llvm-project

2acd6528 - Fix lldb-dap non-leaf frame source resolution issue (#165944)

Fix lldb-dap non-leaf frame source resolution issue (#165944) Summary ------- While dogfooding lldb-dap, I observed that VSCode frequently displays certain stack frames as greyed out. Although these frames have valid debug information, double-clicking them shows disassembly instead of source code. However, running `bt` from the LLDB command line correctly displays source file and line information for these same frames, indicating this is an lldb-dap specific issue. Root Cause ---------- Investigation revealed that `DAP::ResolveSource()` incorrectly uses a frame's PC address directly to determine whether valid source line information exists. This approach works for leaf frames, but fails for non-leaf (caller) frames where the PC points to the return address immediately after a call instruction. This return address may fall into compiler-generated code with no associated line information, even though the actual call site has valid source location data. The correct approach is to use the symbol context's line entry, which LLDB resolves by effectively checking PC-1 for non-leaf frames, properly identifying the line information for the call instruction rather than the return address. Testing ------- Manually tested with VSCode debugging sessions on production workloads. Verified that non-leaf frames now correctly display source code instead of disassembly view. Before the change symptom: <img width="1013" height="216" alt="image" src="https://github.com/user-attachments/assets/9487fbc0-f438-4892-a8d2-1437dc25399b" /> And here is after the fix: <img width="1068" height="198" alt="image" src="https://github.com/user-attachments/assets/0d2ebaa7-cca6-4983-a1d1-1a26ae62c86f" /> --------- Co-authored-by: Jeffrey Tan <jeffreytan@fb.com>