This patch is needed to make c++ exceptions work for mips16.

Mips16 is really a processor decoding mode (ala thumb 1) and in the same
program, mips16 and mips32 functions can exist and can call each other.

If a jal type instruction encounters an address with the lower bit set, then
the processor switches to mips16 mode (if it is not already in it). If the
lower bit is not set, then it switches to mips32 mode.

The linker knows which functions are mips16 and which are mips32.
When relocation is performed on code labels, this lower order bit is
set if the code label is a mips16 code label.

In general this works just fine, however when creating exception handling
tables and dwarf, there are cases where you don't want this lower order
bit added in.

This has been traditionally distinguished in gas assembly source by using a
different syntax for the label.

lab1:      ; this will cause the lower order bit to be added
lab2=.     ; this will not cause the lower order bit to be added

In some cases, it does not matter because in dwarf and debug tables
the difference of two labels is used and in that case the lower order
bits subtract each other out.

To fix this, I have added to mcstreamer the notion of a debuglabel.
The default is for label and debug label to be the same. So calling
EmitLabel and EmitDebugLabel produce the same result.

For various reasons, there is only one set of labels that needs to be
modified for the mips exceptions to work. These are the "$eh_func_beginXXX" 
labels.

Mips overrides the debug label suffix from ":" to "=." .

This initial patch fixes exceptions. More changes most likely
will be needed to DwarfCFException to make all of this work
for actual debugging. These changes will be to emit debug labels in some
places where a simple label is emitted now.

Some historical discussion on this from gcc can be found at:
http://gcc.gnu.org/ml/gcc-patches/2008-08/msg00623.html
http://gcc.gnu.org/ml/gcc-patches/2008-11/msg01273.html 



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@170279 91177308-0d34-0410-b5e6-96231b3b80d8

9 files changed, 39 insertions, 1 deletions

diff --git a/lib/MC/MCAsmInfo.cpp b/lib/MC/MCAsmInfo.cpp
index 7ea0f3b85a..a6fa6582ab 100644
--- a/lib/MC/MCAsmInfo.cpp
+++ b/lib/MC/MCAsmInfo.cpp
@@ -37,6 +37,7 @@ MCAsmInfo::MCAsmInfo() {
   CommentColumn = 40;
   CommentString = "#";
   LabelSuffix = ":";
+  DebugLabelSuffix = ":";
   GlobalPrefix = "";
   PrivateGlobalPrefix = ".";
   LinkerPrivateGlobalPrefix = "";
diff --git a/lib/MC/MCAsmStreamer.cpp b/lib/MC/MCAsmStreamer.cpp
index 6537e4e685..6302f970d8 100644
--- a/lib/MC/MCAsmStreamer.cpp
+++ b/lib/MC/MCAsmStreamer.cpp
@@ -135,6 +135,8 @@ public:
   }
 
   virtual void EmitLabel(MCSymbol *Symbol);
+  virtual void EmitDebugLabel(MCSymbol *Symbol);
+
   virtual void EmitEHSymAttributes(const MCSymbol *Symbol,
                                    MCSymbol *EHSymbol);
   virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
@@ -345,6 +347,14 @@ void MCAsmStreamer::EmitLabel(MCSymbol *Symbol) {
   EmitEOL();
 }
 
+void MCAsmStreamer::EmitDebugLabel(MCSymbol *Symbol) {
+  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
+  MCStreamer::EmitDebugLabel(Symbol);
+
+  OS << *Symbol << MAI.getDebugLabelSuffix();
+  EmitEOL();
+}
+
 void MCAsmStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
   switch (Flag) {
   case MCAF_SyntaxUnified:         OS << "\t.syntax unified"; break;
diff --git a/lib/MC/MCELFStreamer.cpp b/lib/MC/MCELFStreamer.cpp
index 8b9bdb14a0..9771ef0549 100644
--- a/lib/MC/MCELFStreamer.cpp
+++ b/lib/MC/MCELFStreamer.cpp
@@ -86,6 +86,10 @@ void MCELFStreamer::EmitLabel(MCSymbol *Symbol) {
     MCELF::SetType(SD, ELF::STT_TLS);
 }
 
+void MCELFStreamer::EmitDebugLabel(MCSymbol *Symbol) {
+  EmitLabel(Symbol);
+}
+
 void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
   switch (Flag) {
   case MCAF_SyntaxUnified: return; // no-op here.
diff --git a/lib/MC/MCMachOStreamer.cpp b/lib/MC/MCMachOStreamer.cpp
index f279e74e38..82ccdd4ac0 100644
--- a/lib/MC/MCMachOStreamer.cpp
+++ b/lib/MC/MCMachOStreamer.cpp
@@ -43,6 +43,7 @@ public:
 
   virtual void InitSections();
   virtual void EmitLabel(MCSymbol *Symbol);
+  virtual void EmitDebugLabel(MCSymbol *Symbol);
   virtual void EmitEHSymAttributes(const MCSymbol *Symbol,
                                    MCSymbol *EHSymbol);
   virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
@@ -130,6 +131,9 @@ void MCMachOStreamer::EmitLabel(MCSymbol *Symbol) {
   SD.setFlags(SD.getFlags() & ~SF_ReferenceTypeMask);
 }
 
