1 //===- X86_64.cpp ---------------------------------------------------------===//
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 "InputFiles.h"
10 #include "Symbols.h"
11 #include "SyntheticSections.h"
12 #include "Target.h"
13 
14 #include "lld/Common/ErrorHandler.h"
15 #include "mach-o/compact_unwind_encoding.h"
16 #include "llvm/BinaryFormat/MachO.h"
17 #include "llvm/Support/Endian.h"
18 
19 using namespace llvm::MachO;
20 using namespace llvm::support::endian;
21 using namespace lld;
22 using namespace lld::macho;
23 
24 namespace {
25 
26 struct X86_64 : TargetInfo {
27   X86_64();
28 
29   int64_t getEmbeddedAddend(MemoryBufferRef, uint64_t offset,
30                             const relocation_info) const override;
31   void relocateOne(uint8_t *loc, const Reloc &, uint64_t va,
32                    uint64_t relocVA) const override;
33 
34   void writeStub(uint8_t *buf, const Symbol &,
35                  uint64_t pointerVA) const override;
36   void writeStubHelperHeader(uint8_t *buf) const override;
37   void writeStubHelperEntry(uint8_t *buf, const Symbol &,
38                             uint64_t entryAddr) const override;
39 
40   void writeObjCMsgSendStub(uint8_t *buf, Symbol *sym, uint64_t stubsAddr,
41                             uint64_t &stubOffset, uint64_t selrefsVA,
42                             uint64_t selectorIndex,
43                             Symbol *objcMsgSend) const override;
44 
45   void relaxGotLoad(uint8_t *loc, uint8_t type) const override;
46   uint64_t getPageSize() const override { return 4 * 1024; }
47 
48   void handleDtraceReloc(const Symbol *sym, const Reloc &r,
49                          uint8_t *loc) const override;
50 };
51 } // namespace
52 
53 static constexpr std::array<RelocAttrs, 10> relocAttrsArray{{
54 #define B(x) RelocAttrBits::x
55     {"UNSIGNED",
56      B(UNSIGNED) | B(ABSOLUTE) | B(EXTERN) | B(LOCAL) | B(BYTE4) | B(BYTE8)},
57     {"SIGNED", B(PCREL) | B(EXTERN) | B(LOCAL) | B(BYTE4)},
58     {"BRANCH", B(PCREL) | B(EXTERN) | B(BRANCH) | B(BYTE4)},
59     {"GOT_LOAD", B(PCREL) | B(EXTERN) | B(GOT) | B(LOAD) | B(BYTE4)},
60     {"GOT", B(PCREL) | B(EXTERN) | B(GOT) | B(POINTER) | B(BYTE4)},
61     {"SUBTRACTOR", B(SUBTRAHEND) | B(EXTERN) | B(BYTE4) | B(BYTE8)},
62     {"SIGNED_1", B(PCREL) | B(EXTERN) | B(LOCAL) | B(BYTE4)},
63     {"SIGNED_2", B(PCREL) | B(EXTERN) | B(LOCAL) | B(BYTE4)},
64     {"SIGNED_4", B(PCREL) | B(EXTERN) | B(LOCAL) | B(BYTE4)},
65     {"TLV", B(PCREL) | B(EXTERN) | B(TLV) | B(LOAD) | B(BYTE4)},
66 #undef B
67 }};
68 
69 static int pcrelOffset(uint8_t type) {
70   switch (type) {
71   case X86_64_RELOC_SIGNED_1:
72     return 1;
73   case X86_64_RELOC_SIGNED_2:
74     return 2;
75   case X86_64_RELOC_SIGNED_4:
76     return 4;
77   default:
78     return 0;
79   }
80 }
81 
82 int64_t X86_64::getEmbeddedAddend(MemoryBufferRef mb, uint64_t offset,
83                                   relocation_info rel) const {
84   auto *buf = reinterpret_cast<const uint8_t *>(mb.getBufferStart());
85   const uint8_t *loc = buf + offset + rel.r_address;
86 
87   switch (rel.r_length) {
88   case 2:
