[LLD][BPF] Enable BPF shared object creation (#1)

Author: dmakarov

lld/ELF/Arch/BPF.cpp

@@ -0,0 +1,85 @@
+//===- BPF.cpp ------------------------------------------------------------===//
+//
+//                             The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "InputFiles.h"
+#include "Symbols.h"
+#include "Target.h"
+#include "lld/Common/ErrorHandler.h"
+#include "llvm/Object/ELF.h"
+#include "llvm/Support/Endian.h"
+
+using namespace llvm;
+using namespace llvm::object;
+using namespace llvm::support::endian;
+using namespace llvm::ELF;
+
+namespace lld {
+namespace elf {
+
+namespace {
+class BPF final : public TargetInfo {
+public:
+  BPF();
+  RelExpr getRelExpr(RelType type, const Symbol &s,
+                     const uint8_t *loc) const override;
+  RelType getDynRel(RelType type) const override;
+  void relocateOne(uint8_t *loc, RelType type, uint64_t val) const override;
+};
+} // namespace
+
+BPF::BPF() {
+  noneRel = R_BPF_NONE;
+  relativeRel = R_BPF_64_RELATIVE;
+  symbolicRel = R_BPF_64_64;
+}
+
+RelExpr BPF::getRelExpr(RelType type, const Symbol &s,
+                        const uint8_t *loc) const {
+  switch (type) {
+    case R_BPF_64_32:
+      return R_PC;
+    case R_BPF_64_64:
+      return R_ABS;
+    default:
+      error(getErrorLocation(loc) + "unrecognized reloc " + toString(type));
+  }
+  return R_NONE;
+}
+
+RelType BPF::getDynRel(RelType type) const {
+  return type;
+}
+
+void BPF::relocateOne(uint8_t *loc, RelType type, uint64_t val) const {
+  switch (type) {
+    case R_BPF_64_32: {
+      // Relocation of a symbol
+      write32le(loc + 4, ((val - 8) / 8) & 0xFFFFFFFF);
+      break;
+    }
+    case R_BPF_64_64: {
+      // Relocation of a lddw instruction
+      // 64 bit address is divided into the imm of this and the following
+      // instructions, lower 32 first.
+      write32le(loc + 4, val & 0xFFFFFFFF);
+      write32le(loc + 8 + 4, val >> 32);
+      break;
+    }
+    default:
+      error(getErrorLocation(loc) + "unrecognized reloc " + toString(type));
+  }
+}
+
+TargetInfo *getBPFTargetInfo() {
+  static BPF target;
+  return ⌖
+}
+
+} // namespace elf
+} // namespace lld

lld/ELF/CMakeLists.txt

@@ -12,6 +12,7 @@ add_lld_library(lldELF
   Arch/AMDGPU.cpp
   Arch/ARM.cpp
   Arch/AVR.cpp
+  Arch/BPF.cpp
   Arch/Hexagon.cpp
   Arch/Mips.cpp
   Arch/MipsArchTree.cpp

lld/ELF/Target.cpp

@@ -60,6 +60,8 @@ TargetInfo *getTarget() {
     return getARMTargetInfo();
   case EM_AVR:
     return getAVRTargetInfo();
+  case EM_BPF:
+    return getBPFTargetInfo();
   case EM_HEXAGON:
     return getHexagonTargetInfo();
   case EM_MIPS:

lld/ELF/Target.h

@@ -147,6 +147,7 @@ TargetInfo *getAArch64TargetInfo();
 TargetInfo *getAMDGPUTargetInfo();
 TargetInfo *getARMTargetInfo();
 TargetInfo *getAVRTargetInfo();
+TargetInfo *getBPFTargetInfo();
 TargetInfo *getHexagonTargetInfo();
 TargetInfo *getMSP430TargetInfo();
 TargetInfo *getPPC64TargetInfo();

llvm/include/llvm/BinaryFormat/ELFRelocs/BPF.def

@@ -5,4 +5,5 @@
 // No relocation
 ELF_RELOC(R_BPF_NONE,        0)
 ELF_RELOC(R_BPF_64_64,       1)
+ELF_RELOC(R_BPF_64_RELATIVE, 8)  // B + A
 ELF_RELOC(R_BPF_64_32,      10)

llvm/lib/Target/BPF/MCTargetDesc/BPFELFObjectWriter.cpp

@@ -34,7 +34,7 @@ class BPFELFObjectWriter : public MCELFObjectTargetWriter {
 
 } // end anonymous namespace
 
-// Avoid section relocations because the BPF backend can only handle 
+// Avoid section relocations because the BPF backend can only handle
 // section relocations with values (offset into the section containing
 // the symbol being relocated).  Forcing a relocation with a symbol
 // will result in the symbol's index being used in the .o file instead.