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      1 //===- ELFAsmParser.cpp - ELF Assembly Parser -----------------------------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 
     10 #include "llvm/MC/MCParser/MCAsmParserExtension.h"
     11 #include "llvm/ADT/StringSwitch.h"
     12 #include "llvm/ADT/Twine.h"
     13 #include "llvm/MC/MCAsmInfo.h"
     14 #include "llvm/MC/MCContext.h"
     15 #include "llvm/MC/MCExpr.h"
     16 #include "llvm/MC/MCParser/MCAsmLexer.h"
     17 #include "llvm/MC/MCSectionELF.h"
     18 #include "llvm/MC/MCStreamer.h"
     19 #include "llvm/Support/ELF.h"
     20 using namespace llvm;
     21 
     22 namespace {
     23 
     24 class ELFAsmParser : public MCAsmParserExtension {
     25   template<bool (ELFAsmParser::*HandlerMethod)(StringRef, SMLoc)>
     26   void addDirectiveHandler(StringRef Directive) {
     27     MCAsmParser::ExtensionDirectiveHandler Handler = std::make_pair(
     28         this, HandleDirective<ELFAsmParser, HandlerMethod>);
     29 
     30     getParser().addDirectiveHandler(Directive, Handler);
     31   }
     32 
     33   bool ParseSectionSwitch(StringRef Section, unsigned Type,
     34                           unsigned Flags, SectionKind Kind);
     35   bool SeenIdent;
     36 
     37 public:
     38   ELFAsmParser() : SeenIdent(false) {
     39     BracketExpressionsSupported = true;
     40   }
     41 
     42   virtual void Initialize(MCAsmParser &Parser) {
     43     // Call the base implementation.
     44     this->MCAsmParserExtension::Initialize(Parser);
     45 
     46     addDirectiveHandler<&ELFAsmParser::ParseSectionDirectiveData>(".data");
     47     addDirectiveHandler<&ELFAsmParser::ParseSectionDirectiveText>(".text");
     48     addDirectiveHandler<&ELFAsmParser::ParseSectionDirectiveBSS>(".bss");
     49     addDirectiveHandler<&ELFAsmParser::ParseSectionDirectiveRoData>(".rodata");
     50     addDirectiveHandler<&ELFAsmParser::ParseSectionDirectiveTData>(".tdata");
     51     addDirectiveHandler<&ELFAsmParser::ParseSectionDirectiveTBSS>(".tbss");
     52     addDirectiveHandler<
     53       &ELFAsmParser::ParseSectionDirectiveDataRel>(".data.rel");
     54     addDirectiveHandler<
     55       &ELFAsmParser::ParseSectionDirectiveDataRelRo>(".data.rel.ro");
     56     addDirectiveHandler<
     57       &ELFAsmParser::ParseSectionDirectiveDataRelRoLocal>(".data.rel.ro.local");
     58     addDirectiveHandler<
     59       &ELFAsmParser::ParseSectionDirectiveEhFrame>(".eh_frame");
     60     addDirectiveHandler<&ELFAsmParser::ParseDirectiveSection>(".section");
     61     addDirectiveHandler<
     62       &ELFAsmParser::ParseDirectivePushSection>(".pushsection");
     63     addDirectiveHandler<&ELFAsmParser::ParseDirectivePopSection>(".popsection");
     64     addDirectiveHandler<&ELFAsmParser::ParseDirectiveSize>(".size");
     65     addDirectiveHandler<&ELFAsmParser::ParseDirectivePrevious>(".previous");
     66     addDirectiveHandler<&ELFAsmParser::ParseDirectiveType>(".type");
     67     addDirectiveHandler<&ELFAsmParser::ParseDirectiveIdent>(".ident");
     68     addDirectiveHandler<&ELFAsmParser::ParseDirectiveSymver>(".symver");
     69     addDirectiveHandler<&ELFAsmParser::ParseDirectiveVersion>(".version");
     70     addDirectiveHandler<&ELFAsmParser::ParseDirectiveWeakref>(".weakref");
     71     addDirectiveHandler<&ELFAsmParser::ParseDirectiveSymbolAttribute>(".weak");
     72     addDirectiveHandler<&ELFAsmParser::ParseDirectiveSymbolAttribute>(".local");
     73     addDirectiveHandler<
     74       &ELFAsmParser::ParseDirectiveSymbolAttribute>(".protected");
     75     addDirectiveHandler<
     76       &ELFAsmParser::ParseDirectiveSymbolAttribute>(".internal");
     77     addDirectiveHandler<
     78       &ELFAsmParser::ParseDirectiveSymbolAttribute>(".hidden");
     79     addDirectiveHandler<&ELFAsmParser::ParseDirectiveSubsection>(".subsection");
     80   }
     81 
     82   // FIXME: Part of this logic is duplicated in the MCELFStreamer. What is
     83   // the best way for us to get access to it?
