0x60000012,
+
   DT_GNU_HASH = 0x6FFFFEF5, // Reference to the GNU hash table.
   DT_TLSDESC_PLT =
       0x6FFFFEF6, // Location of PLT entry for TLS descriptor resolver calls.
@@ -1387,6 +1398,14 @@ enum {
   GNU_ABI_TAG_NACL = 6,
 };
 
+// Android packed relocation group flags.
+enum {
+  RELOCATION_GROUPED_BY_INFO_FLAG = 1,
+  RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG = 2,
+  RELOCATION_GROUPED_BY_ADDEND_FLAG = 4,
+  RELOCATION_GROUP_HAS_ADDEND_FLAG = 8,
+};
+
 // Compressed section header for ELF32.
 struct Elf32_Chdr {
   Elf32_Word ch_type;

llvm/include/llvm/Object/ELF.h

@@ -142,6 +142,8 @@ class ELFFile {
     return getSectionContentsAsArray<Elf_Rel>(Sec);
   }
 
+  Expected<std::vector<Elf_Rela>> android_relas(const Elf_Shdr *Sec) const;
+
   /// \brief Iterate over program header table.
   Expected<Elf_Phdr_Range> program_headers() const {
     if (getHeader()->e_phnum && getHeader()->e_phentsize != sizeof(Elf_Phdr))

llvm/lib/Object/ELF.cpp

@@ -9,6 +9,7 @@
 
 #include "llvm/Object/ELF.h"
 #include "llvm/BinaryFormat/ELF.h"
+#include "llvm/Support/LEB128.h"
 
 using namespace llvm;
 using namespace object;
@@ -210,3 +211,92 @@ StringRef llvm::object::getELFSectionTypeName(uint32_t Machine, unsigned Type) {
     return "Unknown";
   }
 }
+
+template <class ELFT>
+Expected<std::vector<typename ELFT::Rela>>
+ELFFile<ELFT>::android_relas(const Elf_Shdr *Sec) const {
+  // This function reads relocations in Android's packed relocation format,
+  // which is based on SLEB128 and delta encoding.
+  Expected<ArrayRef<uint8_t>> ContentsOrErr = getSectionContents(Sec);
+  if (!ContentsOrErr)
+    return ContentsOrErr.takeError();
+  const uint8_t *Cur = ContentsOrErr->begin();
+  const uint8_t *End = ContentsOrErr->end();
+  if (ContentsOrErr->size() < 4 || Cur[0] != 'A' || Cur[1] != 'P' ||
+      Cur[2] != 'S' || Cur[3] != '2')
+    return createError("invalid packed relocation header");
+  Cur += 4;
+
+  const char *ErrStr = nullptr;
+  auto ReadSLEB = [&]() -> int64_t {
+    if (ErrStr)
+      return 0;
+    unsigned Len;
+    int64_t Result = decodeSLEB128(Cur, &Len, End, &ErrStr);
+    Cur += Len;
+    return Result;
+  };
+
+  uint64_t NumRelocs = ReadSLEB();
+  uint64_t Offset = ReadSLEB();
+  uint64_t Addend = 0;
+
+  if (ErrStr)
+    return createError(ErrStr);
+
+  std::vector<Elf_Rela> Relocs;
+  Relocs.reserve(NumRelocs);
+  while (NumRelocs) {
+    uint64_t NumRelocsInGroup = ReadSLEB();
+    if (NumRelocsInGroup > NumRelocs)
+      return createError("relocation group unexpectedly large");
+    NumRelocs -= NumRelocsInGroup;
+
+    uint64_t GroupFlags = ReadSLEB();
+    bool GroupedByInfo = GroupFlags & ELF::RELOCATION_GROUPED_BY_INFO_FLAG;
+    bool GroupedByOffsetDelta = GroupFlags & ELF::RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG;
+    bool GroupedByAddend = GroupFlags & ELF::RELOCATION_GROUPED_BY_ADDEND_FLAG;
+    bool GroupHasAddend = GroupFlags & ELF::RELOCATION_GROUP_HAS_ADDEND_FLAG;
+
+    uint64_t GroupOffsetDelta;
+    if (GroupedByOffsetDelta)
+      GroupOffsetDelta = ReadSLEB();
+
+    uint64_t GroupRInfo;
+    if (GroupedByInfo)
+      GroupRInfo = ReadSLEB();
+
+    if (GroupedByAddend && GroupHasAddend)
+      Addend += ReadSLEB();
+
+    for (uint64_t I = 0; I != NumRelocsInGroup; ++I) {
+      Elf_Rela R;
+      Offset += GroupedByOffsetDelta ? GroupOffsetDelta : ReadSLEB();
+      R.r_offset = Offset;
+      R.r_info = GroupedByInfo ? GroupRInfo : ReadSLEB();
+
+      if (GroupHasAddend) {
+        if (!GroupedByAddend)
+          Addend += ReadSLEB();
+        R.r_addend = Addend;
+      } else {
+        R.r_addend = 0;
+      }
+
+      Relocs.push_back(R);
+
+      if (ErrStr)
+        return createError(ErrStr);
+    }
+
+    if (ErrStr)
+      return createError(ErrStr);
+  }
+
+  return Relocs;
+}
+
+template class llvm::object::ELFFile<ELF32LE>;
+template class llvm::object::ELFFile<ELF32BE>;
+template class llvm::object::ELFFile<ELF64LE>;
+template class llvm::object::ELFFile<ELF64BE>;