89     return static_cast<int32_t>(read32le(loc)) + pcrelOffset(rel.r_type);
90   case 3:
91     return read64le(loc) + pcrelOffset(rel.r_type);
92   default:
93     llvm_unreachable("invalid r_length");
94   }
95 }
96 
97 void X86_64::relocateOne(uint8_t *loc, const Reloc &r, uint64_t value,
98                          uint64_t relocVA) const {
99   if (r.pcrel) {
100     uint64_t pc = relocVA + 4 + pcrelOffset(r.type);
101     value -= pc;
102   }
103 
104   switch (r.length) {
105   case 2:
106     if (r.type == X86_64_RELOC_UNSIGNED)
107       checkUInt(loc, r, value, 32);
108     else
109       checkInt(loc, r, value, 32);
110     write32le(loc, value);
111     break;
112   case 3:
113     write64le(loc, value);
114     break;
115   default:
116     llvm_unreachable("invalid r_length");
117   }
118 }
119 
120 // The following methods emit a number of assembly sequences with RIP-relative
121 // addressing. Note that RIP-relative addressing on X86-64 has the RIP pointing
122 // to the next instruction, not the current instruction, so we always have to
123 // account for the current instruction's size when calculating offsets.
124 // writeRipRelative helps with that.
125 //
126 // bufAddr:  The virtual address corresponding to buf[0].
127 // bufOff:   The offset within buf of the next instruction.
128 // destAddr: The destination address that the current instruction references.
129 static void writeRipRelative(SymbolDiagnostic d, uint8_t *buf, uint64_t bufAddr,
130                              uint64_t bufOff, uint64_t destAddr) {
131   uint64_t rip = bufAddr + bufOff;
132   checkInt(buf, d, destAddr - rip, 32);
133   // For the instructions we care about, the RIP-relative address is always
134   // stored in the last 4 bytes of the instruction.
135   write32le(buf + bufOff - 4, destAddr - rip);
136 }
137 
138 static constexpr uint8_t stub[] = {
139     0xff, 0x25, 0, 0, 0, 0, // jmpq *__la_symbol_ptr(%rip)
140 };
141 
142 void X86_64::writeStub(uint8_t *buf, const Symbol &sym,
143                        uint64_t pointerVA) const {
144   memcpy(buf, stub, 2); // just copy the two nonzero bytes
145   uint64_t stubAddr = in.stubs->addr + sym.stubsIndex * sizeof(stub);
146   writeRipRelative({&sym, "stub"}, buf, stubAddr, sizeof(stub), pointerVA);
147 }
148 
149 static constexpr uint8_t stubHelperHeader[] = {
150     0x4c, 0x8d, 0x1d, 0, 0, 0, 0, // 0x0: leaq ImageLoaderCache(%rip), %r11
151     0x41, 0x53,                   // 0x7: pushq %r11
152     0xff, 0x25, 0,    0, 0, 0,    // 0x9: jmpq *dyld_stub_binder@GOT(%rip)
153     0x90,                         // 0xf: nop
154 };
155 
156 void X86_64::writeStubHelperHeader(uint8_t *buf) const {
157   memcpy(buf, stubHelperHeader, sizeof(stubHelperHeader));
158   SymbolDiagnostic d = {nullptr, "stub helper header"};
159   writeRipRelative(d, buf, in.stubHelper->addr, 7,
160                    in.imageLoaderCache->getVA());
161   writeRipRelative(d, buf, in.stubHelper->addr, 0xf,
162                    in.got->addr +
163                        in.stubHelper->stubBinder->gotIndex * LP64::wordSize);
164 }
165 
166 static constexpr uint8_t stubHelperEntry[] = {
167     0x68, 0, 0, 0, 0, // 0x0: pushq <bind offset>