     84   bool ParseSectionDirectiveData(StringRef, SMLoc) {
     85     return ParseSectionSwitch(".data", ELF::SHT_PROGBITS,
     86                               ELF::SHF_WRITE |ELF::SHF_ALLOC,
     87                               SectionKind::getDataRel());
     88   }
     89   bool ParseSectionDirectiveText(StringRef, SMLoc) {
     90     return ParseSectionSwitch(".text", ELF::SHT_PROGBITS,
     91                               ELF::SHF_EXECINSTR |
     92                               ELF::SHF_ALLOC, SectionKind::getText());
     93   }
     94   bool ParseSectionDirectiveBSS(StringRef, SMLoc) {
     95     return ParseSectionSwitch(".bss", ELF::SHT_NOBITS,
     96                               ELF::SHF_WRITE |
     97                               ELF::SHF_ALLOC, SectionKind::getBSS());
     98   }
     99   bool ParseSectionDirectiveRoData(StringRef, SMLoc) {
    100     return ParseSectionSwitch(".rodata", ELF::SHT_PROGBITS,
    101                               ELF::SHF_ALLOC,
    102                               SectionKind::getReadOnly());
    103   }
    104   bool ParseSectionDirectiveTData(StringRef, SMLoc) {
    105     return ParseSectionSwitch(".tdata", ELF::SHT_PROGBITS,
    106                               ELF::SHF_ALLOC |
    107                               ELF::SHF_TLS | ELF::SHF_WRITE,
    108                               SectionKind::getThreadData());
    109   }
    110   bool ParseSectionDirectiveTBSS(StringRef, SMLoc) {
    111     return ParseSectionSwitch(".tbss", ELF::SHT_NOBITS,
    112                               ELF::SHF_ALLOC |
    113                               ELF::SHF_TLS | ELF::SHF_WRITE,
    114                               SectionKind::getThreadBSS());
    115   }
    116   bool ParseSectionDirectiveDataRel(StringRef, SMLoc) {
    117     return ParseSectionSwitch(".data.rel", ELF::SHT_PROGBITS,
    118                               ELF::SHF_ALLOC |
    119                               ELF::SHF_WRITE,
    120                               SectionKind::getDataRel());
    121   }
    122   bool ParseSectionDirectiveDataRelRo(StringRef, SMLoc) {
    123     return ParseSectionSwitch(".data.rel.ro", ELF::SHT_PROGBITS,
    124                               ELF::SHF_ALLOC |
    125                               ELF::SHF_WRITE,
    126                               SectionKind::getReadOnlyWithRel());
    127   }
    128   bool ParseSectionDirectiveDataRelRoLocal(StringRef, SMLoc) {
    129     return ParseSectionSwitch(".data.rel.ro.local", ELF::SHT_PROGBITS,
    130                               ELF::SHF_ALLOC |
    131                               ELF::SHF_WRITE,
    132                               SectionKind::getReadOnlyWithRelLocal());
    133   }
    134   bool ParseSectionDirectiveEhFrame(StringRef, SMLoc) {
    135     return ParseSectionSwitch(".eh_frame", ELF::SHT_PROGBITS,
    136                               ELF::SHF_ALLOC |
    137                               ELF::SHF_WRITE,
    138                               SectionKind::getDataRel());
    139   }
    140   bool ParseDirectivePushSection(StringRef, SMLoc);
    141   bool ParseDirectivePopSection(StringRef, SMLoc);
    142   bool ParseDirectiveSection(StringRef, SMLoc);
    143   bool ParseDirectiveSize(StringRef, SMLoc);
    144   bool ParseDirectivePrevious(StringRef, SMLoc);
    145   bool ParseDirectiveType(StringRef, SMLoc);
