Bug Summary

File:lib/Target/AArch64/MCTargetDesc/AArch64MachObjectWriter.cpp
Location:line 177, column 7
Description:Value stored to 'IsExtern' is never read

Annotated Source Code

1//===-- AArch64MachObjectWriter.cpp - ARM Mach Object Writer --------------===//
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 "MCTargetDesc/AArch64FixupKinds.h"
11#include "MCTargetDesc/AArch64MCTargetDesc.h"
12#include "llvm/ADT/Twine.h"
13#include "llvm/MC/MCAsmLayout.h"
14#include "llvm/MC/MCAssembler.h"
15#include "llvm/MC/MCContext.h"
16#include "llvm/MC/MCExpr.h"
17#include "llvm/MC/MCFixup.h"
18#include "llvm/MC/MCMachObjectWriter.h"
19#include "llvm/MC/MCSectionMachO.h"
20#include "llvm/MC/MCValue.h"
21#include "llvm/Support/ErrorHandling.h"
22#include "llvm/Support/MachO.h"
23using namespace llvm;
24
25namespace {
26class AArch64MachObjectWriter : public MCMachObjectTargetWriter {
27 bool getAArch64FixupKindMachOInfo(const MCFixup &Fixup, unsigned &RelocType,
28 const MCSymbolRefExpr *Sym,
29 unsigned &Log2Size, const MCAssembler &Asm);
30
31public:
32 AArch64MachObjectWriter(uint32_t CPUType, uint32_t CPUSubtype)
33 : MCMachObjectTargetWriter(true /* is64Bit */, CPUType, CPUSubtype,
34 /*UseAggressiveSymbolFolding=*/true) {}
35
36 void RecordRelocation(MachObjectWriter *Writer, const MCAssembler &Asm,
37 const MCAsmLayout &Layout, const MCFragment *Fragment,
38 const MCFixup &Fixup, MCValue Target,
39 uint64_t &FixedValue) override;
40};
41}
42
43bool AArch64MachObjectWriter::getAArch64FixupKindMachOInfo(
44 const MCFixup &Fixup, unsigned &RelocType, const MCSymbolRefExpr *Sym,
45 unsigned &Log2Size, const MCAssembler &Asm) {
46 RelocType = unsigned(MachO::ARM64_RELOC_UNSIGNED);
47 Log2Size = ~0U;
48
49 switch ((unsigned)Fixup.getKind()) {
50 default:
51 return false;
52
53 case FK_Data_1:
54 Log2Size = llvm::Log2_32(1);
55 return true;
56 case FK_Data_2:
57 Log2Size = llvm::Log2_32(2);
58 return true;
59 case FK_Data_4:
60 Log2Size = llvm::Log2_32(4);
61 if (Sym->getKind() == MCSymbolRefExpr::VK_GOT)
62 RelocType = unsigned(MachO::ARM64_RELOC_POINTER_TO_GOT);
63 return true;
64 case FK_Data_8:
65 Log2Size = llvm::Log2_32(8);
66 if (Sym->getKind() == MCSymbolRefExpr::VK_GOT)
67 RelocType = unsigned(MachO::ARM64_RELOC_POINTER_TO_GOT);
68 return true;
69 case AArch64::fixup_aarch64_add_imm12:
70 case AArch64::fixup_aarch64_ldst_imm12_scale1:
71 case AArch64::fixup_aarch64_ldst_imm12_scale2:
72 case AArch64::fixup_aarch64_ldst_imm12_scale4:
73 case AArch64::fixup_aarch64_ldst_imm12_scale8:
74 case AArch64::fixup_aarch64_ldst_imm12_scale16:
75 Log2Size = llvm::Log2_32(4);
76 switch (Sym->getKind()) {
77 default:
78 llvm_unreachable("Unexpected symbol reference variant kind!")::llvm::llvm_unreachable_internal("Unexpected symbol reference variant kind!"
, "/tmp/buildd/llvm-toolchain-snapshot-3.7~svn226502/lib/Target/AArch64/MCTargetDesc/AArch64MachObjectWriter.cpp"
, 78);
79 case MCSymbolRefExpr::VK_PAGEOFF:
80 RelocType = unsigned(MachO::ARM64_RELOC_PAGEOFF12);
81 return true;
82 case MCSymbolRefExpr::VK_GOTPAGEOFF:
83 RelocType = unsigned(MachO::ARM64_RELOC_GOT_LOAD_PAGEOFF12);
84 return true;
85 case MCSymbolRefExpr::VK_TLVPPAGEOFF:
86 RelocType = unsigned(MachO::ARM64_RELOC_TLVP_LOAD_PAGEOFF12);
87 return true;
88 }
89 case AArch64::fixup_aarch64_pcrel_adrp_imm21:
90 Log2Size = llvm::Log2_32(4);
91 // This encompasses the relocation for the whole 21-bit value.
