1 //===- lib/MC/MCSectionMachO.cpp - MachO 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/MCSectionMachO.h"
10 #include "llvm/MC/SectionKind.h"
11 #include "llvm/Support/raw_ostream.h"
12 
13 namespace llvm {
14 class MCAsmInfo;
15 class MCExpr;
16 class MCSymbol;
17 class Triple;
18 } // namespace llvm
19 
20 using namespace llvm;
21 
22 /// SectionTypeDescriptors - These are strings that describe the various section
23 /// types.  This *must* be kept in order with and stay synchronized with the
24 /// section type list.
25 static constexpr struct {
26   StringLiteral AssemblerName, EnumName;
27 } SectionTypeDescriptors[MachO::LAST_KNOWN_SECTION_TYPE + 1] = {
28     {StringLiteral("regular"), StringLiteral("S_REGULAR")}, // 0x00
29     {StringLiteral("zerofill"), StringLiteral("S_ZEROFILL")}, // 0x01
30     {StringLiteral("cstring_literals"),
31      StringLiteral("S_CSTRING_LITERALS")}, // 0x02
32     {StringLiteral("4byte_literals"),
33      StringLiteral("S_4BYTE_LITERALS")}, // 0x03
34     {StringLiteral("8byte_literals"),
35      StringLiteral("S_8BYTE_LITERALS")}, // 0x04
36     {StringLiteral("literal_pointers"),
37      StringLiteral("S_LITERAL_POINTERS")}, // 0x05
38     {StringLiteral("non_lazy_symbol_pointers"),
39      StringLiteral("S_NON_LAZY_SYMBOL_POINTERS")}, // 0x06
40     {StringLiteral("lazy_symbol_pointers"),
41      StringLiteral("S_LAZY_SYMBOL_POINTERS")},                        // 0x07
42     {StringLiteral("symbol_stubs"), StringLiteral("S_SYMBOL_STUBS")}, // 0x08
43     {StringLiteral("mod_init_funcs"),
44      StringLiteral("S_MOD_INIT_FUNC_POINTERS")}, // 0x09
45     {StringLiteral("mod_term_funcs"),
46      StringLiteral("S_MOD_TERM_FUNC_POINTERS")},                     // 0x0A
47     {StringLiteral("coalesced"), StringLiteral("S_COALESCED")},      // 0x0B
48     {StringLiteral("") /*FIXME??*/, StringLiteral("S_GB_ZEROFILL")}, // 0x0C
49     {StringLiteral("interposing"), StringLiteral("S_INTERPOSING")},  // 0x0D
50     {StringLiteral("16byte_literals"),
51      StringLiteral("S_16BYTE_LITERALS")},                           // 0x0E
52     {StringLiteral("") /*FIXME??*/, StringLiteral("S_DTRACE_DOF")}, // 0x0F
53     {StringLiteral("") /*FIXME??*/,
54      StringLiteral("S_LAZY_DYLIB_SYMBOL_POINTERS")}, // 0x10
55     {StringLiteral("thread_local_regular"),
56      StringLiteral("S_THREAD_LOCAL_REGULAR")}, // 0x11
57     {StringLiteral("thread_local_zerofill"),
58      StringLiteral("S_THREAD_LOCAL_ZEROFILL")}, // 0x12
59     {StringLiteral("thread_local_variables"),
60      StringLiteral("S_THREAD_LOCAL_VARIABLES")}, // 0x13
61     {StringLiteral("thread_local_variable_pointers"),
62      StringLiteral("S_THREAD_LOCAL_VARIABLE_POINTERS")}, // 0x14
63     {StringLiteral("thread_local_init_function_pointers"),
64      StringLiteral("S_THREAD_LOCAL_INIT_FUNCTION_POINTERS")}, // 0x15
65     {StringLiteral("") /* linker-synthesized */,
66      StringLiteral("S_INIT_FUNC_OFFSETS")}, // 0x16
67 };
68 
69 /// SectionAttrDescriptors - This is an array of descriptors for section
70 /// attributes.  Unlike the SectionTypeDescriptors, this is not directly indexed
71 /// by attribute, instead it is searched.
