[RuntimeDyld][BPF] load additional sections

[yonghong-song]

Summary

With target bpf and -g, current clang/llvm compiler generates
two sections, .BTF and .BTF.ext, for BPF debugging.
The .BTF does not have any symbols, and does not have any
relocations either. Hence, even with ProcessAllSections
enabled, it is not loaded by runtime dynamic linker.

This patch extended RuntimeDyldELF with a BPF subclass.
The RuntimeDyldELFBPF overrided finalizeLoad() such that
first loads .BTF section if it exists and then proceeds
with the rest finalizeLoad() operation.

Signed-off-by: Yonghong Song <[e-mail]>

[yonghong-song]

Hi, @lhames this is an alternative implementation w.r.t. D55943. In D55943, if ProcessAllSections is set to true, all sections will be loaded.
I am not sure whether this is the original intention of not as it says ProcessAllSections, not meaning LoadAllSections.

So this patch extends RuntimeDyldELF for BPF target. It will load .BTF section, which is what we want in the bcc or other JIT implementations.

Could you let me know which method you prefer? I think this patch is better. Thanks!

[yonghong-song]

Abandon this patch. D55943 is the recommended approach.

lib/ExecutionEngine/RuntimeDyld/CMakeLists.txt

 add_llvm_library(LLVMRuntimeDyld
   JITSymbol.cpp
   RTDyldMemoryManager.cpp
   RuntimeDyld.cpp
   RuntimeDyldChecker.cpp
   RuntimeDyldCOFF.cpp
   RuntimeDyldELF.cpp
   RuntimeDyldMachO.cpp
+  Targets/RuntimeDyldELFBPF.cpp
   Targets/RuntimeDyldELFMips.cpp
 
   DEPENDS
   intrinsics_gen
   )

lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp

 //===-- RuntimeDyldELF.cpp - Run-time dynamic linker for MC-JIT -*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // Implementation of ELF support for the MC-JIT runtime dynamic linker.
 //
 //===----------------------------------------------------------------------===//
 
 #include "RuntimeDyldELF.h"
 #include "RuntimeDyldCheckerImpl.h"
+#include "Targets/RuntimeDyldELFBPF.h"
 #include "Targets/RuntimeDyldELFMips.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/BinaryFormat/ELF.h"
 #include "llvm/Object/ELFObjectFile.h"
 #include "llvm/Object/ObjectFile.h"
 #include "llvm/Support/Endian.h"

 
 std::unique_ptr<RuntimeDyldELF>
 llvm::RuntimeDyldELF::create(Triple::ArchType Arch,
                              RuntimeDyld::MemoryManager &MemMgr,
                              JITSymbolResolver &Resolver) {
   switch (Arch) {
   default:
     return make_unique<RuntimeDyldELF>(MemMgr, Resolver);
+  case Triple::bpfel:
+  case Triple::bpfeb:
+    return make_unique<RuntimeDyldELFBPF>(MemMgr, Resolver);
   case Triple::mips:
   case Triple::mipsel:
   case Triple::mips64:
   case Triple::mips64el:
     return make_unique<RuntimeDyldELFMips>(MemMgr, Resolver);
   }
 }
 

lib/ExecutionEngine/RuntimeDyld/Targets/RuntimeDyldELFBPF.h

+//===-- RuntimeDyldELFBPF.h ---- ELF/BPF specific code. ---------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_EXECUTIONENGINE_RUNTIMEDYLD_TARGETS_RUNTIMEDYLDELFBPF_H
+#define LLVM_LIB_EXECUTIONENGINE_RUNTIMEDYLD_TARGETS_RUNTIMEDYLDELFBPF_H
+
+#include "../RuntimeDyldELF.h"
+#include <string>
+
+#define DEBUG_TYPE "dyld"
+
+namespace llvm {
+
+class RuntimeDyldELFBPF : public RuntimeDyldELF {
+public:
+  RuntimeDyldELFBPF(RuntimeDyld::MemoryManager &MM, JITSymbolResolver &Resolver)
+      : RuntimeDyldELF(MM, Resolver) {}
+
+  Error finalizeLoad(const ObjectFile &Obj,
+                     ObjSectionToIDMap &SectionMap) override;
+};
+} // namespace llvm
+
+#undef DEBUG_TYPE
+
+#endif

lib/ExecutionEngine/RuntimeDyld/Targets/RuntimeDyldELFBPF.cpp

+//===-- RuntimeDyldELFBPF.cpp ---- ELF/BPF specific code. -------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "RuntimeDyldELFBPF.h"
+
+#define DEBUG_TYPE "dyld"
+
+// The .BTF section has no symbols or any relocations. Hence
+// runtime dyld won't load it. Load it here.
+Error RuntimeDyldELFBPF::finalizeLoad(const ObjectFile &Obj,
+                                      ObjSectionToIDMap &SectionMap) {
+  for (section_iterator SI = Obj.section_begin(), SE = Obj.section_end();
+       SI != SE; ++SI) {
+    // Ignore sections already in SectionMap
+    if (SectionMap.find(*SI) != SectionMap.end())
+      continue;
+
+    StringRef SectionName;
+    SI->getName(SectionName);
+
+    if (SectionName != ".BTF")
+      continue;
+
+    // Load .BTF section.
+    bool IsCode = SI->isText();
+    if (auto SectionIDOrErr = findOrEmitSection(Obj, *SI, IsCode, SectionMap)) {
+      LLVM_DEBUG(dbgs() << "\tSectionID: " << (*SectionIDOrErr) << "\n");
+    } else {
+      return make_error<RuntimeDyldError>(
+          "RuntimeDyldELFBPF load section error");
+    }
+
+    break;
+  }
+
+  return RuntimeDyldELF::finalizeLoad(Obj, SectionMap);
+}