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      1 //===- MCSectionCOFF.h - COFF Machine Code Sections -------------*- C++ -*-===//
      2 //
      3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
      4 // See https://llvm.org/LICENSE.txt for license information.
      5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
      6 //
      7 //===----------------------------------------------------------------------===//
      8 //
      9 // This file declares the MCSectionCOFF class.
     10 //
     11 //===----------------------------------------------------------------------===//
     12 
     13 #ifndef LLVM_MC_MCSECTIONCOFF_H
     14 #define LLVM_MC_MCSECTIONCOFF_H
     15 
     16 #include "llvm/ADT/StringRef.h"
     17 #include "llvm/MC/MCSection.h"
     18 #include "llvm/MC/SectionKind.h"
     19 #include <cassert>
     20 
     21 namespace llvm {
     22 
     23 class MCSymbol;
     24 
     25 /// This represents a section on Windows
     26 class MCSectionCOFF final : public MCSection {
     27   // FIXME: The following fields should not be mutable, but are for now so the
     28   // asm parser can honor the .linkonce directive.
     29 
     30   /// This is the Characteristics field of a section, drawn from the enums
     31   /// below.
     32   mutable unsigned Characteristics;
     33 
     34   /// The unique IDs used with the .pdata and .xdata sections created internally
     35   /// by the assembler. This ID is used to ensure that for every .text section,
     36   /// there is exactly one .pdata and one .xdata section, which is required by
     37   /// the Microsoft incremental linker. This data is mutable because this ID is
     38   /// not notionally part of the section.
     39   mutable unsigned WinCFISectionID = ~0U;
     40 
     41   /// The COMDAT symbol of this section. Only valid if this is a COMDAT section.
     42   /// Two COMDAT sections are merged if they have the same COMDAT symbol.
     43   MCSymbol *COMDATSymbol;
     44 
     45   /// This is the Selection field for the section symbol, if it is a COMDAT
     46   /// section (Characteristics & IMAGE_SCN_LNK_COMDAT) != 0
     47   mutable int Selection;
     48 
     49 private:
     50   friend class MCContext;
     51   // The storage of Name is owned by MCContext's COFFUniquingMap.
     52   MCSectionCOFF(StringRef Name, unsigned Characteristics,
     53                 MCSymbol *COMDATSymbol, int Selection, SectionKind K,
     54                 MCSymbol *Begin)
     55       : MCSection(SV_COFF, Name, K, Begin), Characteristics(Characteristics),
     56         COMDATSymbol(COMDATSymbol), Selection(Selection) {
     57     assert((Characteristics & 0x00F00000) == 0 &&
     58            "alignment must not be set upon section creation");
     59   }
     60 
     61 public:
     62   /// Decides whether a '.section' directive should be printed before the
     63   /// section name
     64   bool ShouldOmitSectionDirective(StringRef Name, const MCAsmInfo &MAI) const;
     65 
     66   unsigned getCharacteristics() const { return Characteristics; }
     67   MCSymbol *getCOMDATSymbol() const { return COMDATSymbol; }
     68   int getSelection() const { return Selection; }
     69 
     70   void setSelection(int Selection) const;
     71 
     72   void PrintSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
     73                             raw_ostream &OS,
     74                             const MCExpr *Subsection) const override;
     75   bool UseCodeAlign() const override;
     76   bool isVirtualSection() const override;
     77   StringRef getVirtualSectionKind() const override;
     78 
     79   unsigned getOrAssignWinCFISectionID(unsigned *NextID) const {
     80     if (WinCFISectionID == ~0U)
     81       WinCFISectionID = (*NextID)++;
     82     return WinCFISectionID;
     83   }
     84 
     85   static bool isImplicitlyDiscardable(StringRef Name) {
     86     return Name.startswith(".debug");
     87   }
     88 
     89   static bool classof(const MCSection *S) { return S->getVariant() == SV_COFF; }
     90 };
     91 
     92 } // end namespace llvm
     93 
     94 #endif // LLVM_MC_MCSECTIONCOFF_H
     95