[Lldb-commits] [PATCH] D22266: Add "support" for DW_CFA_GNU_args_size to the unwinder

Pavel Labath via lldb-commits lldb-commits at lists.llvm.org
Tue Jul 12 08:09:23 PDT 2016

labath created this revision.
labath added a reviewer: jasonmolenda.
labath added a subscriber: lldb-commits.

This adds the knowledge of the DW_CFA_GNU_args_size instruction to the eh_frame parsing code.
Right now it is ignored as I am unsure how is it supposed to be handled, but now we are at least
able to parse the rest of the FDE containing this instruction.

I also add a fix for a bug which was exposed by this instruction. Namely, a mismatched sequence
of remember/restore instructions in the input could cause us to pop an empty stack and crash. Now
we just log the error and ignore the offending instruction.



Index: source/Symbol/DWARFCallFrameInfo.cpp
--- source/Symbol/DWARFCallFrameInfo.cpp
+++ source/Symbol/DWARFCallFrameInfo.cpp
@@ -408,6 +408,7 @@
 DWARFCallFrameInfo::FDEToUnwindPlan (dw_offset_t dwarf_offset, Address startaddr, UnwindPlan& unwind_plan)
+    Log *log = GetLogIfAllCategoriesSet(LIBLLDB_LOG_UNWIND);
     lldb::offset_t offset = dwarf_offset;
     lldb::offset_t current_entry = offset;
@@ -648,13 +649,32 @@
                         // the stack and place them in the current row. (This operation is
                         // useful for compilers that move epilogue code into the body of a
                         // function.)
+                        if (stack.empty())
+                        {
+                            if (log)
+                                log->Printf(
+                                    "DWARFCallFrameInfo::%s(dwarf_offset: %" PRIx32 ", startaddr: %" PRIx64
+                                    " encountered DW_CFA_restore_state but state stack is empty. Corrupt unwind info?",
+                                    __FUNCTION__, dwarf_offset, startaddr.GetFileAddress());
+                            break;
+                        }
                         lldb::addr_t offset = row->GetOffset ();
                         row = stack.back ();
                         stack.pop_back ();
                         row->SetOffset (offset);
+                    case DW_CFA_GNU_args_size: // 0x2e
+                    {
+                        // The DW_CFA_GNU_args_size instruction takes an unsigned LEB128 operand
+                        // representing an argument size. This instruction specifies the total of
+                        // the size of the arguments which have been pushed onto the stack.
+                        // TODO: Figure out how we should handle this.
+                        m_cfi_data.GetULEB128(&offset);
+                    }
                     case DW_CFA_val_offset          :   // 0x14
                     case DW_CFA_val_offset_sf       :   // 0x15

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