1 //===- lib/MC/MCSectionELF.cpp - ELF Code Section Representation ----------===//
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 "llvm/MC/MCSectionELF.h"
11 #include "llvm/ADT/Triple.h"
12 #include "llvm/BinaryFormat/ELF.h"
13 #include "llvm/MC/MCAsmInfo.h"
14 #include "llvm/MC/MCExpr.h"
15 #include "llvm/Support/ErrorHandling.h"
16 #include "llvm/Support/raw_ostream.h"
17 #include <cassert>
18 
19 using namespace llvm;
20 
21 MCSectionELF::~MCSectionELF() = default; // anchor.
22 
23 // Decides whether a '.section' directive
24 // should be printed before the section name.
25 bool MCSectionELF::ShouldOmitSectionDirective(StringRef Name,
26                                               const MCAsmInfo &MAI) const {
27   if (isUnique())
28     return false;
29 
30   return MAI.shouldOmitSectionDirective(Name);
31 }
32 
33 static void printName(raw_ostream &OS, StringRef Name) {
34   if (Name.find_first_not_of("0123456789_."
35                              "abcdefghijklmnopqrstuvwxyz"
36                              "ABCDEFGHIJKLMNOPQRSTUVWXYZ") == Name.npos) {
37     OS << Name;
38     return;
39   }
40   OS << '"';
41   for (const char *B = Name.begin(), *E = Name.end(); B < E; ++B) {
42     if (*B == '"') // Unquoted "
43       OS << "\\\"";
44     else if (*B != '\\') // Neither " or backslash
45       OS << *B;
46     else if (B + 1 == E) // Trailing backslash
47       OS << "\\\\";
48     else {
49       OS << B[0] << B[1]; // Quoted character
50       ++B;
51     }
52   }
53   OS << '"';
54 }
55 
56 void MCSectionELF::PrintSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
57                                         raw_ostream &OS,
58                                         const MCExpr *Subsection) const {
59   if (ShouldOmitSectionDirective(SectionName, MAI)) {
60     OS << '\t' << getSectionName();
61     if (Subsection) {
62       OS << '\t';
63       Subsection->print(OS, &MAI);
64     }
65     OS << '\n';
66     return;
67   }
68 
69   OS << "\t.section\t";
70   printName(OS, getSectionName());
71 
72   // Handle the weird solaris syntax if desired.
73   if (MAI.usesSunStyleELFSectionSwitchSyntax() &&
74       !(Flags & ELF::SHF_MERGE)) {
75     if (Flags & ELF::SHF_ALLOC)
76       OS << ",#alloc";
77     if (Flags & ELF::SHF_EXECINSTR)
78       OS << ",#execinstr";
79     if (Flags & ELF::SHF_WRITE)
80       OS << ",#write";
81     if (Flags & ELF::SHF_EXCLUDE)
82       OS << ",#exclude";
83     if (Flags & ELF::SHF_TLS)
84       OS << ",#tls";
85     OS << '\n';
86     return;
87   }
88 
89   OS << ",\"";
90   if (Flags & ELF::SHF_ALLOC)
91     OS << 'a';
92   if (Flags & ELF::SHF_EXCLUDE)
93     OS << 'e';
94   if (Flags & ELF::SHF_EXECINSTR)
95     OS << 'x';
96   if (Flags & ELF::SHF_GROUP)
97     OS << 'G';
98   if (Flags & ELF::SHF_WRITE)
99     OS << 'w';
100   if (Flags & ELF::SHF_MERGE)
101     OS << 'M';
102   if (Flags & ELF::SHF_STRINGS)
103     OS << 'S';
104   if (Flags & ELF::SHF_TLS)
105     OS << 'T';
106   if (Flags & ELF::SHF_LINK_ORDER)
107     OS << 'o';
108 
109   // If there are target-specific flags, print them.
110   Triple::ArchType Arch = T.getArch();
111   if (Arch == Triple::xcore) {
112     if (Flags & ELF::XCORE_SHF_CP_SECTION)
113       OS << 'c';
114     if (Flags & ELF::XCORE_SHF_DP_SECTION)
115       OS << 'd';
116   } else if (Arch == Triple::arm || Arch == Triple::armeb ||
117              Arch == Triple::thumb || Arch == Triple::thumbeb) {
118     if (Flags & ELF::SHF_ARM_PURECODE)
119       OS << 'y';
120   }
121 
122   OS << '"';
123 
124   OS << ',';
125 
126   // If comment string is '@', e.g. as on ARM - use '%' instead
127   if (MAI.getCommentString()[0] == '@')
128     OS << '%';
129   else
130     OS << '@';
131 
132   if (Type == ELF::SHT_INIT_ARRAY)
133     OS << "init_array";
134   else if (Type == ELF::SHT_FINI_ARRAY)
135     OS << "fini_array";
136   else if (Type == ELF::SHT_PREINIT_ARRAY)
137     OS << "preinit_array";
138   else if (Type == ELF::SHT_NOBITS)
139     OS << "nobits";
140   else if (Type == ELF::SHT_NOTE)
141     OS << "note";
142   else if (Type == ELF::SHT_PROGBITS)
143     OS << "progbits";
144   else if (Type == ELF::SHT_X86_64_UNWIND)
145     OS << "unwind";
146   else if (Type == ELF::SHT_MIPS_DWARF)
147     // Print hex value of the flag while we do not have
148     // any standard symbolic representation of the flag.
149     OS << "0x7000001e";
150   else
151     report_fatal_error("unsupported type 0x" + Twine::utohexstr(Type) +
152                        " for section " + getSectionName());
153 
154   if (EntrySize) {
155     assert(Flags & ELF::SHF_MERGE);
156     OS << "," << EntrySize;
157   }
158 
159   if (Flags & ELF::SHF_GROUP) {
160     OS << ",";
161     printName(OS, Group->getName());
162     OS << ",comdat";
163   }
164 
165   if (Flags & ELF::SHF_LINK_ORDER) {
166     assert(AssociatedSymbol);
167     OS << ",";
168     printName(OS, AssociatedSymbol->getName());
169   }
170 
171   if (isUnique())
172     OS << ",unique," << UniqueID;
173 
174   OS << '\n';
175 
176   if (Subsection) {
177     OS << "\t.subsection\t";
178     Subsection->print(OS, &MAI);
179     OS << '\n';
180   }
181 }
182 
183 bool MCSectionELF::UseCodeAlign() const {
184   return getFlags() & ELF::SHF_EXECINSTR;
185 }
186 
187 bool MCSectionELF::isVirtualSection() const {
188   return getType() == ELF::SHT_NOBITS;
189 }
190