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      1 //===- MCSectionCOFF.h - COFF Machine Code Sections -------------*- C++ -*-===//
      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 // This file declares the MCSectionCOFF class.
     11 //
     12 //===----------------------------------------------------------------------===//
     13 
     14 #ifndef LLVM_MC_MCSECTIONCOFF_H
     15 #define LLVM_MC_MCSECTIONCOFF_H
     16 
     17 #include "llvm/ADT/StringRef.h"
     18 #include "llvm/MC/MCSection.h"
     19 #include "llvm/MC/SectionKind.h"
     20 #include <cassert>
     21 
     22 namespace llvm {
     23 
     24 class MCSymbol;
     25 
     26 /// This represents a section on Windows
     27 class MCSectionCOFF final : public MCSection {
     28   // The memory for this string is stored in the same MCContext as *this.
     29   StringRef SectionName;
     30 
     31   // FIXME: The following fields should not be mutable, but are for now so the
     32   // asm parser can honor the .linkonce directive.
     33 
     34   /// This is the Characteristics field of a section, drawn from the enums
     35   /// below.
     36   mutable unsigned Characteristics;
     37 
     38   /// The unique IDs used with the .pdata and .xdata sections created internally
     39   /// by the assembler. This ID is used to ensure that for every .text section,
     40   /// there is exactly one .pdata and one .xdata section, which is required by
     41   /// the Microsoft incremental linker. This data is mutable because this ID is
     42   /// not notionally part of the section.
     43   mutable unsigned WinCFISectionID = ~0U;
     44 
     45   /// The COMDAT symbol of this section. Only valid if this is a COMDAT section.
     46   /// Two COMDAT sections are merged if they have the same COMDAT symbol.
     47   MCSymbol *COMDATSymbol;
     48 
     49   /// This is the Selection field for the section symbol, if it is a COMDAT
     50   /// section (Characteristics & IMAGE_SCN_LNK_COMDAT) != 0
     51   mutable int Selection;
     52 
     53 private:
     54   friend class MCContext;
     55   MCSectionCOFF(StringRef Section, unsigned Characteristics,
     56                 MCSymbol *COMDATSymbol, int Selection, SectionKind K,
     57                 MCSymbol *Begin)
     58       : MCSection(SV_COFF, K, Begin), SectionName(Section),
     59         Characteristics(Characteristics), COMDATSymbol(COMDATSymbol),
     60         Selection(Selection) {
     61     assert((Characteristics & 0x00F00000) == 0 &&
     62            "alignment must not be set upon section creation");
     63   }
     64 
     65 public:
     66   ~MCSectionCOFF();
     67 
     68   /// Decides whether a '.section' directive should be printed before the
     69   /// section name
     70   bool ShouldOmitSectionDirective(StringRef Name, const MCAsmInfo &MAI) const;
     71 
     72   StringRef getSectionName() const { return SectionName; }
     73   unsigned getCharacteristics() const { return Characteristics; }
     74   MCSymbol *getCOMDATSymbol() const { return COMDATSymbol; }
     75   int getSelection() const { return Selection; }
     76 
     77   void setSelection(int Selection) const;
     78 
     79   void PrintSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
     80                             raw_ostream &OS,
     81                             const MCExpr *Subsection) const override;
     82   bool UseCodeAlign() const override;
     83   bool isVirtualSection() const override;
     84 
     85   unsigned getOrAssignWinCFISectionID(unsigned *NextID) const {
     86     if (WinCFISectionID == ~0U)
     87       WinCFISectionID = (*NextID)++;
     88     return WinCFISectionID;
     89   }
     90 
     91   static bool isImplicitlyDiscardable(StringRef Name) {
     92     return Name.startswith(".debug");
     93   }
     94 
     95   static bool classof(const MCSection *S) { return S->getVariant() == SV_COFF; }
     96 };
     97 
     98 } // end namespace llvm
     99 
    100 #endif // LLVM_MC_MCSECTIONCOFF_H
    101