92 switch (Sym->getKind()) {
93 default:
94 Asm.getContext().FatalError(Fixup.getLoc(),
95 "ADR/ADRP relocations must be GOT relative");
96 case MCSymbolRefExpr::VK_PAGE:
97 RelocType = unsigned(MachO::ARM64_RELOC_PAGE21);
98 return true;
99 case MCSymbolRefExpr::VK_GOTPAGE:
100 RelocType = unsigned(MachO::ARM64_RELOC_GOT_LOAD_PAGE21);
101 return true;
102 case MCSymbolRefExpr::VK_TLVPPAGE:
103 RelocType = unsigned(MachO::ARM64_RELOC_TLVP_LOAD_PAGE21);
104 return true;
105 }
106 return true;
107 case AArch64::fixup_aarch64_pcrel_branch26:
108 case AArch64::fixup_aarch64_pcrel_call26:
109 Log2Size = llvm::Log2_32(4);
110 RelocType = unsigned(MachO::ARM64_RELOC_BRANCH26);
111 return true;
112 }
113}
114
115void AArch64MachObjectWriter::RecordRelocation(
116 MachObjectWriter *Writer, const MCAssembler &Asm, const MCAsmLayout &Layout,
117 const MCFragment *Fragment, const MCFixup &Fixup, MCValue Target,
118 uint64_t &FixedValue) {
119 unsigned IsPCRel = Writer->isFixupKindPCRel(Asm, Fixup.getKind());
120
121 // See <reloc.h>.
122 uint32_t FixupOffset = Layout.getFragmentOffset(Fragment);
123 unsigned Log2Size = 0;
124 int64_t Value = 0;
125 unsigned Index = 0;
126 unsigned IsExtern = 0;
127 unsigned Type = 0;
128 unsigned Kind = Fixup.getKind();
129
130 FixupOffset += Fixup.getOffset();
131
132 // AArch64 pcrel relocation addends do not include the section offset.
133 if (IsPCRel)
134 FixedValue += FixupOffset;
135
136 // ADRP fixups use relocations for the whole symbol value and only
137 // put the addend in the instruction itself. Clear out any value the
138 // generic code figured out from the sybmol definition.
139 if (Kind == AArch64::fixup_aarch64_pcrel_adrp_imm21)
140 FixedValue = 0;
141
142 // imm19 relocations are for conditional branches, which require
143 // assembler local symbols. If we got here, that's not what we have,
144 // so complain loudly.
145 if (Kind == AArch64::fixup_aarch64_pcrel_branch19) {
146 Asm.getContext().FatalError(Fixup.getLoc(),
147 "conditional branch requires assembler-local"
148 " label. '" +
149 Target.getSymA()->getSymbol().getName() +
150 "' is external.");
151 return;
152 }
153
154 // 14-bit branch relocations should only target internal labels, and so
155 // should never get here.
156 if (Kind == AArch64::fixup_aarch64_pcrel_branch14) {
157 Asm.getContext().FatalError(Fixup.getLoc(),
158 "Invalid relocation on conditional branch!");
159 return;
160 }
161
162 if (!getAArch64FixupKindMachOInfo(Fixup, Type, Target.getSymA(), Log2Size,
163 Asm)) {
164 Asm.getContext().FatalError(Fixup.getLoc(), "unknown AArch64 fixup kind!");
165 return;
166 }
167
168 Value = Target.getConstant();
169
170 if (Target.isAbsolute()) { // constant
171 // FIXME: Should this always be extern?
172 // SymbolNum of 0 indicates the absolute section.
173 Type = MachO::ARM64_RELOC_UNSIGNED;
174 Index = 0;
175
176 if (IsPCRel) {
177 IsExtern = 1;
Value stored to 'IsExtern' is never read
178 Asm.getContext().FatalError(Fixup.getLoc(),
179 "PC relative absolute relocation!");
180
181 // FIXME: x86_64 sets the type to a branch reloc here. Should we do
182 // something similar?
183 }
184 } else if (Target.getSymB()) { // A - B + constant
185 const MCSymbol *A = &Target.getSymA()->getSymbol();
186 const MCSymbolData &A_SD = Asm.getSymbolData(*A);
187 const MCSymbolData *A_Base = Asm.getAtom(&A_SD);
188
189 const MCSymbol *B = &Target.getSymB()->getSymbol();
190 const MCSymbolData &B_SD = Asm.getSymbolData(*B);
191 const MCSymbolData *B_Base = Asm.getAtom(&B_SD);
192
193 // Check for "_foo@got - .", which comes through here as:
194 // Ltmp0:
195 // ... _foo@got - Ltmp0
196 if (Target.getSymA()->getKind() == MCSymbolRefExpr::VK_GOT &&
197 Target.getSymB()->getKind() == MCSymbolRefExpr::VK_None &&
198 Layout.getSymbolOffset(&B_SD) ==
199 Layout.getFragmentOffset(Fragment) + Fixup.getOffset()) {
200 // SymB is the PC, so use a PC-rel pointer-to-GOT relocation.
