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      1 //===- lib/MC/MCWin64EH.cpp - MCWin64EH implementation --------------------===//
      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/MCWin64EH.h"
     11 #include "llvm/ADT/Twine.h"
     12 #include "llvm/MC/MCContext.h"
     13 #include "llvm/MC/MCExpr.h"
     14 #include "llvm/MC/MCObjectFileInfo.h"
     15 #include "llvm/MC/MCSectionCOFF.h"
     16 #include "llvm/MC/MCStreamer.h"
     17 #include "llvm/MC/MCSymbol.h"
     18 
     19 namespace llvm {
     20 
     21 // NOTE: All relocations generated here are 4-byte image-relative.
     22 
     23 static uint8_t CountOfUnwindCodes(std::vector<MCWin64EHInstruction> &instArray){
     24   uint8_t count = 0;
     25   for (std::vector<MCWin64EHInstruction>::const_iterator I = instArray.begin(),
     26        E = instArray.end(); I != E; ++I) {
     27     switch (I->getOperation()) {
     28     case Win64EH::UOP_PushNonVol:
     29     case Win64EH::UOP_AllocSmall:
     30     case Win64EH::UOP_SetFPReg:
     31     case Win64EH::UOP_PushMachFrame:
     32       count += 1;
     33       break;
     34     case Win64EH::UOP_SaveNonVol:
     35     case Win64EH::UOP_SaveXMM128:
     36       count += 2;
     37       break;
     38     case Win64EH::UOP_SaveNonVolBig:
     39     case Win64EH::UOP_SaveXMM128Big:
     40       count += 3;
     41       break;
     42     case Win64EH::UOP_AllocLarge:
     43       if (I->getSize() > 512*1024-8)
     44         count += 3;
     45       else
     46         count += 2;
     47       break;
     48     }
     49   }
     50   return count;
     51 }
     52 
     53 static void EmitAbsDifference(MCStreamer &streamer, MCSymbol *lhs,
     54                               MCSymbol *rhs) {
     55   MCContext &context = streamer.getContext();
     56   const MCExpr *diff = MCBinaryExpr::CreateSub(MCSymbolRefExpr::Create(
     57                                                                   lhs, context),
     58                                                MCSymbolRefExpr::Create(
     59                                                                   rhs, context),
     60                                                context);
     61   streamer.EmitAbsValue(diff, 1);
     62 
     63 }
     64 
     65 static void EmitUnwindCode(MCStreamer &streamer, MCSymbol *begin,
     66                            MCWin64EHInstruction &inst) {
     67   uint8_t b1, b2;
     68   uint16_t w;
     69   b2 = (inst.getOperation() & 0x0F);
     70   switch (inst.getOperation()) {
     71   case Win64EH::UOP_PushNonVol:
     72     EmitAbsDifference(streamer, inst.getLabel(), begin);
     73     b2 |= (inst.getRegister() & 0x0F) << 4;
     74     streamer.EmitIntValue(b2, 1);
     75     break;
     76   case Win64EH::UOP_AllocLarge:
     77     EmitAbsDifference(streamer, inst.getLabel(), begin);
     78     if (inst.getSize() > 512*1024-8) {
     79       b2 |= 0x10;
     80       streamer.EmitIntValue(b2, 1);
     81       w = inst.getSize() & 0xFFF8;
     82       streamer.EmitIntValue(w, 2);
     83       w = inst.getSize() >> 16;
     84     } else {
     85       streamer.EmitIntValue(b2, 1);
     86       w = inst.getSize() >> 3;
     87     }
     88     streamer.EmitIntValue(w, 2);
     89     break;
     90   case Win64EH::UOP_AllocSmall:
     91     b2 |= (((inst.getSize()-8) >> 3) & 0x0F) << 4;
     92     EmitAbsDifference(streamer, inst.getLabel(), begin);
     93     streamer.EmitIntValue(b2, 1);
     94     break;
