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 const struct {
20   const char *AssemblerName, *EnumName;
21 } SectionTypeDescriptors[MachO::LAST_KNOWN_SECTION_TYPE+1] = {
22   { "regular",                  "S_REGULAR" },                    // 0x00
23   { nullptr,                    "S_ZEROFILL" },                   // 0x01
24   { "cstring_literals",         "S_CSTRING_LITERALS" },           // 0x02
25   { "4byte_literals",           "S_4BYTE_LITERALS" },             // 0x03
26   { "8byte_literals",           "S_8BYTE_LITERALS" },             // 0x04
27   { "literal_pointers",         "S_LITERAL_POINTERS" },           // 0x05
28   { "non_lazy_symbol_pointers", "S_NON_LAZY_SYMBOL_POINTERS" },   // 0x06
29   { "lazy_symbol_pointers",     "S_LAZY_SYMBOL_POINTERS" },       // 0x07
30   { "symbol_stubs",             "S_SYMBOL_STUBS" },               // 0x08
31   { "mod_init_funcs",           "S_MOD_INIT_FUNC_POINTERS" },     // 0x09
32   { "mod_term_funcs",           "S_MOD_TERM_FUNC_POINTERS" },     // 0x0A
33   { "coalesced",                "S_COALESCED" },                  // 0x0B
34   { nullptr, /*FIXME??*/        "S_GB_ZEROFILL" },                // 0x0C
35   { "interposing",              "S_INTERPOSING" },                // 0x0D
36   { "16byte_literals",          "S_16BYTE_LITERALS" },            // 0x0E
37   { nullptr, /*FIXME??*/        "S_DTRACE_DOF" },                 // 0x0F
38   { nullptr, /*FIXME??*/        "S_LAZY_DYLIB_SYMBOL_POINTERS" }, // 0x10
39   { "thread_local_regular",     "S_THREAD_LOCAL_REGULAR" },       // 0x11
40   { "thread_local_zerofill",    "S_THREAD_LOCAL_ZEROFILL" },      // 0x12
41   { "thread_local_variables",   "S_THREAD_LOCAL_VARIABLES" },     // 0x13
42   { "thread_local_variable_pointers",
43     "S_THREAD_LOCAL_VARIABLE_POINTERS" },                         // 0x14
44   { "thread_local_init_function_pointers",
45     "S_THREAD_LOCAL_INIT_FUNCTION_POINTERS"},                     // 0x15
46 };
47 
48 
49 /// SectionAttrDescriptors - This is an array of descriptors for section
50 /// attributes.  Unlike the SectionTypeDescriptors, this is not directly indexed
51 /// by attribute, instead it is searched.
52 static const struct {
53   unsigned AttrFlag;
54   const char *AssemblerName, *EnumName;
55 } SectionAttrDescriptors[] = {
56 #define ENTRY(ASMNAME, ENUM) \
57   { MachO::ENUM, ASMNAME, #ENUM },
58 ENTRY("pure_instructions",   S_ATTR_PURE_INSTRUCTIONS)
59 ENTRY("no_toc",              S_ATTR_NO_TOC)
60 ENTRY("strip_static_syms",   S_ATTR_STRIP_STATIC_SYMS)
61 ENTRY("no_dead_strip",       S_ATTR_NO_DEAD_STRIP)
62 ENTRY("live_support",        S_ATTR_LIVE_SUPPORT)
63 ENTRY("self_modifying_code", S_ATTR_SELF_MODIFYING_CODE)
64 ENTRY("debug",               S_ATTR_DEBUG)
65 ENTRY(nullptr /*FIXME*/,     S_ATTR_SOME_INSTRUCTIONS)
66 ENTRY(nullptr /*FIXME*/,     S_ATTR_EXT_RELOC)
67 ENTRY(nullptr /*FIXME*/,     S_ATTR_LOC_RELOC)
68 #undef ENTRY
69   { 0, "none", nullptr }, // used if section has no attributes but has a stub size
70 };
71 
MCSectionMachO(StringRef Segment,StringRef Section,unsigned TAA,unsigned reserved2,SectionKind K,MCSymbol * Begin)72 MCSectionMachO::MCSectionMachO(StringRef Segment, StringRef Section,
73                                unsigned TAA, unsigned reserved2, SectionKind K,
74                                MCSymbol *Begin)
75     : MCSection(SV_MachO, K, Begin), TypeAndAttributes(TAA),
76       Reserved2(reserved2) {
77   assert(Segment.size() <= 16 && Section.size() <= 16 &&
78          "Segment or section string too long");
79   for (unsigned i = 0; i != 16; ++i) {
80     if (i < Segment.size())
81       SegmentName[i] = Segment[i];
82     else
83       SegmentName[i] = 0;
84 
85     if (i < Section.size())
86       SectionName[i] = Section[i];
87     else
88       SectionName[i] = 0;
89   }
90 }
91 
PrintSwitchToSection(const MCAsmInfo & MAI,raw_ostream & OS,const MCExpr * Subsection) const92 void MCSectionMachO::PrintSwitchToSection(const MCAsmInfo &MAI,
93                                           raw_ostream &OS,
94                                           const MCExpr *Subsection) const {
95   OS << "\t.section\t" << getSegmentName() << ',' << getSectionName();
96 
97   // Get the section type and attributes.
