[DWARF CFI] Add support for DW_CFA_def_cfa_sf when parsing CIE

[labath]

Summary

Just what it says on the box.

[jasonmolenda]

Looks good to me, thanks.

source/Symbol/DWARFCallFrameInfo.cpp

if (length > 0 && ((!m_is_eh_frame && cie_id == UINT32_MAX) || (m_is_eh_frame && cie_id == 0ul)))
                 // number and a (non-factored) offset. The required action
                 // is to define the current CFA rule to use the provided
                 // register and offset.
                 uint32_t reg_num = (uint32_t)m_cfi_data.GetULEB128(&offset);
                 int op_offset = (int32_t)m_cfi_data.GetULEB128(&offset);
                 cie_sp->initial_row.GetCFAValue().SetIsRegisterPlusOffset (reg_num, op_offset);
                 continue;
             }
+            if (extended_opcode == DW_CFA_def_cfa_sf)
+            {
+                // The DW_CFA_def_cfa_sf instruction takes two operands: an unsigned LEB128 value
+                // representing a register number and a signed LEB128 factored offset. This
+                // instruction is identical to DW_CFA_def_cfa except that the second operand is
+                // signed and factored.
+                // The resulting offset is factored_offset * data_alignment_factor.
+                uint32_t reg_num = (uint32_t)m_cfi_data.GetULEB128(&offset);
+                int op_offset = (int32_t)m_cfi_data.GetSLEB128(&offset);
+                cie_sp->initial_row.GetCFAValue().SetIsRegisterPlusOffset (
+                        reg_num, op_offset * cie_sp->data_align);
+                continue;
+            }
             if (primary_opcode == DW_CFA_offset)
             {   
                 // 0x80 - high 2 bits are 0x2, lower 6 bits are register.
                 // Takes two arguments: an unsigned LEB128 constant representing a
                 // factored offset and a register number. The required action is to
                 // change the rule for the register indicated by the register number
                 // to be an offset(N) rule with a value of
                 // (N = factored offset * data_align).