<div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote">On Tue, May 17, 2016 at 4:12 PM, Adrian Prantl via llvm-commits <span dir="ltr"><<a href="mailto:llvm-commits@lists.llvm.org" target="_blank">llvm-commits@lists.llvm.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">Author: adrian<br>
Date: Tue May 17 15:12:08 2016<br>
New Revision: 269827<br>
<br>
URL: <a href="http://llvm.org/viewvc/llvm-project?rev=269827&view=rev" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project?rev=269827&view=rev</a><br>
Log:<br>
Debug Info: Don't emit bitfields in the DWARF4 format when tuning for GDB.<br>
As discovered in PR27758, GDB does not fully support the DWARF 4 format.<br>
This patch ensures we always emit bitfields in the DWARF 2 when tuning for GDB.<br>
<br>
Modified:<br>
    llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.cpp<br>
    llvm/trunk/test/DebugInfo/ARM/big-endian-bitfield.ll<br>
    llvm/trunk/test/DebugInfo/X86/bitfields-dwarf4.ll<br>
<br>
Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.cpp?rev=269827&r1=269826&r2=269827&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.cpp?rev=269827&r1=269826&r2=269827&view=diff</a><br>
==============================================================================<br>
--- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.cpp (original)<br>
+++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.cpp Tue May 17 15:12:08 2016<br>
@@ -1390,10 +1390,14 @@ void DwarfUnit::constructMemberDIE(DIE &<br>
     uint64_t Size = DT->getSizeInBits();<br>
     uint64_t FieldSize = getBaseTypeSize(DD, DT);<br>
     uint64_t OffsetInBytes;<br>
+<br>
+    // GDB does not fully support the DWARF 4 representation for bitfields.<br>
+    bool EmitDWARF2Bitfields = (DD->getDwarfVersion() < 4) || (DD->tuneForGDB());<br>
     bool IsBitfield = FieldSize && Size != FieldSize;<br>
+<br>
     if (IsBitfield) {<br>
       // Handle bitfield, assume bytes are 8 bits.<br>
-      if (DD->getDwarfVersion() < 4)<br>
+      if (EmitDWARF2Bitfields)<br>
         addUInt(MemberDie, dwarf::DW_AT_byte_size, None, FieldSize/8);<br>
       addUInt(MemberDie, dwarf::DW_AT_bit_size, None, Size);<br>
<br>
@@ -1405,9 +1409,7 @@ void DwarfUnit::constructMemberDIE(DIE &<br>
       // The byte offset of the field's aligned storage unit inside the struct.<br>
       OffsetInBytes = (Offset - StartBitOffset) / 8;<br>
<br>
-      if (DD->getDwarfVersion() >= 4)<br>
-        addUInt(MemberDie, dwarf::DW_AT_data_bit_offset, None, Offset);<br>
-      else {<br>
+      if (EmitDWARF2Bitfields) {<br>
         uint64_t HiMark = (Offset + FieldSize) & AlignMask;<br>
         uint64_t FieldOffset = (HiMark - FieldSize);<br>
         Offset -= FieldOffset;<br>
@@ -1418,17 +1420,20 @@ void DwarfUnit::constructMemberDIE(DIE &<br>
<br>
         addUInt(MemberDie, dwarf::DW_AT_bit_offset, None, Offset);<br>
         OffsetInBytes = FieldOffset >> 3;<br>
+      } else {<br>
+        addUInt(MemberDie, dwarf::DW_AT_data_bit_offset, None, Offset);<br>
       }<br></blockquote><div><br></div><div class="gmail-adn gmail-ads" style="padding-bottom:0px;font-size:medium"><div class="gmail-gs"><div id="gmail-:1g8" class="gmail-ii gmail-gt gmail-adP gmail-adO" style="font-size:12.8px"><div id="gmail-:1g7" class="gmail-a3s gmail-aXjCH gmail-m156323bd86ffe488"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><div>I tested this on a big endian system and it doesn't work.</div><div><br></div><div>The dwarf spec say that the <span class="gmail-il">DW_AT_data_bit_offset</span> value must be the same for big or litttle endian. LLDB will do the appropriate calculation.</div><div>But at the point Offset wont have the same value on little or big endian system.</div><div class="gmail-yj6qo"></div></div></div></div></div></div><div class="gmail-hi"></div></div><div class="gmail-ajx"></div></div><div class="gmail-gA gmail-gt gmail-acV" style="font-size:12.8px;background-color:rgb(255,255,255)"><div class="gmail-gB gmail-xu"><div class="gmail-ip gmail-iq" style="padding-top:8px;padding-right:0px;padding-left:4px;border-top-width:1px;border-top-style:solid;border-top-color:rgb(216,216,216)"></div></div></div><div><br></div><div> </div></div></div></div>