Support evaluation of DWARF expressions setting CFA

Summary:
This patch enables evaluation of DWARF expressions setting the CFA during stack unwinding.

This makes TestSigtrampUnwind "almost" pass on linux. I am not enabling the test yet since the
symbol name for the signal trampoline does not get resolved properly due to a different bug, but
apart from that, the backtrace is sane.

I am unsure how this change affects Mac. I think it makes the unwinder prefer the DWARF unwind
plan instead of some custom platform-dependant plan. However, it does not affect the end result
- the stack unwinding works as expected.

Reviewers: jasonmolenda

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D7792

llvm-svn: 230211

2 files changed, 4 insertions, 4 deletions

diff --git a/lldb/source/Symbol/DWARFCallFrameInfo.cpp b/lldb/source/Symbol/DWARFCallFrameInfo.cpp
index 39c58d6bb4e..92d9f8b808d 100644
--- a/lldb/source/Symbol/DWARFCallFrameInfo.cpp
+++ b/lldb/source/Symbol/DWARFCallFrameInfo.cpp
@@ -748,7 +748,9 @@ DWARFCallFrameInfo::FDEToUnwindPlan (dw_offset_t dwarf_offset, Address startaddr
                 case DW_CFA_def_cfa_expression  : // 0xF    (CFA Definition Instruction)
                     {
                         size_t block_len = (size_t)m_cfi_data.GetULEB128(&offset);
-                        offset += (uint32_t)block_len;
+                        const uint8_t *block_data =
+                            static_cast<const uint8_t *>(m_cfi_data.GetData(&offset, block_len));
+                        row->GetCFAValue().SetIsDWARFExpression(block_data, block_len);
                     }
                     break;
 
diff --git a/lldb/source/Symbol/UnwindPlan.cpp b/lldb/source/Symbol/UnwindPlan.cpp
index d4b06d5c925..b35a6e7b28a 100644
--- a/lldb/source/Symbol/UnwindPlan.cpp
+++ b/lldb/source/Symbol/UnwindPlan.cpp
@@ -434,10 +434,8 @@ UnwindPlan::PlanValidAtAddress (Address addr)
 
     // If the 0th Row of unwind instructions is missing, or if it doesn't provide
     // a register to use to find the Canonical Frame Address, this is not a valid UnwindPlan.
-    // CFA set by a DWARF expression is not currently supported, so ignore that as well.
     if (GetRowAtIndex(0).get() == nullptr ||
-            GetRowAtIndex(0)->GetCFAValue().GetValueType() == Row::CFAValue::unspecified ||
-            GetRowAtIndex(0)->GetCFAValue().GetValueType() == Row::CFAValue::isDWARFExpression)
+            GetRowAtIndex(0)->GetCFAValue().GetValueType() == Row::CFAValue::unspecified)
     {
         Log *log(GetLogIfAllCategoriesSet (LIBLLDB_LOG_UNWIND));
         if (log)