[ORC] Force eh-frame use for older Darwins on x86-64 in MachOPlatform, LLJIT.

The system libunwind on older Darwins does not support JIT registration of
compact-unwind. Since the CompactUnwindManager utility discards redundant
eh-frame FDEs by default we need to remove the compact-unwind section first
when targeting older libunwinds in order to preserve eh-frames.

While LLJIT was already doing this as of eae6d6d, MachOPlatform was not.
This was causing buildbot failures in the ORC runtime (e.g. in
https://green.lab.llvm.org/job/llvm.org/job/clang-stage1-RA/3479/).

This patch updates both LLJIT and MachOPlatform to check a bootstrap value,
"darwin-use-ehframes-only", to determine whether to forcibly preserve
eh-frame sections. If this value is present and set to true then compact-unwind
sections will be discarded, causing eh-frames to be preserved. If the value is
absent or set to false then compact-unwind will be used and redundant FDEs in
eh-frames discarded (FDEs that are needed by the compact-unwind section are
always preserved).

rdar://143895614
(cherry picked from commit e2eaf8d)

Author: lhames

llvm/include/llvm/ExecutionEngine/Orc/MachOPlatform.h

@@ -368,6 +368,7 @@ class MachOPlatform : public Platform {
   DenseMap<JITDylib *, SymbolLookupSet> RegisteredInitSymbols;
 
   std::mutex PlatformMutex;
+  bool ForceEHFrames = false;
   BootstrapInfo *Bootstrap = nullptr;
   DenseMap<JITDylib *, ExecutorAddr> JITDylibToHeaderAddr;
   DenseMap<ExecutorAddr, JITDylib *> HeaderAddrToJITDylib;

llvm/include/llvm/ExecutionEngine/Orc/TargetProcess/DefaultHostBootstrapValues.h

@@ -0,0 +1,28 @@
+//===- DefaultHostBootstrapValues.h - Defaults for host process -*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Set sensible default bootstrap values for JIT execution in the host process.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_EXECUTIONENGINE_ORC_TARGETPROCESS_DEFAULTHOSTBOOTSTRAPVALUES_H
+#define LLVM_EXECUTIONENGINE_ORC_TARGETPROCESS_DEFAULTHOSTBOOTSTRAPVALUES_H
+
+#include "llvm/ADT/StringMap.h"
+#include "llvm/ExecutionEngine/Orc/Shared/ExecutorAddress.h"
+#include <vector>
+
+namespace llvm::orc {
+
+void addDefaultBootstrapValuesForHostProcess(
+    StringMap<std::vector<char>> &BootstrapMap,
+    StringMap<ExecutorAddr> &BootstrapSymbols);
+
+} // namespace llvm::orc
+
+#endif // LLVM_EXECUTIONENGINE_ORC_TARGETPROCESS_DEFAULTHOSTBOOTSTRAPVALUES_H

llvm/lib/ExecutionEngine/Orc/ExecutorProcessControl.cpp

@@ -9,8 +9,7 @@
 #include "llvm/ExecutionEngine/Orc/ExecutorProcessControl.h"
 
 #include "llvm/ExecutionEngine/Orc/Core.h"
-#include "llvm/ExecutionEngine/Orc/Shared/OrcRTBridge.h"
-#include "llvm/ExecutionEngine/Orc/TargetProcess/RegisterEHFrames.h"
+#include "llvm/ExecutionEngine/Orc/TargetProcess/DefaultHostBootstrapValues.h"
 #include "llvm/ExecutionEngine/Orc/TargetProcess/TargetExecutionUtils.h"
 #include "llvm/Support/Process.h"
 #include "llvm/TargetParser/Host.h"
@@ -49,10 +48,7 @@ SelfExecutorProcessControl::SelfExecutorProcessControl(
   if (this->TargetTriple.isOSBinFormatMachO())
     GlobalManglingPrefix = '_';
 
-  this->BootstrapSymbols[rt::RegisterEHFrameSectionWrapperName] =
-      ExecutorAddr::fromPtr(&llvm_orc_registerEHFrameSectionWrapper);
-  this->BootstrapSymbols[rt::DeregisterEHFrameSectionWrapperName] =
-      ExecutorAddr::fromPtr(&llvm_orc_deregisterEHFrameSectionWrapper);
+  addDefaultBootstrapValuesForHostProcess(BootstrapMap, BootstrapSymbols);
 
