[lldb] Fix evaluation of expressions with static initializers

[labath]

After 281d716, llvm generates 32-bit relocations, which overflow when we load these objects into high memory. Interestingly, setting the code model to "large" does not help here (perhaps it is the default?). I'm not completely sure that this is the right thing to do, but it doesn't seem to cause any ill effects. I'll follow up with the author of that patch about the expected behavior here.

[llvmbot]

@llvm/pr-subscribers-lldb

Author: Pavel Labath (labath)

Changes

After 281d716, llvm generates 32-bit relocations, which overflow when we load these objects into high memory. Interestingly, setting the code model to "large" does not help here (perhaps it is the default?). I'm not completely sure that this is the right thing to do, but it doesn't seem to cause any ill effects. I'll follow up with the author of that patch about the expected behavior here.

---

Full diff: https://github.com/llvm/llvm-project/pull/89063.diff

1 Files Affected:

• (modified) lldb/source/Expression/IRExecutionUnit.cpp (+6-2)

diff --git a/lldb/source/Expression/IRExecutionUnit.cpp b/lldb/source/Expression/IRExecutionUnit.cpp
index cb9bee8733e15d..7ad0e5ff22b2f6 100644
--- a/lldb/source/Expression/IRExecutionUnit.cpp
+++ b/lldb/source/Expression/IRExecutionUnit.cpp
@@ -13,6 +13,7 @@
 #include "llvm/IR/DiagnosticInfo.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Module.h"
+#include "llvm/Support/CodeGen.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/raw_ostream.h"
 
@@ -279,10 +280,13 @@ void IRExecutionUnit::GetRunnableInfo(Status &error, lldb::addr_t &func_addr,
   llvm::EngineBuilder builder(std::move(m_module_up));
   llvm::Triple triple(m_module->getTargetTriple());
 
+  // PIC needed for ELF to avoid generating 32-bit relocations (which overflow
+  // if the object is loaded into high memory).
+  bool want_pic = triple.isOSBinFormatMachO() || triple.isOSBinFormatELF();
+
   builder.setEngineKind(llvm::EngineKind::JIT)
       .setErrorStr(&error_string)
-      .setRelocationModel(triple.isOSBinFormatMachO() ? llvm::Reloc::PIC_
-                                                      : llvm::Reloc::Static)
+      .setRelocationModel(want_pic ? llvm::Reloc::PIC_ : llvm::Reloc::Static)
       .setMCJITMemoryManager(std::make_unique<MemoryManager>(*this))
       .setOptLevel(llvm::CodeGenOptLevel::Less);