[Lldb-commits] [lldb] [lldb] Add DWARFExpressionEntry and GetExpressionEntryAtAddress() to … (PR #144238)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lldb

Author: Abdullah Mohammad Amin (UltimateForce21)

<details>
<summary>Changes</summary>

This patch introduces a new struct and helper API in `DWARFExpressionList` to expose 
variable location metadata (base address, end address, and DWARFExpression pointer) for 
a given PC address. It will be used in later patches to annotate disassembly instructions 
with source-level variable locations.

## New struct
```
/// Represents one entry in a DWARFExpressionList, with its range and expr.
struct DWARFExpressionEntry {
  lldb::addr_t base;           // file‐address start of this location range
  lldb::addr_t end;            // file‐address end of this range (exclusive)
  const DWARFExpression *expr; // the DWARF expression for this range
};
```

## New API
```
/// Retrieve the DWARFExpressionEntry covering a particular instruction.
///
/// \param func_load_addr
///     The load address of the start of the function containing this location list;
///     used to translate between file offsets and load addresses. If this is
///     LLDB_INVALID_ADDRESS, the stored CU base (m_func_file_addr) is used.
///
/// \param load_addr
///     The load address of the *current* PC (i.e., the instruction for which
///     we want its variable‐location entry). We first convert this back into
///     the function’s file‐address space to find the correct DWARF range.
///
/// \returns
///     On success, an entry whose `[base,end)` covers this PC; else an Error.
llvm::Expected<DWARFExpressionEntry>
GetExpressionEntryAtAddress(lldb::addr_t func_load_addr,
                            lldb::addr_t load_addr) const;
```

## Rationale
LLDB already provides:
```
const DWARFExpression *
GetExpressionAtAddress(lldb::addr_t func_load_addr,
                       lldb::addr_t load_addr) const;

```
However, this only returns the DWARF expression itself, without the file‐address start (base) and end (end) of the location range. Those bounds are crucial for:

1) Detecting range beginnings: render a var = <location> annotation exactly when a variable’s live‐range starts.

2) Detecting range continuation: optionally display a “|” on subsequent instructions in the same range.

3) Detecting state changes: know when a variable moves (e.g. from one register to another), becomes a constant, or goes out of scope.

These primitives form the foundation for the Rich Disassembler feature proposed for GSoC 25.

                              
     


---
Full diff: https://github.com/llvm/llvm-project/pull/144238.diff


2 Files Affected:

- (modified) lldb/include/lldb/Expression/DWARFExpressionList.h (+12) 
- (modified) lldb/source/Expression/DWARFExpressionList.cpp (+21) 


``````````diff
diff --git a/lldb/include/lldb/Expression/DWARFExpressionList.h b/lldb/include/lldb/Expression/DWARFExpressionList.h
index d8f8ec247ed56..a329b37393018 100644
--- a/lldb/include/lldb/Expression/DWARFExpressionList.h
+++ b/lldb/include/lldb/Expression/DWARFExpressionList.h
@@ -59,6 +59,18 @@ class DWARFExpressionList {
 
   lldb::addr_t GetFuncFileAddress() { return m_func_file_addr; }
 
+  /// Represents an entry in the DWARFExpressionList with all needed metadata
+  struct DWARFExpressionEntry {
+    lldb::addr_t base;
+    lldb::addr_t end;
+    const DWARFExpression *expr;
+  };
+
+  /// Returns the entry (base, end, data) for a given PC address
+  llvm::Expected<DWARFExpressionEntry>
+  GetExpressionEntryAtAddress(lldb::addr_t func_load_addr,
+                              lldb::addr_t load_addr) const;
+
   const DWARFExpression *GetExpressionAtAddress(lldb::addr_t func_load_addr,
                                                 lldb::addr_t load_addr) const;
 
diff --git a/lldb/source/Expression/DWARFExpressionList.cpp b/lldb/source/Expression/DWARFExpressionList.cpp
index 04592a1eb7ff4..b55bc7120c4af 100644
--- a/lldb/source/Expression/DWARFExpressionList.cpp
+++ b/lldb/source/Expression/DWARFExpressionList.cpp
@@ -53,6 +53,27 @@ bool DWARFExpressionList::ContainsAddress(lldb::addr_t func_load_addr,
   return GetExpressionAtAddress(func_load_addr, addr) != nullptr;
 }
 
+llvm::Expected<DWARFExpressionList::DWARFExpressionEntry>
+DWARFExpressionList::GetExpressionEntryAtAddress(lldb::addr_t func_load_addr,
+                                                 lldb::addr_t load_addr) const {
+  if (const DWARFExpression *expr = GetAlwaysValidExpr()) {
+    return DWARFExpressionEntry{0, LLDB_INVALID_ADDRESS, expr};
+  }
+
+  if (func_load_addr == LLDB_INVALID_ADDRESS)
+    func_load_addr = m_func_file_addr;
+
+  addr_t addr = load_addr - func_load_addr + m_func_file_addr;
+  uint32_t index = m_exprs.FindEntryIndexThatContains(addr);
+  if (index == UINT32_MAX) {
+    return llvm::createStringError(llvm::inconvertibleErrorCode(),
+                                   "No DWARF expression found for address 0x%llx", addr);
+  }
+
+  const Entry &entry = *m_exprs.GetEntryAtIndex(index);
+  return DWARFExpressionEntry{entry.base, entry.GetRangeEnd(), &entry.data};
+}
+
 const DWARFExpression *
 DWARFExpressionList::GetExpressionAtAddress(lldb::addr_t func_load_addr,
                                             lldb::addr_t load_addr) const {

``````````

</details>


https://github.com/llvm/llvm-project/pull/144238