201 Index = A_Base->getIndex();
202 IsExtern = 1;
203 Type = MachO::ARM64_RELOC_POINTER_TO_GOT;
204 IsPCRel = 1;
205 MachO::any_relocation_info MRE;
206 MRE.r_word0 = FixupOffset;
207 MRE.r_word1 = ((Index << 0) | (IsPCRel << 24) | (Log2Size << 25) |
208 (IsExtern << 27) | (Type << 28));
209 Writer->addRelocation(Fragment->getParent(), MRE);
210 return;
211 } else if (Target.getSymA()->getKind() != MCSymbolRefExpr::VK_None ||
212 Target.getSymB()->getKind() != MCSymbolRefExpr::VK_None)
213 // Otherwise, neither symbol can be modified.
214 Asm.getContext().FatalError(Fixup.getLoc(),
215 "unsupported relocation of modified symbol");
216
217 // We don't support PCrel relocations of differences.
218 if (IsPCRel)
219 Asm.getContext().FatalError(Fixup.getLoc(),
220 "unsupported pc-relative relocation of "
221 "difference");
222
223 // AArch64 always uses external relocations. If there is no symbol to use as
224 // a base address (a local symbol with no preceding non-local symbol),
225 // error out.
226 //
227 // FIXME: We should probably just synthesize an external symbol and use
228 // that.
229 if (!A_Base)
230 Asm.getContext().FatalError(
231 Fixup.getLoc(),
232 "unsupported relocation of local symbol '" + A->getName() +
233 "'. Must have non-local symbol earlier in section.");
234 if (!B_Base)
235 Asm.getContext().FatalError(
236 Fixup.getLoc(),
237 "unsupported relocation of local symbol '" + B->getName() +
238 "'. Must have non-local symbol earlier in section.");
239
240 if (A_Base == B_Base && A_Base)
241 Asm.getContext().FatalError(Fixup.getLoc(),
242 "unsupported relocation with identical base");
243
244 Value += (!A_SD.getFragment() ? 0
245 : Writer->getSymbolAddress(&A_SD, Layout)) -
246 (!A_Base || !A_Base->getFragment()
247 ? 0
248 : Writer->getSymbolAddress(A_Base, Layout));
249 Value -= (!B_SD.getFragment() ? 0
250 : Writer->getSymbolAddress(&B_SD, Layout)) -
251 (!B_Base || !B_Base->getFragment()
252 ? 0
253 : Writer->getSymbolAddress(B_Base, Layout));
254
255 Index = A_Base->getIndex();
256 IsExtern = 1;
257 Type = MachO::ARM64_RELOC_UNSIGNED;
258
259 MachO::any_relocation_info MRE;
260 MRE.r_word0 = FixupOffset;
261 MRE.r_word1 = ((Index << 0) | (IsPCRel << 24) | (Log2Size << 25) |
262 (IsExtern << 27) | (Type << 28));
263 Writer->addRelocation(Fragment->getParent(), MRE);
264
265 Index = B_Base->getIndex();
266 IsExtern = 1;
267 Type = MachO::ARM64_RELOC_SUBTRACTOR;
268 } else { // A + constant
269 const MCSymbol *Symbol = &Target.getSymA()->getSymbol();
270 const MCSymbolData &SD = Asm.getSymbolData(*Symbol);
271 const MCSymbolData *Base = Asm.getAtom(&SD);
272 const MCSectionMachO &Section = static_cast<const MCSectionMachO &>(
273 Fragment->getParent()->getSection());
274
275 // If the symbol is a variable and we weren't able to get a Base for it
276 // (i.e., it's not in the symbol table associated with a section) resolve
277 // the relocation based its expansion instead.
278 if (Symbol->isVariable() && !Base) {
279 // If the evaluation is an absolute value, just use that directly
280 // to keep things easy.
281 int64_t Res;
282 if (SD.getSymbol().getVariableValue()->EvaluateAsAbsolute(
283 Res, Layout, Writer->getSectionAddressMap())) {
284 FixedValue = Res;
285 return;
286 }
287
288 // FIXME: Will the Target we already have ever have any data in it
289 // we need to preserve and merge with the new Target? How about
290 // the FixedValue?