    146   bool ParseDirectiveIdent(StringRef, SMLoc);
    147   bool ParseDirectiveSymver(StringRef, SMLoc);
    148   bool ParseDirectiveVersion(StringRef, SMLoc);
    149   bool ParseDirectiveWeakref(StringRef, SMLoc);
    150   bool ParseDirectiveSymbolAttribute(StringRef, SMLoc);
    151   bool ParseDirectiveSubsection(StringRef, SMLoc);
    152 
    153 private:
    154   bool ParseSectionName(StringRef &SectionName);
    155   bool ParseSectionArguments(bool IsPush);
    156 };
    157 
    158 }
    159 
    160 /// ParseDirectiveSymbolAttribute
    161 ///  ::= { ".local", ".weak", ... } [ identifier ( , identifier )* ]
    162 bool ELFAsmParser::ParseDirectiveSymbolAttribute(StringRef Directive, SMLoc) {
    163   MCSymbolAttr Attr = StringSwitch<MCSymbolAttr>(Directive)
    164     .Case(".weak", MCSA_Weak)
    165     .Case(".local", MCSA_Local)
    166     .Case(".hidden", MCSA_Hidden)
    167     .Case(".internal", MCSA_Internal)
    168     .Case(".protected", MCSA_Protected)
    169     .Default(MCSA_Invalid);
    170   assert(Attr != MCSA_Invalid && "unexpected symbol attribute directive!");
    171   if (getLexer().isNot(AsmToken::EndOfStatement)) {
    172     for (;;) {
    173       StringRef Name;
    174 
    175       if (getParser().parseIdentifier(Name))
    176         return TokError("expected identifier in directive");
    177 
    178       MCSymbol *Sym = getContext().GetOrCreateSymbol(Name);
    179 
    180       getStreamer().EmitSymbolAttribute(Sym, Attr);
    181 
    182       if (getLexer().is(AsmToken::EndOfStatement))
    183         break;
    184 
    185       if (getLexer().isNot(AsmToken::Comma))
    186         return TokError("unexpected token in directive");
    187       Lex();
    188     }
    189   }
    190 
    191   Lex();
    192   return false;
    193 }
    194 
    195 bool ELFAsmParser::ParseSectionSwitch(StringRef Section, unsigned Type,
    196                                       unsigned Flags, SectionKind Kind) {
    197   const MCExpr *Subsection = 0;
    198   if (getLexer().isNot(AsmToken::EndOfStatement)) {
    199     if (getParser().parseExpression(Subsection))
    200       return true;
    201   }
    202 
    203   getStreamer().SwitchSection(getContext().getELFSection(
    204                                 Section, Type, Flags, Kind),
    205                               Subsection);
    206 
    207   return false;
    208 }
    209 
    210 bool ELFAsmParser::ParseDirectiveSize(StringRef, SMLoc) {
    211   StringRef Name;
    212   if (getParser().parseIdentifier(Name))
    213     return TokError("expected identifier in directive");
    214   MCSymbol *Sym = getContext().GetOrCreateSymbol(Name);
    215 
    216   if (getLexer().isNot(AsmToken::Comma))
    217     return TokError("unexpected token in directive");
    218   Lex();
    219 
    220   const MCExpr *Expr;
    221   if (getParser().parseExpression(Expr))
    222     return true;
    223 
    224   if (getLexer().isNot(AsmToken::EndOfStatement))
    225     return TokError("unexpected token in directive");
    226 
    227   getStreamer().EmitELFSize(Sym, Expr);
    228   return false;
    229 }
    230 
    231 bool ELFAsmParser::ParseSectionName(StringRef &SectionName) {
    232   // A section name can contain -, so we cannot just use
    233   // parseIdentifier.
