1 //===- MCSection.h - 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 MCSection class.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #ifndef LLVM_MC_MCSECTION_H
14 #define LLVM_MC_MCSECTION_H
15 
16 #include "llvm/ADT/SmallVector.h"
17 #include "llvm/ADT/ilist.h"
18 #include "llvm/MC/MCFragment.h"
19 #include "llvm/MC/SectionKind.h"
20 #include "llvm/Support/Alignment.h"
21 #include <cassert>
22 #include <utility>
23 
24 namespace llvm {
25 
26 class MCAsmInfo;
27 class MCContext;
28 class MCExpr;
29 class MCSymbol;
30 class raw_ostream;
31 class Triple;
32 
33 template <> struct ilist_alloc_traits<MCFragment> {
34   static void deleteNode(MCFragment *V);
35 };
36 
37 /// Instances of this class represent a uniqued identifier for a section in the
38 /// current translation unit.  The MCContext class uniques and creates these.
39 class MCSection {
40 public:
41   static constexpr unsigned NonUniqueID = ~0U;
42 
43   enum SectionVariant { SV_COFF = 0, SV_ELF, SV_MachO, SV_Wasm, SV_XCOFF };
44 
45   /// Express the state of bundle locked groups while emitting code.
46   enum BundleLockStateType {
47     NotBundleLocked,
48     BundleLocked,
49     BundleLockedAlignToEnd
50   };
51 
52   using FragmentListType = iplist<MCFragment>;
53 
54   using const_iterator = FragmentListType::const_iterator;
55   using iterator = FragmentListType::iterator;
56 
57   using const_reverse_iterator = FragmentListType::const_reverse_iterator;
58   using reverse_iterator = FragmentListType::reverse_iterator;
59 
60 private:
61   MCSymbol *Begin;
62   MCSymbol *End = nullptr;
63   /// The alignment requirement of this section.
64   Align Alignment;
65   /// The section index in the assemblers section list.
66   unsigned Ordinal = 0;
67   /// The index of this section in the layout order.
68   unsigned LayoutOrder;
69 
70   /// Keeping track of bundle-locked state.
71   BundleLockStateType BundleLockState = NotBundleLocked;
72 
73   /// Current nesting depth of bundle_lock directives.
74   unsigned BundleLockNestingDepth = 0;
75 
76   /// We've seen a bundle_lock directive but not its first instruction
77   /// yet.
78   bool BundleGroupBeforeFirstInst : 1;
79 
80   /// Whether this section has had instructions emitted into it.
81   bool HasInstructions : 1;
82 
83   bool IsRegistered : 1;
84 
85   MCDummyFragment DummyFragment;
86 
87   FragmentListType Fragments;
88 
89   /// Mapping from subsection number to insertion point for subsection numbers
90   /// below that number.
91   SmallVector<std::pair<unsigned, MCFragment *>, 1> SubsectionFragmentMap;
92 
93   /// State for tracking labels that don't yet have Fragments
94   struct PendingLabel {
95     MCSymbol* Sym;
96     unsigned Subsection;
97     PendingLabel(MCSymbol* Sym, unsigned Subsection = 0)
98       : Sym(Sym), Subsection(Subsection) {}
99   };
100   SmallVector<PendingLabel, 2> PendingLabels;
101 
102 protected:
103   // TODO Make Name private when possible.
104   StringRef Name;
105   SectionVariant Variant;
106   SectionKind Kind;
107 
108   MCSection(SectionVariant V, StringRef Name, SectionKind K, MCSymbol *Begin);
109   ~MCSection();
110 
111 public:
112   MCSection(const MCSection &) = delete;
113   MCSection &operator=(const MCSection &) = delete;
114 
115   StringRef getName() const { return Name; }
116   SectionKind getKind() const { return Kind; }
117 
118   SectionVariant getVariant() const { return Variant; }
119 
120   MCSymbol *getBeginSymbol() { return Begin; }
121   const MCSymbol *getBeginSymbol() const {
122     return const_cast<MCSection *>(this)->getBeginSymbol();
123   }
124   void setBeginSymbol(MCSymbol *Sym) {
125     assert(!Begin);
126     Begin = Sym;
127   }
128   MCSymbol *getEndSymbol(MCContext &Ctx);
129   bool hasEnded() const;
130 
131   unsigned getAlignment() const { return Alignment.value(); }
132   void setAlignment(Align Value) { Alignment = Value; }
133 
134   unsigned getOrdinal() const { return Ordinal; }
135   void setOrdinal(unsigned Value) { Ordinal = Value; }
136 
137   unsigned getLayoutOrder() const { return LayoutOrder; }
138   void setLayoutOrder(unsigned Value) { LayoutOrder = Value; }
139 
140   BundleLockStateType getBundleLockState() const { return BundleLockState; }
141   void setBundleLockState(BundleLockStateType NewState);
142   bool isBundleLocked() const { return BundleLockState != NotBundleLocked; }
143 
144   bool isBundleGroupBeforeFirstInst() const {
145     return BundleGroupBeforeFirstInst;
146   }
147   void setBundleGroupBeforeFirstInst(bool IsFirst) {
148     BundleGroupBeforeFirstInst = IsFirst;
149   }
150 
151   bool hasInstructions() const { return HasInstructions; }
152   void setHasInstructions(bool Value) { HasInstructions = Value; }
153 
154   bool isRegistered() const { return IsRegistered; }
155   void setIsRegistered(bool Value) { IsRegistered = Value; }
156 
157   MCSection::FragmentListType &getFragmentList() { return Fragments; }
158   const MCSection::FragmentListType &getFragmentList() const {
159     return const_cast<MCSection *>(this)->getFragmentList();
160   }
161 
162   /// Support for MCFragment::getNextNode().
163   static FragmentListType MCSection::*getSublistAccess(MCFragment *) {
164     return &MCSection::Fragments;
165   }
166 
167   const MCDummyFragment &getDummyFragment() const { return DummyFragment; }
168   MCDummyFragment &getDummyFragment() { return DummyFragment; }
169 
170   iterator begin() { return Fragments.begin(); }
171   const_iterator begin() const { return Fragments.begin(); }
172 
173   iterator end() { return Fragments.end(); }
174   const_iterator end() const { return Fragments.end(); }
175 
176   MCSection::iterator getSubsectionInsertionPoint(unsigned Subsection);
177 
178   void dump() const;
179 
180   virtual void PrintSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
181                                     raw_ostream &OS,
182                                     const MCExpr *Subsection) const = 0;
183 
184   /// Return true if a .align directive should use "optimized nops" to fill
185   /// instead of 0s.
186   virtual bool UseCodeAlign() const = 0;
187 
188   /// Check whether this section is "virtual", that is has no actual object
189   /// file contents.
190   virtual bool isVirtualSection() const = 0;
191 
192   virtual StringRef getVirtualSectionKind() const;
193 
194   /// Add a pending label for the requested subsection. This label will be
195   /// associated with a fragment in flushPendingLabels()
196   void addPendingLabel(MCSymbol* label, unsigned Subsection = 0);
197 
198   /// Associate all pending labels in a subsection with a fragment.
199   void flushPendingLabels(MCFragment *F, uint64_t FOffset = 0,
200 			  unsigned Subsection = 0);
201 
202   /// Associate all pending labels with empty data fragments. One fragment
203   /// will be created for each subsection as necessary.
204   void flushPendingLabels();
205 };
206 
207 } // end namespace llvm
208 
209 #endif // LLVM_MC_MCSECTION_H
210