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      1 //===-- llvm/Target/TargetLoweringObjectFile.h - Object Info ----*- 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 implements classes used to handle lowerings specific to common
     11 // object file formats.
     12 //
     13 //===----------------------------------------------------------------------===//
     14 
     15 #ifndef LLVM_MC_SECTIONKIND_H
     16 #define LLVM_MC_SECTIONKIND_H
     17 
     18 namespace llvm {
     19 
     20 /// SectionKind - This is a simple POD value that classifies the properties of
     21 /// a section.  A section is classified into the deepest possible
     22 /// classification, and then the target maps them onto their sections based on
     23 /// what capabilities they have.
     24 ///
     25 /// The comments below describe these as if they were an inheritance hierarchy
     26 /// in order to explain the predicates below.
     27 ///
     28 class SectionKind {
     29   enum Kind {
     30     /// Metadata - Debug info sections or other metadata.
     31     Metadata,
     32 
     33     /// Text - Text section, used for functions and other executable code.
     34     Text,
     35 
     36     /// ReadOnly - Data that is never written to at program runtime by the
     37     /// program or the dynamic linker.  Things in the top-level readonly
     38     /// SectionKind are not mergeable.
     39     ReadOnly,
     40 
     41         /// MergableCString - Any null-terminated string which allows merging.
     42         /// These values are known to end in a nul value of the specified size,
     43         /// not otherwise contain a nul value, and be mergable.  This allows the
     44         /// linker to unique the strings if it so desires.
     45 
     46            /// Mergeable1ByteCString - 1 byte mergable, null terminated, string.
     47            Mergeable1ByteCString,
     48 
     49            /// Mergeable2ByteCString - 2 byte mergable, null terminated, string.
     50            Mergeable2ByteCString,
     51 
     52            /// Mergeable4ByteCString - 4 byte mergable, null terminated, string.
     53            Mergeable4ByteCString,
     54 
     55         /// MergeableConst - These are sections for merging fixed-length
     56         /// constants together.  For example, this can be used to unique
     57         /// constant pool entries etc.
     58         MergeableConst,
     59 
     60             /// MergeableConst4 - This is a section used by 4-byte constants,
     61             /// for example, floats.
     62             MergeableConst4,
     63 
     64             /// MergeableConst8 - This is a section used by 8-byte constants,
     65             /// for example, doubles.
     66             MergeableConst8,
     67 
     68             /// MergeableConst16 - This is a section used by 16-byte constants,
     69             /// for example, vectors.
     70             MergeableConst16,
     71 
     72     /// Writeable - This is the base of all segments that need to be written
     73     /// to during program runtime.
     74 
     75        /// ThreadLocal - This is the base of all TLS segments.  All TLS
     76        /// objects must be writeable, otherwise there is no reason for them to
     77        /// be thread local!
     78 
     79            /// ThreadBSS - Zero-initialized TLS data objects.
     80            ThreadBSS,
     81 
     82            /// ThreadData - Initialized TLS data objects.
     83            ThreadData,
     84 
     85        /// GlobalWriteableData - Writeable data that is global (not thread
     86        /// local).
     87 
     88            /// BSS - Zero initialized writeable data.
     89            BSS,
     90 
     91                /// BSSLocal - This is BSS (zero initialized and writable) data
     92                /// which has local linkage.
     93                BSSLocal,
     94 
     95                /// BSSExtern - This is BSS data with normal external linkage.
     96                BSSExtern,
     97 
     98            /// Common - Data with common linkage.  These represent tentative
     99            /// definitions, which always have a zero initializer and are never
    100            /// marked 'constant'.
    101            Common,
    102 
    103            /// DataRel - This is the most general form of data that is written
    104            /// to by the program, it can have random relocations to arbitrary
    105            /// globals.
    106            DataRel,
    107 
    108                /// DataRelLocal - This is writeable data that has a non-zero
    109                /// initializer and has relocations in it, but all of the
    110                /// relocations are known to be within the final linked image
    111                /// the global is linked into.
    112                DataRelLocal,
    113 
    114                    /// DataNoRel - This is writeable data that has a non-zero
    115                    /// initializer, but whose initializer is known to have no
    116                    /// relocations.
    117                    DataNoRel,
    118 
    119            /// ReadOnlyWithRel - These are global variables that are never
    120            /// written to by the program, but that have relocations, so they
    121            /// must be stuck in a writeable section so that the dynamic linker
    122            /// can write to them.  If it chooses to, the dynamic linker can
    123            /// mark the pages these globals end up on as read-only after it is
    124            /// done with its relocation phase.
    125            ReadOnlyWithRel,
    126 
    127                /// ReadOnlyWithRelLocal - This is data that is readonly by the
    128                /// program, but must be writeable so that the dynamic linker
    129                /// can perform relocations in it.  This is used when we know
    130                /// that all the relocations are to globals in this final
    131                /// linked image.