 #ifdef __APPLE__
   // FIXME: Don't add an UnwindInfoManager by default -- it's redundant when

llvm/lib/ExecutionEngine/Orc/LLJIT.cpp

@@ -1221,22 +1221,37 @@ Expected<JITDylibSP> setUpGenericLLVMIRPlatform(LLJIT &J) {
 
   if (auto *OLL = dyn_cast<ObjectLinkingLayer>(&J.getObjLinkingLayer())) {
 
-    bool CompactUnwindInfoSupported = false;
+    bool UseEHFrames = true;
 
     // Enable compact-unwind support if possible.
     if (J.getTargetTriple().isOSDarwin() ||
         J.getTargetTriple().isOSBinFormatMachO()) {
-      if (auto UIRP = UnwindInfoRegistrationPlugin::Create(
-              J.getIRCompileLayer(), PlatformJD)) {
-        CompactUnwindInfoSupported = true;
-        OLL->addPlugin(std::move(*UIRP));
-        LLVM_DEBUG(dbgs() << "Enabled compact-unwind support.\n");
-      } else
-        consumeError(UIRP.takeError());
+
+      // Check if the bootstrap map says that we should force eh-frames:
+      // Older libunwinds require this as they don't have a dynamic
+      // registration API for compact-unwind.
+      std::optional<bool> ForceEHFrames;
+      if (auto Err = J.getExecutionSession().getBootstrapMapValue<bool, bool>(
+              "darwin-use-ehframes-only", ForceEHFrames))
+        return Err;
+      if (ForceEHFrames.has_value())
+        UseEHFrames = *ForceEHFrames;
+      else
+        UseEHFrames = false;
+
+      // If UseEHFrames hasn't been set then we're good to use compact-unwind.
+      if (!UseEHFrames) {
+        if (auto UIRP = UnwindInfoRegistrationPlugin::Create(
+                J.getIRCompileLayer(), PlatformJD)) {
+          OLL->addPlugin(std::move(*UIRP));
+          LLVM_DEBUG(dbgs() << "Enabled compact-unwind support.\n");
+        } else
+          return UIRP.takeError();
+      }
     }
 
     // Otherwise fall back to standard unwind registration.
-    if (!CompactUnwindInfoSupported) {
+    if (UseEHFrames) {
       auto &ES = J.getExecutionSession();
       if (auto EHFrameRegistrar = EPCEHFrameRegistrar::Create(ES)) {
         OLL->addPlugin(std::make_unique<EHFrameRegistrationPlugin>(

llvm/lib/ExecutionEngine/Orc/MachOPlatform.cpp

@@ -481,6 +481,15 @@ MachOPlatform::MachOPlatform(
   ObjLinkingLayer.addPlugin(std::make_unique<MachOPlatformPlugin>(*this));
   PlatformJD.addGenerator(std::move(OrcRuntimeGenerator));
 
+  {
+    // Check for force-eh-frame
+    std::optional<bool> ForceEHFrames;
+    if ((Err = ES.getBootstrapMapValue<bool, bool>("darwin-use-ehframes-only",
+                                                   ForceEHFrames)))
+      return;
+    this->ForceEHFrames = ForceEHFrames.has_value() ? *ForceEHFrames : false;
+  }
+
   BootstrapInfo BI;
   Bootstrap = &BI;
 
@@ -811,6 +820,12 @@ void MachOPlatform::MachOPlatformPlugin::modifyPassConfig(
       HeaderAddr = I->second;
   }
 
+  // If we're forcing eh-frame use then discard the compact-unwind section
+  // immediately to prevent FDEs from being stripped.
+  if (MP.ForceEHFrames)
+    if (auto *CUSec = LG.findSectionByName(MachOCompactUnwindSectionName))
+      LG.removeSection(*CUSec);
+
   // Point the libunwind dso-base absolute symbol at the header for the
   // JITDylib. This will prevent us from synthesizing a new header for
   // every object.