72 static constexpr struct {
73   unsigned AttrFlag;
74   StringLiteral AssemblerName, EnumName;
75 } SectionAttrDescriptors[] = {
76 #define ENTRY(ASMNAME, ENUM) \
77   { MachO::ENUM, StringLiteral(ASMNAME), StringLiteral(#ENUM) },
78 ENTRY("pure_instructions",   S_ATTR_PURE_INSTRUCTIONS)
79 ENTRY("no_toc",              S_ATTR_NO_TOC)
80 ENTRY("strip_static_syms",   S_ATTR_STRIP_STATIC_SYMS)
81 ENTRY("no_dead_strip",       S_ATTR_NO_DEAD_STRIP)
82 ENTRY("live_support",        S_ATTR_LIVE_SUPPORT)
83 ENTRY("self_modifying_code", S_ATTR_SELF_MODIFYING_CODE)
84 ENTRY("debug",               S_ATTR_DEBUG)
85 ENTRY("" /*FIXME*/,          S_ATTR_SOME_INSTRUCTIONS)
86 ENTRY("" /*FIXME*/,          S_ATTR_EXT_RELOC)
87 ENTRY("" /*FIXME*/,          S_ATTR_LOC_RELOC)
88 #undef ENTRY
89   { 0, StringLiteral("none"), StringLiteral("") }, // used if section has no attributes but has a stub size
90 };
91 
MCSectionMachO(StringRef Segment,StringRef Section,unsigned TAA,unsigned reserved2,SectionKind K,MCSymbol * Begin)92 MCSectionMachO::MCSectionMachO(StringRef Segment, StringRef Section,
93                                unsigned TAA, unsigned reserved2, SectionKind K,
94                                MCSymbol *Begin)
95     : MCSection(SV_MachO, Section, K, Begin), TypeAndAttributes(TAA),
96       Reserved2(reserved2) {
97   assert(Segment.size() <= 16 && Section.size() <= 16 &&
98          "Segment or section string too long");
99   for (unsigned i = 0; i != 16; ++i) {
100     if (i < Segment.size())
101       SegmentName[i] = Segment[i];
102     else
103       SegmentName[i] = 0;
104   }
105 }
106 
printSwitchToSection(const MCAsmInfo & MAI,const Triple & T,raw_ostream & OS,const MCExpr * Subsection) const107 void MCSectionMachO::printSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
108                                           raw_ostream &OS,
109                                           const MCExpr *Subsection) const {
110   OS << "\t.section\t" << getSegmentName() << ',' << getName();
111 
112   // Get the section type and attributes.
113   unsigned TAA = getTypeAndAttributes();
114   if (TAA == 0) {
115     OS << '\n';
116     return;
117   }
118 
119   MachO::SectionType SectionType = getType();
120   assert(SectionType <= MachO::LAST_KNOWN_SECTION_TYPE &&
121          "Invalid SectionType specified!");
122 
123   if (!SectionTypeDescriptors[SectionType].AssemblerName.empty()) {
124     OS << ',';
125     OS << SectionTypeDescriptors[SectionType].AssemblerName;
126   } else {
127     // If we have no name for the attribute, stop here.
128     OS << '\n';
129     return;
130   }
131 
132   // If we don't have any attributes, we're done.
133   unsigned SectionAttrs = TAA & MachO::SECTION_ATTRIBUTES;
134   if (SectionAttrs == 0) {
135     // If we have a S_SYMBOL_STUBS size specified, print it along with 'none' as
136     // the attribute specifier.
137     if (Reserved2 != 0)
138       OS << ",none," << Reserved2;
139     OS << '\n';
140     return;
141   }
142 
143   // Check each attribute to see if we have it.
144   char Separator = ',';
145   for (unsigned i = 0;
146        SectionAttrs != 0 && SectionAttrDescriptors[i].AttrFlag;
147        ++i) {
148     // Check to see if we have this attribute.
149     if ((SectionAttrDescriptors[i].AttrFlag & SectionAttrs) == 0)
150       continue;
151 
152     // Yep, clear it and print it.
153     SectionAttrs &= ~SectionAttrDescriptors[i].AttrFlag;
154 
155     OS << Separator;
156     if (!SectionAttrDescriptors[i].AssemblerName.empty())
157       OS << SectionAttrDescriptors[i].AssemblerName;
158     else
159       OS << "<<" << SectionAttrDescriptors[i].EnumName << ">>";
160     Separator = '+';
161   }
162 
163   assert(SectionAttrs == 0 && "Unknown section attributes!");
164 
165   // If we have a S_SYMBOL_STUBS size specified, print it.
166   if (Reserved2 != 0)
167     OS << ',' << Reserved2;
168   OS << '\n';
169 }
170 
useCodeAlign() const171 bool MCSectionMachO::useCodeAlign() const {
172   return hasAttribute(MachO::S_ATTR_PURE_INSTRUCTIONS);
173 }
174 
isVirtualSection() const175 bool MCSectionMachO::isVirtualSection() const {
176   return (getType() == MachO::S_ZEROFILL ||
177           getType() == MachO::S_GB_ZEROFILL ||
178           getType() == MachO::S_THREAD_LOCAL_ZEROFILL);
179 }
180 
181 /// ParseSectionSpecifier - Parse the section specifier indicated by "Spec".
182 /// This is a string that can appear after a .section directive in a mach-o
183 /// flavored .s file.  If successful, this fills in the specified Out
184 /// parameters and returns an empty string.  When an invalid section
185 /// specifier is present, this returns a string indicating the problem.
