1 //===- ELFObjectReader.cpp ------------------------------------------------===//
2 //
3 //                     The MCLinker Project
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 #include "mcld/LD/ELFObjectReader.h"
10 
11 #include "mcld/IRBuilder.h"
12 #include "mcld/MC/Input.h"
13 #include "mcld/LD/ELFReader.h"
14 #include "mcld/LD/EhFrameReader.h"
15 #include "mcld/LD/EhFrame.h"
16 #include "mcld/LD/LDContext.h"
17 #include "mcld/Target/GNULDBackend.h"
18 #include "mcld/Support/MsgHandling.h"
19 #include "mcld/Support/MemoryArea.h"
20 #include "mcld/Object/ObjectBuilder.h"
21 
22 #include <llvm/Support/ELF.h>
23 #include <llvm/ADT/Twine.h>
24 #include <llvm/ADT/StringRef.h>
25 
26 #include <string>
27 #include <cassert>
28 
29 namespace mcld {
30 
31 //===----------------------------------------------------------------------===//
32 // ELFObjectReader
33 //===----------------------------------------------------------------------===//
34 /// constructor
ELFObjectReader(GNULDBackend & pBackend,IRBuilder & pBuilder,const LinkerConfig & pConfig)35 ELFObjectReader::ELFObjectReader(GNULDBackend& pBackend,
36                                  IRBuilder& pBuilder,
37                                  const LinkerConfig& pConfig)
38     : ObjectReader(),
39       m_pELFReader(NULL),
40       m_pEhFrameReader(NULL),
41       m_Builder(pBuilder),
42       m_ReadFlag(ParseEhFrame),
43       m_Backend(pBackend),
44       m_Config(pConfig) {
45   if (pConfig.targets().is32Bits() && pConfig.targets().isLittleEndian()) {
46     m_pELFReader = new ELFReader<32, true>(pBackend);
47   } else if (pConfig.targets().is64Bits() &&
48              pConfig.targets().isLittleEndian()) {
49     m_pELFReader = new ELFReader<64, true>(pBackend);
50   }
51 
52   m_pEhFrameReader = new EhFrameReader();
53 }
54 
55 /// destructor
~ELFObjectReader()56 ELFObjectReader::~ELFObjectReader() {
57   delete m_pELFReader;
58   delete m_pEhFrameReader;
59 }
60 
61 /// isMyFormat
isMyFormat(Input & pInput,bool & pContinue) const62 bool ELFObjectReader::isMyFormat(Input& pInput, bool& pContinue) const {
63   assert(pInput.hasMemArea());
64 
65   // Don't warning about the frequently requests.
66   // MemoryArea has a list of cache to handle this.
67   size_t hdr_size = m_pELFReader->getELFHeaderSize();
68   if (pInput.memArea()->size() < hdr_size)
69     return false;
70 
71   llvm::StringRef region =
72       pInput.memArea()->request(pInput.fileOffset(), hdr_size);
73 
74   const char* ELF_hdr = region.begin();
75   bool result = true;
76   if (!m_pELFReader->isELF(ELF_hdr)) {
77     pContinue = true;
78     result = false;
79   } else if (Input::Object != m_pELFReader->fileType(ELF_hdr)) {
80     pContinue = true;
81     result = false;
82   } else if (!m_pELFReader->isMyEndian(ELF_hdr)) {
83     pContinue = false;
84     result = false;
85   } else if (!m_pELFReader->isMyMachine(ELF_hdr)) {
86     pContinue = false;
87     result = false;
88   }
89   return result;
90 }
91 
92 /// readHeader - read section header and create LDSections.
readHeader(Input & pInput)93 bool ELFObjectReader::readHeader(Input& pInput) {
94   assert(pInput.hasMemArea());
95 
96   size_t hdr_size = m_pELFReader->getELFHeaderSize();
97   if (pInput.memArea()->size() < hdr_size)
98     return false;
99 
100   llvm::StringRef region =
101       pInput.memArea()->request(pInput.fileOffset(), hdr_size);
102   const char* ELF_hdr = region.begin();
103   bool result = m_pELFReader->readSectionHeaders(pInput, ELF_hdr);
104   return result;
105 }
106 
107 /// readSections - read all regular sections.
readSections(Input & pInput)108 bool ELFObjectReader::readSections(Input& pInput) {
109   // handle sections
110   LDContext::sect_iterator section, sectEnd = pInput.context()->sectEnd();
111   for (section = pInput.context()->sectBegin(); section != sectEnd; ++section) {
112     // ignore the section if the LDSection* in input context is NULL
113     if (*section == NULL)
114       continue;
115 
116     switch ((*section)->kind()) {
117       /** group sections **/
118       case LDFileFormat::Group: {
119         assert((*section)->getLink() != NULL);
120         ResolveInfo* signature = m_pELFReader->readSignature(
121             pInput, *(*section)->getLink(), (*section)->getInfo());
122 
123         bool exist = false;
124         if (signature->nameSize() == 0 &&
125             ResolveInfo::Section == signature->type()) {
126           // if the signature is a section symbol in input object, we use the
127           // section name as group signature.