98   unsigned TAA = getTypeAndAttributes();
99   if (TAA == 0) {
100     OS << '\n';
101     return;
102   }
103 
104   MachO::SectionType SectionType = getType();
105   assert(SectionType <= MachO::LAST_KNOWN_SECTION_TYPE &&
106          "Invalid SectionType specified!");
107 
108   if (SectionTypeDescriptors[SectionType].AssemblerName) {
109     OS << ',';
110     OS << SectionTypeDescriptors[SectionType].AssemblerName;
111   } else {
112     // If we have no name for the attribute, stop here.
113     OS << '\n';
114     return;
115   }
116 
117   // If we don't have any attributes, we're done.
118   unsigned SectionAttrs = TAA & MachO::SECTION_ATTRIBUTES;
119   if (SectionAttrs == 0) {
120     // If we have a S_SYMBOL_STUBS size specified, print it along with 'none' as
121     // the attribute specifier.
122     if (Reserved2 != 0)
123       OS << ",none," << Reserved2;
124     OS << '\n';
125     return;
126   }
127 
128   // Check each attribute to see if we have it.
129   char Separator = ',';
130   for (unsigned i = 0;
131        SectionAttrs != 0 && SectionAttrDescriptors[i].AttrFlag;
132        ++i) {
133     // Check to see if we have this attribute.
134     if ((SectionAttrDescriptors[i].AttrFlag & SectionAttrs) == 0)
135       continue;
136 
137     // Yep, clear it and print it.
138     SectionAttrs &= ~SectionAttrDescriptors[i].AttrFlag;
139 
140     OS << Separator;
141     if (SectionAttrDescriptors[i].AssemblerName)
142       OS << SectionAttrDescriptors[i].AssemblerName;
143     else
144       OS << "<<" << SectionAttrDescriptors[i].EnumName << ">>";
145     Separator = '+';
146   }
147 
148   assert(SectionAttrs == 0 && "Unknown section attributes!");
149 
150   // If we have a S_SYMBOL_STUBS size specified, print it.
151   if (Reserved2 != 0)
152     OS << ',' << Reserved2;
153   OS << '\n';
154 }
155 
UseCodeAlign() const156 bool MCSectionMachO::UseCodeAlign() const {
157   return hasAttribute(MachO::S_ATTR_PURE_INSTRUCTIONS);
158 }
159 
isVirtualSection() const160 bool MCSectionMachO::isVirtualSection() const {
161   return (getType() == MachO::S_ZEROFILL ||
162           getType() == MachO::S_GB_ZEROFILL ||
163           getType() == MachO::S_THREAD_LOCAL_ZEROFILL);
164 }
165 
166 /// ParseSectionSpecifier - Parse the section specifier indicated by "Spec".
167 /// This is a string that can appear after a .section directive in a mach-o
168 /// flavored .s file.  If successful, this fills in the specified Out
169 /// parameters and returns an empty string.  When an invalid section
170 /// specifier is present, this returns a string indicating the problem.
ParseSectionSpecifier(StringRef Spec,StringRef & Segment,StringRef & Section,unsigned & TAA,bool & TAAParsed,unsigned & StubSize)171 std::string MCSectionMachO::ParseSectionSpecifier(StringRef Spec,        // In.
172                                                   StringRef &Segment,    // Out.
173                                                   StringRef &Section,    // Out.
174                                                   unsigned  &TAA,        // Out.
