[MC/DWARF] Support .debug_frame / .debug_line code alignment factors

I've been comparing the object file output of LLVM's integrated
assembler against the external assembler on PowerPC, and one
area where differences still remain are in DWARF sections.

In particular, the GNU assembler generates .debug_frame and
.debug_line sections using a code alignment factor of 4, since
all PowerPC instructions have size 4 and must be aligned to a
multiple of 4.  However, current MC code hard-codes a code
alignment factor of 1.

This patch changes this by adding a "minimum instruction alignment"
data element to MCAsmInfo and using this as code alignment factor.

This requires passing a MCContext into MCDwarfLineAddr::Encode
and MCDwarfLineAddr::EncodeAdvanceLoc.  Note that one caller,
MCDwarfLineAddr::Write, didn't actually have that information
available.  However, it turns out that this routine is in fact
never used in the whole code base, so the patch simply removes
it.  If it turns out to be needed again at a later time, it
could be re-added with an updated interface.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183834 91177308-0d34-0410-b5e6-96231b3b80d8

7 files changed, 38 insertions, 40 deletions

diff --git a/include/llvm/MC/MCAsmInfo.h b/include/llvm/MC/MCAsmInfo.h
index 72d325f..781a9d0 100644
--- a/include/llvm/MC/MCAsmInfo.h
+++ b/include/llvm/MC/MCAsmInfo.h
@@ -89,6 +89,10 @@ namespace llvm {
     /// which is needed to compute the size of an inline asm.
     unsigned MaxInstLength;                  // Defaults to 4.
 
+    /// MinInstAlignment - Every possible instruction length is a multiple of
+    /// this value.  Factored out in .debug_frame and .debug_line.
+    unsigned MinInstAlignment;                  // Defaults to 1.
+
     /// PCSymbol - The symbol used to represent the current PC.  Used in PC
     /// relative expressions.
     const char *PCSymbol;                    // Defaults to "$".
@@ -429,6 +433,9 @@ namespace llvm {
     unsigned getMaxInstLength() const {
       return MaxInstLength;
     }
+    unsigned getMinInstAlignment() const {
+      return MinInstAlignment;
+    }
     const char *getPCSymbol() const {
       return PCSymbol;
     }
diff --git a/include/llvm/MC/MCDwarf.h b/include/llvm/MC/MCDwarf.h
index 1a392e8..3ece262 100644
--- a/include/llvm/MC/MCDwarf.h
+++ b/include/llvm/MC/MCDwarf.h
@@ -24,7 +24,6 @@
 
 namespace llvm {
   class MCContext;
-  class MCObjectWriter;
   class MCSection;
   class MCStreamer;
   class MCSymbol;
@@ -229,15 +228,12 @@ namespace llvm {
   class MCDwarfLineAddr {
   public:
     /// Utility function to encode a Dwarf pair of LineDelta and AddrDeltas.
-    static void Encode(int64_t LineDelta, uint64_t AddrDelta, raw_ostream &OS);
+    static void Encode(MCContext &Context, int64_t LineDelta,
+                       uint64_t AddrDelta, raw_ostream &OS);
 
     /// Utility function to emit the encoding to a streamer.
     static void Emit(MCStreamer *MCOS,
                      int64_t LineDelta,uint64_t AddrDelta);
-
-    /// Utility function to write the encoding to an object writer.
-    static void Write(MCObjectWriter *OW,
-                      int64_t LineDelta, uint64_t AddrDelta);
   };
 
   class MCGenDwarfInfo {
@@ -418,7 +414,8 @@ namespace llvm {
     static void Emit(MCStreamer &streamer, bool usingCFI,
                      bool isEH);
     static void EmitAdvanceLoc(MCStreamer &Streamer, uint64_t AddrDelta);
-    static void EncodeAdvanceLoc(uint64_t AddrDelta, raw_ostream &OS);
+    static void EncodeAdvanceLoc(MCContext &Context, uint64_t AddrDelta,
+                                 raw_ostream &OS);
   };
 } // end namespace llvm
 
diff --git a/lib/MC/MCAsmInfo.cpp b/lib/MC/MCAsmInfo.cpp
index 9e60884..3d843b7 100644
--- a/lib/MC/MCAsmInfo.cpp
+++ b/lib/MC/MCAsmInfo.cpp
@@ -34,6 +34,7 @@ MCAsmInfo::MCAsmInfo() {
   HasStaticCtorDtorReferenceInStaticMode = false;
   LinkerRequiresNonEmptyDwarfLines = false;
   MaxInstLength = 4;
+  MinInstAlignment = 1;
   PCSymbol = "$";
   SeparatorString = ";";
   CommentColumn = 40;
diff --git a/lib/MC/MCAssembler.cpp b/lib/MC/MCAssembler.cpp
index fb5ab28..97f675a 100644
--- a/lib/MC/MCAssembler.cpp
+++ b/lib/MC/MCAssembler.cpp
@@ -904,6 +904,7 @@ bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
 
 bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
                                      MCDwarfLineAddrFragment &DF) {
+  MCContext &Context = Layout.getAssembler().getContext();
   int64_t AddrDelta = 0;
   uint64_t OldSize = DF.getContents().size();
   bool IsAbs = DF.getAddrDelta().EvaluateAsAbsolute(AddrDelta, Layout);
@@ -914,13 +915,14 @@ bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
   SmallString<8> &Data = DF.getContents();
   Data.clear();
   raw_svector_ostream OSE(Data);
-  MCDwarfLineAddr::Encode(LineDelta, AddrDelta, OSE);
+  MCDwarfLineAddr::Encode(Context, LineDelta, AddrDelta, OSE);
   OSE.flush();
   return OldSize != Data.size();
 }
 
 bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
                                               MCDwarfCallFrameFragment &DF) {
+  MCContext &Context = Layout.getAssembler().getContext();
   int64_t AddrDelta = 0;
   uint64_t OldSize = DF.getContents().size();
   bool IsAbs = DF.getAddrDelta().EvaluateAsAbsolute(AddrDelta, Layout);
@@ -929,7 +931,7 @@ bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
   SmallString<8> &Data = DF.getContents();
   Data.clear();
   raw_svector_ostream OSE(Data);
-  MCDwarfFrameEmitter::EncodeAdvanceLoc(AddrDelta, OSE);
+  MCDwarfFrameEmitter::EncodeAdvanceLoc(Context, AddrDelta, OSE);
   OSE.flush();
   return OldSize != Data.size();
 }
diff --git a/lib/MC/MCDwarf.cpp b/lib/MC/MCDwarf.cpp
index 90221a1..21ccc3e 100644
--- a/lib/MC/MCDwarf.cpp
+++ b/lib/MC/MCDwarf.cpp
@@ -16,7 +16,6 @@
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCObjectFileInfo.h"
-#include "llvm/MC/MCObjectWriter.h"
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSymbol.h"
@@ -47,20 +46,15 @@ using namespace llvm;
 // Range of line offsets in a special line info. opcode.
 #define DWARF2_LINE_RANGE               14
 
-// Define the architecture-dependent minimum instruction length (in bytes).
-// This value should be rather too small than too big.
-#define DWARF2_LINE_MIN_INSN_LENGTH     1
-
-// Note: when DWARF2_LINE_MIN_INSN_LENGTH == 1 which is the current setting,
-// this routine is a nop and will be optimized away.
-static inline uint64_t ScaleAddrDelta(uint64_t AddrDelta) {
-  if (DWARF2_LINE_MIN_INSN_LENGTH == 1)
+static inline uint64_t ScaleAddrDelta(MCContext &Context, uint64_t AddrDelta) {
+  unsigned MinInsnLength = Context.getAsmInfo().getMinInstAlignment();
+  if (MinInsnLength == 1)
     return AddrDelta;
-  if (AddrDelta % DWARF2_LINE_MIN_INSN_LENGTH != 0) {
+  if (AddrDelta % MinInsnLength != 0) {
     // TODO: report this error, but really only once.
     ;
   }
-  return AddrDelta / DWARF2_LINE_MIN_INSN_LENGTH;
+  return AddrDelta / MinInsnLength;
 }
 
 //
@@ -277,7 +271,7 @@ const MCSymbol *MCDwarfFileTable::EmitCU(MCStreamer *MCOS, unsigned CUID) {
                                            (4 + 2 + 4)), 4, 0);
 
   // Parameters of the state machine, are next.
-  MCOS->EmitIntValue(DWARF2_LINE_MIN_INSN_LENGTH, 1);
+  MCOS->EmitIntValue(context.getAsmInfo().getMinInstAlignment(), 1);
   MCOS->EmitIntValue(DWARF2_LINE_DEFAULT_IS_STMT, 1);
   MCOS->EmitIntValue(DWARF2_LINE_BASE, 1);
   MCOS->EmitIntValue(DWARF2_LINE_RANGE, 1);
@@ -357,32 +351,24 @@ const MCSymbol *MCDwarfFileTable::EmitCU(MCStreamer *MCOS, unsigned CUID) {
   return LineStartSym;
 }
 
-/// Utility function to write the encoding to an object writer.
-void MCDwarfLineAddr::Write(MCObjectWriter *OW, int64_t LineDelta,
-                            uint64_t AddrDelta) {
-  SmallString<256> Tmp;
-  raw_svector_ostream OS(Tmp);
-  MCDwarfLineAddr::Encode(LineDelta, AddrDelta, OS);
-  OW->WriteBytes(OS.str());
-}
-
 /// Utility function to emit the encoding to a streamer.
 void MCDwarfLineAddr::Emit(MCStreamer *MCOS, int64_t LineDelta,
                            uint64_t AddrDelta) {
+  MCContext &Context = MCOS->getContext();
   SmallString<256> Tmp;
   raw_svector_ostream OS(Tmp);
-  MCDwarfLineAddr::Encode(LineDelta, AddrDelta, OS);
+  MCDwarfLineAddr::Encode(Context, LineDelta, AddrDelta, OS);
   MCOS->EmitBytes(OS.str());
 }
 