168     0xe9, 0, 0, 0, 0, // 0x5: jmp <__stub_helper>
169 };
170 
171 void X86_64::writeStubHelperEntry(uint8_t *buf, const Symbol &sym,
172                                   uint64_t entryAddr) const {
173   memcpy(buf, stubHelperEntry, sizeof(stubHelperEntry));
174   write32le(buf + 1, sym.lazyBindOffset);
175   writeRipRelative({&sym, "stub helper"}, buf, entryAddr,
176                    sizeof(stubHelperEntry), in.stubHelper->addr);
177 }
178 
179 static constexpr uint8_t objcStubsFastCode[] = {
180     0x48, 0x8b, 0x35, 0, 0, 0, 0, // 0x0: movq selrefs@selector(%rip), %rsi
181     0xff, 0x25, 0,    0, 0, 0,    // 0x7: jmpq *_objc_msgSend@GOT(%rip)
182 };
183 
184 void X86_64::writeObjCMsgSendStub(uint8_t *buf, Symbol *sym, uint64_t stubsAddr,
185                                   uint64_t &stubOffset, uint64_t selrefsVA,
186                                   uint64_t selectorIndex,
187                                   Symbol *objcMsgSend) const {
188   uint64_t objcMsgSendAddr = in.got->addr;
189   uint64_t objcMsgSendIndex = objcMsgSend->gotIndex;
190 
191   memcpy(buf, objcStubsFastCode, sizeof(objcStubsFastCode));
192   SymbolDiagnostic d = {sym, sym->getName()};
193   uint64_t stubAddr = stubsAddr + stubOffset;
194   writeRipRelative(d, buf, stubAddr, 7,
195                    selrefsVA + selectorIndex * LP64::wordSize);
196   writeRipRelative(d, buf, stubAddr, 0xd,
197                    objcMsgSendAddr + objcMsgSendIndex * LP64::wordSize);
198   stubOffset += target->objcStubsFastSize;
199 }
200 
201 void X86_64::relaxGotLoad(uint8_t *loc, uint8_t type) const {
202   // Convert MOVQ to LEAQ
203   if (loc[-2] != 0x8b)
204     error(getRelocAttrs(type).name + " reloc requires MOVQ instruction");
205   loc[-2] = 0x8d;
206 }
207 
208 X86_64::X86_64() : TargetInfo(LP64()) {
209   cpuType = CPU_TYPE_X86_64;
210   cpuSubtype = CPU_SUBTYPE_X86_64_ALL;
211 
212   modeDwarfEncoding = UNWIND_X86_MODE_DWARF;
213   subtractorRelocType = X86_64_RELOC_SUBTRACTOR;
214   unsignedRelocType = X86_64_RELOC_UNSIGNED;
215 
216   stubSize = sizeof(stub);
217   stubHelperHeaderSize = sizeof(stubHelperHeader);
218   stubHelperEntrySize = sizeof(stubHelperEntry);
219 
220   objcStubsFastSize = sizeof(objcStubsFastCode);
221   objcStubsFastAlignment = 1;
222 
223   relocAttrs = {relocAttrsArray.data(), relocAttrsArray.size()};
224 }
225 
226 TargetInfo *macho::createX86_64TargetInfo() {
227   static X86_64 t;
228   return &t;
229 }
230 
231 void X86_64::handleDtraceReloc(const Symbol *sym, const Reloc &r,
232                                uint8_t *loc) const {
233   assert(r.type == X86_64_RELOC_BRANCH);
234 
235   if (config->outputType == MH_OBJECT)
236     return;
237 
238   if (sym->getName().starts_with("___dtrace_probe")) {
239     // change call site to a NOP
240     loc[-1] = 0x90;
241     write32le(loc, 0x00401F0F);
242   } else if (sym->getName().starts_with("___dtrace_isenabled")) {
243     // change call site to a clear eax
244     loc[-1] = 0x33;
245     write32le(loc, 0x909090C0);
246   } else {
247     error("Unrecognized dtrace symbol prefix: " + toString(*sym));
248   }
249 }
250