elf_object.cc revision 2476 
1/*
2 * Copyright (c) 2003-2005 The Regents of The University of Michigan
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions are
7 * met: redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer;
9 * redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution;
12 * neither the name of the copyright holders nor the names of its
13 * contributors may be used to endorse or promote products derived from
14 * this software without specific prior written permission.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
18 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
19 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
20 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
26 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 */
28
29#include <string>
30
31// Because of the -Wundef flag we have to do this
32#define __LIBELF_INTERNAL__     0
33// counterintuitive, but the flag below causes libelf to define
34// 64-bit elf types that apparently didn't exist in some older
35// versions of Linux.  They seem to be there in 2.4.x, so don't
36// set this now (it causes things to break on 64-bit platforms).
37#define __LIBELF64_LINUX        0
38#define __LIBELF_NEED_LINK_H    0
39#define __LIBELF_SYMBOL_VERSIONS 0
40
41#include "libelf/libelf.h"
42#include "libelf/gelf.h"
43
44#include "base/loader/elf_object.hh"
45#include "base/misc.hh"
46
47#include "base/loader/symtab.hh"
48
49#include "base/trace.hh"	// for DPRINTF
50
51#include "sim/byteswap.hh"
52
53
54using namespace std;
55
56ObjectFile *
57ElfObject::tryFile(const string &fname, int fd, size_t len, uint8_t *data)
58{
59    Elf *elf;
60    GElf_Ehdr ehdr;
61    Arch arch = UnknownArch;
62    OpSys opSys = UnknownOpSys;
63
64    // check that header matches library version
65    if (elf_version(EV_CURRENT) == EV_NONE)
66        panic("wrong elf version number!");
67
68    // get a pointer to elf structure
69    elf = elf_memory((char*)data,len);
70    // will only fail if fd is invalid
71    assert(elf != NULL);
72
73    // Check that we actually have a elf file
74    if (gelf_getehdr(elf, &ehdr) ==0) {
75        DPRINTFR(Loader, "Not ELF\n");
76        elf_end(elf);
77        return NULL;
78    } else {
79        //Detect the architecture
80        //Versioning issues in libelf need to be resolved to get the correct
81        //SPARC constants.
82        //If MIPS supports 32 bit executables, this may need to be changed.
83        //Also, there are other MIPS constants which may be used, like
84        //EM_MIPS_RS3_LE and EM_MIPS_X
85        //Since we don't know how to check for alpha right now, we'll
86        //just assume if it wasn't something else and it's 64 bit, that's
87        //what it must be.
88        if (ehdr.e_machine == EM_SPARC64 ||
89                ehdr.e_machine == EM_SPARC ||
90                ehdr.e_machine == EM_SPARCV9) {
91            arch = ObjectFile::SPARC;
92        } else if (ehdr.e_machine == EM_MIPS
93                && ehdr.e_ident[EI_CLASS] == ELFCLASS32) {
94            arch = ObjectFile::MIPS;
95        } else if (ehdr.e_ident[EI_CLASS] == ELFCLASS64) {
96            arch = ObjectFile::Alpha;
97        } else {
98            arch = ObjectFile::UnknownArch;
99        }
100
101        //Detect the operating system
102        switch (ehdr.e_ident[EI_OSABI])
103        {
104
105          case ELFOSABI_LINUX:
106            opSys = ObjectFile::Linux;
107            break;
108          case ELFOSABI_SOLARIS:
109            opSys = ObjectFile::Solaris;
110            break;
111          case ELFOSABI_TRU64:
112            opSys = ObjectFile::Tru64;
113            break;
114          default:
115            opSys = ObjectFile::UnknownOpSys;
116        }
117
118        //take a look at the .note.ABI section
119        //It can let us know what's what.
120        if (opSys == ObjectFile::UnknownOpSys)
121        {
122            Elf_Scn *section;
123            GElf_Shdr shdr;
124            Elf_Data *data;
125            uint32_t osAbi;;
126            int secIdx = 1;
127
128            // Get the first section
129            section = elf_getscn(elf, secIdx);
130
131            // While there are no more sections
132            while (section != NULL) {
133                gelf_getshdr(section, &shdr);
134                if (shdr.sh_type == SHT_NOTE && !strcmp(".note.ABI-tag",
135                            elf_strptr(elf, ehdr.e_shstrndx, shdr.sh_name))) {
136                    // we have found a ABI note section
137                    // Check the 5th 32bit word for OS  0 == linux, 1 == hurd,
138                    // 2 == solaris, 3 == freebsd
139                    data = elf_rawdata(section, NULL);
140                    assert(data->d_buf);
141                    if(ehdr.e_ident[EI_DATA] == ELFDATA2LSB)
142                        osAbi = htole(((uint32_t*)data->d_buf)[4]);
143                    else
144                        osAbi = htobe(((uint32_t*)data->d_buf)[4]);
145
146                    switch(osAbi) {
147                      case 0:
148                        opSys = ObjectFile::Linux;
149                        break;
150                      case 2:
151                        opSys = ObjectFile::Solaris;
152                        break;
153                    }
154                } // if section found
155            section = elf_getscn(elf, ++secIdx);
156            } // while sections
157        }
158        elf_end(elf);
159        return new ElfObject(fname, fd, len, data, arch, opSys);
160    }
161}
162
163
164ElfObject::ElfObject(const string &_filename, int _fd,
165                     size_t _len, uint8_t *_data,
166                     Arch _arch, OpSys _opSys)
167    : ObjectFile(_filename, _fd, _len, _data, _arch, _opSys)
168
169{
170    Elf *elf;
171    GElf_Ehdr ehdr;
172
173    // check that header matches library version
174    if (elf_version(EV_CURRENT) == EV_NONE)
175        panic("wrong elf version number!");
176
177    // get a pointer to elf structure
178    elf = elf_memory((char*)fileData,len);
179    // will only fail if fd is invalid
180    assert(elf != NULL);
181
182    // Check that we actually have a elf file
183    if (gelf_getehdr(elf, &ehdr) ==0) {
184        panic("Not ELF, shouldn't be here");
185    }
186
187    entry = ehdr.e_entry;
188
189    // initialize segment sizes to 0 in case they're not present
190    text.size = data.size = bss.size = 0;
191
192    for (int i = 0; i < ehdr.e_phnum; ++i) {
193        GElf_Phdr phdr;
194        if (gelf_getphdr(elf, i, &phdr) == 0) {
195            panic("gelf_getphdr failed for section %d", i);
196        }
197
198        // for now we don't care about non-loadable segments
199        if (!(phdr.p_type & PT_LOAD))
200            continue;
201
202        // the headers don't explicitly distinguish text from data,
203        // but empirically the text segment comes first.
