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/STLExtras.h"
11 #include "llvm/ADT/SmallVector.h"
12 #include "llvm/Config/llvm-config.h"
13 #include "llvm/MC/MCContext.h"
14 #include "llvm/MC/MCFragment.h"
15 #include "llvm/MC/MCSymbol.h"
16 #include "llvm/Support/Compiler.h"
17 #include "llvm/Support/ErrorHandling.h"
18 #include "llvm/Support/raw_ostream.h"
19 #include <utility>
20 
21 using namespace llvm;
22 
23 MCSection::MCSection(SectionVariant V, StringRef Name, SectionKind K,
24                      MCSymbol *Begin)
25     : Begin(Begin), BundleGroupBeforeFirstInst(false), HasInstructions(false),
26       IsRegistered(false), DummyFragment(this), Name(Name), Variant(V),
27       Kind(K) {}
28 
29 MCSymbol *MCSection::getEndSymbol(MCContext &Ctx) {
30   if (!End)
31     End = Ctx.createTempSymbol("sec_end");
32   return End;
33 }
34 
35 bool MCSection::hasEnded() const { return End && End->isInSection(); }
36 
37 MCSection::~MCSection() = default;
38 
39 void MCSection::setBundleLockState(BundleLockStateType NewState) {
40   if (NewState == NotBundleLocked) {
41     if (BundleLockNestingDepth == 0) {
42       report_fatal_error("Mismatched bundle_lock/unlock directives");
43     }
44     if (--BundleLockNestingDepth == 0) {
45       BundleLockState = NotBundleLocked;
46     }
47     return;
48   }
49 
50   // If any of the directives is an align_to_end directive, the whole nested
51   // group is align_to_end. So don't downgrade from align_to_end to just locked.
52   if (BundleLockState != BundleLockedAlignToEnd) {
53     BundleLockState = NewState;
54   }
55   ++BundleLockNestingDepth;
56 }
57 
58 MCSection::iterator
59 MCSection::getSubsectionInsertionPoint(unsigned Subsection) {
60   if (Subsection == 0 && SubsectionFragmentMap.empty())
61     return end();
62 
63   SmallVectorImpl<std::pair<unsigned, MCFragment *>>::iterator MI = lower_bound(
64       SubsectionFragmentMap, std::make_pair(Subsection, (MCFragment *)nullptr));
65   bool ExactMatch = false;
66   if (MI != SubsectionFragmentMap.end()) {
67     ExactMatch = MI->first == Subsection;
68     if (ExactMatch)
69       ++MI;
70   }
71   iterator IP;
72   if (MI == SubsectionFragmentMap.end())
73     IP = end();
74   else
75     IP = MI->second->getIterator();
76   if (!ExactMatch && Subsection != 0) {
77     // The GNU as documentation claims that subsections have an alignment of 4,
78     // although this appears not to be the case.
79     MCFragment *F = new MCDataFragment();
80     SubsectionFragmentMap.insert(MI, std::make_pair(Subsection, F));
81     getFragmentList().insert(IP, F);
82     F->setParent(this);
83     F->setSubsectionNumber(Subsection);
84   }
85 
86   return IP;
87 }
88 
89 StringRef MCSection::getVirtualSectionKind() const { return "virtual"; }
90 
91 void MCSection::addPendingLabel(MCSymbol *label, unsigned Subsection) {
92   PendingLabels.push_back(PendingLabel(label, Subsection));
93 }
94 
95 void MCSection::flushPendingLabels(MCFragment *F, uint64_t FOffset,
96 				   unsigned Subsection) {
97   // Set the fragment and fragment offset for all pending symbols in the
98   // specified Subsection, and remove those symbols from the pending list.
99   for (auto It = PendingLabels.begin(); It != PendingLabels.end(); ++It) {
100     PendingLabel& Label = *It;
101     if (Label.Subsection == Subsection) {
102       Label.Sym->setFragment(F);
103       Label.Sym->setOffset(FOffset);
104       PendingLabels.erase(It--);
105     }
106   }
107 }
108 
109 void MCSection::flushPendingLabels() {
110   // Make sure all remaining pending labels point to data fragments, by
111   // creating new empty data fragments for each Subsection with labels pending.
112   while (!PendingLabels.empty()) {
113     PendingLabel& Label = PendingLabels[0];
114     iterator CurInsertionPoint =
115       this->getSubsectionInsertionPoint(Label.Subsection);
116     const MCSymbol *Atom = nullptr;
117     if (CurInsertionPoint != begin())
118       Atom = std::prev(CurInsertionPoint)->getAtom();
119     MCFragment *F = new MCDataFragment();
120     getFragmentList().insert(CurInsertionPoint, F);
121     F->setParent(this);
122     F->setAtom(Atom);
123     flushPendingLabels(F, 0, Label.Subsection);
124   }
125 }
126 
127 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
128 LLVM_DUMP_METHOD void MCSection::dump() const {
129   raw_ostream &OS = errs();
130 
131   OS << "<MCSection";
132   OS << " Fragments:[\n      ";
133   for (auto it = begin(), ie = end(); it != ie; ++it) {
134     if (it != begin())
135       OS << ",\n      ";
136     it->dump();
137   }
138   OS << "]>";
139 }
140 #endif
141