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