[ELF][X86_64] Handle R_X86_64_PC64 relocation

[davide]

Summary

First of a series of relocation patches.

[shankarke]

LGTM.

[ruiu]

lib/ReaderWriter/ELF/X86_64/X86_64RelocationHandler.cpp

62

Can you add using llvm::support::ulittle64_t at beginning of the file and use that here?

64

Not sure if clang-format formatted like this, but I think there should be no space around "*".

[davide]

Commments inline.

lib/ReaderWriter/ELF/X86_64/X86_64RelocationHandler.cpp

62

This follows the style of the rest of the file, wouldn't be better commit the patch as is and change the style for the whole file in a subsequent pass?

64

Ditto. No, it did not, I tried to be consistent to what was already there.

[ruiu]

LGTM

[silvas]

lib/ReaderWriter/ELF/X86_64/X86_64RelocationHandler.cpp

64

Can you just use endian::read and endian::write functions?

[ruiu]

Can we add llvm::support::endian::read{le,be}{16,32,64}(void *)
and llvm::support::endian::write{le,be}{16,32,64}(void *, uint64_t)?

lib/ReaderWriter/ELF/X86_64/X86_64RelocationHandler.cpp

   // TODO: Check for overflow.
 }
 
+/// \brief R_X86_64_PC64 - word64: S + A - P
+static void relocPC64(uint8_t *location, uint64_t P, uint64_t S, uint64_t A) {
+  int64_t result = (uint64_t)((S + A) - P);
+  *reinterpret_cast<llvm::support::ulittle64_t *>(location) =
+      result |
+      (uint64_t) * reinterpret_cast<llvm::support::ulittle64_t *>(location);
+}
+
 std::error_code X86_64TargetRelocationHandler::applyRelocation(
     ELFWriter &writer, llvm::FileOutputBuffer &buf, const lld::AtomLayout &atom,
     const Reference &ref) const {

     std::memcpy(location - 3, instr, sizeof(instr));
     break;
   }
+  case R_X86_64_PC64:
+    relocPC64(location, relocVAddress, targetVAddress, ref.addend());
+    break;
   case LLD_R_X86_64_GOTRELINDEX: {
     const DefinedAtom *target = cast<const DefinedAtom>(ref.target());
     for (const Reference *r : *target) {

test/elf/X86_64/reloc_r_x86_64_pc64.test

+# Tests that lld can handle relocations of type R_X86_64_PC64
+#RUN: yaml2obj -format=elf -docnum 1 %s -o %t1.o
+#RUN: lld -flavor gnu -target x86_64 %t1.o --noinhibit-exec -o %t2.out -static
+#RUN: llvm-objdump -s %t2.out | FileCheck %s
+#CHECK: Contents of section .data:
+#CHECK: 401000 0a00
+---
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  OSABI:           ELFOSABI_GNU
+  Type:            ET_REL
+  Machine:         EM_X86_64
+Sections:
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    AddressAlign:    0x0000000000000004
+    Content:         ''
+  - Name:            .data
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_WRITE, SHF_ALLOC ]
+    AddressAlign:    0x0000000000000008
+    Content:         '0000'
+  - Name:            .rela.data
+    Type:            SHT_RELA
+    Link:            .symtab
+    AddressAlign:    0x0000000000000008
+    Info:            .data
+    Relocations:
+      - Offset:          0x0000000000000000
+        Symbol:          foo
+        Type:            R_X86_64_PC64
+        Addend:          8
+  - Name:            .bss
+    Type:            SHT_NOBITS
+    Flags:           [ SHF_WRITE, SHF_ALLOC ]
+    AddressAlign:    0x0000000000000004
+    Content:         ''
+Symbols:
+  Local:
+    - Name:            .text
+      Type:            STT_SECTION
+      Section:         .text
+    - Name:            .data
+      Type:            STT_SECTION
+      Section:         .data
+    - Name:            .bss
+      Type:            STT_SECTION
+      Section:         .bss
+  Global:
+    - Name:            bar
+      Type:            STT_OBJECT
+      Section:         .data
+      Size:            0x0000000000000008
+    - Name:            foo
+      Type:            STT_OBJECT
+      Section:         .data
+      Value:           0x0000000000000002
+      Size:            0x0000000000000002
+...