[LLD] [COFF] Add initial support for some ARM64 relocations and import thunks

[mstorsjo]

Summary

This is enough to link a working hello world executable, with a call to an imported function, a string constant passed to the imported function, and loads from a global variable.

[mstorsjo]

Added support for the IMAGE_REL_ARM64_PAGEOFFSET_12L relocation as well (and testing of it), improved parts of the test.

[mstorsjo]

Added support for yet another few relocations, added a missed ARM64 part for getBaserelType (tested with wine, loading the exe at a non-default address so the base relocations need to be applied).

[ruiu]

Generally looking good.

COFF/Chunks.cpp

382–383

Is this a to-do, or really empty?

[mstorsjo]

COFF/Chunks.cpp

382–383

I think it's ok to leave it empty; the instructions in the import thunk load the actual target address using position independent addressing. I've tested this with wine, with the exe loaded at a different address than the base address, and they run fine.

[mstorsjo]

Minor tweaks to the test, made the PAGEOFFSET_12A/L relocations read the existing immediate value and add that into the value from the relocation.

[ruiu]

COFF/Chunks.h

314

Then do not override this function. The base class provides a function that does nothing.

[mstorsjo]

No longer overriding getBaserels with an empty implementation.

[ruiu]

LGTM

COFF/Chunks.h

public:
   void getBaserels(std::vector<Baserel> *Res) override;
   bool isCOMDAT() const;
   void applyRelX64(uint8_t *Off, uint16_t Type, OutputSection *OS, uint64_t S,
                    uint64_t P) const;
   void applyRelX86(uint8_t *Off, uint16_t Type, OutputSection *OS, uint64_t S,
                    uint64_t P) const;
   void applyRelARM(uint8_t *Off, uint16_t Type, OutputSection *OS, uint64_t S,
                    uint64_t P) const;
+  void applyRelARM64(uint8_t *Off, uint16_t Type, OutputSection *OS, uint64_t S,
+                     uint64_t P) const;
 
   // Called if the garbage collector decides to not include this chunk
   // in a final output. It's supposed to print out a log message to stdout.
   void printDiscardedMessage() const;
 
   // Adds COMDAT associative sections to this COMDAT section. A chunk
   // and its children are treated as a group by the garbage collector.
   void addAssociative(SectionChunk *Child);

 };
 
 static const uint8_t ImportThunkARM[] = {
     0x40, 0xf2, 0x00, 0x0c, // mov.w ip, #0
     0xc0, 0xf2, 0x00, 0x0c, // mov.t ip, #0
     0xdc, 0xf8, 0x00, 0xf0, // ldr.w pc, [ip]
 };
 
+static const uint8_t ImportThunkARM64[] = {
+    0x10, 0x00, 0x00, 0x90, // adrp x16, #0
+    0x10, 0x02, 0x40, 0xf9, // ldr  x16, [x16]
+    0x00, 0x02, 0x1f, 0xd6, // br   x16
+};
+
 // Windows-specific.
 // A chunk for DLL import jump table entry. In a final output, it's
 // contents will be a JMP instruction to some __imp_ symbol.
 class ImportThunkChunkX64 : public Chunk {
 public:
   explicit ImportThunkChunkX64(Defined *S);
   size_t getSize() const override { return sizeof(ImportThunkX86); }
   void writeTo(uint8_t *Buf) const override;
public:
   size_t getSize() const override { return sizeof(ImportThunkARM); }
   void getBaserels(std::vector<Baserel> *Res) override;
   void writeTo(uint8_t *Buf) const override;
 
 private:
   Defined *ImpSymbol;
 };
 
+class ImportThunkChunkARM64 : public Chunk {
+public:
+  explicit ImportThunkChunkARM64(Defined *S) : ImpSymbol(S) {}
+  size_t getSize() const override { return sizeof(ImportThunkARM64); }
+  void getBaserels(std::vector<Baserel> *Res) override;
+  void writeTo(uint8_t *Buf) const override;
+
+private:
+  Defined *ImpSymbol;
+};
+
 // Windows-specific.
 // See comments for DefinedLocalImport class.
 class LocalImportChunk : public Chunk {
 public:
   explicit LocalImportChunk(Defined *S) : Sym(S) {}
   size_t getSize() const override;
   void getBaserels(std::vector<Baserel> *Res) override;
   void writeTo(uint8_t *Buf) const override;