128           signatures().insert((*section)->name(), exist);
129         } else {
130           signatures().insert(signature->name(), exist);
131         }
132 
133         if (exist) {
134           // if this is not the first time we see this group signature, then
135           // ignore all the members in this group (set Ignore)
136           llvm::StringRef region = pInput.memArea()->request(
137               pInput.fileOffset() + (*section)->offset(), (*section)->size());
138           const llvm::ELF::Elf32_Word* value =
139               reinterpret_cast<const llvm::ELF::Elf32_Word*>(region.begin());
140 
141           size_t size = region.size() / sizeof(llvm::ELF::Elf32_Word);
142           if (llvm::ELF::GRP_COMDAT == *value) {
143             for (size_t index = 1; index < size; ++index) {
144               pInput.context()->getSection(value[index])->setKind(
145                   LDFileFormat::Ignore);
146             }
147           }
148         }
149         ResolveInfo::Destroy(signature);
150         break;
151       }
152       /** linkonce sections **/
153       case LDFileFormat::LinkOnce: {
154         bool exist = false;
155         // .gnu.linkonce + "." + type + "." + name
156         llvm::StringRef name(
157             llvm::StringRef((*section)->name()).drop_front(14));
158         signatures().insert(name.split(".").second, exist);
159         if (!exist) {
160           if (name.startswith("wi")) {
161             (*section)->setKind(LDFileFormat::Debug);
162             if (m_Config.options().stripDebug())
163               (*section)->setKind(LDFileFormat::Ignore);
164             else {
165               SectionData* sd = IRBuilder::CreateSectionData(**section);
166               if (!m_pELFReader->readRegularSection(pInput, *sd))
167                 fatal(diag::err_cannot_read_section) << (*section)->name();
168             }
169           } else {
170             if (((*section)->flag() & llvm::ELF::SHF_EXECINSTR) != 0)
171               (*section)->setKind(LDFileFormat::TEXT);
172             else
173               (*section)->setKind(LDFileFormat::DATA);
174             SectionData* sd = IRBuilder::CreateSectionData(**section);
175             if (!m_pELFReader->readRegularSection(pInput, *sd))
176               fatal(diag::err_cannot_read_section) << (*section)->name();
177           }
178         } else {
179           (*section)->setKind(LDFileFormat::Ignore);
180         }
181         break;
182       }
183       /** relocation sections **/
184       case LDFileFormat::Relocation: {
185         assert((*section)->getLink() != NULL);
186         size_t link_index = (*section)->getLink()->index();
187         LDSection* link_sect = pInput.context()->getSection(link_index);
188         if (link_sect == NULL || link_sect->kind() == LDFileFormat::Ignore) {
189           // Relocation sections of group members should also be part of the
190           // group. Thus, if the associated member sections are ignored, the
191           // related relocations should be also ignored.
192           (*section)->setKind(LDFileFormat::Ignore);
193         }
194         break;
195       }
196       /** normal sections **/
197       // FIXME: support Version Kind
198       case LDFileFormat::Version:
199       // FIXME: support GCCExceptTable Kind
200       case LDFileFormat::GCCExceptTable:
201       /** Fall through **/
202       case LDFileFormat::TEXT:
203       case LDFileFormat::DATA:
204       case LDFileFormat::Note:
205       case LDFileFormat::MetaData: {
206         SectionData* sd = IRBuilder::CreateSectionData(**section);
207         if (!m_pELFReader->readRegularSection(pInput, *sd))
208           fatal(diag::err_cannot_read_section) << (*section)->name();
209         break;
210       }
211       case LDFileFormat::Debug:
212       case LDFileFormat::DebugString: {
213         if (m_Config.options().stripDebug()) {
214           (*section)->setKind(LDFileFormat::Ignore);
215         } else {
216           SectionData* sd = IRBuilder::CreateSectionData(**section);
217           if (!m_pELFReader->readRegularSection(pInput, *sd)) {
218             fatal(diag::err_cannot_read_section) << (*section)->name();
219           }
220         }
221         break;
222       }
223       case LDFileFormat::EhFrame: {
224         EhFrame* eh_frame = IRBuilder::CreateEhFrame(**section);
225 
226         // We don't really parse EhFrame if this is a partial linking
227         if ((m_Config.codeGenType() != LinkerConfig::Object) &&
228             (m_ReadFlag & ParseEhFrame)) {
229           if (!m_pEhFrameReader->read<32, true>(pInput, *eh_frame)) {
230             // if we failed to parse a .eh_frame, we should not parse the rest
231             // .eh_frame.
