Fix PR21189 -- Emit symbol subsection required to debug LLVM-built binaries with VS2012+

[timurrrr]

Summary

David, Eric,

This is a preliminary version.
I haven't updated some of the test/DebugInfo/COFF lit tests since changing the code just a little [which might happend during the review] requires significant amount of work to update the tests.
Please comment on the code and an example test modification and I'll update the rest of the tests if everything's OK with you.

––
Tim

[timurrrr]

ping?

[timurrrr]

Rebase now that r220526 has landed.

[timurrrr]

Using getDISubprogram(F).getDisplayName() to get demangled function name now

[timurrrr]

Oops, I've uploaded a few wrong hunks. Lemme fix that in a minute!

[timurrrr]

Fixed issues with the previous patch

[majnemer]

LGTM

[timurrrr]

Updated the rest of the tests.
I'm going to try a few more things locally and commit if everything's OK.

[timurrrr]

r220544!

lib/CodeGen/AsmPrinter/WinCodeViewLineTables.cpp

void WinCodeViewLineTables::endModule() {
 
   // No more subsections. Fill with zeros to align the end of the section by 4.
   Asm->OutStreamer.EmitFill((-FileNameRegistry.LastOffset) % 4, 0);
 
   clear();
 }
 
 static void EmitLabelDiff(MCStreamer &Streamer,
-                          const MCSymbol *From, const MCSymbol *To) {
+                          const MCSymbol *From, const MCSymbol *To,
+                          unsigned int Size = 4) {
   MCSymbolRefExpr::VariantKind Variant = MCSymbolRefExpr::VK_None;
   MCContext &Context = Streamer.getContext();
   const MCExpr *FromRef = MCSymbolRefExpr::Create(From, Variant, Context),
                *ToRef   = MCSymbolRefExpr::Create(To, Variant, Context);
   const MCExpr *AddrDelta =
       MCBinaryExpr::Create(MCBinaryExpr::Sub, ToRef, FromRef, Context);
-  Streamer.EmitValue(AddrDelta, 4);
+  Streamer.EmitValue(AddrDelta, Size);
 }
 
 void WinCodeViewLineTables::emitDebugInfoForFunction(const Function *GV) {
   // For each function there is a separate subsection
   // which holds the PC to file:line table.
   const MCSymbol *Fn = Asm->getSymbol(GV);
   assert(Fn);
 
   const FunctionInfo &FI = FnDebugInfo[GV];
   if (FI.Instrs.empty())
     return;
   assert(FI.End && "Don't know where the function ends?");
 