    234   SMLoc FirstLoc = getLexer().getLoc();
    235   unsigned Size = 0;
    236 
    237   if (getLexer().is(AsmToken::String)) {
    238     SectionName = getTok().getIdentifier();
    239     Lex();
    240     return false;
    241   }
    242 
    243   for (;;) {
    244     StringRef Tmp;
    245     unsigned CurSize;
    246 
    247     SMLoc PrevLoc = getLexer().getLoc();
    248     if (getLexer().is(AsmToken::Minus)) {
    249       CurSize = 1;
    250       Lex(); // Consume the "-".
    251     } else if (getLexer().is(AsmToken::String)) {
    252       CurSize = getTok().getIdentifier().size() + 2;
    253       Lex();
    254     } else if (getLexer().is(AsmToken::Identifier)) {
    255       CurSize = getTok().getIdentifier().size();
    256       Lex();
    257     } else {
    258       break;
    259     }
    260 
    261     Size += CurSize;
    262     SectionName = StringRef(FirstLoc.getPointer(), Size);
    263 
    264     // Make sure the following token is adjacent.
    265     if (PrevLoc.getPointer() + CurSize != getTok().getLoc().getPointer())
    266       break;
    267   }
    268   if (Size == 0)
    269     return true;
    270 
    271   return false;
    272 }
    273 
    274 static SectionKind computeSectionKind(unsigned Flags) {
    275   if (Flags & ELF::SHF_EXECINSTR)
    276     return SectionKind::getText();
    277   if (Flags & ELF::SHF_TLS)
    278     return SectionKind::getThreadData();
    279   return SectionKind::getDataRel();
    280 }
    281 
    282 static int parseSectionFlags(StringRef flagsStr) {
    283   int flags = 0;
    284 
    285   for (unsigned i = 0; i < flagsStr.size(); i++) {
    286     switch (flagsStr[i]) {
    287     case 'a':
    288       flags |= ELF::SHF_ALLOC;
    289       break;
    290     case 'x':
    291       flags |= ELF::SHF_EXECINSTR;
    292       break;
    293     case 'w':
    294       flags |= ELF::SHF_WRITE;
    295       break;
    296     case 'M':
    297       flags |= ELF::SHF_MERGE;
    298       break;
    299     case 'S':
    300       flags |= ELF::SHF_STRINGS;
    301       break;
    302     case 'T':
    303       flags |= ELF::SHF_TLS;
    304       break;
    305     case 'c':
    306       flags |= ELF::XCORE_SHF_CP_SECTION;
    307       break;
    308     case 'd':
    309       flags |= ELF::XCORE_SHF_DP_SECTION;
    310       break;
    311     case 'G':
    312       flags |= ELF::SHF_GROUP;
    313       break;
    314     default:
    315       return -1;
    316     }
    317   }
    318 
    319   return flags;
    320 }
    321 
    322 bool ELFAsmParser::ParseDirectivePushSection(StringRef s, SMLoc loc) {
    323   getStreamer().PushSection();
    324 
    325   if (ParseSectionArguments(/*IsPush=*/true)) {
    326     getStreamer().PopSection();
    327     return true;
    328   }
    329 
    330   return false;
    331 }
    332 
    333 bool ELFAsmParser::ParseDirectivePopSection(StringRef, SMLoc) {
    334   if (!getStreamer().PopSection())
    335     return TokError(".popsection without corresponding .pushsection");
    336   return false;
    337 }
    338 
    339 // FIXME: This is a work in progress.
    340 bool ELFAsmParser::ParseDirectiveSection(StringRef, SMLoc) {
    341   return ParseSectionArguments(/*IsPush=*/false);
    342 }
    343 
    344 bool ELFAsmParser::ParseSectionArguments(bool IsPush) {
    345   StringRef SectionName;
    346 
    347   if (ParseSectionName(SectionName))
    348     return TokError("expected identifier in directive");
    349 
    350   StringRef TypeName;
    351   int64_t Size = 0;
    352   StringRef GroupName;
    353   unsigned Flags = 0;
    354   const MCExpr *Subsection = 0;
    355 
    356   // Set the defaults first.
