MCSectionELF.h revision 7d996d907f593d9d1a4c9d79805b2b7adee63f24 
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  std::string SectionName;
25
26  /// Type - This is the sh_type field of a section, drawn from the enums below.
27  unsigned Type;
28
29  /// Flags - This is the sh_flags field of a section, drawn from the enums.
30  /// below.
31  unsigned Flags;
32
33  /// IsExplicit - Indicates that this section comes from globals with an
34  /// explicit section specfied.
35  bool IsExplicit;
36
37protected:
38  MCSectionELF(const StringRef &Section, unsigned type, unsigned flags,
39               SectionKind K, bool isExplicit)
40    : MCSection(K), SectionName(Section.str()), Type(type), Flags(flags),
41      IsExplicit(isExplicit) {}
42public:
43
44  static MCSectionELF *Create(const StringRef &Section, unsigned Type,
45                              unsigned Flags, SectionKind K, bool isExplicit,
46                              MCContext &Ctx);
47
48  /// ShouldOmitSectionDirective - Decides whether a '.section' directive
49  /// should be printed before the section name
50  bool ShouldOmitSectionDirective(const char *Name,
51                                  const TargetAsmInfo &TAI) const;
52
53  /// ShouldPrintSectionType - Only prints the section type if supported
54  bool ShouldPrintSectionType(unsigned Ty) const;
55
56  /// HasCommonSymbols - True if this section holds common symbols, this is
57  /// indicated on the ELF object file by a symbol with SHN_COMMON section
58  /// header index.
59  bool HasCommonSymbols() const;
60
61  /// These are the section type and flags fields.  An ELF section can have
62  /// only one Type, but can have more than one of the flags specified.
63  ///
64  /// Valid section types.
65  enum {
66    // This value marks the section header as inactive.
67    SHT_NULL             = 0x00U,
68
69    // Holds information defined by the program, with custom format and meaning.
70    SHT_PROGBITS         = 0x01U,
71
72    // This section holds a symbol table.
73    SHT_SYMTAB           = 0x02U,
74
75    // The section holds a string table.
76    SHT_STRTAB           = 0x03U,
77
78    // The section holds relocation entries with explicit addends.
79    SHT_RELA             = 0x04U,
80
81    // The section holds a symbol hash table.
82    SHT_HASH             = 0x05U,
83
84    // Information for dynamic linking.
85    SHT_DYNAMIC          = 0x06U,
86
87    // The section holds information that marks the file in some way.
88    SHT_NOTE             = 0x07U,
89
90    // A section of this type occupies no space in the file.
91    SHT_NOBITS           = 0x08U,
92
93    // The section holds relocation entries without explicit addends.
94    SHT_REL              = 0x09U,
95
96    // This section type is reserved but has unspecified semantics.
97    SHT_SHLIB            = 0x0AU,
98
99    // This section holds a symbol table.
100    SHT_DYNSYM           = 0x0BU,
101
102    // This section contains an array of pointers to initialization functions.
103    SHT_INIT_ARRAY       = 0x0EU,
104
105    // This section contains an array of pointers to termination functions.
106    SHT_FINI_ARRAY       = 0x0FU,
107
108    // This section contains an array of pointers to functions that are invoked
109    // before all other initialization functions.
110    SHT_PREINIT_ARRAY    = 0x10U,
111
112    // A section group is a set of sections that are related and that must be
113    // treated specially by the linker.
114    SHT_GROUP            = 0x11U,
115
116    // This section is associated with a section of type SHT_SYMTAB, when the
117    // referenced symbol table contain the escape value SHN_XINDEX
118    SHT_SYMTAB_SHNDX     = 0x12U,
119
120    LAST_KNOWN_SECTION_TYPE = SHT_SYMTAB_SHNDX
121  };
122
123  /// Valid section flags.
124  enum {
125    // The section contains data that should be writable.
126    SHF_WRITE            = 0x1U,
127
128    // The section occupies memory during execution.
129    SHF_ALLOC            = 0x2U,
130
131    // The section contains executable machine instructions.
132    SHF_EXECINSTR        = 0x4U,
133
134    // The data in the section may be merged to eliminate duplication.
135    SHF_MERGE            = 0x10U,
136
137    // Elements in the section consist of null-terminated character strings.
138    SHF_STRINGS          = 0x20U,
139
140    // A field in this section holds a section header table index.
141    SHF_INFO_LINK        = 0x40U,
142
143    // Adds special ordering requirements for link editors.
144    SHF_LINK_ORDER       = 0x80U,
145
146    // This section requires special OS-specific processing to avoid incorrect
147    // behavior.
148    SHF_OS_NONCONFORMING = 0x100U,
149
150    // This section is a member of a section group.
151    SHF_GROUP            = 0x200U,
152
153    // This section holds Thread-Local Storage.
154    SHF_TLS              = 0x400U,
155
156    /// FIRST_TARGET_DEP_FLAG - This is the first flag that subclasses are
157    /// allowed to specify.
158    FIRST_TARGET_DEP_FLAG = 0x800U,
159
160    /// TARGET_INDEP_SHF - This is the bitmask for all the target independent
161    /// section flags.  Targets can define their own target flags above these.
162    /// If they do that, they should implement their own MCSectionELF subclasses
163    /// and implement the virtual method hooks below to handle printing needs.
164    TARGET_INDEP_SHF     = FIRST_TARGET_DEP_FLAG-1U
165  };
166
167  StringRef getSectionName() const {
168    return StringRef(SectionName);
169  }
170
171  unsigned getType() const { return Type; }
172  unsigned getFlags() const { return Flags; }
173
174  virtual void PrintSwitchToSection(const TargetAsmInfo &TAI,
175                                    raw_ostream &OS) const;
176
177
178  /// PrintTargetSpecificSectionFlags - Targets that define their own
179  /// MCSectionELF subclasses with target specific section flags should
180  /// implement this method if they end up adding letters to the attributes
181  /// list.
182  virtual void PrintTargetSpecificSectionFlags(const TargetAsmInfo &TAI,
183                                               raw_ostream &OS) const {
184  }
185
186
187};
188
189} // end namespace llvm
190
191#endif
192