+  // FIXME: Find a way to get the demangled function name.
+  const StringRef FuncName = Fn->getName();
+  // Emit a symbol subsection, required by VS2012+ to find function boundaries.
+  MCSymbol *SymbolsBegin = Asm->MMI->getContext().CreateTempSymbol(),
+           *SymbolsEnd = Asm->MMI->getContext().CreateTempSymbol();
+  Asm->OutStreamer.AddComment("Symbol subsection for " + Twine(FuncName));
+  Asm->EmitInt32(COFF::DEBUG_SYMBOL_SUBSECTION);
+  EmitLabelDiff(Asm->OutStreamer, SymbolsBegin, SymbolsEnd);
+  Asm->OutStreamer.EmitLabel(SymbolsBegin);
+  {
+    MCSymbol *ProcSegmentBegin = Asm->MMI->getContext().CreateTempSymbol(),
+             *ProcSegmentEnd = Asm->MMI->getContext().CreateTempSymbol();
+    EmitLabelDiff(Asm->OutStreamer, ProcSegmentBegin, ProcSegmentEnd, 2);
+    Asm->OutStreamer.EmitLabel(ProcSegmentBegin);
+
+    Asm->EmitInt16(COFF::DEBUG_SYMBOL_TYPE_PROC_START);
+    // Some bytes of this segment don't seem to be required for basic debugging,
+    // so just fill them with zeroes.
+    Asm->OutStreamer.EmitFill(12, 0);
+    // This is the important bit that tells the debugger where the function
+    // code is located and what's its size:
+    EmitLabelDiff(Asm->OutStreamer, Fn, FI.End);
+    Asm->OutStreamer.EmitFill(12, 0);
+    Asm->OutStreamer.EmitCOFFSecRel32(Fn);
+    Asm->OutStreamer.EmitCOFFSectionIndex(Fn);
+    Asm->EmitInt8(0);
+    // Emit the function name as a null-terminated string.
+    Asm->OutStreamer.EmitBytes(FuncName);
+    Asm->EmitInt8(0);
+    Asm->OutStreamer.EmitLabel(ProcSegmentEnd);
+
+    // We're done with this function.
+    Asm->EmitInt16(0x0002);
+    Asm->EmitInt16(COFF::DEBUG_SYMBOL_TYPE_PROC_END);
+  }
+  Asm->OutStreamer.EmitLabel(SymbolsEnd);
+  // Every subsection must be aligned to a 4-byte boundary.
+  Asm->OutStreamer.EmitFill((-FuncName.size()) % 4, 0);
+
   // PCs/Instructions are grouped into segments sharing the same filename.
   // Pre-calculate the lengths (in instructions) of these segments and store
   // them in a map for convenience.  Each index in the map is the sequential
   // number of the respective instruction that starts a new segment.
   DenseMap<size_t, size_t> FilenameSegmentLengths;
   size_t LastSegmentEnd = 0;
   StringRef PrevFilename = InstrInfo[FI.Instrs[0]].Filename;
   for (size_t J = 1, F = FI.Instrs.size(); J != F; ++J) {
     if (PrevFilename == InstrInfo[FI.Instrs[J]].Filename)
       continue;
     FilenameSegmentLengths[LastSegmentEnd] = J - LastSegmentEnd;
     LastSegmentEnd = J;
     PrevFilename = InstrInfo[FI.Instrs[J]].Filename;
   }
   FilenameSegmentLengths[LastSegmentEnd] = FI.Instrs.size() - LastSegmentEnd;
 
   // Emit a line table subsection, requred to do PC-to-file:line lookup.
-  Asm->OutStreamer.AddComment(
-      "Line table subsection for " + Twine(Fn->getName()));
+  Asm->OutStreamer.AddComment("Line table subsection for " + Twine(FuncName));
   Asm->EmitInt32(COFF::DEBUG_LINE_TABLE_SUBSECTION);
-  MCSymbol *SubsectionBegin = Asm->MMI->getContext().CreateTempSymbol(),
-           *SubsectionEnd = Asm->MMI->getContext().CreateTempSymbol();
-  EmitLabelDiff(Asm->OutStreamer, SubsectionBegin, SubsectionEnd);
-  Asm->OutStreamer.EmitLabel(SubsectionBegin);
+  MCSymbol *LineTableBegin = Asm->MMI->getContext().CreateTempSymbol(),
+           *LineTableEnd = Asm->MMI->getContext().CreateTempSymbol();
+  EmitLabelDiff(Asm->OutStreamer, LineTableBegin, LineTableEnd);
+  Asm->OutStreamer.EmitLabel(LineTableBegin);
 
   // Identify the function this subsection is for.
   Asm->OutStreamer.EmitCOFFSecRel32(Fn);
   Asm->OutStreamer.EmitCOFFSectionIndex(Fn);
   // Insert padding after a 16-bit section index.
   Asm->EmitInt16(0);
 
   // Length of the function's code, in bytes.
for (size_t J = 0, F = FI.Instrs.size(); J != F; ++J) {
 
     // The first PC with the given linenumber and the linenumber itself.
     EmitLabelDiff(Asm->OutStreamer, Fn, Instr);
     Asm->EmitInt32(InstrInfo[Instr].LineNumber);
   }
 
   if (FileSegmentEnd)
     Asm->OutStreamer.EmitLabel(FileSegmentEnd);
-  Asm->OutStreamer.EmitLabel(SubsectionEnd);
+  Asm->OutStreamer.EmitLabel(LineTableEnd);
 }
 
 void WinCodeViewLineTables::beginFunction(const MachineFunction *MF) {
   assert(!CurFn && "Can't process two functions at once!");
 
   if (!Asm || !Asm->MMI->hasDebugInfo())
     return;
 