    357   if (SectionName == ".fini" || SectionName == ".init" ||
    358       SectionName == ".rodata")
    359     Flags |= ELF::SHF_ALLOC;
    360   if (SectionName == ".fini" || SectionName == ".init")
    361     Flags |= ELF::SHF_EXECINSTR;
    362 
    363   if (getLexer().is(AsmToken::Comma)) {
    364     Lex();
    365 
    366     if (IsPush && getLexer().isNot(AsmToken::String)) {
    367       if (getParser().parseExpression(Subsection))
    368         return true;
    369       if (getLexer().isNot(AsmToken::Comma))
    370         goto EndStmt;
    371       Lex();
    372     }
    373 
    374     if (getLexer().isNot(AsmToken::String))
    375       return TokError("expected string in directive");
    376 
    377     StringRef FlagsStr = getTok().getStringContents();
    378     Lex();
    379 
    380     int extraFlags = parseSectionFlags(FlagsStr);
    381     if (extraFlags < 0)
    382       return TokError("unknown flag");
    383     Flags |= extraFlags;
    384 
    385     bool Mergeable = Flags & ELF::SHF_MERGE;
    386     bool Group = Flags & ELF::SHF_GROUP;
    387 
    388     if (getLexer().isNot(AsmToken::Comma)) {
    389       if (Mergeable)
    390         return TokError("Mergeable section must specify the type");
    391       if (Group)
    392         return TokError("Group section must specify the type");
    393     } else {
    394       Lex();
    395       if (getLexer().isNot(AsmToken::Percent) && getLexer().isNot(AsmToken::At))
    396         return TokError("expected '@' or '%' before type");
    397 
    398       Lex();
    399       if (getParser().parseIdentifier(TypeName))
    400         return TokError("expected identifier in directive");
    401 
    402       if (Mergeable) {
    403         if (getLexer().isNot(AsmToken::Comma))
    404           return TokError("expected the entry size");
    405         Lex();
    406         if (getParser().parseAbsoluteExpression(Size))
    407           return true;
    408         if (Size <= 0)
    409           return TokError("entry size must be positive");
    410       }
    411 
    412       if (Group) {
    413         if (getLexer().isNot(AsmToken::Comma))
    414           return TokError("expected group name");
    415         Lex();
    416         if (getParser().parseIdentifier(GroupName))
    417           return true;
    418         if (getLexer().is(AsmToken::Comma)) {
    419           Lex();
    420           StringRef Linkage;
    421           if (getParser().parseIdentifier(Linkage))
    422             return true;
    423           if (Linkage != "comdat")
    424             return TokError("Linkage must be 'comdat'");
    425         }
    426       }
    427     }
    428   }
    429 
    430 EndStmt:
    431   if (getLexer().isNot(AsmToken::EndOfStatement))
    432     return TokError("unexpected token in directive");
    433 
    434   unsigned Type = ELF::SHT_PROGBITS;
    435 
    436   if (TypeName.empty()) {
    437     if (SectionName.startswith(".note"))
    438       Type = ELF::SHT_NOTE;
    439     else if (SectionName == ".init_array")
    440       Type = ELF::SHT_INIT_ARRAY;
    441     else if (SectionName == ".fini_array")
    442       Type = ELF::SHT_FINI_ARRAY;
    443     else if (SectionName == ".preinit_array")
    444       Type = ELF::SHT_PREINIT_ARRAY;
    445   } else {
    446     if (TypeName == "init_array")
    447       Type = ELF::SHT_INIT_ARRAY;
    448     else if (TypeName == "fini_array")
    449       Type = ELF::SHT_FINI_ARRAY;
    450     else if (TypeName == "preinit_array")
    451       Type = ELF::SHT_PREINIT_ARRAY;
    452     else if (TypeName == "nobits")
    453       Type = ELF::SHT_NOBITS;
    454     else if (TypeName == "progbits")
    455       Type = ELF::SHT_PROGBITS;
    456     else if (TypeName == "note")
