1 //===- yaml2elf - Convert YAML to a ELF object file -----------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
11 /// \brief The ELF component of yaml2obj.
13 //===----------------------------------------------------------------------===//
16 #include "llvm/Object/ELF.h"
17 #include "llvm/Object/ELFYAML.h"
18 #include "llvm/Support/ELF.h"
19 #include "llvm/Support/MemoryBuffer.h"
20 #include "llvm/Support/YAMLTraits.h"
21 #include "llvm/Support/raw_ostream.h"
25 // There is similar code in yaml2coff, but with some slight COFF-specific
26 // variations like different initial state. Might be able to deduplicate
27 // some day, but also want to make sure that the Mach-O use case is served.
29 // This class has a deliberately small interface, since a lot of
30 // implementation variation is possible.
32 // TODO: Use an ordered container with a suffix-based comparison in order
33 // to deduplicate suffixes. std::map<> with a custom comparator is likely
34 // to be the simplest implementation, but a suffix trie could be more
35 // suitable for the job.
37 class StringTableBuilder {
38 /// \brief Indices of strings currently present in `Buf`.
39 StringMap<unsigned> StringIndices;
40 /// \brief The contents of the string table as we build it.
43 StringTableBuilder() {
46 /// \returns Index of string in string table.
47 unsigned addString(StringRef S) {
48 StringMapEntry<unsigned> &Entry = StringIndices.GetOrCreateValue(S);
49 unsigned &I = Entry.getValue();
53 Buf.append(S.begin(), S.end());
60 void writeToStream(raw_ostream &OS) {
61 OS.write(Buf.data(), Buf.size());
64 } // end anonymous namespace
66 // This class is used to build up a contiguous binary blob while keeping
67 // track of an offset in the output (which notionally begins at
70 class ContiguousBlobAccumulator {
71 const uint64_t InitialOffset;
72 raw_svector_ostream OS;
75 ContiguousBlobAccumulator(uint64_t InitialOffset_, SmallVectorImpl<char> &Buf)
76 : InitialOffset(InitialOffset_), OS(Buf) {}
77 raw_ostream &getOS() { return OS; }
78 uint64_t currentOffset() const { return InitialOffset + OS.tell(); }
79 void writeBlobToStream(raw_ostream &Out) { Out << OS.str(); }
81 } // end anonymous namespace
83 // Used to keep track of section names, so that in the YAML file sections
84 // can be referenced by name instead of by index.
86 class SectionNameToIdxMap {
89 /// \returns true if name is already present in the map.
90 bool addName(StringRef SecName, unsigned i) {
91 StringMapEntry<int> &Entry = Map.GetOrCreateValue(SecName, -1);
92 if (Entry.getValue() != -1)
94 Entry.setValue((int)i);
97 /// \returns true if name is not present in the map
98 bool lookupSection(StringRef SecName, unsigned &Idx) const {
99 StringMap<int>::const_iterator I = Map.find(SecName);
106 } // end anonymous namespace
109 static size_t vectorDataSize(const std::vector<T> &Vec) {
110 return Vec.size() * sizeof(T);
114 static void writeVectorData(raw_ostream &OS, const std::vector<T> &Vec) {
115 OS.write((const char *)Vec.data(), vectorDataSize(Vec));
119 static void zero(T &Obj) {
120 memset(&Obj, 0, sizeof(Obj));
123 /// \brief Create a string table in `SHeader`, which we assume is already
125 template <class Elf_Shdr>
126 static void createStringTableSectionHeader(Elf_Shdr &SHeader,
127 StringTableBuilder &STB,
128 ContiguousBlobAccumulator &CBA) {
129 SHeader.sh_type = ELF::SHT_STRTAB;
130 SHeader.sh_offset = CBA.currentOffset();
131 SHeader.sh_size = STB.size();
132 STB.writeToStream(CBA.getOS());
133 SHeader.sh_addralign = 1;
136 template <class ELFT>
137 static int writeELF(raw_ostream &OS, const ELFYAML::Object &Doc) {
138 using namespace llvm::ELF;
139 using namespace llvm::object;
140 typedef typename ELFObjectFile<ELFT>::Elf_Ehdr Elf_Ehdr;
141 typedef typename ELFObjectFile<ELFT>::Elf_Shdr Elf_Shdr;
143 const ELFYAML::FileHeader &Hdr = Doc.Header;
147 Header.e_ident[EI_MAG0] = 0x7f;
148 Header.e_ident[EI_MAG1] = 'E';
149 Header.e_ident[EI_MAG2] = 'L';
150 Header.e_ident[EI_MAG3] = 'F';
151 Header.e_ident[EI_CLASS] = ELFT::Is64Bits ? ELFCLASS64 : ELFCLASS32;
152 bool IsLittleEndian = ELFT::TargetEndianness == support::little;
153 Header.e_ident[EI_DATA] = IsLittleEndian ? ELFDATA2LSB : ELFDATA2MSB;
154 Header.e_ident[EI_VERSION] = EV_CURRENT;
155 // TODO: Implement ELF_ELFOSABI enum.