llvm/lib/ObjectYAML/ELFYAML.cpp

@@ -405,6 +405,8 @@ void ScalarEnumerationTraits<ELFYAML::ELF_SHT>::enumeration(
   ECase(SHT_GROUP);
   ECase(SHT_SYMTAB_SHNDX);
   ECase(SHT_LOOS);
+  ECase(SHT_ANDROID_REL);
+  ECase(SHT_ANDROID_RELA);
   ECase(SHT_LLVM_ODRTAB);
   ECase(SHT_GNU_ATTRIBUTES);
   ECase(SHT_GNU_HASH);

llvm/test/tools/llvm-readobj/Inputs/elf-packed-relocs1.s

@@ -0,0 +1,37 @@
+.ascii "APS2"
+.sleb128 8    // Number of relocations
+.sleb128 4096 // Initial offset
+
+.sleb128 2 // Number of relocations in group
+.sleb128 1 // RELOCATION_GROUPED_BY_INFO_FLAG
+.sleb128 8 // R_X86_RELATIVE
+
+.sleb128 256 // Reloc 1: r_offset delta
+.sleb128 128 // Reloc 2: r_offset delta
+
+.sleb128 2 // Number of relocations in group
+.sleb128 2 // RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG
+.sleb128 8 // offset delta
+
+.sleb128 (1 << 32) | 1 // R_X86_64_64 (sym index 1)
+.sleb128 (2 << 32) | 1 // R_X86_64_64 (sym index 2)
+
+.sleb128 2 // Number of relocations in group
+.sleb128 8 // RELOCATION_GROUP_HAS_ADDEND_FLAG
+
+.sleb128 1             // offset delta
+.sleb128 (1 << 32) | 1 // R_X86_64_64 (sym index 1)
+.sleb128 8             // addend delta
+
+.sleb128 2             // offset delta
+.sleb128 (2 << 32) | 1 // R_X86_64_64 (sym index 2)
+.sleb128 4             // addend delta
+
+.sleb128 2  // Number of relocations in group
+.sleb128 12 // RELOCATION_GROUP_HAS_ADDEND_FLAG | RELOCATION_GROUPED_BY_ADDEND_FLAG
+.sleb128 -2 // addend delta
+
+.sleb128 4             // offset delta
+.sleb128 (1 << 32) | 1 // R_X86_64_64 (sym index 1)
+.sleb128 8             // offset delta
+.sleb128 (2 << 32) | 1 // R_X86_64_64 (sym index 2)

llvm/test/tools/llvm-readobj/Inputs/elf-packed-relocs2.s

@@ -0,0 +1,15 @@
+.ascii "APS2"
+.sleb128 10   // Number of relocations
+.sleb128 4096 // Initial offset
+
+.sleb128 2 // Number of relocations in group
+.sleb128 2 // RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG
+.sleb128 8 // offset delta
+
+.sleb128 (1 << 8) | 1 // R_386_32    (sym index 1)
+.sleb128 (2 << 8) | 3 // R_386_GOT32 (sym index 2)
+
+.sleb128 8  // Number of relocations in group
+.sleb128 3  // RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG | RELOCATION_GROUPED_BY_INFO_FLAG
+.sleb128 -4 // offset delta
+.sleb128 8  // R_386_RELATIVE

