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/MCContext.h"
11 #include "llvm/Support/raw_ostream.h"
12 #include <cctype>
13 using namespace llvm;
14 
15 /// SectionTypeDescriptors - These are strings that describe the various section
16 /// types.  This *must* be kept in order with and stay synchronized with the
17 /// section type list.
18 static constexpr struct {
19   StringLiteral AssemblerName, EnumName;
20 } SectionTypeDescriptors[MachO::LAST_KNOWN_SECTION_TYPE + 1] = {
21     {StringLiteral("regular"), StringLiteral("S_REGULAR")}, // 0x00
22     {StringLiteral(""), StringLiteral("S_ZEROFILL")},       // 0x01
23     {StringLiteral("cstring_literals"),
24      StringLiteral("S_CSTRING_LITERALS")}, // 0x02
25     {StringLiteral("4byte_literals"),
26      StringLiteral("S_4BYTE_LITERALS")}, // 0x03
27     {StringLiteral("8byte_literals"),
28      StringLiteral("S_8BYTE_LITERALS")}, // 0x04
29     {StringLiteral("literal_pointers"),
30      StringLiteral("S_LITERAL_POINTERS")}, // 0x05
31     {StringLiteral("non_lazy_symbol_pointers"),
32      StringLiteral("S_NON_LAZY_SYMBOL_POINTERS")}, // 0x06
33     {StringLiteral("lazy_symbol_pointers"),
34      StringLiteral("S_LAZY_SYMBOL_POINTERS")},                        // 0x07
35     {StringLiteral("symbol_stubs"), StringLiteral("S_SYMBOL_STUBS")}, // 0x08
36     {StringLiteral("mod_init_funcs"),
37      StringLiteral("S_MOD_INIT_FUNC_POINTERS")}, // 0x09
38     {StringLiteral("mod_term_funcs"),
39      StringLiteral("S_MOD_TERM_FUNC_POINTERS")},                     // 0x0A
40     {StringLiteral("coalesced"), StringLiteral("S_COALESCED")},      // 0x0B
41     {StringLiteral("") /*FIXME??*/, StringLiteral("S_GB_ZEROFILL")}, // 0x0C
42     {StringLiteral("interposing"), StringLiteral("S_INTERPOSING")},  // 0x0D
43     {StringLiteral("16byte_literals"),
44      StringLiteral("S_16BYTE_LITERALS")},                           // 0x0E
45     {StringLiteral("") /*FIXME??*/, StringLiteral("S_DTRACE_DOF")}, // 0x0F
46     {StringLiteral("") /*FIXME??*/,
47      StringLiteral("S_LAZY_DYLIB_SYMBOL_POINTERS")}, // 0x10
48     {StringLiteral("thread_local_regular"),
49      StringLiteral("S_THREAD_LOCAL_REGULAR")}, // 0x11
50     {StringLiteral("thread_local_zerofill"),
51      StringLiteral("S_THREAD_LOCAL_ZEROFILL")}, // 0x12
52     {StringLiteral("thread_local_variables"),
53      StringLiteral("S_THREAD_LOCAL_VARIABLES")}, // 0x13
54     {StringLiteral("thread_local_variable_pointers"),
55      StringLiteral("S_THREAD_LOCAL_VARIABLE_POINTERS")}, // 0x14
56     {StringLiteral("thread_local_init_function_pointers"),
57      StringLiteral("S_THREAD_LOCAL_INIT_FUNCTION_POINTERS")}, // 0x15
58 };
59 
60 /// SectionAttrDescriptors - This is an array of descriptors for section
61 /// attributes.  Unlike the SectionTypeDescriptors, this is not directly indexed
62 /// by attribute, instead it is searched.