COFF/Chunks.cpp

SectionChunk::SectionChunk(ObjectFile *F, const coff_section *H)
   // stripping will be in a comdat.
   Live = !Config->DoGC || !isCOMDAT();
 }
 
 static void add16(uint8_t *P, int16_t V) { write16le(P, read16le(P) + V); }
 static void add32(uint8_t *P, int32_t V) { write32le(P, read32le(P) + V); }
 static void add64(uint8_t *P, int64_t V) { write64le(P, read64le(P) + V); }
 static void or16(uint8_t *P, uint16_t V) { write16le(P, read16le(P) | V); }
+static void or32(uint8_t *P, uint32_t V) { write32le(P, read32le(P) | V); }
 
 static void applySecRel(const SectionChunk *Sec, uint8_t *Off,
                         OutputSection *OS, uint64_t S) {
   if (!OS) {
     if (Sec->isCodeView())
       return;
     fatal("SECREL relocation cannot be applied to absolute symbols");
   }
void SectionChunk::applyRelARM(uint8_t *Off, uint16_t Type, OutputSection *OS,
   case IMAGE_REL_ARM_BLX23T:    applyBranch24T(Off, SX - P - 4); break;
   case IMAGE_REL_ARM_SECTION:   applySecIdx(Off, OS); break;
   case IMAGE_REL_ARM_SECREL:    applySecRel(this, Off, OS, S); break;
   default:
     fatal("unsupported relocation type 0x" + Twine::utohexstr(Type));
   }
 }
 
+static void applyArm64Addr(uint8_t *Off, uint64_t Imm) {
+  uint32_t ImmLo = (Imm & 0x3) << 29;
+  uint32_t ImmHi = (Imm & 0x1FFFFC) << 3;
+  uint64_t Mask = (0x3 << 29) | (0x1FFFFC << 3);
+  write32le(Off, (read32le(Off) & ~Mask) | ImmLo | ImmHi);
+}
+
+// Update the immediate field in a AARCH64 ldr, str, and add instruction.
+static void or32Arm64Imm(uint8_t *Off, uint64_t Imm) {
+  or32(Off, (Imm & 0xFFF) << 10);
+}
+
+static void applyArm64Ldr(uint8_t *Off, uint64_t Imm) {
+  int Size = read32le(Off) >> 30;
+  Imm >>= Size;
+  or32Arm64Imm(Off, Imm);
+}
+
+void SectionChunk::applyRelARM64(uint8_t *Off, uint16_t Type, OutputSection *OS,
+                                 uint64_t S, uint64_t P) const {
+  switch (Type) {
+  case IMAGE_REL_ARM64_PAGEBASE_REL21: applyArm64Addr(Off, (S >> 12) - (P >> 12)); break;
+  case IMAGE_REL_ARM64_PAGEOFFSET_12A: or32Arm64Imm(Off, S & 0xfff); break;
+  case IMAGE_REL_ARM64_PAGEOFFSET_12L: applyArm64Ldr(Off, S & 0xfff); break;
+  case IMAGE_REL_ARM64_BRANCH26:       or32(Off, ((S - P) & 0x0FFFFFFC) >> 2); break;
+  default:
+    fatal("unsupported relocation type 0x" + Twine::utohexstr(Type));
+  }
+}
+
 void SectionChunk::writeTo(uint8_t *Buf) const {
   if (!hasData())
     return;
   // Copy section contents from source object file to output file.
   ArrayRef<uint8_t> A = getContents();
   memcpy(Buf + OutputSectionOff, A.data(), A.size());
 
   // Apply relocations.
case AMD64:
       applyRelX64(Off, Rel.Type, OS, S, P);
       break;
     case I386:
       applyRelX86(Off, Rel.Type, OS, S, P);
       break;
     case ARMNT:
       applyRelARM(Off, Rel.Type, OS, S, P);
       break;
+    case ARM64:
+      applyRelARM64(Off, Rel.Type, OS, S, P);
+      break;
     default:
       llvm_unreachable("unknown machine type");
     }
   }
 }
 
 void SectionChunk::addAssociative(SectionChunk *Child) {
   AssocChildren.push_back(Child);

 }
 
 void ImportThunkChunkARM::writeTo(uint8_t *Buf) const {
   memcpy(Buf + OutputSectionOff, ImportThunkARM, sizeof(ImportThunkARM));
   // Fix mov.w and mov.t operands.
   applyMOV32T(Buf + OutputSectionOff, ImpSymbol->getRVA() + Config->ImageBase);
 }
 
+void ImportThunkChunkARM64::getBaserels(std::vector<Baserel> *Res) {
+}
+
+void ImportThunkChunkARM64::writeTo(uint8_t *Buf) const {
+  int64_t PageOff = (ImpSymbol->getRVA() >> 12) - (RVA >> 12);
+  int64_t Off = ImpSymbol->getRVA() & 0xfff;
+  memcpy(Buf + OutputSectionOff, ImportThunkARM64, sizeof(ImportThunkARM64));
+  applyArm64Addr(Buf + OutputSectionOff, PageOff);
+  or32Arm64Imm(Buf + OutputSectionOff + 4, Off >> 3);
+}
+
 void LocalImportChunk::getBaserels(std::vector<Baserel> *Res) {
   Res->emplace_back(getRVA());
 }
 
 size_t LocalImportChunk::getSize() const {
   return Config->is64() ? 8 : 4;
 }
 

COFF/Symbols.cpp

 
 uint16_t DefinedAbsolute::OutputSectionIndex = 0;
 
 static Chunk *makeImportThunk(DefinedImportData *S, uint16_t Machine) {
   if (Machine == AMD64)
     return make<ImportThunkChunkX64>(S);
   if (Machine == I386)
     return make<ImportThunkChunkX86>(S);
+  if (Machine == ARM64)
+    return make<ImportThunkChunkARM64>(S);
   assert(Machine == ARMNT);
   return make<ImportThunkChunkARM>(S);
 }
 