     95   case Win64EH::UOP_SetFPReg:
     96     b1 = inst.getOffset() & 0xF0;
     97     streamer.EmitIntValue(b1, 1);
     98     streamer.EmitIntValue(b2, 1);
     99     break;
    100   case Win64EH::UOP_SaveNonVol:
    101   case Win64EH::UOP_SaveXMM128:
    102     b2 |= (inst.getRegister() & 0x0F) << 4;
    103     EmitAbsDifference(streamer, inst.getLabel(), begin);
    104     streamer.EmitIntValue(b2, 1);
    105     w = inst.getOffset() >> 3;
    106     if (inst.getOperation() == Win64EH::UOP_SaveXMM128)
    107       w >>= 1;
    108     streamer.EmitIntValue(w, 2);
    109     break;
    110   case Win64EH::UOP_SaveNonVolBig:
    111   case Win64EH::UOP_SaveXMM128Big:
    112     b2 |= (inst.getRegister() & 0x0F) << 4;
    113     EmitAbsDifference(streamer, inst.getLabel(), begin);
    114     streamer.EmitIntValue(b2, 1);
    115     if (inst.getOperation() == Win64EH::UOP_SaveXMM128Big)
    116       w = inst.getOffset() & 0xFFF0;
    117     else
    118       w = inst.getOffset() & 0xFFF8;
    119     streamer.EmitIntValue(w, 2);
    120     w = inst.getOffset() >> 16;
    121     streamer.EmitIntValue(w, 2);
    122     break;
    123   case Win64EH::UOP_PushMachFrame:
    124     if (inst.isPushCodeFrame())
    125       b2 |= 0x10;
    126     EmitAbsDifference(streamer, inst.getLabel(), begin);
    127     streamer.EmitIntValue(b2, 1);
    128     break;
    129   }
    130 }
    131 
    132 static void EmitRuntimeFunction(MCStreamer &streamer,
    133                                 const MCWin64EHUnwindInfo *info) {
    134   MCContext &context = streamer.getContext();
    135 
    136   streamer.EmitValueToAlignment(4);
    137   streamer.EmitValue(MCSymbolRefExpr::Create(info->Begin, context), 4);
    138   streamer.EmitValue(MCSymbolRefExpr::Create(info->End, context), 4);
    139   streamer.EmitValue(MCSymbolRefExpr::Create(info->Symbol, context), 4);
    140 }
    141 
    142 static void EmitUnwindInfo(MCStreamer &streamer, MCWin64EHUnwindInfo *info) {
    143   // If this UNWIND_INFO already has a symbol, it's already been emitted.
    144   if (info->Symbol) return;
    145 
    146   MCContext &context = streamer.getContext();
    147   streamer.EmitValueToAlignment(4);
    148   // Upper 3 bits are the version number (currently 1).
    149   uint8_t flags = 0x01;
    150   info->Symbol = context.CreateTempSymbol();
    151   streamer.EmitLabel(info->Symbol);
    152 
    153   if (info->ChainedParent)
    154     flags |= Win64EH::UNW_ChainInfo << 3;
    155   else {
    156     if (info->HandlesUnwind)
    157       flags |= Win64EH::UNW_TerminateHandler << 3;
    158     if (info->HandlesExceptions)
    159       flags |= Win64EH::UNW_ExceptionHandler << 3;
    160   }
    161   streamer.EmitIntValue(flags, 1);
    162 
    163   if (info->PrologEnd)
    164     EmitAbsDifference(streamer, info->PrologEnd, info->Begin);
    165   else
    166     streamer.EmitIntValue(0, 1);
    167 
    168   uint8_t numCodes = CountOfUnwindCodes(info->Instructions);
    169   streamer.EmitIntValue(numCodes, 1);
    170 
    171   uint8_t frame = 0;
    172   if (info->LastFrameInst >= 0) {
    173     MCWin64EHInstruction &frameInst = info->Instructions[info->LastFrameInst];
    174     assert(frameInst.getOperation() == Win64EH::UOP_SetFPReg);
    175     frame = (frameInst.getRegister() & 0x0F) |
    176             (frameInst.getOffset() & 0xF0);
    177   }
    178   streamer.EmitIntValue(frame, 1);
    179 
    180   // Emit unwind instructions (in reverse order).