llvm/test/tools/llvm-readobj/elf-packed-relocs-empty.s

@@ -0,0 +1,11 @@
+// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - | llvm-readobj -relocations - | FileCheck %s
+
+// CHECK:      Relocations [
+// CHECK-NEXT:   Section (3) .rela.dyn {
+// CHECK-NEXT:   }
+// CHECK-NEXT: ]
+
+.section .rela.dyn, "a", @0x60000001
+.ascii "APS2"
+.sleb128 0
+.sleb128 0

llvm/test/tools/llvm-readobj/elf-packed-relocs-error1.s

@@ -0,0 +1,6 @@
+// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - | not llvm-readobj -relocations - 2>&1 | FileCheck %s
+
+// CHECK: Error reading file: invalid packed relocation header
+
+.section .rela.dyn, "a", @0x60000001
+.ascii "APS9"

llvm/test/tools/llvm-readobj/elf-packed-relocs-error2.s

@@ -0,0 +1,6 @@
+// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - | not llvm-readobj -relocations - 2>&1 | FileCheck %s
+
+// CHECK: Error reading file: malformed sleb128, extends past end
+
+.section .rela.dyn, "a", @0x60000001
+.ascii "APS2"

llvm/test/tools/llvm-readobj/elf-packed-relocs-error3.s

@@ -0,0 +1,8 @@
+// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - | not llvm-readobj -relocations - 2>&1 | FileCheck %s
+
+// CHECK: Error reading file: malformed sleb128, extends past end
+
+.section .rela.dyn, "a", @0x60000001
+.ascii "APS2"
+.sleb128 4 // Number of relocations
+.sleb128 0 // Initial offset

llvm/test/tools/llvm-readobj/elf-packed-relocs-error4.s

@@ -0,0 +1,12 @@
+// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - | not llvm-readobj -relocations - 2>&1 | FileCheck %s
+
+// CHECK: Error reading file: malformed sleb128, extends past end
+
+.section .rela.dyn, "a", @0x60000001
+.ascii "APS2"
+.sleb128 4 // Number of relocations
+.sleb128 0 // Initial offset
+
+.sleb128 2 // Number of relocations in group
+.sleb128 2 // RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG
+.sleb128 8 // offset delta

llvm/test/tools/llvm-readobj/elf-packed-relocs-error5.s

@@ -0,0 +1,12 @@
+// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - | not llvm-readobj -relocations - 2>&1 | FileCheck %s
+
+// CHECK: Error reading file: relocation group unexpectedly large
+
+.section .rela.dyn, "a", @0x60000001
+.ascii "APS2"
+.sleb128 4 // Number of relocations
+.sleb128 0 // Initial offset
+
+.sleb128 5 // Number of relocations in group
+.sleb128 2 // RELOCATION_GROUPED_BY_OFFSET_DELTA_FLAG
+.sleb128 8 // offset delta