+void MCMachOStreamer::EmitDebugLabel(MCSymbol *Symbol) {
+  EmitLabel(Symbol);
+}
 void MCMachOStreamer::EmitDataRegion(DataRegionData::KindTy Kind) {
   if (!getAssembler().getBackend().hasDataInCodeSupport())
     return;
diff --git a/lib/MC/MCNullStreamer.cpp b/lib/MC/MCNullStreamer.cpp
index f5ece10dc4..bb84c4f22f 100644
--- a/lib/MC/MCNullStreamer.cpp
+++ b/lib/MC/MCNullStreamer.cpp
@@ -35,7 +35,9 @@ namespace {
       assert(getCurrentSection() && "Cannot emit before setting section!");
       Symbol->setSection(*getCurrentSection());
     }
-
+    virtual void EmitDebugLabel(MCSymbol *Symbol) {
+      EmitLabel(Symbol);
+    }
     virtual void EmitAssemblerFlag(MCAssemblerFlag Flag) {}
     virtual void EmitThumbFunc(MCSymbol *Func) {}
 
diff --git a/lib/MC/MCObjectStreamer.cpp b/lib/MC/MCObjectStreamer.cpp
index c69d76428c..4d6900f7c4 100644
--- a/lib/MC/MCObjectStreamer.cpp
+++ b/lib/MC/MCObjectStreamer.cpp
@@ -134,6 +134,10 @@ void MCObjectStreamer::EmitLabel(MCSymbol *Symbol) {
   SD.setOffset(F->getContents().size());
 }
 
+void MCObjectStreamer::EmitDebugLabel(MCSymbol *Symbol) {
+  EmitLabel(Symbol);
+}
+
 void MCObjectStreamer::EmitULEB128Value(const MCExpr *Value) {
   int64_t IntValue;
   if (Value->EvaluateAsAbsolute(IntValue, getAssembler())) {
diff --git a/lib/MC/MCPureStreamer.cpp b/lib/MC/MCPureStreamer.cpp
index 1563bdd107..bb1f3d459a 100644
--- a/lib/MC/MCPureStreamer.cpp
+++ b/lib/MC/MCPureStreamer.cpp
@@ -37,6 +37,7 @@ public:
 
   virtual void InitSections();
   virtual void EmitLabel(MCSymbol *Symbol);
+  virtual void EmitDebugLabel(MCSymbol *Symbol);
   virtual void EmitZerofill(const MCSection *Section, MCSymbol *Symbol = 0,
                             uint64_t Size = 0, unsigned ByteAlignment = 0);
   virtual void EmitBytes(StringRef Data, unsigned AddrSpace);
@@ -134,6 +135,7 @@ void MCPureStreamer::EmitLabel(MCSymbol *Symbol) {
   SD.setOffset(F->getContents().size());
 }
 
+
 void MCPureStreamer::EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
                                   uint64_t Size, unsigned ByteAlignment) {
   report_fatal_error("not yet implemented in pure streamer");
diff --git a/lib/MC/MCStreamer.cpp b/lib/MC/MCStreamer.cpp
index 047ab636ab..6f0ada277c 100644
--- a/lib/MC/MCStreamer.cpp
+++ b/lib/MC/MCStreamer.cpp
@@ -195,6 +195,13 @@ void MCStreamer::EmitLabel(MCSymbol *Symbol) {
   LastSymbol = Symbol;
 }
 
+void MCStreamer::EmitDebugLabel(MCSymbol *Symbol) {
+  assert(!Symbol->isVariable() && "Cannot emit a variable symbol!");
+  assert(getCurrentSection() && "Cannot emit before setting section!");
+  Symbol->setSection(*getCurrentSection());
+  LastSymbol = Symbol;
+}
+
 void MCStreamer::EmitCompactUnwindEncoding(uint32_t CompactUnwindEncoding) {
   EnsureValidFrame();
   MCDwarfFrameInfo *CurFrame = getCurrentFrameInfo();
diff --git a/lib/MC/WinCOFFStreamer.cpp b/lib/MC/WinCOFFStreamer.cpp
index 359b388618..d12201a6ca 100644
--- a/lib/MC/WinCOFFStreamer.cpp
+++ b/lib/MC/WinCOFFStreamer.cpp
@@ -51,6 +51,7 @@ public:
 
   virtual void InitSections();
   virtual void EmitLabel(MCSymbol *Symbol);
+  virtual void EmitDebugLabel(MCSymbol *Symbol);
   virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
   virtual void EmitThumbFunc(MCSymbol *Func);
   virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
@@ -176,6 +177,9 @@ void WinCOFFStreamer::EmitLabel(MCSymbol *Symbol) {
   MCObjectStreamer::EmitLabel(Symbol);
 }
 
+void WinCOFFStreamer::EmitDebugLabel(MCSymbol *Symbol) {
+  EmitLabel(Symbol);
+}
 void WinCOFFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
   llvm_unreachable("not implemented");
 }