    457       Type = ELF::SHT_NOTE;
    458     else if (TypeName == "unwind")
    459       Type = ELF::SHT_X86_64_UNWIND;
    460     else
    461       return TokError("unknown section type");
    462   }
    463 
    464   SectionKind Kind = computeSectionKind(Flags);
    465   getStreamer().SwitchSection(getContext().getELFSection(SectionName, Type,
    466                                                          Flags, Kind, Size,
    467                                                          GroupName),
    468                               Subsection);
    469   return false;
    470 }
    471 
    472 bool ELFAsmParser::ParseDirectivePrevious(StringRef DirName, SMLoc) {
    473   MCSectionSubPair PreviousSection = getStreamer().getPreviousSection();
    474   if (PreviousSection.first == NULL)
    475       return TokError(".previous without corresponding .section");
    476   getStreamer().SwitchSection(PreviousSection.first, PreviousSection.second);
    477 
    478   return false;
    479 }
    480 
    481 /// ParseDirectiveELFType
    482 ///  ::= .type identifier , @attribute
    483 bool ELFAsmParser::ParseDirectiveType(StringRef, SMLoc) {
    484   StringRef Name;
    485   if (getParser().parseIdentifier(Name))
    486     return TokError("expected identifier in directive");
    487 
    488   // Handle the identifier as the key symbol.
    489   MCSymbol *Sym = getContext().GetOrCreateSymbol(Name);
    490 
    491   if (getLexer().isNot(AsmToken::Comma))
    492     return TokError("unexpected token in '.type' directive");
    493   Lex();
    494 
    495   if (getLexer().isNot(AsmToken::Percent) && getLexer().isNot(AsmToken::At))
    496     return TokError("expected '@' or '%' before type");
    497   Lex();
    498 
    499   StringRef Type;
    500   SMLoc TypeLoc;
    501 
    502   TypeLoc = getLexer().getLoc();
    503   if (getParser().parseIdentifier(Type))
    504     return TokError("expected symbol type in directive");
    505 
    506   MCSymbolAttr Attr = StringSwitch<MCSymbolAttr>(Type)
    507     .Case("function", MCSA_ELF_TypeFunction)
    508     .Case("object", MCSA_ELF_TypeObject)
    509     .Case("tls_object", MCSA_ELF_TypeTLS)
    510     .Case("common", MCSA_ELF_TypeCommon)
    511     .Case("notype", MCSA_ELF_TypeNoType)
    512     .Case("gnu_unique_object", MCSA_ELF_TypeGnuUniqueObject)
    513     .Case("gnu_indirect_function", MCSA_ELF_TypeIndFunction)
    514     .Default(MCSA_Invalid);
    515 
    516   if (Attr == MCSA_Invalid)
    517     return Error(TypeLoc, "unsupported attribute in '.type' directive");
    518 
    519   if (getLexer().isNot(AsmToken::EndOfStatement))
    520     return TokError("unexpected token in '.type' directive");
    521 
    522   Lex();
    523 
    524   getStreamer().EmitSymbolAttribute(Sym, Attr);
    525 
    526   return false;
    527 }
    528 
    529 /// ParseDirectiveIdent
    530 ///  ::= .ident string
    531 bool ELFAsmParser::ParseDirectiveIdent(StringRef, SMLoc) {
    532   if (getLexer().isNot(AsmToken::String))
    533     return TokError("unexpected token in '.ident' directive");
    534 
    535   StringRef Data = getTok().getIdentifier();
    536 
    537   Lex();
    538 
    539   const MCSection *Comment =
    540     getContext().getELFSection(".comment", ELF::SHT_PROGBITS,
    541                                ELF::SHF_MERGE |
    542                                ELF::SHF_STRINGS,
    543                                SectionKind::getReadOnly(),
    544                                1, "");
    545 
    546   getStreamer().PushSection();
    547   getStreamer().SwitchSection(Comment);
    548   if (!SeenIdent) {
    549     getStreamer().EmitIntValue(0, 1);
    550     SeenIdent = true;
    551   }
    552   getStreamer().EmitBytes(Data);
