1 //===- lib/MC/MCSectionMachO.cpp - MachO 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/MCSectionMachO.h"
11 #include "llvm/MC/MCContext.h"
12 #include "llvm/Support/raw_ostream.h"
13 #include <cctype>
14 using namespace llvm;
15 
16 /// SectionTypeDescriptors - These are strings that describe the various section
17 /// types.  This *must* be kept in order with and stay synchronized with the
18 /// section type list.
19 static constexpr struct {
20   StringLiteral AssemblerName, EnumName;
21 } SectionTypeDescriptors[MachO::LAST_KNOWN_SECTION_TYPE + 1] = {
22     {StringLiteral("regular"), StringLiteral("S_REGULAR")}, // 0x00
23     {StringLiteral(""), StringLiteral("S_ZEROFILL")},       // 0x01
24     {StringLiteral("cstring_literals"),
25      StringLiteral("S_CSTRING_LITERALS")}, // 0x02
26     {StringLiteral("4byte_literals"),
27      StringLiteral("S_4BYTE_LITERALS")}, // 0x03
28     {StringLiteral("8byte_literals"),
29      StringLiteral("S_8BYTE_LITERALS")}, // 0x04
30     {StringLiteral("literal_pointers"),
31      StringLiteral("S_LITERAL_POINTERS")}, // 0x05
32     {StringLiteral("non_lazy_symbol_pointers"),
33      StringLiteral("S_NON_LAZY_SYMBOL_POINTERS")}, // 0x06
34     {StringLiteral("lazy_symbol_pointers"),
35      StringLiteral("S_LAZY_SYMBOL_POINTERS")},                        // 0x07
36     {StringLiteral("symbol_stubs"), StringLiteral("S_SYMBOL_STUBS")}, // 0x08
37     {StringLiteral("mod_init_funcs"),
38      StringLiteral("S_MOD_INIT_FUNC_POINTERS")}, // 0x09
39     {StringLiteral("mod_term_funcs"),
40      StringLiteral("S_MOD_TERM_FUNC_POINTERS")},                     // 0x0A
41     {StringLiteral("coalesced"), StringLiteral("S_COALESCED")},      // 0x0B
42     {StringLiteral("") /*FIXME??*/, StringLiteral("S_GB_ZEROFILL")}, // 0x0C
43     {StringLiteral("interposing"), StringLiteral("S_INTERPOSING")},  // 0x0D
44     {StringLiteral("16byte_literals"),
45      StringLiteral("S_16BYTE_LITERALS")},                           // 0x0E
46     {StringLiteral("") /*FIXME??*/, StringLiteral("S_DTRACE_DOF")}, // 0x0F
47     {StringLiteral("") /*FIXME??*/,
48      StringLiteral("S_LAZY_DYLIB_SYMBOL_POINTERS")}, // 0x10
49     {StringLiteral("thread_local_regular"),
50      StringLiteral("S_THREAD_LOCAL_REGULAR")}, // 0x11
51     {StringLiteral("thread_local_zerofill"),
52      StringLiteral("S_THREAD_LOCAL_ZEROFILL")}, // 0x12
53     {StringLiteral("thread_local_variables"),
54      StringLiteral("S_THREAD_LOCAL_VARIABLES")}, // 0x13
55     {StringLiteral("thread_local_variable_pointers"),
56      StringLiteral("S_THREAD_LOCAL_VARIABLE_POINTERS")}, // 0x14
57     {StringLiteral("thread_local_init_function_pointers"),
58      StringLiteral("S_THREAD_LOCAL_INIT_FUNCTION_POINTERS")}, // 0x15
59 };
60 
61 /// SectionAttrDescriptors - This is an array of descriptors for section
62 /// attributes.  Unlike the SectionTypeDescriptors, this is not directly indexed
63 /// by attribute, instead it is searched.
