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