llvm/test/tools/llvm-readobj/elf-packed-relocs.test

@@ -0,0 +1,94 @@
+# The binary blobs in this file were created like this:
+# llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu Inputs/elf-packed-relocs1.s -o - | obj2yaml | grep Content:
+
+# RUN: yaml2obj -docnum 1 %s | llvm-readobj -elf-output-style=LLVM -relocations - | FileCheck --check-prefix=LLVM1 %s
+# LLVM1:      Section (1) .rela.dyn {
+# LLVM1-NEXT:   0x1100 R_X86_64_RELATIVE - 0x0
+# LLVM1-NEXT:   0x1180 R_X86_64_RELATIVE - 0x0
+# LLVM1-NEXT:   0x1188 R_X86_64_64 sym1 0x0
+# LLVM1-NEXT:   0x1190 R_X86_64_64 sym2 0x0
+# LLVM1-NEXT:   0x1191 R_X86_64_64 sym1 0x8
+# LLVM1-NEXT:   0x1193 R_X86_64_64 sym2 0xC
+# LLVM1-NEXT:   0x1197 R_X86_64_64 sym1 0xA
+# LLVM1-NEXT:   0x119F R_X86_64_64 sym2 0xA
+# LLVM1-NEXT: }
+
+# RUN: yaml2obj -docnum 1 %s | llvm-readobj -elf-output-style=GNU -relocations - | FileCheck --check-prefix=GNU1 %s
+# GNU1:      0000000000001100  0000000000000008 R_X86_64_RELATIVE                 0
+# GNU1-NEXT: 0000000000001180  0000000000000008 R_X86_64_RELATIVE                 0
+# GNU1-NEXT: 0000000000001188  0000000100000001 R_X86_64_64            0000000000000000 sym1 + 0
+# GNU1-NEXT: 0000000000001190  0000000200000001 R_X86_64_64            0000000000000000 sym2 + 0
+# GNU1-NEXT: 0000000000001191  0000000100000001 R_X86_64_64            0000000000000000 sym1 + 8
+# GNU1-NEXT: 0000000000001193  0000000200000001 R_X86_64_64            0000000000000000 sym2 + c
+# GNU1-NEXT: 0000000000001197  0000000100000001 R_X86_64_64            0000000000000000 sym1 + a
+# GNU1-NEXT: 000000000000119f  0000000200000001 R_X86_64_64            0000000000000000 sym2 + a
+
+# elf-packed-relocs1.s
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_DYN
+  Machine:         EM_X86_64
+  Entry:           0x0000000000001000
+Sections:
+  - Name:            .rela.dyn
+    Type:            SHT_ANDROID_RELA
+    Flags:           [ SHF_ALLOC ]
+    Address:         0x00000000000001C8
+    Link:            .symtab
+    AddressAlign:    0x0000000000000001
+    Content:         41505332088020020108800280010202088180808010818080802002080181808080100802818080802004020C7E048180808010088180808020
+Symbols:
+  Global:
+    - Name:            sym1
+    - Name:            sym2
+...
+
+# RUN: yaml2obj -docnum 2 %s | llvm-readobj -elf-output-style=LLVM -relocations - | FileCheck --check-prefix=LLVM2 %s
+# LLVM2:      Section (1) .rel.dyn {
+# LLVM2-NEXT:   0x1008 R_386_32 sym1 0x0
+# LLVM2-NEXT:   0x1010 R_386_GOT32 sym2 0x0
+# LLVM2-NEXT:   0x100C R_386_RELATIVE - 0x0
+# LLVM2-NEXT:   0x1008 R_386_RELATIVE - 0x0
+# LLVM2-NEXT:   0x1004 R_386_RELATIVE - 0x0
+# LLVM2-NEXT:   0x1000 R_386_RELATIVE - 0x0
+# LLVM2-NEXT:   0xFFC R_386_RELATIVE - 0x0
+# LLVM2-NEXT:   0xFF8 R_386_RELATIVE - 0x0
+# LLVM2-NEXT:   0xFF4 R_386_RELATIVE - 0x0
+# LLVM2-NEXT:   0xFF0 R_386_RELATIVE - 0x0
+# LLVM2-NEXT: }
+
+# RUN: yaml2obj -docnum 2 %s | llvm-readobj -elf-output-style=GNU -relocations - | FileCheck --check-prefix=GNU2 %s
+# GNU2:      00001008  00000101 R_386_32               00000000   sym1
+# GNU2-NEXT: 00001010  00000203 R_386_GOT32            00000000   sym2
+# GNU2-NEXT: 0000100c  00000008 R_386_RELATIVE
+# GNU2-NEXT: 00001008  00000008 R_386_RELATIVE
+# GNU2-NEXT: 00001004  00000008 R_386_RELATIVE
+# GNU2-NEXT: 00001000  00000008 R_386_RELATIVE
+# GNU2-NEXT: 00000ffc  00000008 R_386_RELATIVE
+# GNU2-NEXT: 00000ff8  00000008 R_386_RELATIVE
+# GNU2-NEXT: 00000ff4  00000008 R_386_RELATIVE
+# GNU2-NEXT: 00000ff0  00000008 R_386_RELATIVE
+
+# elf-packed-relocs2.s
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS32
+  Data:            ELFDATA2LSB
+  Type:            ET_DYN
+  Machine:         EM_386
+  Entry:           0x0000000000001000
+Sections:
+  - Name:            .rel.dyn
+    Type:            SHT_ANDROID_REL
+    Flags:           [ SHF_ALLOC ]
+    Address:         0x00000000000001C8
+    Link:            .symtab
+    AddressAlign:    0x0000000000000001
+    Content:         415053320A80200202088102830408037C08
+Symbols:
+  Global:
+    - Name:            sym1
+    - Name:            sym2
+...