[LLVMdev] Debug information under windows

[Daniel Kłobuszewski]

W dniu 2012-10-26 16:55, Daniel Kłobuszewski pisze:
> Hello,
>
> Recently I found binaries produced with LLVM impossible to debug under
> Windows. This was probably related to the following bug:
> http://llvm.org/bugs/show_bug.cgi?id=13636
>
> Asm generated from .ll files revealed that some offsets to debug
> information were incorrect: they were absolute instead of relative to
> their sections.
>
> Following patch seemed to have repaired the problem, so I'm just leaving
> it here. Hopefully this will help someone.
>
> Regards,
> Daniel
>
>
> diff -r 547972237a05 -r 6ed9378f04a3 lib/MC/MCAsmInfoCOFF.cpp
> --- a/lib/MC/MCAsmInfoCOFF.cpp    Wed Oct 10 20:39:45 2012 +0200
> +++ b/lib/MC/MCAsmInfoCOFF.cpp    Thu Oct 18 12:41:27 2012 +0200
> @@ -38,6 +38,10 @@
>     HasMicrosoftFastStdCallMangling = true;
>
>     SupportsDataRegions = false;
> +
> +  DwarfUsesLabelOffsetForRanges = false;
> +  DwarfRequiresRelocationForSectionOffset = false;
> +  DwarfUsesRelocationsForStringPool = false;
>   }
>
>   void MCAsmInfoMicrosoft::anchor() { }
>

Hello again,

"fix" from my previous message was helpful only for one compilation 
unit, but was working incorrectly in case when more CUs were linked 
together.

Since the bug I've linked seems to still be unresolved, I'm sending my 
solution to it. Basically all that needed to be done was to emit 
.secrel32 instructions in few places instead of sections offsets in 
label difference form.

Here is how I've been building executable for tests (under MinGW console):

llc test.bc -filetype=asm -march=x86 -x86-asm-syntax=att 
-mtriple=i686-pc-mingw32 -disable-fp-elim
llc test_main.bc -filetype=asm -march=x86 -x86-asm-syntax=att 
-mtriple=i686-pc-mingw32 -disable-fp-elim
gcc -g -c test.s -o test.o
gcc -g -c test_main.s -o test_main.o
gcc -g test_main.o test.o -o test

Someone more familiar with LLVM code than me should probably review my 
proposed patch. My source revision was 3.1 LLVM release.

Regards,
Daniel
-------------- next part --------------
diff -r 547972237a05 -r d28fa29d4b44 lib/CodeGen/AsmPrinter/AsmPrinter.cpp
--- a/lib/CodeGen/AsmPrinter/AsmPrinter.cpp	Wed Oct 10 20:39:45 2012 +0200
+++ b/lib/CodeGen/AsmPrinter/AsmPrinter.cpp	Mon Nov 19 10:31:49 2012 +0100
@@ -1398,6 +1398,13 @@
 void AsmPrinter::EmitLabelPlusOffset(const MCSymbol *Label, uint64_t Offset,
                                       unsigned Size)
   const {
+  // if COFF .secrel32 is available, use it
+  if (MAI->getDwarfSectionOffsetDirective()) {
+    MCSymbol *SetLabel = GetTempSymbol("set", SetCounter++);
+    OutStreamer.EmitAssignment(SetLabel, MCConstantExpr::Create(Offset, OutContext));
+    OutStreamer.EmitCOFFSecRel32(SetLabel);
+    return;
+  }
 
   // Emit Label+Offset
   const MCExpr *Plus =
diff -r 547972237a05 -r d28fa29d4b44 lib/CodeGen/AsmPrinter/DIE.cpp
--- a/lib/CodeGen/AsmPrinter/DIE.cpp	Wed Oct 10 20:39:45 2012 +0200
+++ b/lib/CodeGen/AsmPrinter/DIE.cpp	Mon Nov 19 10:31:49 2012 +0100
@@ -257,6 +257,11 @@
 /// EmitValue - Emit delta value.
 ///
 void DIEDelta::EmitValue(AsmPrinter *AP, unsigned Form) const {
+  if (AP->MAI->getDwarfSectionOffsetDirective()) {
+    // FIXME: Can DIEDelta be used in other contexts than section offset?
+    AP->EmitSectionOffset(LabelHi, LabelLo);
+    return;
+  }
   AP->EmitLabelDifference(LabelHi, LabelLo, SizeOf(AP, Form));
 }
 
diff -r 547972237a05 -r d28fa29d4b44 lib/CodeGen/AsmPrinter/DwarfDebug.cpp
--- a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp	Wed Oct 10 20:39:45 2012 +0200
+++ b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp	Mon Nov 19 10:31:49 2012 +0100
@@ -567,9 +567,14 @@
   NewCU->addUInt(Die, dwarf::DW_AT_low_pc, dwarf::DW_FORM_addr, 0);
   // DW_AT_stmt_list is a offset of line number information for this
   // compile unit in debug_line section.
-  if (Asm->MAI->doesDwarfRequireRelocationForSectionOffset())
-    NewCU->addLabel(Die, dwarf::DW_AT_stmt_list, dwarf::DW_FORM_data4,
+  if (Asm->MAI->doesDwarfRequireRelocationForSectionOffset()) {
+    if (Asm->MAI->getDwarfSectionOffsetDirective()) // COFF
+      NewCU->addDelta(Die, dwarf::DW_AT_stmt_list, dwarf::DW_FORM_data4,
+                    Asm->GetTempSymbol("section_line"), 0); // will expand to secrel32 on COFF. TODO: separate "DieCOFFLabel" class or something
+    else
+      NewCU->addLabel(Die, dwarf::DW_AT_stmt_list, dwarf::DW_FORM_data4,
                     Asm->GetTempSymbol("section_line"));
+  }
   else
     NewCU->addUInt(Die, dwarf::DW_AT_stmt_list, dwarf::DW_FORM_data4, 0);
 
@@ -1638,7 +1643,7 @@
     }
     case dwarf::DW_AT_location: {
       if (DIELabel *L = dyn_cast<DIELabel>(Values[i]))
-        Asm->EmitLabelDifference(L->getValue(), DwarfDebugLocSectionSym, 4);
+        Asm->EmitSectionOffset(L->getValue(), DwarfDebugLocSectionSym);
       else
         Values[i]->EmitValue(Asm, Form);
       break;
diff -r 547972237a05 -r d28fa29d4b44 lib/MC/MCAsmInfoCOFF.cpp
--- a/lib/MC/MCAsmInfoCOFF.cpp	Wed Oct 10 20:39:45 2012 +0200
+++ b/lib/MC/MCAsmInfoCOFF.cpp	Mon Nov 19 10:31:49 2012 +0100
@@ -38,6 +38,8 @@
   HasMicrosoftFastStdCallMangling = true;
 
   SupportsDataRegions = false;
+
+  DwarfUsesRelocationsForStringPool = false;
 }
 
 void MCAsmInfoMicrosoft::anchor() { }