1 //===-- ELFDump.cpp - ELF-specific dumper -----------------------*- C++ -*-===//
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 /// \file
10 /// This file implements the ELF-specific dumper for llvm-objdump.
11 ///
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm-objdump.h"
15 #include "llvm/Demangle/Demangle.h"
16 #include "llvm/Object/ELFObjectFile.h"
17 #include "llvm/Support/Format.h"
18 #include "llvm/Support/MathExtras.h"
19 #include "llvm/Support/raw_ostream.h"
20 
21 using namespace llvm;
22 using namespace llvm::object;
23 
24 template <class ELFT>
25 Expected<StringRef> getDynamicStrTab(const ELFFile<ELFT> *Elf) {
26   typedef ELFFile<ELFT> ELFO;
27 
28   auto DynamicEntriesOrError = Elf->dynamicEntries();
29   if (!DynamicEntriesOrError)
30     return DynamicEntriesOrError.takeError();
31 
32   for (const typename ELFO::Elf_Dyn &Dyn : *DynamicEntriesOrError) {
33     if (Dyn.d_tag == ELF::DT_STRTAB) {
34       auto MappedAddrOrError = Elf->toMappedAddr(Dyn.getPtr());
35       if (!MappedAddrOrError)
36         consumeError(MappedAddrOrError.takeError());
37       return StringRef(reinterpret_cast<const char *>(*MappedAddrOrError));
38     }
39   }
40 
41   // If the dynamic segment is not present, we fall back on the sections.
42   auto SectionsOrError = Elf->sections();
43   if (!SectionsOrError)
44     return SectionsOrError.takeError();
45 
46   for (const typename ELFO::Elf_Shdr &Sec : *SectionsOrError) {
47     if (Sec.sh_type == ELF::SHT_DYNSYM)
48       return Elf->getStringTableForSymtab(Sec);
49   }
50 
51   return createError("dynamic string table not found");
52 }
53 
54 template <class ELFT>
55 static std::error_code getRelocationValueString(const ELFObjectFile<ELFT> *Obj,
56                                                 const RelocationRef &RelRef,
57                                                 SmallVectorImpl<char> &Result) {
58   typedef typename ELFObjectFile<ELFT>::Elf_Sym Elf_Sym;
59   typedef typename ELFObjectFile<ELFT>::Elf_Shdr Elf_Shdr;
60   typedef typename ELFObjectFile<ELFT>::Elf_Rela Elf_Rela;
61 
62   const ELFFile<ELFT> &EF = *Obj->getELFFile();
63   DataRefImpl Rel = RelRef.getRawDataRefImpl();
64   auto SecOrErr = EF.getSection(Rel.d.a);
65   if (!SecOrErr)
66     return errorToErrorCode(SecOrErr.takeError());
67 
68   int64_t Addend = 0;
69   // If there is no Symbol associated with the relocation, we set the undef
70   // boolean value to 'true'. This will prevent us from calling functions that
71   // requires the relocation to be associated with a symbol.
72   //
73   // In SHT_REL case we would need to read the addend from section data.
74   // GNU objdump does not do that and we just follow for simplicity atm.
75   bool Undef = false;
76   if ((*SecOrErr)->sh_type == ELF::SHT_RELA) {
77     const Elf_Rela *ERela = Obj->getRela(Rel);
78     Addend = ERela->r_addend;
79     Undef = ERela->getSymbol(false) == 0;
80   } else if ((*SecOrErr)->sh_type != ELF::SHT_REL) {
81     return object_error::parse_failed;
82   }
83 
84   // Default scheme is to print Target, as well as "+ <addend>" for nonzero
85   // addend. Should be acceptable for all normal purposes.