64 static constexpr struct {
65   unsigned AttrFlag;
66   StringLiteral AssemblerName, EnumName;
67 } SectionAttrDescriptors[] = {
68 #define ENTRY(ASMNAME, ENUM) \
69   { MachO::ENUM, StringLiteral(ASMNAME), StringLiteral(#ENUM) },
70 ENTRY("pure_instructions",   S_ATTR_PURE_INSTRUCTIONS)
71 ENTRY("no_toc",              S_ATTR_NO_TOC)
72 ENTRY("strip_static_syms",   S_ATTR_STRIP_STATIC_SYMS)
73 ENTRY("no_dead_strip",       S_ATTR_NO_DEAD_STRIP)
74 ENTRY("live_support",        S_ATTR_LIVE_SUPPORT)
75 ENTRY("self_modifying_code", S_ATTR_SELF_MODIFYING_CODE)
76 ENTRY("debug",               S_ATTR_DEBUG)
77 ENTRY("" /*FIXME*/,          S_ATTR_SOME_INSTRUCTIONS)
78 ENTRY("" /*FIXME*/,          S_ATTR_EXT_RELOC)
79 ENTRY("" /*FIXME*/,          S_ATTR_LOC_RELOC)
80 #undef ENTRY
81   { 0, StringLiteral("none"), StringLiteral("") }, // used if section has no attributes but has a stub size
82 };
83 
MCSectionMachO(StringRef Segment,StringRef Section,unsigned TAA,unsigned reserved2,SectionKind K,MCSymbol * Begin)84 MCSectionMachO::MCSectionMachO(StringRef Segment, StringRef Section,
85                                unsigned TAA, unsigned reserved2, SectionKind K,
86                                MCSymbol *Begin)
87     : MCSection(SV_MachO, K, Begin), TypeAndAttributes(TAA),
88       Reserved2(reserved2) {
89   assert(Segment.size() <= 16 && Section.size() <= 16 &&
90          "Segment or section string too long");
91   for (unsigned i = 0; i != 16; ++i) {
92     if (i < Segment.size())
93       SegmentName[i] = Segment[i];
94     else
95       SegmentName[i] = 0;
96 
97     if (i < Section.size())
98       SectionName[i] = Section[i];
99     else
100       SectionName[i] = 0;
101   }
102 }
103 
PrintSwitchToSection(const MCAsmInfo & MAI,const Triple & T,raw_ostream & OS,const MCExpr * Subsection) const104 void MCSectionMachO::PrintSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
105                                           raw_ostream &OS,
106                                           const MCExpr *Subsection) const {
107   OS << "\t.section\t" << getSegmentName() << ',' << getSectionName();
108 
109   // Get the section type and attributes.
110   unsigned TAA = getTypeAndAttributes();
111   if (TAA == 0) {
112     OS << '\n';
113     return;
114   }
115 
116   MachO::SectionType SectionType = getType();
117   assert(SectionType <= MachO::LAST_KNOWN_SECTION_TYPE &&
118          "Invalid SectionType specified!");
119 
120   if (!SectionTypeDescriptors[SectionType].AssemblerName.empty()) {
121     OS << ',';
122     OS << SectionTypeDescriptors[SectionType].AssemblerName;
123   } else {
124     // If we have no name for the attribute, stop here.
125     OS << '\n';
126     return;
127   }
128 
129   // If we don't have any attributes, we're done.
130   unsigned SectionAttrs = TAA & MachO::SECTION_ATTRIBUTES;
131   if (SectionAttrs == 0) {
132     // If we have a S_SYMBOL_STUBS size specified, print it along with 'none' as
133     // the attribute specifier.
134     if (Reserved2 != 0)
135       OS << ",none," << Reserved2;
136     OS << '\n';
137     return;
138   }
139 
140   // Check each attribute to see if we have it.
141   char Separator = ',';
142   for (unsigned i = 0;
143        SectionAttrs != 0 && SectionAttrDescriptors[i].AttrFlag;
144        ++i) {
145     // Check to see if we have this attribute.
146     if ((SectionAttrDescriptors[i].AttrFlag & SectionAttrs) == 0)
147       continue;
148 
149     // Yep, clear it and print it.
150     SectionAttrs &= ~SectionAttrDescriptors[i].AttrFlag;
151 
152     OS << Separator;
153     if (!SectionAttrDescriptors[i].AssemblerName.empty())
154       OS << SectionAttrDescriptors[i].AssemblerName;
155     else
156       OS << "<<" << SectionAttrDescriptors[i].EnumName << ">>";
157     Separator = '+';
158   }
159 
160   assert(SectionAttrs == 0 && "Unknown section attributes!");
161 
162   // If we have a S_SYMBOL_STUBS size specified, print it.
163   if (Reserved2 != 0)
164     OS << ',' << Reserved2;
165   OS << '\n';
166 }
167 
UseCodeAlign() const168 bool MCSectionMachO::UseCodeAlign() const {
169   return hasAttribute(MachO::S_ATTR_PURE_INSTRUCTIONS);
170 }
171 
isVirtualSection() const172 bool MCSectionMachO::isVirtualSection() const {
173   return (getType() == MachO::S_ZEROFILL ||
174           getType() == MachO::S_GB_ZEROFILL ||
175           getType() == MachO::S_THREAD_LOCAL_ZEROFILL);
176 }
177 
178 /// ParseSectionSpecifier - Parse the section specifier indicated by "Spec".
179 /// This is a string that can appear after a .section directive in a mach-o
180 /// flavored .s file.  If successful, this fills in the specified Out
181 /// parameters and returns an empty string.  When an invalid section
182 /// specifier is present, this returns a string indicating the problem.
