MCSectionELF.h revision 3d2251361171b1a41bdb2ac71882e69d48617f49 
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
39protected:
40  MCSectionELF(StringRef Section, unsigned type, unsigned flags,
41               SectionKind K, bool isExplicit)
42    : MCSection(K), SectionName(Section), Type(type), Flags(flags),
43      IsExplicit(isExplicit) {}
44public:
45
46  static MCSectionELF *Create(StringRef Section, unsigned Type,
47                              unsigned Flags, SectionKind K, bool isExplicit,
48                              MCContext &Ctx);
49
50  /// ShouldOmitSectionDirective - Decides whether a '.section' directive
51  /// should be printed before the section name
52  bool ShouldOmitSectionDirective(StringRef Name, const MCAsmInfo &MAI) const;
53
54  /// ShouldPrintSectionType - Only prints the section type if supported
55  bool ShouldPrintSectionType(unsigned Ty) const;
56
57  /// HasCommonSymbols - True if this section holds common symbols, this is
58  /// indicated on the ELF object file by a symbol with SHN_COMMON section
59  /// header index.
60  bool HasCommonSymbols() const;
61
62  /// These are the section type and flags fields.  An ELF section can have
63  /// only one Type, but can have more than one of the flags specified.
64  ///
65  /// Valid section types.
66  enum {
67    // This value marks the section header as inactive.
68    SHT_NULL             = 0x00U,
69
70    // Holds information defined by the program, with custom format and meaning.
71    SHT_PROGBITS         = 0x01U,
72
73    // This section holds a symbol table.
74    SHT_SYMTAB           = 0x02U,
75
76    // The section holds a string table.
77    SHT_STRTAB           = 0x03U,
78
79    // The section holds relocation entries with explicit addends.
80    SHT_RELA             = 0x04U,
81
82    // The section holds a symbol hash table.
83    SHT_HASH             = 0x05U,
84
85    // Information for dynamic linking.
86    SHT_DYNAMIC          = 0x06U,
87
88    // The section holds information that marks the file in some way.
89    SHT_NOTE             = 0x07U,
90
91    // A section of this type occupies no space in the file.
92    SHT_NOBITS           = 0x08U,
93
94    // The section holds relocation entries without explicit addends.
95    SHT_REL              = 0x09U,
96
97    // This section type is reserved but has unspecified semantics.
98    SHT_SHLIB            = 0x0AU,
99
100    // This section holds a symbol table.
101    SHT_DYNSYM           = 0x0BU,
102
103    // This section contains an array of pointers to initialization functions.
104    SHT_INIT_ARRAY       = 0x0EU,
105
106    // This section contains an array of pointers to termination functions.
107    SHT_FINI_ARRAY       = 0x0FU,
108
109    // This section contains an array of pointers to functions that are invoked
110    // before all other initialization functions.
111    SHT_PREINIT_ARRAY    = 0x10U,
112
113    // A section group is a set of sections that are related and that must be
114    // treated specially by the linker.
115    SHT_GROUP            = 0x11U,
116
117    // This section is associated with a section of type SHT_SYMTAB, when the
118    // referenced symbol table contain the escape value SHN_XINDEX
119    SHT_SYMTAB_SHNDX     = 0x12U,
120
121    LAST_KNOWN_SECTION_TYPE = SHT_SYMTAB_SHNDX
122  };
123
124  /// Valid section flags.
125  enum {
126    // The section contains data that should be writable.
127    SHF_WRITE            = 0x1U,
128
129    // The section occupies memory during execution.
130    SHF_ALLOC            = 0x2U,
131
132    // The section contains executable machine instructions.
133    SHF_EXECINSTR        = 0x4U,
134
135    // The data in the section may be merged to eliminate duplication.
136    SHF_MERGE            = 0x10U,
137
138    // Elements in the section consist of null-terminated character strings.
139    SHF_STRINGS          = 0x20U,
140
141    // A field in this section holds a section header table index.
142    SHF_INFO_LINK        = 0x40U,
143
144    // Adds special ordering requirements for link editors.
145    SHF_LINK_ORDER       = 0x80U,
146
147    // This section requires special OS-specific processing to avoid incorrect
148    // behavior.
149    SHF_OS_NONCONFORMING = 0x100U,
150
151    // This section is a member of a section group.
152    SHF_GROUP            = 0x200U,
153
154    // This section holds Thread-Local Storage.
155    SHF_TLS              = 0x400U,
156
157    /// FIRST_TARGET_DEP_FLAG - This is the first flag that subclasses are
158    /// allowed to specify.
159    FIRST_TARGET_DEP_FLAG = 0x800U,
160
161    /// TARGET_INDEP_SHF - This is the bitmask for all the target independent
162    /// section flags.  Targets can define their own target flags above these.
163    /// If they do that, they should implement their own MCSectionELF subclasses
164    /// and implement the virtual method hooks below to handle printing needs.
165    TARGET_INDEP_SHF     = FIRST_TARGET_DEP_FLAG-1U
166  };
167
168  StringRef getSectionName() const { return SectionName; }
169  unsigned getType() const { return Type; }
170  unsigned getFlags() const { return Flags; }
171
172  virtual void PrintSwitchToSection(const MCAsmInfo &MAI,
173                                    raw_ostream &OS) const;
174
175  /// isBaseAddressKnownZero - We know that non-allocatable sections (like
176  /// debug info) have a base of zero.
177  virtual bool isBaseAddressKnownZero() const {
178    return (getFlags() & SHF_ALLOC) == 0;
179  }
180
181  /// PrintTargetSpecificSectionFlags - Targets that define their own
182  /// MCSectionELF subclasses with target specific section flags should
183  /// implement this method if they end up adding letters to the attributes
184  /// list.
185  virtual void PrintTargetSpecificSectionFlags(const MCAsmInfo &MAI,
186                                               raw_ostream &OS) const {
187  }
188
189
190};
191
192} // end namespace llvm
193
194#endif
195