175                                                   bool      &TAAParsed,  // Out.
176                                                   unsigned  &StubSize) { // Out.
177   TAAParsed = false;
178 
179   SmallVector<StringRef, 5> SplitSpec;
180   Spec.split(SplitSpec, ',');
181   // Remove leading and trailing whitespace.
182   auto GetEmptyOrTrim = [&SplitSpec](size_t Idx) -> StringRef {
183     return SplitSpec.size() > Idx ? SplitSpec[Idx].trim() : StringRef();
184   };
185   Segment = GetEmptyOrTrim(0);
186   Section = GetEmptyOrTrim(1);
187   StringRef SectionType = GetEmptyOrTrim(2);
188   StringRef Attrs = GetEmptyOrTrim(3);
189   StringRef StubSizeStr = GetEmptyOrTrim(4);
190 
191   // Verify that the segment is present and not too long.
192   if (Segment.empty() || Segment.size() > 16)
193     return "mach-o section specifier requires a segment whose length is "
194            "between 1 and 16 characters";
195 
196   // Verify that the section is present and not too long.
197   if (Section.empty())
198     return "mach-o section specifier requires a segment and section "
199            "separated by a comma";
200 
201   if (Section.size() > 16)
202     return "mach-o section specifier requires a section whose length is "
203            "between 1 and 16 characters";
204 
205   // If there is no comma after the section, we're done.
206   TAA = 0;
207   StubSize = 0;
208   if (SectionType.empty())
209     return "";
210 
211   // Figure out which section type it is.
212   auto TypeDescriptor = std::find_if(
213       std::begin(SectionTypeDescriptors), std::end(SectionTypeDescriptors),
214       [&](decltype(*SectionTypeDescriptors) &Descriptor) {
215         return Descriptor.AssemblerName &&
216                SectionType == Descriptor.AssemblerName;
217       });
218 
219   // If we didn't find the section type, reject it.
220   if (TypeDescriptor == std::end(SectionTypeDescriptors))
221     return "mach-o section specifier uses an unknown section type";
222 
223   // Remember the TypeID.
224   TAA = TypeDescriptor - std::begin(SectionTypeDescriptors);
225   TAAParsed = true;
226 
227   // If we have no comma after the section type, there are no attributes.
228   if (Attrs.empty()) {
229     // S_SYMBOL_STUBS always require a symbol stub size specifier.
230     if (TAA == MachO::S_SYMBOL_STUBS)
231       return "mach-o section specifier of type 'symbol_stubs' requires a size "
232              "specifier";
233     return "";
234   }
235 
236   // The attribute list is a '+' separated list of attributes.
237   SmallVector<StringRef, 1> SectionAttrs;
238   Attrs.split(SectionAttrs, '+', /*MaxSplit=*/-1, /*KeepEmpty=*/false);
239 
240   for (StringRef &SectionAttr : SectionAttrs) {
241     auto AttrDescriptorI = std::find_if(
242         std::begin(SectionAttrDescriptors), std::end(SectionAttrDescriptors),
243         [&](decltype(*SectionAttrDescriptors) &Descriptor) {
244           return Descriptor.AssemblerName &&
245                  SectionAttr.trim() == Descriptor.AssemblerName;
246         });
247     if (AttrDescriptorI == std::end(SectionAttrDescriptors))
248       return "mach-o section specifier has invalid attribute";
249 
250     TAA |= AttrDescriptorI->AttrFlag;
251   }
252 
253   // Okay, we've parsed the section attributes, see if we have a stub size spec.
254   if (StubSizeStr.empty()) {
255     // S_SYMBOL_STUBS always require a symbol stub size specifier.
256     if (TAA == MachO::S_SYMBOL_STUBS)
257       return "mach-o section specifier of type 'symbol_stubs' requires a size "
258       "specifier";
259     return "";
260   }
261 
262   // If we have a stub size spec, we must have a sectiontype of S_SYMBOL_STUBS.
263   if ((TAA & MachO::SECTION_TYPE) != MachO::S_SYMBOL_STUBS)
264     return "mach-o section specifier cannot have a stub size specified because "
265            "it does not have type 'symbol_stubs'";
266 
267   // Convert the stub size from a string to an integer.
268   if (StubSizeStr.getAsInteger(0, StubSize))
269     return "mach-o section specifier has a malformed stub size";
270 
271   return "";
272 }
273