[Lldb-commits] [lldb] [lldb] Fix evaluation of expressions with static initializers (PR #89063)

[Pavel Labath via lldb-commits]

https://github.com/labath created https://github.com/llvm/llvm-project/pull/89063

After 281d71604f418eb952e967d9dc4b26241b7f96a, 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.

>From e9b74aae92b8d8583d3549c6ef7257fd026678f5 Mon Sep 17 00:00:00 2001
From: Pavel Labath <pavel at labath.sk>
Date: Wed, 17 Apr 2024 11:58:44 +0000
Subject: [PATCH] [lldb] Fix evaluation of expressions with static initializers

After 281d71604f418eb952e967d9dc4b26241b7f96a, 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.
---
 lldb/source/Expression/IRExecutionUnit.cpp | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

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);