291 if (!Symbol->getVariableValue()->EvaluateAsRelocatable(Target, &Layout,
292 &Fixup))
293 Asm.getContext().FatalError(Fixup.getLoc(),
294 "unable to resolve variable '" +
295 Symbol->getName() + "'");
296 return RecordRelocation(Writer, Asm, Layout, Fragment, Fixup, Target,
297 FixedValue);
298 }
299
300 // Relocations inside debug sections always use local relocations when
301 // possible. This seems to be done because the debugger doesn't fully
302 // understand relocation entries and expects to find values that
303 // have already been fixed up.
304 if (Symbol->isInSection()) {
305 if (Section.hasAttribute(MachO::S_ATTR_DEBUG))
306 Base = nullptr;
307 }
308
309 // AArch64 uses external relocations as much as possible. For debug
310 // sections, and for pointer-sized relocations (.quad), we allow section
311 // relocations. It's code sections that run into trouble.
312 if (Base) {
313 Index = Base->getIndex();
314 IsExtern = 1;
315
316 // Add the local offset, if needed.
317 if (Base != &SD)
318 Value += Layout.getSymbolOffset(&SD) - Layout.getSymbolOffset(Base);
319 } else if (Symbol->isInSection()) {
320 // Pointer-sized relocations can use a local relocation. Otherwise,
321 // we have to be in a debug info section.
322 if (!Section.hasAttribute(MachO::S_ATTR_DEBUG) && Log2Size != 3)
323 Asm.getContext().FatalError(
324 Fixup.getLoc(),
325 "unsupported relocation of local symbol '" + Symbol->getName() +
326 "'. Must have non-local symbol earlier in section.");
327 // Adjust the relocation to be section-relative.
328 // The index is the section ordinal (1-based).
329 const MCSectionData &SymSD =
330 Asm.getSectionData(SD.getSymbol().getSection());
331 Index = SymSD.getOrdinal() + 1;
332 IsExtern = 0;
333 Value += Writer->getSymbolAddress(&SD, Layout);
334
335 if (IsPCRel)
336 Value -= Writer->getFragmentAddress(Fragment, Layout) +
337 Fixup.getOffset() + (1ULL << Log2Size);
338 } else {
339 // Resolve constant variables.
340 if (SD.getSymbol().isVariable()) {
341 int64_t Res;
342 if (SD.getSymbol().getVariableValue()->EvaluateAsAbsolute(
343 Res, Layout, Writer->getSectionAddressMap())) {
344 FixedValue = Res;
345 return;
346 }
347 }
348 Asm.getContext().FatalError(Fixup.getLoc(),
349 "unsupported relocation of variable '" +
350 Symbol->getName() + "'");
351 }
352 }
353
354 // If the relocation kind is Branch26, Page21, or Pageoff12, any addend
355 // is represented via an Addend relocation, not encoded directly into
356 // the instruction.
357 if ((Type == MachO::ARM64_RELOC_BRANCH26 ||
358 Type == MachO::ARM64_RELOC_PAGE21 ||
359 Type == MachO::ARM64_RELOC_PAGEOFF12) &&
360 Value) {
361 assert((Value & 0xff000000) == 0 && "Added relocation out of range!")(((Value & 0xff000000) == 0 && "Added relocation out of range!"
) ? static_cast<void> (0) : __assert_fail ("(Value & 0xff000000) == 0 && \"Added relocation out of range!\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.7~svn226502/lib/Target/AArch64/MCTargetDesc/AArch64MachObjectWriter.cpp"
, 361, __PRETTY_FUNCTION__));
362
363 MachO::any_relocation_info MRE;
364 MRE.r_word0 = FixupOffset;
365 MRE.r_word1 = ((Index << 0) | (IsPCRel << 24) | (Log2Size << 25) |
366 (IsExtern << 27) | (Type << 28));
367 Writer->addRelocation(Fragment->getParent(), MRE);
368
369 // Now set up the Addend relocation.
370 Type = MachO::ARM64_RELOC_ADDEND;
371 Index = Value;
372 IsPCRel = 0;
373 Log2Size = 2;
374 IsExtern = 0;
375
376 // Put zero into the instruction itself. The addend is in the relocation.
377 Value = 0;
378 }
379
380 // If there's any addend left to handle, encode it in the instruction.
381 FixedValue = Value;
382
383 // struct relocation_info (8 bytes)
384 MachO::any_relocation_info MRE;
385 MRE.r_word0 = FixupOffset;
386 MRE.r_word1 = ((Index << 0) | (IsPCRel << 24) | (Log2Size << 25) |
387 (IsExtern << 27) | (Type << 28));
388 Writer->addRelocation(Fragment->getParent(), MRE);
389}
390
391MCObjectWriter *llvm::createAArch64MachObjectWriter(raw_ostream &OS,
392 uint32_t CPUType,
393 uint32_t CPUSubtype) {
394 return createMachObjectWriter(
395 new AArch64MachObjectWriter(CPUType, CPUSubtype), OS,
396 /*IsLittleEndian=*/true);
397}