86   std::string FmtBuf;
87   raw_string_ostream Fmt(FmtBuf);
88 
89   if (!Undef) {
90     symbol_iterator SI = RelRef.getSymbol();
91     const Elf_Sym *Sym = Obj->getSymbol(SI->getRawDataRefImpl());
92     if (Sym->getType() == ELF::STT_SECTION) {
93       Expected<section_iterator> SymSI = SI->getSection();
94       if (!SymSI)
95         return errorToErrorCode(SymSI.takeError());
96       const Elf_Shdr *SymSec = Obj->getSection((*SymSI)->getRawDataRefImpl());
97       auto SecName = EF.getSectionName(SymSec);
98       if (!SecName)
99         return errorToErrorCode(SecName.takeError());
100       Fmt << *SecName;
101     } else {
102       Expected<StringRef> SymName = SI->getName();
103       if (!SymName)
104         return errorToErrorCode(SymName.takeError());
105       if (Demangle)
106         Fmt << demangle(*SymName);
107       else
108         Fmt << *SymName;
109     }
110   } else {
111     Fmt << "*ABS*";
112   }
113 
114   if (Addend != 0)
115     Fmt << (Addend < 0 ? "" : "+") << Addend;
116   Fmt.flush();
117   Result.append(FmtBuf.begin(), FmtBuf.end());
118   return std::error_code();
119 }
120 
121 std::error_code
122 llvm::getELFRelocationValueString(const ELFObjectFileBase *Obj,
123                                   const RelocationRef &Rel,
124                                   SmallVectorImpl<char> &Result) {
125   if (auto *ELF32LE = dyn_cast<ELF32LEObjectFile>(Obj))
126     return getRelocationValueString(ELF32LE, Rel, Result);
127   if (auto *ELF64LE = dyn_cast<ELF64LEObjectFile>(Obj))
128     return getRelocationValueString(ELF64LE, Rel, Result);
129   if (auto *ELF32BE = dyn_cast<ELF32BEObjectFile>(Obj))
130     return getRelocationValueString(ELF32BE, Rel, Result);
131   auto *ELF64BE = cast<ELF64BEObjectFile>(Obj);
132   return getRelocationValueString(ELF64BE, Rel, Result);
133 }
134 
135 template <class ELFT>
136 static uint64_t getSectionLMA(const ELFFile<ELFT> *Obj,
137                               const object::ELFSectionRef &Sec) {
138   auto PhdrRangeOrErr = Obj->program_headers();
139   if (!PhdrRangeOrErr)
140     report_fatal_error(errorToErrorCode(PhdrRangeOrErr.takeError()).message());
141 
142   // Search for a PT_LOAD segment containing the requested section. Use this
143   // segment's p_addr to calculate the section's LMA.
144   for (const typename ELFFile<ELFT>::Elf_Phdr &Phdr : *PhdrRangeOrErr)
145     if ((Phdr.p_type == ELF::PT_LOAD) && (Phdr.p_vaddr <= Sec.getAddress()) &&
146         (Phdr.p_vaddr + Phdr.p_memsz > Sec.getAddress()))
147       return Sec.getAddress() - Phdr.p_vaddr + Phdr.p_paddr;
148 
149   // Return section's VMA if it isn't in a PT_LOAD segment.
150   return Sec.getAddress();
151 }
152 
153 uint64_t llvm::getELFSectionLMA(const object::ELFSectionRef &Sec) {
154   if (const auto *ELFObj = dyn_cast<ELF32LEObjectFile>(Sec.getObject()))
155     return getSectionLMA(ELFObj->getELFFile(), Sec);
156   else if (const auto *ELFObj = dyn_cast<ELF32BEObjectFile>(Sec.getObject()))
157     return getSectionLMA(ELFObj->getELFFile(), Sec);
158   else if (const auto *ELFObj = dyn_cast<ELF64LEObjectFile>(Sec.getObject()))
159     return getSectionLMA(ELFObj->getELFFile(), Sec);
160   const auto *ELFObj = cast<ELF64BEObjectFile>(Sec.getObject());
161   return getSectionLMA(ELFObj->getELFFile(), Sec);
162 }
163 
164 template <class ELFT>
165 void printDynamicSection(const ELFFile<ELFT> *Elf, StringRef Filename) {
166   auto ProgramHeaderOrError = Elf->program_headers();
167   if (!ProgramHeaderOrError)
168     report_error(Filename, ProgramHeaderOrError.takeError());
169 
170   auto DynamicEntriesOrError = Elf->dynamicEntries();
171   if (!DynamicEntriesOrError)
172     report_error(Filename, DynamicEntriesOrError.takeError());
173 
174   outs() << "Dynamic Section:\n";
175   for (const auto &Dyn : *DynamicEntriesOrError) {
176     if (Dyn.d_tag == ELF::DT_NULL)
177       continue;
178 
179     StringRef Str = StringRef(Elf->getDynamicTagAsString(Dyn.d_tag));
180 
181     if (Str.empty()) {
182       std::string HexStr = utohexstr(static_cast<uint64_t>(Dyn.d_tag), true);
183       outs() << format("  0x%-19s", HexStr.c_str());
184     } else {
185       // We use "-21" in order to match GNU objdump's output.