test/DebugInfo/COFF/simple.ll

 ; X86-NEXT: [[CALL_LINE:^L.*]]:{{$}}
 ; X86-NEXT: calll   _g
 ; X86-NEXT: [[RETURN_STMT:.*]]:
 ; X86-NEXT: ret
 ; X86-NEXT: [[END_OF_F:.*]]:
 ;
 ; X86-LABEL: .section        .debug$S,"rd"
 ; X86-NEXT: .long   4
+; Symbol subsection
+; X86-NEXT: .long   241
+; X86-NEXT: .long [[F1_END:.*]]-[[F1_START:.*]]
+; X86-NEXT: [[F1_START]]:
+; X86-NEXT: .short [[PROC_SEGMENT_END:.*]]-[[PROC_SEGMENT_START:.*]]
+; X86-NEXT: [[PROC_SEGMENT_START]]:
+; X86-NEXT: .short  4423
+; X86-NEXT: .zero   12
+; X86-NEXT: .long [[END_OF_F]]-_f
+; X86-NEXT: .zero   12
+; X86-NEXT: .secrel32 _f
+; X86-NEXT: .secidx _f
+; X86-NEXT: .byte   0
+; X86-NEXT: .ascii  "_f"
+; X86-NEXT: .byte   0
+; X86-NEXT: [[PROC_SEGMENT_END]]:
+; X86-NEXT: .short  2
+; X86-NEXT: .short  4431
+; X86-NEXT: [[F1_END]]:
+; Padding
+; X86-NEXT: .zero   2
+; Line table
 ; X86-NEXT: .long   242
 ; X86-NEXT: .long [[F2_END:.*]]-[[F2_START:.*]]
 ; X86-NEXT: [[F2_START]]:
 ; X86-NEXT: .secrel32 _f
 ; X86-NEXT: .secidx _f
-; X86-NEXT: .short 0
+; X86-NEXT: .short  0
 ; X86-NEXT: .long [[END_OF_F]]-_f
 ; X86-NEXT: [[FILE_SEGMENT_START:[^:]*]]:
 ; X86-NEXT: .long   0
 ; X86-NEXT: .long   2
 ; X86-NEXT: .long [[FILE_SEGMENT_END:.*]]-[[FILE_SEGMENT_START]]
 ; X86-NEXT: .long [[CALL_LINE]]-_f
 ; X86-NEXT: .long   4
 ; X86-NEXT: .long [[RETURN_STMT]]-_f

 ; Padding
 ; X86-NEXT: .zero   1
 
 ; OBJ32:    Section {
 ; OBJ32:      Name: .debug$S (2E 64 65 62 75 67 24 53)
 ; OBJ32:      Characteristics [ (0x42100040)
 ; OBJ32:      ]
 ; OBJ32:      Relocations [
-; OBJ32-NEXT:   0xC IMAGE_REL_I386_SECREL _f
-; OBJ32-NEXT:   0x10 IMAGE_REL_I386_SECTION _f
+; OBJ32-NEXT:   0x2C IMAGE_REL_I386_SECREL _f
+; OBJ32-NEXT:   0x30 IMAGE_REL_I386_SECTION _f
+; OBJ32-NEXT:   0x44 IMAGE_REL_I386_SECREL _f
+; OBJ32-NEXT:   0x48 IMAGE_REL_I386_SECTION _f
+; OBJ32-NEXT: ]
+; OBJ32:      Subsection [
+; OBJ32-NEXT:   Type: 0xF1
+; OBJ32-NOT:    ]
+; OBJ32:        ProcStart {
+; OBJ32-NEXT:     FunctionName: _f
+; OBJ32-NEXT:     Section: _f
+; OBJ32-NEXT:     CodeSize: 0x6
+; OBJ32-NEXT:   }
+; OBJ32-NEXT:   ProcEnd
 ; OBJ32-NEXT: ]
 ; OBJ32:      FunctionLineTable [
 ; OBJ32-NEXT:   Name: _f
 ; OBJ32-NEXT:   CodeSize: 0x6
 ; OBJ32-NEXT:   FilenameSegment [
 ; OBJ32-NEXT:     Filename: D:\test.c
 ; OBJ32-NEXT:     +0x0: 4
 ; OBJ32-NEXT:     +0x5: 5