204        if (text.size == 0) {  // haven't seen text segment yet
205            text.baseAddr = phdr.p_vaddr;
206            text.size = phdr.p_filesz;
207            text.fileImage = fileData + phdr.p_offset;
208            // if there's any padding at the end that's not in the
209            // file, call it the bss.  This happens in the "text"
210            // segment if there's only one loadable segment (as for
211            // kernel images).
212            bss.size = phdr.p_memsz - phdr.p_filesz;
213            bss.baseAddr = phdr.p_vaddr + phdr.p_filesz;
214            bss.fileImage = NULL;
215        } else if (data.size == 0) { // have text, this must be data
216            data.baseAddr = phdr.p_vaddr;
217            data.size = phdr.p_filesz;
218            data.fileImage = fileData + phdr.p_offset;
219            // if there's any padding at the end that's not in the
220            // file, call it the bss.  Warn if this happens for both
221            // the text & data segments (should only have one bss).
222            if (phdr.p_memsz - phdr.p_filesz > 0 && bss.size != 0) {
223                warn("Two implied bss segments in file!\n");
224            }
225            bss.size = phdr.p_memsz - phdr.p_filesz;
226            bss.baseAddr = phdr.p_vaddr + phdr.p_filesz;
227            bss.fileImage = NULL;
228        } else {
229            warn("More than two loadable segments in ELF object.");
230            warn("Ignoring segment @ 0x%x length 0x%x.",
231                 phdr.p_vaddr, phdr.p_filesz);
232        }
233    }
234
235    // should have found at least one loadable segment
236    assert(text.size != 0);
237
238    DPRINTFR(Loader, "text: 0x%x %d\ndata: 0x%x %d\nbss: 0x%x %d\n",
239             text.baseAddr, text.size, data.baseAddr, data.size,
240             bss.baseAddr, bss.size);
241
242    elf_end(elf);
243
244    // We will actually read the sections when we need to load them
245}
246
247
248bool
249ElfObject::loadSomeSymbols(SymbolTable *symtab, int binding)
250{
251    Elf *elf;
252    int sec_idx = 1; // there is a 0 but it is nothing, go figure
253    Elf_Scn *section;
254    GElf_Shdr shdr;
255    Elf_Data *data;
256    int count, ii;
257    bool found = false;
258    GElf_Sym sym;
259
260    if (!symtab)
261        return false;
262
263    // check that header matches library version
264    if (elf_version(EV_CURRENT) == EV_NONE)
265        panic("wrong elf version number!");
266
267    // get a pointer to elf structure
268    elf = elf_memory((char*)fileData,len);
269
270    assert(elf != NULL);
271
272    // Get the first section
273    section = elf_getscn(elf, sec_idx);
274
275    // While there are no more sections
276    while (section != NULL) {
277        gelf_getshdr(section, &shdr);
278
279        if (shdr.sh_type == SHT_SYMTAB) {
280            found = true;
281            data = elf_getdata(section, NULL);
282            count = shdr.sh_size / shdr.sh_entsize;
283            DPRINTF(Loader, "Found Symbol Table, %d symbols present\n", count);
284
285            // loop through all the symbols, only loading global ones
286            for (ii = 0; ii < count; ++ii) {
287                gelf_getsym(data, ii, &sym);
288                if (GELF_ST_BIND(sym.st_info) == binding) {
289                   symtab->insert(sym.st_value,
290                                  elf_strptr(elf, shdr.sh_link, sym.st_name));
291                }
292            }
293        }
294        ++sec_idx;
295        section = elf_getscn(elf, sec_idx);
296    }
297
298    elf_end(elf);
299
300    return found;
301}
302
303bool
304ElfObject::loadGlobalSymbols(SymbolTable *symtab)
305{
306    return loadSomeSymbols(symtab, STB_GLOBAL);
307}
308
309bool
310ElfObject::loadLocalSymbols(SymbolTable *symtab)
311{
312    return loadSomeSymbols(symtab, STB_LOCAL);
313}
314