[Orc] Add JITLink debug support plugin for ELF x86-64

Add a new ObjectLinkingLayer plugin `DebugObjectManagerPlugin` and infrastructure to handle creation of `DebugObject`s as well as their registration in OrcTargetProcess. The current implementation only covers ELF on x86-64, but the infrastructure is not limited to that.

The journey starts with a new `LinkGraph` / `JITLinkContext` pair being created for a `MaterializationResponsibility` in ORC's `ObjectLinkingLayer`. It sends a `notifyMaterializing()` notification, which is forwarded to all registered plugins. The `DebugObjectManagerPlugin` aims to create a  `DebugObject` form the provided target triple and object buffer. (Future implementations might create `DebugObject`s from a `LinkGraph` in other ways.) On success it will track it as the pending `DebugObject` for the `MaterializationResponsibility`.

This patch only implements the `ELFDebugObject` for `x86-64` targets. It follows the RuntimeDyld approach for debug object setup: it captures a copy of the input object, parses all section headers and prepares to patch their load-address fields with their final addresses in target memory. It instructs the plugin to report the section load-addresses once they are available. The plugin overrides `modifyPassConfig()` and installs a JITLink post-allocation pass to capture them.

Once JITLink emitted the finalized executable, the plugin emits and registers the `DebugObject`. For emission it requests a new `JITLinkMemoryManager::Allocation` with a single read-only segment, copies the object with patched section load-addresses over to working memory and triggers finalization to target memory. For registration, it notifies the `DebugObjectRegistrar` provided in the constructor and stores the previously pending`DebugObject` as registered for the corresponding MaterializationResponsibility.

The `DebugObjectRegistrar` registers the `DebugObject` with the target process. `llvm-jitlink` uses the `TPCDebugObjectRegistrar`, which calls `llvm_orc_registerJITLoaderGDBWrapper()` in the target process via `TargetProcessControl` to emit a `jit_code_entry` compatible with the GDB JIT interface [1]. So far the implementation only supports registration and no removal. It appears to me that it wouldn't raise any new design questions, so I left this as an addition for the near future.

[1] https://sourceware.org/gdb/current/onlinedocs/gdb/JIT-Interface.html

Reviewed By: lhames

Differential Revision: https://reviews.llvm.org/D97335

1 files changed, 17 insertions, 5 deletions

diff --git a/llvm/lib/ExecutionEngine/Orc/ObjectLinkingLayer.cpp b/llvm/lib/ExecutionEngine/Orc/ObjectLinkingLayer.cpp
index 6de62f8..24db73e4 100644
--- a/llvm/lib/ExecutionEngine/Orc/ObjectLinkingLayer.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/ObjectLinkingLayer.cpp
@@ -10,6 +10,8 @@
 
 #include "llvm/ADT/Optional.h"
 #include "llvm/ExecutionEngine/JITLink/EHFrameSupport.h"
+#include "llvm/ExecutionEngine/Orc/DebugObjectManagerPlugin.h"
+#include "llvm/Support/MemoryBuffer.h"
 
 #include <vector>
 
@@ -40,6 +42,11 @@ public:
 
   JITLinkMemoryManager &getMemoryManager() override { return Layer.MemMgr; }
 
+  void notifyMaterializing(LinkGraph &G) {
+    for (auto &P : Layer.Plugins)
+      P->notifyMaterializing(*MR, G, *this, ObjBuffer->getMemBufferRef());
+  }
+
   void notifyFailed(Error Err) override {
     for (auto &P : Layer.Plugins)
       Err = joinErrors(std::move(Err), P->notifyFailed(*MR));
@@ -483,19 +490,24 @@ ObjectLinkingLayer::~ObjectLinkingLayer() {
 void ObjectLinkingLayer::emit(std::unique_ptr<MaterializationResponsibility> R,
                               std::unique_ptr<MemoryBuffer> O) {
   assert(O && "Object must not be null");
-  auto ObjBuffer = O->getMemBufferRef();
+  MemoryBufferRef ObjBuffer = O->getMemBufferRef();
+
   auto Ctx = std::make_unique<ObjectLinkingLayerJITLinkContext>(
       *this, std::move(R), std::move(O));
-  if (auto G = createLinkGraphFromObject(ObjBuffer))
+  if (auto G = createLinkGraphFromObject(ObjBuffer)) {
+    Ctx->notifyMaterializing(**G);
     link(std::move(*G), std::move(Ctx));
-  else
+  } else {
     Ctx->notifyFailed(G.takeError());
+  }
 }
 
 void ObjectLinkingLayer::emit(std::unique_ptr<MaterializationResponsibility> R,
                               std::unique_ptr<LinkGraph> G) {
-  link(std::move(G), std::make_unique<ObjectLinkingLayerJITLinkContext>(
-                         *this, std::move(R), nullptr));
+  auto Ctx = std::make_unique<ObjectLinkingLayerJITLinkContext>(
+      *this, std::move(R), nullptr);
+  Ctx->notifyMaterializing(*G);
+  link(std::move(G), std::move(Ctx));
 }
 
 void ObjectLinkingLayer::modifyPassConfig(MaterializationResponsibility &MR,