 ; X64-NEXT: callq   g
 ; X64-NEXT: [[EPILOG_AND_RET:.*]]:
 ; X64-NEXT: addq    $40, %rsp
 ; X64-NEXT: ret
 ; X64-NEXT: [[END_OF_F:.*]]:
 ;
 ; X64-LABEL: .section        .debug$S,"rd"
 ; X64-NEXT: .long   4
+; Symbol subsection
+; X64-NEXT: .long   241
+; X64-NEXT: .long [[F1_END:.*]]-[[F1_START:.*]]
+; X64-NEXT: [[F1_START]]:
+; X64-NEXT: .short [[PROC_SEGMENT_END:.*]]-[[PROC_SEGMENT_START:.*]]
+; X64-NEXT: [[PROC_SEGMENT_START]]:
+; X64-NEXT: .short  4423
+; X64-NEXT: .zero   12
+; X64-NEXT: .long [[END_OF_F]]-f
+; X64-NEXT: .zero   12
+; X64-NEXT: .secrel32 f
+; X64-NEXT: .secidx f
+; X64-NEXT: .byte   0
+; X64-NEXT: .byte   102
+; X64-NEXT: .byte   0
+; X64-NEXT: [[PROC_SEGMENT_END]]:
+; X64-NEXT: .short  2
+; X64-NEXT: .short  4431
+; X64-NEXT: [[F1_END]]:
+; Padding
+; X64-NEXT: .zero   3
+; Line table
 ; X64-NEXT: .long   242
 ; X64-NEXT: .long [[F2_END:.*]]-[[F2_START:.*]]
 ; X64-NEXT: [[F2_START]]:
 ; X64-NEXT: .secrel32 f
 ; X64-NEXT: .secidx f
-; X64-NEXT: .short 0
+; X64-NEXT: .short  0
 ; X64-NEXT: .long [[END_OF_F]]-f
 ; X64-NEXT: [[FILE_SEGMENT_START:[^:]*]]:
 ; X64-NEXT: .long   0
 ; X64-NEXT: .long   3
 ; X64-NEXT: .long [[FILE_SEGMENT_END:.*]]-[[FILE_SEGMENT_START]]
 ; X64-NEXT: .long [[START]]-f
 ; X64-NEXT: .long   3
 ; X64-NEXT: .long [[CALL_LINE]]-f

 ; Padding
 ; X64-NEXT: .zero   1
 
 ; OBJ64:    Section {
 ; OBJ64:      Name: .debug$S (2E 64 65 62 75 67 24 53)
 ; OBJ64:      Characteristics [ (0x42100040)
 ; OBJ64:      ]
 ; OBJ64:      Relocations [
-; OBJ64-NEXT:   0xC IMAGE_REL_AMD64_SECREL f
-; OBJ64-NEXT:   0x10 IMAGE_REL_AMD64_SECTION f
+; OBJ64-NEXT:   0x2C IMAGE_REL_AMD64_SECREL f
+; OBJ64-NEXT:   0x30 IMAGE_REL_AMD64_SECTION f
+; OBJ64-NEXT:   0x44 IMAGE_REL_AMD64_SECREL f
+; OBJ64-NEXT:   0x48 IMAGE_REL_AMD64_SECTION f
+; OBJ64-NEXT: ]
+; OBJ64:      Subsection [
+; OBJ64-NEXT:   Type: 0xF1
+; OBJ64-NOT:    ]
+; OBJ64:        ProcStart {
+; OBJ64-NEXT:     FunctionName: f
+; OBJ64-NEXT:     Section: f
+; OBJ64-NEXT:     CodeSize: 0xE
+; OBJ64-NEXT:   }
+; OBJ64-NEXT:   ProcEnd
 ; OBJ64-NEXT: ]
 ; OBJ64:      FunctionLineTable [
 ; OBJ64-NEXT:   Name: f
 ; OBJ64-NEXT:   CodeSize: 0xE
 ; OBJ64-NEXT:   FilenameSegment [
 ; OBJ64-NEXT:     Filename: D:\test.c
 ; OBJ64-NEXT:     +0x0: 3
 ; OBJ64-NEXT:     +0x4: 4