ParseSectionSpecifier(StringRef Spec,StringRef & Segment,StringRef & Section,unsigned & TAA,bool & TAAParsed,unsigned & StubSize)186 Error MCSectionMachO::ParseSectionSpecifier(StringRef Spec,       // In.
187                                             StringRef &Segment,   // Out.
188                                             StringRef &Section,   // Out.
189                                             unsigned &TAA,        // Out.
190                                             bool &TAAParsed,      // Out.
191                                             unsigned &StubSize) { // Out.
192   TAAParsed = false;
193 
194   SmallVector<StringRef, 5> SplitSpec;
195   Spec.split(SplitSpec, ',');
196   // Remove leading and trailing whitespace.
197   auto GetEmptyOrTrim = [&SplitSpec](size_t Idx) -> StringRef {
198     return SplitSpec.size() > Idx ? SplitSpec[Idx].trim() : StringRef();
199   };
200   Segment = GetEmptyOrTrim(0);
201   Section = GetEmptyOrTrim(1);
202   StringRef SectionType = GetEmptyOrTrim(2);
203   StringRef Attrs = GetEmptyOrTrim(3);
204   StringRef StubSizeStr = GetEmptyOrTrim(4);
205 
206   // Verify that the section is present.
207   if (Section.empty())
208     return createStringError(inconvertibleErrorCode(),
209                              "mach-o section specifier requires a segment "
210                              "and section separated by a comma");
211 
212   // Verify that the section is not too long.
213   if (Section.size() > 16)
214     return createStringError(inconvertibleErrorCode(),
215                              "mach-o section specifier requires a section "
216                              "whose length is between 1 and 16 characters");
217 
218   // If there is no comma after the section, we're done.
219   TAA = 0;
220   StubSize = 0;
221   if (SectionType.empty())
222     return Error::success();
223 
224   // Figure out which section type it is.
225   auto TypeDescriptor =
226       llvm::find_if(SectionTypeDescriptors,
227                     [&](decltype(*SectionTypeDescriptors) &Descriptor) {
228                       return SectionType == Descriptor.AssemblerName;
229                     });
230 
231   // If we didn't find the section type, reject it.
232   if (TypeDescriptor == std::end(SectionTypeDescriptors))
233     return createStringError(inconvertibleErrorCode(),
234                              "mach-o section specifier uses an unknown "
235                              "section type");
236 
237   // Remember the TypeID.
238   TAA = TypeDescriptor - std::begin(SectionTypeDescriptors);
239   TAAParsed = true;
240 
241   // If we have no comma after the section type, there are no attributes.
242   if (Attrs.empty()) {
243     // S_SYMBOL_STUBS always require a symbol stub size specifier.
244     if (TAA == MachO::S_SYMBOL_STUBS)
245       return createStringError(inconvertibleErrorCode(),
246                                "mach-o section specifier of type "
247                                "'symbol_stubs' requires a size specifier");
248     return Error::success();
249   }
250 
251   // The attribute list is a '+' separated list of attributes.
252   SmallVector<StringRef, 1> SectionAttrs;
253   Attrs.split(SectionAttrs, '+', /*MaxSplit=*/-1, /*KeepEmpty=*/false);
254 
255   for (StringRef &SectionAttr : SectionAttrs) {
256     auto AttrDescriptorI =
257         llvm::find_if(SectionAttrDescriptors,
258                       [&](decltype(*SectionAttrDescriptors) &Descriptor) {
259                         return SectionAttr.trim() == Descriptor.AssemblerName;
260                       });
261     if (AttrDescriptorI == std::end(SectionAttrDescriptors))
262       return createStringError(inconvertibleErrorCode(),
263                                "mach-o section specifier has invalid "
264                                "attribute");
265 
266     TAA |= AttrDescriptorI->AttrFlag;
267   }
268 
269   // Okay, we've parsed the section attributes, see if we have a stub size spec.
270   if (StubSizeStr.empty()) {
271     // S_SYMBOL_STUBS always require a symbol stub size specifier.
272     if (TAA == MachO::S_SYMBOL_STUBS)
273       return createStringError(inconvertibleErrorCode(),
274                                "mach-o section specifier of type "
275                                "'symbol_stubs' requires a size specifier");
276     return Error::success();
277   }
278 
279   // If we have a stub size spec, we must have a sectiontype of S_SYMBOL_STUBS.
280   if ((TAA & MachO::SECTION_TYPE) != MachO::S_SYMBOL_STUBS)
281     return createStringError(inconvertibleErrorCode(),
282                              "mach-o section specifier cannot have a stub "
283                              "size specified because it does not have type "
284                              "'symbol_stubs'");
285 
286   // Convert the stub size from a string to an integer.
287   if (StubSizeStr.getAsInteger(0, StubSize))
288     return createStringError(inconvertibleErrorCode(),
289                              "mach-o section specifier has a malformed "
290                              "stub size");
291 
292   return Error::success();
293 }
294