63 static constexpr struct {
64   unsigned AttrFlag;
65   StringLiteral AssemblerName, EnumName;
66 } SectionAttrDescriptors[] = {
67 #define ENTRY(ASMNAME, ENUM) \
68   { MachO::ENUM, StringLiteral(ASMNAME), StringLiteral(#ENUM) },
69 ENTRY("pure_instructions",   S_ATTR_PURE_INSTRUCTIONS)
70 ENTRY("no_toc",              S_ATTR_NO_TOC)
71 ENTRY("strip_static_syms",   S_ATTR_STRIP_STATIC_SYMS)
72 ENTRY("no_dead_strip",       S_ATTR_NO_DEAD_STRIP)
73 ENTRY("live_support",        S_ATTR_LIVE_SUPPORT)
74 ENTRY("self_modifying_code", S_ATTR_SELF_MODIFYING_CODE)
75 ENTRY("debug",               S_ATTR_DEBUG)
76 ENTRY("" /*FIXME*/,          S_ATTR_SOME_INSTRUCTIONS)
77 ENTRY("" /*FIXME*/,          S_ATTR_EXT_RELOC)
78 ENTRY("" /*FIXME*/,          S_ATTR_LOC_RELOC)
79 #undef ENTRY
80   { 0, StringLiteral("none"), StringLiteral("") }, // used if section has no attributes but has a stub size
81 };
82 
MCSectionMachO(StringRef Segment,StringRef Section,unsigned TAA,unsigned reserved2,SectionKind K,MCSymbol * Begin)83 MCSectionMachO::MCSectionMachO(StringRef Segment, StringRef Section,
84                                unsigned TAA, unsigned reserved2, SectionKind K,
85                                MCSymbol *Begin)
86     : MCSection(SV_MachO, Section, K, Begin), TypeAndAttributes(TAA),
87       Reserved2(reserved2) {
88   assert(Segment.size() <= 16 && Section.size() <= 16 &&
89          "Segment or section string too long");
90   for (unsigned i = 0; i != 16; ++i) {
91     if (i < Segment.size())
92       SegmentName[i] = Segment[i];
93     else
94       SegmentName[i] = 0;
95   }
96 }
97 
PrintSwitchToSection(const MCAsmInfo & MAI,const Triple & T,raw_ostream & OS,const MCExpr * Subsection) const98 void MCSectionMachO::PrintSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
99                                           raw_ostream &OS,
100                                           const MCExpr *Subsection) const {
101   OS << "\t.section\t" << getSegmentName() << ',' << getName();
102 
103   // Get the section type and attributes.
104   unsigned TAA = getTypeAndAttributes();
105   if (TAA == 0) {
106     OS << '\n';
107     return;
108   }
109 
110   MachO::SectionType SectionType = getType();
111   assert(SectionType <= MachO::LAST_KNOWN_SECTION_TYPE &&
112          "Invalid SectionType specified!");
113 
114   if (!SectionTypeDescriptors[SectionType].AssemblerName.empty()) {
115     OS << ',';
116     OS << SectionTypeDescriptors[SectionType].AssemblerName;
117   } else {
118     // If we have no name for the attribute, stop here.
119     OS << '\n';
120     return;
121   }
122 
123   // If we don't have any attributes, we're done.
124   unsigned SectionAttrs = TAA & MachO::SECTION_ATTRIBUTES;
125   if (SectionAttrs == 0) {
126     // If we have a S_SYMBOL_STUBS size specified, print it along with 'none' as
127     // the attribute specifier.
128     if (Reserved2 != 0)
129       OS << ",none," << Reserved2;
130     OS << '\n';
131     return;
132   }
133 
134   // Check each attribute to see if we have it.
135   char Separator = ',';
136   for (unsigned i = 0;
137        SectionAttrs != 0 && SectionAttrDescriptors[i].AttrFlag;
138        ++i) {
139     // Check to see if we have this attribute.
140     if ((SectionAttrDescriptors[i].AttrFlag & SectionAttrs) == 0)
141       continue;
142 
143     // Yep, clear it and print it.
144     SectionAttrs &= ~SectionAttrDescriptors[i].AttrFlag;
145 
146     OS << Separator;
147     if (!SectionAttrDescriptors[i].AssemblerName.empty())
148       OS << SectionAttrDescriptors[i].AssemblerName;
149     else
150       OS << "<<" << SectionAttrDescriptors[i].EnumName << ">>";
151     Separator = '+';
152   }
153 
154   assert(SectionAttrs == 0 && "Unknown section attributes!");
155 
156   // If we have a S_SYMBOL_STUBS size specified, print it.
157   if (Reserved2 != 0)
158     OS << ',' << Reserved2;
159   OS << '\n';
160 }
161 
UseCodeAlign() const162 bool MCSectionMachO::UseCodeAlign() const {
163   return hasAttribute(MachO::S_ATTR_PURE_INSTRUCTIONS);
164 }
165 
isVirtualSection() const166 bool MCSectionMachO::isVirtualSection() const {
167   return (getType() == MachO::S_ZEROFILL ||
168           getType() == MachO::S_GB_ZEROFILL ||
169           getType() == MachO::S_THREAD_LOCAL_ZEROFILL);
170 }
171 
172 /// ParseSectionSpecifier - Parse the section specifier indicated by "Spec".
173 /// This is a string that can appear after a .section directive in a mach-o
174 /// flavored .s file.  If successful, this fills in the specified Out
175 /// parameters and returns an empty string.  When an invalid section
176 /// specifier is present, this returns a string indicating the problem.
ParseSectionSpecifier(StringRef Spec,StringRef & Segment,StringRef & Section,unsigned & TAA,bool & TAAParsed,unsigned & StubSize)177 Error MCSectionMachO::ParseSectionSpecifier(StringRef Spec,       // In.