llvm/lib/ExecutionEngine/Orc/TargetProcess/CMakeLists.txt

@@ -11,6 +11,7 @@ endif()
 
 add_llvm_component_library(LLVMOrcTargetProcess
   ExecutorSharedMemoryMapperService.cpp
+  DefaultHostBootstrapValues.cpp
   JITLoaderGDB.cpp
   JITLoaderPerf.cpp
   JITLoaderVTune.cpp

llvm/lib/ExecutionEngine/Orc/TargetProcess/DefaultHostBootstrapValues.cpp

@@ -0,0 +1,36 @@
+//===----- DefaultHostBootstrapValues.cpp - Defaults for host process -----===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ExecutionEngine/Orc/TargetProcess/DefaultHostBootstrapValues.h"
+
+#include "llvm/ExecutionEngine/Orc/Shared/OrcRTBridge.h"
+#include "llvm/ExecutionEngine/Orc/TargetProcess/RegisterEHFrames.h"
+
+#ifdef __APPLE__
+#include <dlfcn.h>
+#endif // __APPLE__
+
+namespace llvm::orc {
+
+void addDefaultBootstrapValuesForHostProcess(
+    StringMap<std::vector<char>> &BootstrapMap,
+    StringMap<ExecutorAddr> &BootstrapSymbols) {
+
+  // FIXME: We probably shouldn't set these on Windows?
+  BootstrapSymbols[rt::RegisterEHFrameSectionWrapperName] =
+      ExecutorAddr::fromPtr(&llvm_orc_registerEHFrameSectionWrapper);
+  BootstrapSymbols[rt::DeregisterEHFrameSectionWrapperName] =
+      ExecutorAddr::fromPtr(&llvm_orc_deregisterEHFrameSectionWrapper);
+
+#ifdef __APPLE__
+  if (!dlsym(RTLD_DEFAULT, "__unw_add_find_dynamic_unwind_sections"))
+    BootstrapMap["darwin-use-ehframes-only"].push_back(1);
+#endif // __APPLE__
+}
+
+} // namespace llvm::orc

llvm/lib/ExecutionEngine/Orc/TargetProcess/OrcRTBootstrap.cpp

@@ -106,10 +106,6 @@ void addTo(StringMap<ExecutorAddr> &M) {
       ExecutorAddr::fromPtr(&writeBuffersWrapper);
   M[rt::MemoryWritePointersWrapperName] =
       ExecutorAddr::fromPtr(&writePointersWrapper);
-  M[rt::RegisterEHFrameSectionWrapperName] =
-      ExecutorAddr::fromPtr(&llvm_orc_registerEHFrameSectionWrapper);
-  M[rt::DeregisterEHFrameSectionWrapperName] =
-      ExecutorAddr::fromPtr(&llvm_orc_deregisterEHFrameSectionWrapper);
   M[rt::RunAsMainWrapperName] = ExecutorAddr::fromPtr(&runAsMainWrapper);
   M[rt::RunAsVoidFunctionWrapperName] =
       ExecutorAddr::fromPtr(&runAsVoidFunctionWrapper);

llvm/tools/llvm-jitlink/llvm-jitlink-executor/llvm-jitlink-executor.cpp

@@ -12,6 +12,7 @@
 
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Config/llvm-config.h" // for LLVM_ON_UNIX, LLVM_ENABLE_THREADS
+#include "llvm/ExecutionEngine/Orc/TargetProcess/DefaultHostBootstrapValues.h"
 #include "llvm/ExecutionEngine/Orc/TargetProcess/ExecutorSharedMemoryMapperService.h"
 #include "llvm/ExecutionEngine/Orc/TargetProcess/JITLoaderGDB.h"
 #include "llvm/ExecutionEngine/Orc/TargetProcess/RegisterEHFrames.h"
@@ -187,6 +188,8 @@ int main(int argc, char *argv[]) {
                 std::make_unique<SimpleRemoteEPCServer::ThreadDispatcher>());
             S.bootstrapSymbols() =
                 SimpleRemoteEPCServer::defaultBootstrapSymbols();
+            addDefaultBootstrapValuesForHostProcess(S.bootstrapMap(),
+                                                    S.bootstrapSymbols());
             S.services().push_back(
                 std::make_unique<rt_bootstrap::SimpleExecutorMemoryManager>());
             S.services().push_back(