 DefinedImportThunk::DefinedImportThunk(StringRef Name, DefinedImportData *S,
                                        uint16_t Machine)
     : Defined(DefinedImportThunkKind, Name), WrappedSym(S),
       Data(makeImportThunk(S, Machine)) {}

test/COFF/arm64-relocs-imports.test

+# REQUIRES: aarch64
+
+# RUN: yaml2obj < %s > %t.obj
+# RUN: llvm-objdump -d %t.obj | FileCheck %s -check-prefix BEFORE
+# RUN: lld-link /entry:main /subsystem:console /out:%t.exe %t.obj %p/Inputs/library-arm64.lib
+# RUN: llvm-objdump -d %t.exe | FileCheck %s -check-prefix AFTER
+
+# BEFORE: Disassembly of section .text:
+# BEFORE:        0:       fe 0f 1f f8     str     x30, [sp, #-16]!
+# BEFORE:        4:       00 00 00 90     adrp    x0, #0
+# BEFORE:        8:       00 00 00 91     add     x0, x0, #0
+# BEFORE:        c:       00 00 00 94     bl      #0
+# BEFORE:       10:       00 01 40 39     ldrb    w0, [x8]
+# BEFORE:       14:       00 01 40 79     ldrh    w0, [x8]
+# BEFORE:       18:       00 01 40 b9     ldr     w0, [x8]
+# BEFORE:       1c:       00 01 40 f9     ldr     x0, [x8]
+# BEFORE:       20:       e0 03 1f 2a     mov      w0, wzr
+# BEFORE:       24:       fe 07 41 f8     ldr     x30, [sp], #16
+# BEFORE:       28:       c0 03 5f d6     ret
+
+# AFTER: Disassembly of section .text:
+# AFTER:  140002000:      fe 0f 1f f8     str     x30, [sp, #-16]!
+# AFTER:  140002004:      e0 ff ff f0     adrp    x0, #-4096
+# AFTER:  140002008:      00 10 00 91     add     x0, x0, #4
+# AFTER:  14000200c:      08 00 00 94     bl      #32
+# AFTER:  140002010:      00 21 40 39     ldrb    w0, [x8, #8]
+# AFTER:  140002014:      00 11 40 79     ldrh    w0, [x8, #8]
+# AFTER:  140002018:      00 09 40 b9     ldr     w0, [x8, #8]
+# AFTER:  14000201c:      00 05 40 f9     ldr     x0, [x8, #8]
+# AFTER:  140002020:      e0 03 1f 2a     mov      w0, wzr
+# AFTER:  140002024:      fe 07 41 f8     ldr     x30, [sp], #16
+# AFTER:  140002028:      c0 03 5f d6     ret
+# AFTER:  14000202c:      10 00 00 b0     adrp    x16, #4096
+# AFTER:  140002030:      10 1e 40 f9     ldr     x16, [x16, #56]
+# AFTER:  140002034:      00 02 1f d6     br      x16
+
+--- !COFF
+header:
+  Machine:         IMAGE_FILE_MACHINE_ARM64
+  Characteristics: [  ]
+sections:
+  - Name:            .text
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       4
+    SectionData:     FE0F1FF80000009000000091000000940001403900014079000140B9000140F9E0031F2AFE0741F8C0035FD6
+    Relocations:
+      - VirtualAddress:  4
+        SymbolName:      .Lstr
+        Type:            4
+      - VirtualAddress:  8
+        SymbolName:      .Lstr
+        Type:            6
+      - VirtualAddress:  12
+        SymbolName:      function
+        Type:            3
+      - VirtualAddress:  16
+        SymbolName:      .Lglobal
+        Type:            7
+      - VirtualAddress:  20
+        SymbolName:      .Lglobal
+        Type:            7
+      - VirtualAddress:  24
+        SymbolName:      .Lglobal
+        Type:            7
+      - VirtualAddress:  28
+        SymbolName:      .Lglobal
+        Type:            7
+  - Name:            .data
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE ]
+    Alignment:       4
+    SectionData:     ''
+  - Name:            .bss
+    Characteristics: [ IMAGE_SCN_CNT_UNINITIALIZED_DATA, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE ]
+    Alignment:       4
+    SectionData:     ''
+  - Name:            .rdata
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ ]
+    Alignment:       1
+    SectionData:     0000000068656C6C6F20776F726C6400
+symbols:
+  - Name:            .text
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          28
+      NumberOfRelocations: 3
+      NumberOfLinenumbers: 0
+      CheckSum:        1438860354
+      Number:          1
+  - Name:            .rdata
+    Value:           0
+    SectionNumber:   4
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          12
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        872944732
+      Number:          4
+  - Name:            main
+    Value:           4
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            .Lstr
+    Value:           4
+    SectionNumber:   4
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+  - Name:            .Lglobal
+    Value:           8
+    SectionNumber:   4
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+  - Name:            function
+    Value:           0
+    SectionNumber:   0
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+...