 /// Utility function to encode a Dwarf pair of LineDelta and AddrDeltas.
-void MCDwarfLineAddr::Encode(int64_t LineDelta, uint64_t AddrDelta,
-                             raw_ostream &OS) {
+void MCDwarfLineAddr::Encode(MCContext &Context, int64_t LineDelta,
+                             uint64_t AddrDelta, raw_ostream &OS) {
   uint64_t Temp, Opcode;
   bool NeedCopy = false;
 
   // Scale the address delta by the minimum instruction length.
-  AddrDelta = ScaleAddrDelta(AddrDelta);
+  AddrDelta = ScaleAddrDelta(Context, AddrDelta);
 
   // A LineDelta of INT64_MAX is a signal that this is actually a
   // DW_LNE_end_sequence. We cannot use special opcodes here, since we want the
@@ -1256,7 +1242,7 @@ const MCSymbol &FrameEmitterImpl::EmitCIE(MCStreamer &streamer,
 
   // Code Alignment Factor
   if (verboseAsm) streamer.AddComment("CIE Code Alignment Factor");
-  streamer.EmitULEB128IntValue(1);
+  streamer.EmitULEB128IntValue(context.getAsmInfo().getMinInstAlignment());
 
   // Data Alignment Factor
   if (verboseAsm) streamer.AddComment("CIE Data Alignment Factor");
@@ -1493,15 +1479,19 @@ void MCDwarfFrameEmitter::Emit(MCStreamer &Streamer,
 
 void MCDwarfFrameEmitter::EmitAdvanceLoc(MCStreamer &Streamer,
                                          uint64_t AddrDelta) {
+  MCContext &Context = Streamer.getContext();
   SmallString<256> Tmp;
   raw_svector_ostream OS(Tmp);
-  MCDwarfFrameEmitter::EncodeAdvanceLoc(AddrDelta, OS);
+  MCDwarfFrameEmitter::EncodeAdvanceLoc(Context, AddrDelta, OS);
   Streamer.EmitBytes(OS.str());
 }
 
-void MCDwarfFrameEmitter::EncodeAdvanceLoc(uint64_t AddrDelta,
+void MCDwarfFrameEmitter::EncodeAdvanceLoc(MCContext &Context,
+                                           uint64_t AddrDelta,
                                            raw_ostream &OS) {
-  // FIXME: Assumes the code alignment factor is 1.
+  // Scale the address delta by the minimum instruction length.
+  AddrDelta = ScaleAddrDelta(Context, AddrDelta);
+
   if (AddrDelta == 0) {
   } else if (isUIntN(6, AddrDelta)) {
     uint8_t Opcode = dwarf::DW_CFA_advance_loc | AddrDelta;
diff --git a/lib/Target/PowerPC/MCTargetDesc/PPCMCAsmInfo.cpp b/lib/Target/PowerPC/MCTargetDesc/PPCMCAsmInfo.cpp
index a25d7fe..bb7ce6f 100644
--- a/lib/Target/PowerPC/MCTargetDesc/PPCMCAsmInfo.cpp
+++ b/lib/Target/PowerPC/MCTargetDesc/PPCMCAsmInfo.cpp
@@ -59,6 +59,7 @@ PPCLinuxMCAsmInfo::PPCLinuxMCAsmInfo(bool is64Bit) {
 
   // Set up DWARF directives
   HasLEB128 = true;  // Target asm supports leb128 directives (little-endian)
+  MinInstAlignment = 4;
 
   // Exceptions handling
   ExceptionsType = ExceptionHandling::DwarfCFI;
diff --git a/test/MC/PowerPC/ppc64-initial-cfa.s b/test/MC/PowerPC/ppc64-initial-cfa.s
index fb45474..f976ae9 100644
--- a/test/MC/PowerPC/ppc64-initial-cfa.s
+++ b/test/MC/PowerPC/ppc64-initial-cfa.s
@@ -23,7 +23,7 @@
 # STATIC-NEXT:   Relocations [
 # STATIC-NEXT:   ]
 # STATIC-NEXT:   SectionData (
-# STATIC-NEXT:     0000: 00000010 00000000 017A5200 01784101
+# STATIC-NEXT:     0000: 00000010 00000000 017A5200 04784101
 # STATIC-NEXT:     0010: 1B0C0100 00000010 00000018 00000000
 # STATIC-NEXT:     0020: 00000004 00000000
 # STATIC-NEXT:   )
@@ -61,7 +61,7 @@
 # PIC-NEXT:   Relocations [
 # PIC-NEXT:   ]
 # PIC-NEXT:   SectionData (
-# PIC-NEXT:     0000: 00000010 00000000 017A5200 01784101
+# PIC-NEXT:     0000: 00000010 00000000 017A5200 04784101
 # PIC-NEXT:     0010: 1B0C0100 00000010 00000018 00000000
 # PIC-NEXT:     0020: 00000004 00000000
 # PIC-NEXT:   )