1 //===- llvm/CodeGen/DwarfFile.cpp - Dwarf Debug Framework -----------------===//
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 #include "DwarfFile.h"
11 #include "DwarfCompileUnit.h"
12 #include "DwarfDebug.h"
13 #include "DwarfUnit.h"
14 #include "llvm/ADT/SmallVector.h"
15 #include "llvm/CodeGen/AsmPrinter.h"
16 #include "llvm/CodeGen/DIE.h"
17 #include "llvm/IR/DebugInfoMetadata.h"
18 #include "llvm/MC/MCStreamer.h"
19 #include <algorithm>
20 #include <cstdint>
21 
22 using namespace llvm;
23 
24 DwarfFile::DwarfFile(AsmPrinter *AP, StringRef Pref, BumpPtrAllocator &DA)
25     : Asm(AP), Abbrevs(AbbrevAllocator), StrPool(DA, *Asm, Pref) {}
26 
27 void DwarfFile::addUnit(std::unique_ptr<DwarfCompileUnit> U) {
28   CUs.push_back(std::move(U));
29 }
30 
31 void DwarfFile::emitStringOffsetsTableHeader(MCSection *Section) {
32   if (StrPool.empty())
33     return;
34   Asm->OutStreamer->SwitchSection(Section);
35   unsigned EntrySize = 4;
36   // FIXME: DWARF64
37   // We are emitting the header for a contribution to the string offsets
38   // table. The header consists of an entry with the contribution's
39   // size (not including the size of the header), the DWARF version and
40   // 2 bytes of padding.
41   Asm->EmitInt32(StrPool.size() * EntrySize);
42   Asm->EmitInt16(Asm->getDwarfVersion());
43   Asm->EmitInt16(0);
44   // Define the symbol that marks the start of the contribution. It is
45   // referenced by most unit headers via DW_AT_str_offsets_base.
46   // Split units do not use the attribute.
47   if (StringOffsetsStartSym)
48     Asm->OutStreamer->EmitLabel(StringOffsetsStartSym);
49 }
50 
51 // Emit the various dwarf units to the unit section USection with
52 // the abbreviations going into ASection.
53 void DwarfFile::emitUnits(bool UseOffsets) {
54   for (const auto &TheU : CUs)
55     emitUnit(TheU.get(), UseOffsets);
56 }
57 
58 void DwarfFile::emitUnit(DwarfUnit *TheU, bool UseOffsets) {
59   DIE &Die = TheU->getUnitDie();
60   MCSection *USection = TheU->getSection();
61   Asm->OutStreamer->SwitchSection(USection);
62 
63   TheU->emitHeader(UseOffsets);
64 
65   Asm->emitDwarfDIE(Die);
66 }
67 
68 // Compute the size and offset for each DIE.
69 void DwarfFile::computeSizeAndOffsets() {
70   // Offset from the first CU in the debug info section is 0 initially.
71   unsigned SecOffset = 0;
72 
73   // Iterate over each compile unit and set the size and offsets for each
74   // DIE within each compile unit. All offsets are CU relative.
75   for (const auto &TheU : CUs) {
76     TheU->setDebugSectionOffset(SecOffset);
77     SecOffset += computeSizeAndOffsetsForUnit(TheU.get());
78   }
79 }
80 
81 unsigned DwarfFile::computeSizeAndOffsetsForUnit(DwarfUnit *TheU) {
82   // CU-relative offset is reset to 0 here.
83   unsigned Offset = sizeof(int32_t) +      // Length of Unit Info
84                     TheU->getHeaderSize(); // Unit-specific headers
85 
86   // The return value here is CU-relative, after laying out
87   // all of the CU DIE.
88   return computeSizeAndOffset(TheU->getUnitDie(), Offset);
89 }
90 
91 // Compute the size and offset of a DIE. The offset is relative to start of the
92 // CU. It returns the offset after laying out the DIE.
93 unsigned DwarfFile::computeSizeAndOffset(DIE &Die, unsigned Offset) {
94   return Die.computeOffsetsAndAbbrevs(Asm, Abbrevs, Offset);
95 }
96 
97 void DwarfFile::emitAbbrevs(MCSection *Section) { Abbrevs.Emit(Asm, Section); }
98 
99 // Emit strings into a string section.
100 void DwarfFile::emitStrings(MCSection *StrSection, MCSection *OffsetSection,
101                             bool UseRelativeOffsets) {
102   StrPool.emit(*Asm, StrSection, OffsetSection, UseRelativeOffsets);
103 }
104 
105 bool DwarfFile::addScopeVariable(LexicalScope *LS, DbgVariable *Var) {
106   SmallVectorImpl<DbgVariable *> &Vars = ScopeVariables[LS];
107   const DILocalVariable *DV = Var->getVariable();
108   // Variables with positive arg numbers are parameters.
109   if (unsigned ArgNum = DV->getArg()) {
110     // Keep all parameters in order at the start of the variable list to ensure
111     // function types are correct (no out-of-order parameters)
112     //
113     // This could be improved by only doing it for optimized builds (unoptimized
114     // builds have the right order to begin with), searching from the back (this
115     // would catch the unoptimized case quickly), or doing a binary search
116     // rather than linear search.
117     auto I = Vars.begin();
118     while (I != Vars.end()) {
119       unsigned CurNum = (*I)->getVariable()->getArg();
120       // A local (non-parameter) variable has been found, insert immediately
121       // before it.
122       if (CurNum == 0)
123         break;
124       // A later indexed parameter has been found, insert immediately before it.
125       if (CurNum > ArgNum)
126         break;
127       if (CurNum == ArgNum) {
128         (*I)->addMMIEntry(*Var);
129         return false;
130       }
131       ++I;
132     }
133     Vars.insert(I, Var);
134     return true;
135   }
136 
137   Vars.push_back(Var);
138   return true;
139 }
140