178                                             StringRef &Segment,   // Out.
179                                             StringRef &Section,   // Out.
180                                             unsigned &TAA,        // Out.
181                                             bool &TAAParsed,      // Out.
182                                             unsigned &StubSize) { // Out.
183   TAAParsed = false;
184 
185   SmallVector<StringRef, 5> SplitSpec;
186   Spec.split(SplitSpec, ',');
187   // Remove leading and trailing whitespace.
188   auto GetEmptyOrTrim = [&SplitSpec](size_t Idx) -> StringRef {
189     return SplitSpec.size() > Idx ? SplitSpec[Idx].trim() : StringRef();
190   };
191   Segment = GetEmptyOrTrim(0);
192   Section = GetEmptyOrTrim(1);
193   StringRef SectionType = GetEmptyOrTrim(2);
194   StringRef Attrs = GetEmptyOrTrim(3);
195   StringRef StubSizeStr = GetEmptyOrTrim(4);
196 
197   // Verify that the section is present.
198   if (Section.empty())
199     return createStringError(inconvertibleErrorCode(),
200                              "mach-o section specifier requires a segment "
201                              "and section separated by a comma");
202 
203   // Verify that the section is not too long.
204   if (Section.size() > 16)
205     return createStringError(inconvertibleErrorCode(),
206                              "mach-o section specifier requires a section "
207                              "whose length is between 1 and 16 characters");
208 
209   // If there is no comma after the section, we're done.
210   TAA = 0;
211   StubSize = 0;
212   if (SectionType.empty())
213     return Error::success();
214 
215   // Figure out which section type it is.
216   auto TypeDescriptor =
217       llvm::find_if(SectionTypeDescriptors,
218                     [&](decltype(*SectionTypeDescriptors) &Descriptor) {
219                       return SectionType == Descriptor.AssemblerName;
220                     });
221 
222   // If we didn't find the section type, reject it.
223   if (TypeDescriptor == std::end(SectionTypeDescriptors))
224     return createStringError(inconvertibleErrorCode(),
225                              "mach-o section specifier uses an unknown "
226                              "section type");
227 
228   // Remember the TypeID.
229   TAA = TypeDescriptor - std::begin(SectionTypeDescriptors);
230   TAAParsed = true;
231 
232   // If we have no comma after the section type, there are no attributes.
233   if (Attrs.empty()) {
234     // S_SYMBOL_STUBS always require a symbol stub size specifier.
235     if (TAA == MachO::S_SYMBOL_STUBS)
236       return createStringError(inconvertibleErrorCode(),
237                                "mach-o section specifier of type "
238                                "'symbol_stubs' requires a size specifier");
239     return Error::success();
240   }
241 
242   // The attribute list is a '+' separated list of attributes.
243   SmallVector<StringRef, 1> SectionAttrs;
244   Attrs.split(SectionAttrs, '+', /*MaxSplit=*/-1, /*KeepEmpty=*/false);
245 
246   for (StringRef &SectionAttr : SectionAttrs) {
247     auto AttrDescriptorI =
248         llvm::find_if(SectionAttrDescriptors,
249                       [&](decltype(*SectionAttrDescriptors) &Descriptor) {
250                         return SectionAttr.trim() == Descriptor.AssemblerName;
251                       });
252     if (AttrDescriptorI == std::end(SectionAttrDescriptors))
253       return createStringError(inconvertibleErrorCode(),
254                                "mach-o section specifier has invalid "
255                                "attribute");
256 
257     TAA |= AttrDescriptorI->AttrFlag;
258   }
259 
260   // Okay, we've parsed the section attributes, see if we have a stub size spec.
261   if (StubSizeStr.empty()) {
262     // S_SYMBOL_STUBS always require a symbol stub size specifier.
263     if (TAA == MachO::S_SYMBOL_STUBS)
264       return createStringError(inconvertibleErrorCode(),
265                                "mach-o section specifier of type "
266                                "'symbol_stubs' requires a size specifier");
267     return Error::success();
268   }
269 
270   // If we have a stub size spec, we must have a sectiontype of S_SYMBOL_STUBS.
271   if ((TAA & MachO::SECTION_TYPE) != MachO::S_SYMBOL_STUBS)
272     return createStringError(inconvertibleErrorCode(),
273                              "mach-o section specifier cannot have a stub "
274                              "size specified because it does not have type "
275                              "'symbol_stubs'");
276 
277   // Convert the stub size from a string to an integer.
278   if (StubSizeStr.getAsInteger(0, StubSize))
279     return createStringError(inconvertibleErrorCode(),
280                              "mach-o section specifier has a malformed "
281                              "stub size");
282 
283   return Error::success();
284 }
285