MCSectionELF.h revision 9a744e38607bc3046dffea56efec0b2dfc51d5e4 
1//===- MCSectionELF.h - ELF 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 MCSectionELF class.
11//
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_MC_MCSECTIONELF_H
15#define LLVM_MC_MCSECTIONELF_H
16
17#include "llvm/MC/MCSection.h"
18
19namespace llvm {
20
21/// MCSectionELF - This represents a section on linux, lots of unix variants
22/// and some bare metal systems.
23class MCSectionELF : public MCSection {
24  /// SectionName - This is the name of the section.  The referenced memory is
25  /// owned by TargetLoweringObjectFileELF's ELFUniqueMap.
26  StringRef SectionName;
27
28  /// Type - This is the sh_type field of a section, drawn from the enums below.
29  unsigned Type;
30
31  /// Flags - This is the sh_flags field of a section, drawn from the enums.
32  /// below.
33  unsigned Flags;
34
35  /// IsExplicit - Indicates that this section comes from globals with an
36  /// explicit section specified.
37  bool IsExplicit;
38
39private:
40  friend class MCContext;
41  MCSectionELF(StringRef Section, unsigned type, unsigned flags,
42               SectionKind K, bool isExplicit)
43    : MCSection(SV_ELF, K), SectionName(Section), Type(type), Flags(flags),
44      IsExplicit(isExplicit) {}
45  ~MCSectionELF();
46public:
47
48  /// ShouldOmitSectionDirective - Decides whether a '.section' directive
49  /// should be printed before the section name
50  bool ShouldOmitSectionDirective(StringRef Name, const MCAsmInfo &MAI) const;
51
52  /// ShouldPrintSectionType - Only prints the section type if supported
53  bool ShouldPrintSectionType(unsigned Ty) const;
54
55  /// HasCommonSymbols - True if this section holds common symbols, this is
56  /// indicated on the ELF object file by a symbol with SHN_COMMON section
57  /// header index.
58  bool HasCommonSymbols() const;
59
60  /// These are the section type and flags fields.  An ELF section can have
61  /// only one Type, but can have more than one of the flags specified.
62  ///
63  /// Valid section types.
64  enum {
65    // This value marks the section header as inactive.
66    SHT_NULL             = 0x00U,
67
68    // Holds information defined by the program, with custom format and meaning.
69    SHT_PROGBITS         = 0x01U,
70
71    // This section holds a symbol table.
72    SHT_SYMTAB           = 0x02U,
73
74    // The section holds a string table.
75    SHT_STRTAB           = 0x03U,
76
77    // The section holds relocation entries with explicit addends.
78    SHT_RELA             = 0x04U,
79
80    // The section holds a symbol hash table.
81    SHT_HASH             = 0x05U,
82
83    // Information for dynamic linking.
84    SHT_DYNAMIC          = 0x06U,
85
86    // The section holds information that marks the file in some way.
87    SHT_NOTE             = 0x07U,
88
89    // A section of this type occupies no space in the file.
90    SHT_NOBITS           = 0x08U,
91
92    // The section holds relocation entries without explicit addends.
93    SHT_REL              = 0x09U,
94
95    // This section type is reserved but has unspecified semantics.
96    SHT_SHLIB            = 0x0AU,
97
98    // This section holds a symbol table.
99    SHT_DYNSYM           = 0x0BU,
100
101    // This section contains an array of pointers to initialization functions.
102    SHT_INIT_ARRAY       = 0x0EU,
103
104    // This section contains an array of pointers to termination functions.
105    SHT_FINI_ARRAY       = 0x0FU,
106
107    // This section contains an array of pointers to functions that are invoked
108    // before all other initialization functions.
109    SHT_PREINIT_ARRAY    = 0x10U,
110
111    // A section group is a set of sections that are related and that must be
112    // treated specially by the linker.
113    SHT_GROUP            = 0x11U,
114
115    // This section is associated with a section of type SHT_SYMTAB, when the
116    // referenced symbol table contain the escape value SHN_XINDEX
117    SHT_SYMTAB_SHNDX     = 0x12U,
118
119    LAST_KNOWN_SECTION_TYPE = SHT_SYMTAB_SHNDX
120  };
121
122  /// Valid section flags.
123  enum {
124    // The section contains data that should be writable.
125    SHF_WRITE            = 0x1U,
126
127    // The section occupies memory during execution.
128    SHF_ALLOC            = 0x2U,
129
130    // The section contains executable machine instructions.
131    SHF_EXECINSTR        = 0x4U,
132
133    // The data in the section may be merged to eliminate duplication.
134    SHF_MERGE            = 0x10U,
135
136    // Elements in the section consist of null-terminated character strings.
137    SHF_STRINGS          = 0x20U,
138
139    // A field in this section holds a section header table index.
140    SHF_INFO_LINK        = 0x40U,
141
142    // Adds special ordering requirements for link editors.
143    SHF_LINK_ORDER       = 0x80U,
144
145    // This section requires special OS-specific processing to avoid incorrect
146    // behavior.
147    SHF_OS_NONCONFORMING = 0x100U,
148
149    // This section is a member of a section group.
150    SHF_GROUP            = 0x200U,
151
152    // This section holds Thread-Local Storage.
153    SHF_TLS              = 0x400U,
154
155
156    // Start of target-specific flags.
157
158    /// XCORE_SHF_CP_SECTION - All sections with the "c" flag are grouped
159    /// together by the linker to form the constant pool and the cp register is
160    /// set to the start of the constant pool by the boot code.
161    XCORE_SHF_CP_SECTION = 0x800U,
162
163    /// XCORE_SHF_DP_SECTION - All sections with the "d" flag are grouped
164    /// together by the linker to form the data section and the dp register is
165    /// set to the start of the section by the boot code.
166    XCORE_SHF_DP_SECTION = 0x1000U
167  };
168
169  StringRef getSectionName() const { return SectionName; }
170  unsigned getType() const { return Type; }
171  unsigned getFlags() const { return Flags; }
172
173  void PrintSwitchToSection(const MCAsmInfo &MAI,
174                            raw_ostream &OS) const;
175
176  /// isBaseAddressKnownZero - We know that non-allocatable sections (like
177  /// debug info) have a base of zero.
178  virtual bool isBaseAddressKnownZero() const {
179    return (getFlags() & SHF_ALLOC) == 0;
180  }
181
182  static bool classof(const MCSection *S) {
183    return S->getVariant() == SV_ELF;
184  }
185  static bool classof(const MCSectionELF *) { return true; }
186};
187
188} // end namespace llvm
189
190#endif
191