156 Header.e_ident[EI_OSABI] = ELFOSABI_NONE;
157 // TODO: Implement ELF_ABIVERSION enum.
158 Header.e_ident[EI_ABIVERSION] = 0;
159 Header.e_type = Hdr.Type;
160 Header.e_machine = Hdr.Machine;
161 Header.e_version = EV_CURRENT;
162 Header.e_entry = Hdr.Entry;
163 Header.e_ehsize = sizeof(Elf_Ehdr);
165 // TODO: Flesh out section header support.
166 // TODO: Program headers.
168 Header.e_shentsize = sizeof(Elf_Shdr);
169 // Immediately following the ELF header.
170 Header.e_shoff = sizeof(Header);
171 std::vector<ELFYAML::Section> Sections = Doc.Sections;
172 if (Sections.empty() || Sections.front().Type != SHT_NULL) {
177 zero(S.AddressAlign);
178 Sections.insert(Sections.begin(), S);
180 // "+ 1" for string table.
181 Header.e_shnum = Sections.size() + 1;
182 // Place section header string table last.
183 Header.e_shstrndx = Sections.size();
185 SectionNameToIdxMap SN2I;
186 for (unsigned i = 0, e = Sections.size(); i != e; ++i) {
187 StringRef Name = Sections[i].Name;
190 if (SN2I.addName(Name, i)) {
191 errs() << "error: Repeated section name: '" << Name
192 << "' at YAML section number " << i << ".\n";
197 StringTableBuilder SHStrTab;
198 SmallVector<char, 128> Buf;
199 // XXX: This offset is tightly coupled with the order that we write
201 const size_t SectionContentBeginOffset =
202 Header.e_ehsize + Header.e_shentsize * Header.e_shnum;
203 ContiguousBlobAccumulator CBA(SectionContentBeginOffset, Buf);
204 std::vector<Elf_Shdr> SHeaders;
205 for (unsigned i = 0, e = Sections.size(); i != e; ++i) {
206 const ELFYAML::Section &Sec = Sections[i];
209 SHeader.sh_name = SHStrTab.addString(Sec.Name);
210 SHeader.sh_type = Sec.Type;
211 SHeader.sh_flags = Sec.Flags;
212 SHeader.sh_addr = Sec.Address;
214 SHeader.sh_offset = CBA.currentOffset();
215 SHeader.sh_size = Sec.Content.binary_size();
216 Sec.Content.writeAsBinary(CBA.getOS());
218 if (!Sec.Link.empty()) {
220 if (SN2I.lookupSection(Sec.Link, Index)) {
221 errs() << "error: Unknown section referenced: '" << Sec.Link
222 << "' at YAML section number " << i << ".\n";
225 SHeader.sh_link = Index;
228 SHeader.sh_addralign = Sec.AddressAlign;
229 SHeader.sh_entsize = 0;
230 SHeaders.push_back(SHeader);
233 // Section header string table header.
234 Elf_Shdr SHStrTabSHeader;
235 zero(SHStrTabSHeader);
236 createStringTableSectionHeader(SHStrTabSHeader, SHStrTab, CBA);
238 OS.write((const char *)&Header, sizeof(Header));
239 writeVectorData(OS, SHeaders);
240 OS.write((const char *)&SHStrTabSHeader, sizeof(SHStrTabSHeader));
241 CBA.writeBlobToStream(OS);
245 int yaml2elf(llvm::raw_ostream &Out, llvm::MemoryBuffer *Buf) {
246 yaml::Input YIn(Buf->getBuffer());
250 errs() << "yaml2obj: Failed to parse YAML file!\n";
253 if (Doc.Header.Class == ELFYAML::ELF_ELFCLASS(ELF::ELFCLASS64)) {
254 if (Doc.Header.Data == ELFYAML::ELF_ELFDATA(ELF::ELFDATA2LSB))
255 return writeELF<object::ELFType<support::little, 8, true> >(outs(), Doc);
257 return writeELF<object::ELFType<support::big, 8, true> >(outs(), Doc);
259 if (Doc.Header.Data == ELFYAML::ELF_ELFDATA(ELF::ELFDATA2LSB))
260 return writeELF<object::ELFType<support::little, 4, false> >(outs(), Doc);
262 return writeELF<object::ELFType<support::big, 4, false> >(outs(), Doc);