elf_object.cc revision 2439 
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    }
79    else {
80        //Detect the architecture
81        //Versioning issues in libelf need to be resolved to get the correct
82        //SPARC constants.
83        //If MIPS supports 32 bit executables, this may need to be changed.
84        //Also, there are other MIPS constants which may be used, like
85        //EM_MIPS_RS3_LE and EM_MIPS_X
86        //Since we don't know how to check for alpha right now, we'll
87        //just assume if it wasn't something else and it's 64 bit, that's
88        //what it must be.
89        if (ehdr.e_machine == EM_SPARC64 ||
90                ehdr.e_machine == EM_SPARC ||
91                ehdr.e_machine == EM_SPARCV9) {
92            arch = ObjectFile::SPARC;
93        } else if (ehdr.e_machine == EM_MIPS
94                && ehdr.e_ident[EI_CLASS] == ELFCLASS32) {
95            arch = ObjectFile::MIPS;
96        } else if (ehdr.e_ident[EI_CLASS] == ELFCLASS64) {
97            arch = ObjectFile::Alpha;
98        } else {
99            arch = ObjectFile::UnknownArch;
100        }
101
102        //Detect the operating system
103        switch (ehdr.e_ident[EI_OSABI])
104        {
105
106          case ELFOSABI_LINUX:
107            opSys = ObjectFile::Linux;
108            break;
109          case ELFOSABI_SOLARIS:
110            opSys = ObjectFile::Solaris;
111            break;
112          case ELFOSABI_TRU64:
113            opSys = ObjectFile::Tru64;
114            break;
115          default:
116            opSys = ObjectFile::UnknownOpSys;
117        }
118
119        //take a look at the .note.ABI section
120        //It can let us know what's what.
121        if (opSys == ObjectFile::UnknownOpSys)
122        {
123            Elf_Scn *section;
124            GElf_Shdr shdr;
125            Elf_Data *data;
126            uint32_t osAbi;;
127            int secIdx = 1;
128
129            // Get the first section
130            section = elf_getscn(elf, secIdx);
131
132            // While there are no more sections
133            while (section != NULL) {
134                gelf_getshdr(section, &shdr);
135                if (shdr.sh_type == SHT_NOTE && !strcmp(".note.ABI-tag",
136                            elf_strptr(elf, ehdr.e_shstrndx, shdr.sh_name))) {
137                    // we have found a ABI note section
138                    // Check the 5th 32bit word for OS  0 == linux, 1 == hurd,
139                    // 2 == solaris, 3 == freebsd
140                    data = elf_rawdata(section, NULL);
141                    assert(data->d_buf);
142                    if(ehdr.e_ident[EI_DATA] == ELFDATA2LSB)
143                        osAbi = htole(((uint32_t*)data->d_buf)[4]);
144                    else
145                        osAbi = htobe(((uint32_t*)data->d_buf)[4]);
146
147                    switch(osAbi) {
148                      case 0:
149                        opSys = ObjectFile::Linux;
150                        break;
151                      case 2:
152                        opSys = ObjectFile::Solaris;
153                        break;
154                    }
155                } // if section found
156            section = elf_getscn(elf, ++secIdx);
157            } // while sections
158        }
159        elf_end(elf);
160        return new ElfObject(fname, fd, len, data, arch, opSys);
161    }
162}
163
164
165ElfObject::ElfObject(const string &_filename, int _fd,
166                     size_t _len, uint8_t *_data,
167                     Arch _arch, OpSys _opSys)
168    : ObjectFile(_filename, _fd, _len, _data, _arch, _opSys)
169
170{
171    Elf *elf;
172    GElf_Ehdr ehdr;
173
174    // check that header matches library version
175    if (elf_version(EV_CURRENT) == EV_NONE)
176        panic("wrong elf version number!");
177
178    // get a pointer to elf structure
179    elf = elf_memory((char*)fileData,len);
180    // will only fail if fd is invalid
181    assert(elf != NULL);
182
183    // Check that we actually have a elf file
184    if (gelf_getehdr(elf, &ehdr) ==0) {
185        panic("Not ELF, shouldn't be here");
186    }
187
188    entry = ehdr.e_entry;
189
190    // initialize segment sizes to 0 in case they're not present
191    text.size = data.size = bss.size = 0;
192
193    for (int i = 0; i < ehdr.e_phnum; ++i) {
194        GElf_Phdr phdr;
195        if (gelf_getphdr(elf, i, &phdr) == 0) {
196            panic("gelf_getphdr failed for section %d", i);
197        }
198
199        // for now we don't care about non-loadable segments
200        if (!(phdr.p_type & PT_LOAD))
201            continue;
202
203        // the headers don't explicitly distinguish text from data,
204        // but empirically the text segment comes first.