    181   uint8_t numInst = info->Instructions.size();
    182   for (uint8_t c = 0; c < numInst; ++c) {
    183     MCWin64EHInstruction inst = info->Instructions.back();
    184     info->Instructions.pop_back();
    185     EmitUnwindCode(streamer, info->Begin, inst);
    186   }
    187 
    188   if (flags & (Win64EH::UNW_ChainInfo << 3))
    189     EmitRuntimeFunction(streamer, info->ChainedParent);
    190   else if (flags &
    191            ((Win64EH::UNW_TerminateHandler|Win64EH::UNW_ExceptionHandler) << 3))
    192     streamer.EmitValue(MCSymbolRefExpr::Create(info->ExceptionHandler, context),
    193                        4);
    194   else if (numCodes < 2) {
    195     // The minimum size of an UNWIND_INFO struct is 8 bytes. If we're not
    196     // a chained unwind info, if there is no handler, and if there are fewer
    197     // than 2 slots used in the unwind code array, we have to pad to 8 bytes.
    198     if (numCodes == 1)
    199       streamer.EmitIntValue(0, 2);
    200     else
    201       streamer.EmitIntValue(0, 4);
    202   }
    203 }
    204 
    205 StringRef MCWin64EHUnwindEmitter::GetSectionSuffix(const MCSymbol *func) {
    206   if (!func || !func->isInSection()) return "";
    207   const MCSection *section = &func->getSection();
    208   const MCSectionCOFF *COFFSection;
    209   if ((COFFSection = dyn_cast<MCSectionCOFF>(section))) {
    210     StringRef name = COFFSection->getSectionName();
    211     size_t dollar = name.find('$');
    212     size_t dot = name.find('.', 1);
    213     if (dollar == StringRef::npos && dot == StringRef::npos)
    214       return "";
    215     if (dot == StringRef::npos)
    216       return name.substr(dollar);
    217     if (dollar == StringRef::npos || dot < dollar)
    218       return name.substr(dot);
    219     return name.substr(dollar);
    220   }
    221   return "";
    222 }
    223 
    224 static const MCSection *getWin64EHTableSection(StringRef suffix,
    225                                                MCContext &context) {
    226   if (suffix == "")
    227     return context.getObjectFileInfo()->getXDataSection();
    228 
    229   return context.getCOFFSection((".xdata"+suffix).str(),
    230                                 COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
    231                                 COFF::IMAGE_SCN_MEM_READ,
    232                                 SectionKind::getDataRel());
    233 }
    234 
    235 static const MCSection *getWin64EHFuncTableSection(StringRef suffix,
    236                                                    MCContext &context) {
    237   if (suffix == "")
    238     return context.getObjectFileInfo()->getPDataSection();
    239   return context.getCOFFSection((".pdata"+suffix).str(),
    240                                 COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
    241                                 COFF::IMAGE_SCN_MEM_READ,
    242                                 SectionKind::getDataRel());
    243 }
    244 
    245 void MCWin64EHUnwindEmitter::EmitUnwindInfo(MCStreamer &streamer,
    246                                             MCWin64EHUnwindInfo *info) {
    247   // Switch sections (the static function above is meant to be called from
    248   // here and from Emit().
    249   MCContext &context = streamer.getContext();
    250   const MCSection *xdataSect =
    251     getWin64EHTableSection(GetSectionSuffix(info->Function), context);
    252   streamer.SwitchSection(xdataSect);
    253 
    254   llvm::EmitUnwindInfo(streamer, info);
    255 }
    256 
    257 void MCWin64EHUnwindEmitter::Emit(MCStreamer &streamer) {
    258   MCContext &context = streamer.getContext();
    259   // Emit the unwind info structs first.
    260   for (unsigned i = 0; i < streamer.getNumW64UnwindInfos(); ++i) {
    261     MCWin64EHUnwindInfo &info = streamer.getW64UnwindInfo(i);
    262     const MCSection *xdataSect =
    263       getWin64EHTableSection(GetSectionSuffix(info.Function), context);
    264     streamer.SwitchSection(xdataSect);
    265     llvm::EmitUnwindInfo(streamer, &info);
    266   }
    267   // Now emit RUNTIME_FUNCTION entries.
    268   for (unsigned i = 0; i < streamer.getNumW64UnwindInfos(); ++i) {
    269     MCWin64EHUnwindInfo &info = streamer.getW64UnwindInfo(i);
    270     const MCSection *pdataSect =
    271       getWin64EHFuncTableSection(GetSectionSuffix(info.Function), context);
    272     streamer.SwitchSection(pdataSect);
    273     EmitRuntimeFunction(streamer, &info);
    274   }
    275 }
    276 
    277 } // End of namespace llvm
    278 
    279