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      1 //===- lib/MC/MCWinEH.cpp - Windows EH 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/ADT/StringRef.h"
     11 #include "llvm/MC/MCContext.h"
     12 #include "llvm/MC/MCObjectFileInfo.h"
     13 #include "llvm/MC/MCSectionCOFF.h"
     14 #include "llvm/MC/MCStreamer.h"
     15 #include "llvm/MC/MCSymbol.h"
     16 #include "llvm/MC/MCWinEH.h"
     17 #include "llvm/Support/COFF.h"
     18 
     19 namespace llvm {
     20 namespace WinEH {
     21 
     22 /// We can't have one section for all .pdata or .xdata because the Microsoft
     23 /// linker seems to want all code relocations to refer to the same object file
     24 /// section. If the code described is comdat, create a new comdat section
     25 /// associated with that comdat. If the code described is not in the main .text
     26 /// section, make a new section for it. Otherwise use the main unwind info
     27 /// section.
     28 static MCSection *getUnwindInfoSection(StringRef SecName,
     29                                        MCSectionCOFF *UnwindSec,
     30                                        const MCSymbol *Function,
     31                                        MCContext &Context) {
     32   if (Function && Function->isInSection()) {
     33     // If Function is in a COMDAT, get or create an unwind info section in that
     34     // COMDAT group.
     35     const MCSectionCOFF *FunctionSection =
     36         cast<MCSectionCOFF>(&Function->getSection());
     37     if (FunctionSection->getCharacteristics() & COFF::IMAGE_SCN_LNK_COMDAT) {
     38       return Context.getAssociativeCOFFSection(
     39           UnwindSec, FunctionSection->getCOMDATSymbol());
     40     }
     41 
     42     // If Function is in a section other than .text, create a new .pdata section.
     43     // Otherwise use the plain .pdata section.
     44     if (const auto *Section = dyn_cast<MCSectionCOFF>(FunctionSection)) {
     45       StringRef CodeSecName = Section->getSectionName();
     46       if (CodeSecName == ".text")
     47         return UnwindSec;
     48 
     49       if (CodeSecName.startswith(".text$"))
     50         CodeSecName = CodeSecName.substr(6);
     51 
     52       return Context.getCOFFSection((SecName + Twine('$') + CodeSecName).str(),
     53                                     COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
     54                                         COFF::IMAGE_SCN_MEM_READ,
     55                                     SectionKind::getData());
     56     }
     57   }
     58 
     59   return UnwindSec;
     60 
     61 }
     62 
     63 MCSection *UnwindEmitter::getPDataSection(const MCSymbol *Function,
     64                                           MCContext &Context) {
     65   MCSectionCOFF *PData =
     66       cast<MCSectionCOFF>(Context.getObjectFileInfo()->getPDataSection());
     67   return getUnwindInfoSection(".pdata", PData, Function, Context);
     68 }
     69 
     70 MCSection *UnwindEmitter::getXDataSection(const MCSymbol *Function,
     71                                           MCContext &Context) {
     72   MCSectionCOFF *XData =
     73       cast<MCSectionCOFF>(Context.getObjectFileInfo()->getXDataSection());
     74   return getUnwindInfoSection(".xdata", XData, Function, Context);
     75 }
     76 
     77 }
     78 }
     79 
     80