ParseSectionSpecifier(StringRef Spec,StringRef & Segment,StringRef & Section,unsigned & TAA,bool & TAAParsed,unsigned & StubSize)183 std::string MCSectionMachO::ParseSectionSpecifier(StringRef Spec,        // In.
184                                                   StringRef &Segment,    // Out.
185                                                   StringRef &Section,    // Out.
186                                                   unsigned  &TAA,        // Out.
187                                                   bool      &TAAParsed,  // Out.
188                                                   unsigned  &StubSize) { // Out.
189   TAAParsed = false;
190 
191   SmallVector<StringRef, 5> SplitSpec;
192   Spec.split(SplitSpec, ',');
193   // Remove leading and trailing whitespace.
194   auto GetEmptyOrTrim = [&SplitSpec](size_t Idx) -> StringRef {
195     return SplitSpec.size() > Idx ? SplitSpec[Idx].trim() : StringRef();
196   };
197   Segment = GetEmptyOrTrim(0);
198   Section = GetEmptyOrTrim(1);
199   StringRef SectionType = GetEmptyOrTrim(2);
200   StringRef Attrs = GetEmptyOrTrim(3);
201   StringRef StubSizeStr = GetEmptyOrTrim(4);
202 
203   // Verify that the segment is present and not too long.
204   if (Segment.empty() || Segment.size() > 16)
205     return "mach-o section specifier requires a segment whose length is "
206            "between 1 and 16 characters";
207 
208   // Verify that the section is present and not too long.
209   if (Section.empty())
210     return "mach-o section specifier requires a segment and section "
211            "separated by a comma";
212 
213   if (Section.size() > 16)
214     return "mach-o section specifier requires a section whose length is "
215            "between 1 and 16 characters";
216 
217   // If there is no comma after the section, we're done.
218   TAA = 0;
219   StubSize = 0;
220   if (SectionType.empty())
221     return "";
222 
223   // Figure out which section type it is.
224   auto TypeDescriptor = std::find_if(
225       std::begin(SectionTypeDescriptors), std::end(SectionTypeDescriptors),
226       [&](decltype(*SectionTypeDescriptors) &Descriptor) {
227         return SectionType == Descriptor.AssemblerName;
228       });
229 
230   // If we didn't find the section type, reject it.
231   if (TypeDescriptor == std::end(SectionTypeDescriptors))
232     return "mach-o section specifier uses an unknown section type";
233 
234   // Remember the TypeID.
235   TAA = TypeDescriptor - std::begin(SectionTypeDescriptors);
236   TAAParsed = true;
237 
238   // If we have no comma after the section type, there are no attributes.
239   if (Attrs.empty()) {
240     // S_SYMBOL_STUBS always require a symbol stub size specifier.
241     if (TAA == MachO::S_SYMBOL_STUBS)
242       return "mach-o section specifier of type 'symbol_stubs' requires a size "
243              "specifier";
244     return "";
245   }
246 
247   // The attribute list is a '+' separated list of attributes.
248   SmallVector<StringRef, 1> SectionAttrs;
249   Attrs.split(SectionAttrs, '+', /*MaxSplit=*/-1, /*KeepEmpty=*/false);
250 
251   for (StringRef &SectionAttr : SectionAttrs) {
252     auto AttrDescriptorI = std::find_if(
253         std::begin(SectionAttrDescriptors), std::end(SectionAttrDescriptors),
254         [&](decltype(*SectionAttrDescriptors) &Descriptor) {
255           return SectionAttr.trim() == Descriptor.AssemblerName;
256         });
257     if (AttrDescriptorI == std::end(SectionAttrDescriptors))
258       return "mach-o section specifier has invalid attribute";
259 
260     TAA |= AttrDescriptorI->AttrFlag;
261   }
262 
263   // Okay, we've parsed the section attributes, see if we have a stub size spec.
264   if (StubSizeStr.empty()) {
265     // S_SYMBOL_STUBS always require a symbol stub size specifier.
266     if (TAA == MachO::S_SYMBOL_STUBS)
267       return "mach-o section specifier of type 'symbol_stubs' requires a size "
268       "specifier";
269     return "";
270   }
271 
272   // If we have a stub size spec, we must have a sectiontype of S_SYMBOL_STUBS.
273   if ((TAA & MachO::SECTION_TYPE) != MachO::S_SYMBOL_STUBS)
274     return "mach-o section specifier cannot have a stub size specified because "
275            "it does not have type 'symbol_stubs'";
276 
277   // Convert the stub size from a string to an integer.
278   if (StubSizeStr.getAsInteger(0, StubSize))
279     return "mach-o section specifier has a malformed stub size";
280 
281   return "";
282 }
283