205        if (text.size == 0) {  // haven't seen text segment yet
206            text.baseAddr = phdr.p_vaddr;
207            text.size = phdr.p_filesz;
208            text.fileImage = fileData + phdr.p_offset;
209            // if there's any padding at the end that's not in the
210            // file, call it the bss.  This happens in the "text"
211            // segment if there's only one loadable segment (as for
212            // kernel images).
213            bss.size = phdr.p_memsz - phdr.p_filesz;
214            bss.baseAddr = phdr.p_vaddr + phdr.p_filesz;
215            bss.fileImage = NULL;
216        }
217        else if (data.size == 0) { // have text, this must be data
218            data.baseAddr = phdr.p_vaddr;
219            data.size = phdr.p_filesz;
220            data.fileImage = fileData + phdr.p_offset;
221            // if there's any padding at the end that's not in the
222            // file, call it the bss.  Warn if this happens for both
223            // the text & data segments (should only have one bss).
224            if (phdr.p_memsz - phdr.p_filesz > 0 && bss.size != 0) {
225                warn("Two implied bss segments in file!\n");
226            }
227            bss.size = phdr.p_memsz - phdr.p_filesz;
228            bss.baseAddr = phdr.p_vaddr + phdr.p_filesz;
229            bss.fileImage = NULL;
230        }
231    }
232
233    // should have found at least one loadable segment
234    assert(text.size != 0);
235
236    DPRINTFR(Loader, "text: 0x%x %d\ndata: 0x%x %d\nbss: 0x%x %d\n",
237             text.baseAddr, text.size, data.baseAddr, data.size,
238             bss.baseAddr, bss.size);
239
240    elf_end(elf);
241
242    // We will actually read the sections when we need to load them
243}
244
245
246bool
247ElfObject::loadSomeSymbols(SymbolTable *symtab, int binding)
248{
249    Elf *elf;
250    int sec_idx = 1; // there is a 0 but it is nothing, go figure
251    Elf_Scn *section;
252    GElf_Shdr shdr;
253    Elf_Data *data;
254    int count, ii;
255    bool found = false;
256    GElf_Sym sym;
257
258    if (!symtab)
259        return false;
260
261    // check that header matches library version
262    if (elf_version(EV_CURRENT) == EV_NONE)
263        panic("wrong elf version number!");
264
265    // get a pointer to elf structure
266    elf = elf_memory((char*)fileData,len);
267
268    assert(elf != NULL);
269
270    // Get the first section
271    section = elf_getscn(elf, sec_idx);
272
273    // While there are no more sections
274    while (section != NULL) {
275        gelf_getshdr(section, &shdr);
276
277        if (shdr.sh_type == SHT_SYMTAB) {
278            found = true;
279            data = elf_getdata(section, NULL);
280            count = shdr.sh_size / shdr.sh_entsize;
281            DPRINTF(Loader, "Found Symbol Table, %d symbols present\n", count);
282
283            // loop through all the symbols, only loading global ones
284            for (ii = 0; ii < count; ++ii) {
285                gelf_getsym(data, ii, &sym);
286                if (GELF_ST_BIND(sym.st_info) == binding) {
287                   symtab->insert(sym.st_value,
288                                  elf_strptr(elf, shdr.sh_link, sym.st_name));
289                }
290            }
291        }
292        ++sec_idx;
293        section = elf_getscn(elf, sec_idx);
294    }
295
296    elf_end(elf);
297
298    return found;
299}
300
301bool
302ElfObject::loadGlobalSymbols(SymbolTable *symtab)
303{
304    return loadSomeSymbols(symtab, STB_GLOBAL);
305}
306
307bool
308ElfObject::loadLocalSymbols(SymbolTable *symtab)
309{
310    return loadSomeSymbols(symtab, STB_LOCAL);
311}
312