232             m_ReadFlag ^= ParseEhFrame;
233           }
234         } else {
235           if (!m_pELFReader->readRegularSection(pInput,
236                                                 *eh_frame->getSectionData())) {
237             fatal(diag::err_cannot_read_section) << (*section)->name();
238           }
239         }
240         break;
241       }
242       /** target dependent sections **/
243       case LDFileFormat::Target: {
244         SectionData* sd = IRBuilder::CreateSectionData(**section);
245         if (!m_Backend.readSection(pInput, *sd)) {
246           fatal(diag::err_cannot_read_target_section) << (*section)->name();
247         }
248         break;
249       }
250       /** BSS sections **/
251       case LDFileFormat::BSS: {
252         IRBuilder::CreateBSS(**section);
253         break;
254       }
255       // ignore
256       case LDFileFormat::Null:
257       case LDFileFormat::NamePool:
258       case LDFileFormat::Ignore:
259       case LDFileFormat::StackNote:
260         continue;
261       // warning
262       case LDFileFormat::EhFrameHdr:
263       default: {
264         warning(diag::warn_illegal_input_section)
265             << (*section)->name() << pInput.name() << pInput.path();
266         break;
267       }
268     }
269   }  // end of for all sections
270 
271   return true;
272 }
273 
274 /// readSymbols - read symbols from the input relocatable object.
readSymbols(Input & pInput)275 bool ELFObjectReader::readSymbols(Input& pInput) {
276   assert(pInput.hasMemArea());
277 
278   LDSection* symtab_shdr = pInput.context()->getSection(".symtab");
279   if (symtab_shdr == NULL) {
280     note(diag::note_has_no_symtab) << pInput.name() << pInput.path()
281                                    << ".symtab";
282     return true;
283   }
284 
285   LDSection* strtab_shdr = symtab_shdr->getLink();
286   if (strtab_shdr == NULL) {
287     fatal(diag::fatal_cannot_read_strtab) << pInput.name() << pInput.path()
288                                           << ".symtab";
289     return false;
290   }
291 
292   llvm::StringRef symtab_region = pInput.memArea()->request(
293       pInput.fileOffset() + symtab_shdr->offset(), symtab_shdr->size());
294   llvm::StringRef strtab_region = pInput.memArea()->request(
295       pInput.fileOffset() + strtab_shdr->offset(), strtab_shdr->size());
296   const char* strtab = strtab_region.begin();
297   bool result =
298       m_pELFReader->readSymbols(pInput, m_Builder, symtab_region, strtab);
299   return result;
300 }
301 
readRelocations(Input & pInput)302 bool ELFObjectReader::readRelocations(Input& pInput) {
303   assert(pInput.hasMemArea());
304 
305   MemoryArea* mem = pInput.memArea();
306   LDContext::sect_iterator rs, rsEnd = pInput.context()->relocSectEnd();
307   for (rs = pInput.context()->relocSectBegin(); rs != rsEnd; ++rs) {
308     if (LDFileFormat::Ignore == (*rs)->kind())
309       continue;
310 
311     uint32_t offset = pInput.fileOffset() + (*rs)->offset();
312     uint32_t size = (*rs)->size();
313     llvm::StringRef region = mem->request(offset, size);
314     IRBuilder::CreateRelocData(
315         **rs);  ///< create relocation data for the header
316     switch ((*rs)->type()) {
317       case llvm::ELF::SHT_RELA: {
318         if (!m_pELFReader->readRela(pInput, **rs, region)) {
319           return false;
320         }
321         break;
322       }
323       case llvm::ELF::SHT_REL: {
324         if (!m_pELFReader->readRel(pInput, **rs, region)) {
325           return false;
326         }
327         break;
328       }
329       default: {  ///< should not enter
330         return false;
331       }
332     }  // end of switch
333   }  // end of for all relocation data
334 
335   return true;
336 }
337 
338 }  // namespace mcld
339