    132                ReadOnlyWithRelLocal
    133 
    134   } K : 8;
    135 public:
    136 
    137   bool isMetadata() const { return K == Metadata; }
    138   bool isText() const { return K == Text; }
    139 
    140   bool isReadOnly() const {
    141     return K == ReadOnly || isMergeableCString() ||
    142            isMergeableConst();
    143   }
    144 
    145   bool isMergeableCString() const {
    146     return K == Mergeable1ByteCString || K == Mergeable2ByteCString ||
    147            K == Mergeable4ByteCString;
    148   }
    149   bool isMergeable1ByteCString() const { return K == Mergeable1ByteCString; }
    150   bool isMergeable2ByteCString() const { return K == Mergeable2ByteCString; }
    151   bool isMergeable4ByteCString() const { return K == Mergeable4ByteCString; }
    152 
    153   bool isMergeableConst() const {
    154     return K == MergeableConst || K == MergeableConst4 ||
    155            K == MergeableConst8 || K == MergeableConst16;
    156   }
    157   bool isMergeableConst4() const { return K == MergeableConst4; }
    158   bool isMergeableConst8() const { return K == MergeableConst8; }
    159   bool isMergeableConst16() const { return K == MergeableConst16; }
    160 
    161   bool isWriteable() const {
    162     return isThreadLocal() || isGlobalWriteableData();
    163   }
    164 
    165   bool isThreadLocal() const {
    166     return K == ThreadData || K == ThreadBSS;
    167   }
    168 
    169   bool isThreadBSS() const { return K == ThreadBSS; }
    170   bool isThreadData() const { return K == ThreadData; }
    171 
    172   bool isGlobalWriteableData() const {
    173     return isBSS() || isCommon() || isDataRel() || isReadOnlyWithRel();
    174   }
    175 
    176   bool isBSS() const { return K == BSS || K == BSSLocal || K == BSSExtern; }
    177   bool isBSSLocal() const { return K == BSSLocal; }
    178   bool isBSSExtern() const { return K == BSSExtern; }
    179 
    180   bool isCommon() const { return K == Common; }
    181 
    182   bool isDataRel() const {
    183     return K == DataRel || K == DataRelLocal || K == DataNoRel;
    184   }
    185 
    186   bool isDataRelLocal() const {
    187     return K == DataRelLocal || K == DataNoRel;
    188   }
    189 
    190   bool isDataNoRel() const { return K == DataNoRel; }
    191 
    192   bool isReadOnlyWithRel() const {
    193     return K == ReadOnlyWithRel || K == ReadOnlyWithRelLocal;
    194   }
    195 
    196   bool isReadOnlyWithRelLocal() const {
    197     return K == ReadOnlyWithRelLocal;
    198   }
    199 private:
    200   static SectionKind get(Kind K) {
    201     SectionKind Res;
    202     Res.K = K;
    203     return Res;
    204   }
    205 public:
    206 
    207   static SectionKind getMetadata() { return get(Metadata); }
    208   static SectionKind getText() { return get(Text); }
    209   static SectionKind getReadOnly() { return get(ReadOnly); }
    210   static SectionKind getMergeable1ByteCString() {
    211     return get(Mergeable1ByteCString);
    212   }
    213   static SectionKind getMergeable2ByteCString() {
    214     return get(Mergeable2ByteCString);
    215   }
    216   static SectionKind getMergeable4ByteCString() {
    217     return get(Mergeable4ByteCString);
    218   }
    219   static SectionKind getMergeableConst() { return get(MergeableConst); }
    220   static SectionKind getMergeableConst4() { return get(MergeableConst4); }
    221   static SectionKind getMergeableConst8() { return get(MergeableConst8); }
    222   static SectionKind getMergeableConst16() { return get(MergeableConst16); }
    223   static SectionKind getThreadBSS() { return get(ThreadBSS); }
    224   static SectionKind getThreadData() { return get(ThreadData); }
    225   static SectionKind getBSS() { return get(BSS); }
    226   static SectionKind getBSSLocal() { return get(BSSLocal); }
    227   static SectionKind getBSSExtern() { return get(BSSExtern); }
    228   static SectionKind getCommon() { return get(Common); }
    229   static SectionKind getDataRel() { return get(DataRel); }
    230   static SectionKind getDataRelLocal() { return get(DataRelLocal); }
    231   static SectionKind getDataNoRel() { return get(DataNoRel); }
    232   static SectionKind getReadOnlyWithRel() { return get(ReadOnlyWithRel); }
    233   static SectionKind getReadOnlyWithRelLocal(){
    234     return get(ReadOnlyWithRelLocal);
    235   }
    236 };
    237 
    238 } // end namespace llvm
    239 
    240 #endif
    241