    553   getStreamer().EmitIntValue(0, 1);
    554   getStreamer().PopSection();
    555   return false;
    556 }
    557 
    558 /// ParseDirectiveSymver
    559 ///  ::= .symver foo, bar2@zed
    560 bool ELFAsmParser::ParseDirectiveSymver(StringRef, SMLoc) {
    561   StringRef Name;
    562   if (getParser().parseIdentifier(Name))
    563     return TokError("expected identifier in directive");
    564 
    565   if (getLexer().isNot(AsmToken::Comma))
    566     return TokError("expected a comma");
    567 
    568   Lex();
    569 
    570   StringRef AliasName;
    571   if (getParser().parseIdentifier(AliasName))
    572     return TokError("expected identifier in directive");
    573 
    574   if (AliasName.find('@') == StringRef::npos)
    575     return TokError("expected a '@' in the name");
    576 
    577   MCSymbol *Alias = getContext().GetOrCreateSymbol(AliasName);
    578   MCSymbol *Sym = getContext().GetOrCreateSymbol(Name);
    579   const MCExpr *Value = MCSymbolRefExpr::Create(Sym, getContext());
    580 
    581   getStreamer().EmitAssignment(Alias, Value);
    582   return false;
    583 }
    584 
    585 /// ParseDirectiveVersion
    586 ///  ::= .version string
    587 bool ELFAsmParser::ParseDirectiveVersion(StringRef, SMLoc) {
    588   if (getLexer().isNot(AsmToken::String))
    589     return TokError("unexpected token in '.version' directive");
    590 
    591   StringRef Data = getTok().getIdentifier();
    592 
    593   Lex();
    594 
    595   const MCSection *Note =
    596     getContext().getELFSection(".note", ELF::SHT_NOTE, 0,
    597                                SectionKind::getReadOnly());
    598 
    599   getStreamer().PushSection();
    600   getStreamer().SwitchSection(Note);
    601   getStreamer().EmitIntValue(Data.size()+1, 4); // namesz.
    602   getStreamer().EmitIntValue(0, 4);             // descsz = 0 (no description).
    603   getStreamer().EmitIntValue(1, 4);             // type = NT_VERSION.
    604   getStreamer().EmitBytes(Data);                // name.
    605   getStreamer().EmitIntValue(0, 1);             // terminate the string.
    606   getStreamer().EmitValueToAlignment(4);        // ensure 4 byte alignment.
    607   getStreamer().PopSection();
    608   return false;
    609 }
    610 
    611 /// ParseDirectiveWeakref
    612 ///  ::= .weakref foo, bar
    613 bool ELFAsmParser::ParseDirectiveWeakref(StringRef, SMLoc) {
    614   // FIXME: Share code with the other alias building directives.
    615 
    616   StringRef AliasName;
    617   if (getParser().parseIdentifier(AliasName))
    618     return TokError("expected identifier in directive");
    619 
    620   if (getLexer().isNot(AsmToken::Comma))
    621     return TokError("expected a comma");
    622 
    623   Lex();
    624 
    625   StringRef Name;
    626   if (getParser().parseIdentifier(Name))
    627     return TokError("expected identifier in directive");
    628 
    629   MCSymbol *Alias = getContext().GetOrCreateSymbol(AliasName);
    630 
    631   MCSymbol *Sym = getContext().GetOrCreateSymbol(Name);
    632 
    633   getStreamer().EmitWeakReference(Alias, Sym);
    634   return false;
    635 }
    636 
    637 bool ELFAsmParser::ParseDirectiveSubsection(StringRef, SMLoc) {
    638   const MCExpr *Subsection = 0;
    639   if (getLexer().isNot(AsmToken::EndOfStatement)) {
    640     if (getParser().parseExpression(Subsection))
    641      return true;
    642   }
    643 
    644   if (getLexer().isNot(AsmToken::EndOfStatement))
    645     return TokError("unexpected token in directive");
    646 
    647   getStreamer().SubSection(Subsection);
    648   return false;
    649 }
    650 
    651 namespace llvm {
    652 
    653 MCAsmParserExtension *createELFAsmParser() {
    654   return new ELFAsmParser;
    655 }
    656 
    657 }
    658