186       outs() << format("  %-21s", Str.data());
187     }
188 
189     const char *Fmt =
190         ELFT::Is64Bits ? "0x%016" PRIx64 "\n" : "0x%08" PRIx64 "\n";
191     if (Dyn.d_tag == ELF::DT_NEEDED) {
192       Expected<StringRef> StrTabOrErr = getDynamicStrTab(Elf);
193       if (StrTabOrErr) {
194         const char *Data = StrTabOrErr.get().data();
195         outs() << (Data + Dyn.d_un.d_val) << "\n";
196         continue;
197       }
198       warn(errorToErrorCode(StrTabOrErr.takeError()).message());
199       consumeError(StrTabOrErr.takeError());
200     }
201     outs() << format(Fmt, (uint64_t)Dyn.d_un.d_val);
202   }
203 }
204 
205 template <class ELFT> void printProgramHeaders(const ELFFile<ELFT> *o) {
206   typedef ELFFile<ELFT> ELFO;
207   outs() << "Program Header:\n";
208   auto ProgramHeaderOrError = o->program_headers();
209   if (!ProgramHeaderOrError)
210     report_fatal_error(
211         errorToErrorCode(ProgramHeaderOrError.takeError()).message());
212   for (const typename ELFO::Elf_Phdr &Phdr : *ProgramHeaderOrError) {
213     switch (Phdr.p_type) {
214     case ELF::PT_DYNAMIC:
215       outs() << " DYNAMIC ";
216       break;
217     case ELF::PT_GNU_EH_FRAME:
218       outs() << "EH_FRAME ";
219       break;
220     case ELF::PT_GNU_RELRO:
221       outs() << "   RELRO ";
222       break;
223     case ELF::PT_GNU_STACK:
224       outs() << "   STACK ";
225       break;
226     case ELF::PT_INTERP:
227       outs() << "  INTERP ";
228       break;
229     case ELF::PT_LOAD:
230       outs() << "    LOAD ";
231       break;
232     case ELF::PT_NOTE:
233       outs() << "    NOTE ";
234       break;
235     case ELF::PT_OPENBSD_BOOTDATA:
236       outs() << "    OPENBSD_BOOTDATA ";
237       break;
238     case ELF::PT_OPENBSD_RANDOMIZE:
239       outs() << "    OPENBSD_RANDOMIZE ";
240       break;
241     case ELF::PT_OPENBSD_WXNEEDED:
242       outs() << "    OPENBSD_WXNEEDED ";
243       break;
244     case ELF::PT_PHDR:
245       outs() << "    PHDR ";
246       break;
247     case ELF::PT_TLS:
248       outs() << "    TLS ";
249       break;
250     default:
251       outs() << " UNKNOWN ";
252     }
253 
254     const char *Fmt = ELFT::Is64Bits ? "0x%016" PRIx64 " " : "0x%08" PRIx64 " ";
255 
256     outs() << "off    " << format(Fmt, (uint64_t)Phdr.p_offset) << "vaddr "
257            << format(Fmt, (uint64_t)Phdr.p_vaddr) << "paddr "
258            << format(Fmt, (uint64_t)Phdr.p_paddr)
259            << format("align 2**%u\n",
260                      countTrailingZeros<uint64_t>(Phdr.p_align))
261            << "         filesz " << format(Fmt, (uint64_t)Phdr.p_filesz)
262            << "memsz " << format(Fmt, (uint64_t)Phdr.p_memsz) << "flags "
263            << ((Phdr.p_flags & ELF::PF_R) ? "r" : "-")
264            << ((Phdr.p_flags & ELF::PF_W) ? "w" : "-")
265            << ((Phdr.p_flags & ELF::PF_X) ? "x" : "-") << "\n";
266   }
267   outs() << "\n";
268 }
269 
270 void llvm::printELFFileHeader(const object::ObjectFile *Obj) {
271   if (const auto *ELFObj = dyn_cast<ELF32LEObjectFile>(Obj))
272     printProgramHeaders(ELFObj->getELFFile());
273   else if (const auto *ELFObj = dyn_cast<ELF32BEObjectFile>(Obj))
274     printProgramHeaders(ELFObj->getELFFile());
275   else if (const auto *ELFObj = dyn_cast<ELF64LEObjectFile>(Obj))
276     printProgramHeaders(ELFObj->getELFFile());
277   else if (const auto *ELFObj = dyn_cast<ELF64BEObjectFile>(Obj))
278     printProgramHeaders(ELFObj->getELFFile());
279 }
280 
281 void llvm::printELFDynamicSection(const object::ObjectFile *Obj) {
282   if (const auto *ELFObj = dyn_cast<ELF32LEObjectFile>(Obj))
283     printDynamicSection(ELFObj->getELFFile(), Obj->getFileName());
284   else if (const auto *ELFObj = dyn_cast<ELF32BEObjectFile>(Obj))
285     printDynamicSection(ELFObj->getELFFile(), Obj->getFileName());
286   else if (const auto *ELFObj = dyn_cast<ELF64LEObjectFile>(Obj))
287     printDynamicSection(ELFObj->getELFFile(), Obj->getFileName());
288   else if (const auto *ELFObj = dyn_cast<ELF64BEObjectFile>(Obj))
289     printDynamicSection(ELFObj->getELFFile(), Obj->getFileName());
290 }
291