1 //===- lib/MC/MCSection.cpp - Machine Code Section Representation ---------===//
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 #include "llvm/MC/MCSection.h"
10 #include "llvm/ADT/SmallVector.h"
11 #include "llvm/Config/llvm-config.h"
12 #include "llvm/MC/MCContext.h"
13 #include "llvm/MC/MCFragment.h"
14 #include "llvm/MC/MCSymbol.h"
15 #include "llvm/Support/Compiler.h"
16 #include "llvm/Support/ErrorHandling.h"
17 #include "llvm/Support/raw_ostream.h"
18 #include <algorithm>
19 #include <utility>
20 
21 using namespace llvm;
22 
23 MCSection::MCSection(SectionVariant V, SectionKind K, MCSymbol *Begin)
24     : Begin(Begin), BundleGroupBeforeFirstInst(false), HasInstructions(false),
25       HasData(false), IsRegistered(false), DummyFragment(this), Variant(V),
26       Kind(K) {}
27 
28 MCSymbol *MCSection::getEndSymbol(MCContext &Ctx) {
29   if (!End)
30     End = Ctx.createTempSymbol("sec_end", true);
31   return End;
32 }
33 
34 bool MCSection::hasEnded() const { return End && End->isInSection(); }
35 
36 MCSection::~MCSection() = default;
37 
38 void MCSection::setBundleLockState(BundleLockStateType NewState) {
39   if (NewState == NotBundleLocked) {
40     if (BundleLockNestingDepth == 0) {
41       report_fatal_error("Mismatched bundle_lock/unlock directives");
42     }
43     if (--BundleLockNestingDepth == 0) {
44       BundleLockState = NotBundleLocked;
45     }
46     return;
47   }
48 
49   // If any of the directives is an align_to_end directive, the whole nested
50   // group is align_to_end. So don't downgrade from align_to_end to just locked.
51   if (BundleLockState != BundleLockedAlignToEnd) {
52     BundleLockState = NewState;
53   }
54   ++BundleLockNestingDepth;
55 }
56 
57 MCSection::iterator
58 MCSection::getSubsectionInsertionPoint(unsigned Subsection) {
59   if (Subsection == 0 && SubsectionFragmentMap.empty())
60     return end();
61 
62   SmallVectorImpl<std::pair<unsigned, MCFragment *>>::iterator MI =
63       std::lower_bound(SubsectionFragmentMap.begin(),
64                        SubsectionFragmentMap.end(),
65                        std::make_pair(Subsection, (MCFragment *)nullptr));
66   bool ExactMatch = false;
67   if (MI != SubsectionFragmentMap.end()) {
68     ExactMatch = MI->first == Subsection;
69     if (ExactMatch)
70       ++MI;
71   }
72   iterator IP;
73   if (MI == SubsectionFragmentMap.end())
74     IP = end();
75   else
76     IP = MI->second->getIterator();
77   if (!ExactMatch && Subsection != 0) {
78     // The GNU as documentation claims that subsections have an alignment of 4,
79     // although this appears not to be the case.
80     MCFragment *F = new MCDataFragment();
81     SubsectionFragmentMap.insert(MI, std::make_pair(Subsection, F));
82     getFragmentList().insert(IP, F);
83     F->setParent(this);
84   }
85 
86   return IP;
87 }
88 
89 void MCSection::addPendingLabel(MCSymbol* label, unsigned Subsection) {
90   PendingLabels.push_back(PendingLabel(label, Subsection));
91 }
92 
93 void MCSection::flushPendingLabels(MCFragment *F, uint64_t FOffset,
94 				   unsigned Subsection) {
95   if (PendingLabels.empty())
96     return;
97 
98   // Set the fragment and fragment offset for all pending symbols in the
99   // specified Subsection, and remove those symbols from the pending list.
100   for (auto It = PendingLabels.begin(); It != PendingLabels.end(); ++It) {
101     PendingLabel& Label = *It;
102     if (Label.Subsection == Subsection) {
103       Label.Sym->setFragment(F);
104       Label.Sym->setOffset(FOffset);
105       PendingLabels.erase(It--);
106     }
107   }
108 }
109 
110 void MCSection::flushPendingLabels() {
111   // Make sure all remaining pending labels point to data fragments, by
112   // creating new empty data fragments for each Subsection with labels pending.
113   while (!PendingLabels.empty()) {
114     PendingLabel& Label = PendingLabels[0];
115     iterator CurInsertionPoint =
116       this->getSubsectionInsertionPoint(Label.Subsection);
117     MCFragment *F = new MCDataFragment();
118     getFragmentList().insert(CurInsertionPoint, F);
119     F->setParent(this);
120     flushPendingLabels(F, 0, Label.Subsection);
121   }
122 }
123 
124 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
125 LLVM_DUMP_METHOD void MCSection::dump() const {
126   raw_ostream &OS = errs();
127 
128   OS << "<MCSection";
129   OS << " Fragments:[\n      ";
130   for (auto it = begin(), ie = end(); it != ie; ++it) {
131     if (it != begin())
132       OS << ",\n      ";
133     it->dump();
134   }
135   OS << "]>";
136 }
137 #endif
138