elf_object.cc revision 661 
1/*
2 * Copyright (c) 2003 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
46#include "mem/functional_mem/functional_memory.hh"
47#include "base/loader/symtab.hh"
48
49#include "base/trace.hh"	// for DPRINTF
50
51
52using namespace std;
53
54ObjectFile *
55ElfObject::tryFile(const string &fname, int fd, size_t len, uint8_t *data)
56{
57    Elf *elf;
58    GElf_Ehdr ehdr;
59
60    // check that header matches library version
61    assert(elf_version(EV_CURRENT) != EV_NONE);
62
63    // get a pointer to elf structure
64    elf = elf_memory((char*)data,len);
65    // will only fail if fd is invalid
66    assert(elf != NULL);
67
68    // Check that we actually have a elf file
69    if (gelf_getehdr(elf, &ehdr) ==0) {
70        DPRINTFR(Loader, "Not ELF\n");
71        elf_end(elf);
72        return NULL;
73    }
74    else {
75        if (ehdr.e_ident[EI_CLASS] == ELFCLASS32)
76            panic("32 bit ELF Binary, Not Supported");
77        if (ehdr.e_machine != EM_ALPHA)
78            panic("Non Alpha Binary, Not Supported");
79
80        elf_end(elf);
81
82        return new ElfObject(fname, fd, len, data,
83                             ObjectFile::Alpha, ObjectFile::Linux);
84    }
85}
86
87
88ElfObject::ElfObject(const string &_filename, int _fd,
89                     size_t _len, uint8_t *_data,
90                     Arch _arch, OpSys _opSys)
91    : ObjectFile(_filename, _fd, _len, _data, _arch, _opSys)
92
93{
94    Elf *elf;
95    GElf_Ehdr ehdr;
96
97    // check that header matches library version
98    assert(elf_version(EV_CURRENT) != EV_NONE);
99
100    // get a pointer to elf structure
101    elf = elf_memory((char*)fileData,len);
102    // will only fail if fd is invalid
103    assert(elf != NULL);
104
105    // Check that we actually have a elf file
106    if (gelf_getehdr(elf, &ehdr) ==0) {
107        panic("Not ELF, shouldn't be here");
108    }
109
110    entry = ehdr.e_entry;
111
112    // initialize segment sizes to 0 in case they're not present
113    text.size = data.size = bss.size = 0;
114
115    for (int i = 0; i < ehdr.e_phnum; ++i) {
116        GElf_Phdr phdr;
117        if (gelf_getphdr(elf, i, &phdr) == 0) {
118            panic("gelf_getphdr failed for section %d", i);
119        }
120
121        // for now we don't care about non-loadable segments
122        if (!(phdr.p_type & PT_LOAD))
123            continue;
124
125        // the headers don't explicitly distinguish text from data,
126        // but empirically the text segment comes first.
127        if (text.size == 0) {  // haven't seen text segment yet
128            text.baseAddr = phdr.p_vaddr;
129            text.size = phdr.p_filesz;
130            // remember where the data is for loadSections()
131            fileTextBits = fileData + phdr.p_offset;
132            // if there's any padding at the end that's not in the
133            // file, call it the bss.  This happens in the "text"
134            // segment if there's only one loadable segment (as for
135            // kernel images).
136            bss.size = phdr.p_memsz - phdr.p_filesz;
137            bss.baseAddr = phdr.p_vaddr + phdr.p_filesz;
138        }
139        else if (data.size == 0) { // have text, this must be data
140            data.baseAddr = phdr.p_vaddr;
141            data.size = phdr.p_filesz;
142            // remember where the data is for loadSections()
143            fileDataBits = fileData + phdr.p_offset;
144            // if there's any padding at the end that's not in the
145            // file, call it the bss.  Warn if this happens for both
146            // the text & data segments (should only have one bss).
147            if (phdr.p_memsz - phdr.p_filesz > 0 && bss.size != 0) {
148                warn("Two implied bss segments in file!\n");
149            }
150            bss.size = phdr.p_memsz - phdr.p_filesz;
151            bss.baseAddr = phdr.p_vaddr + phdr.p_filesz;
152        }
153    }
154
155    // should have found at least one loadable segment
156    assert(text.size != 0);
157
158    DPRINTFR(Loader, "text: 0x%x %d\ndata: 0x%x %d\nbss: 0x%x %d\n",
159             text.baseAddr, text.size, data.baseAddr, data.size,
160             bss.baseAddr, bss.size);
161
162    elf_end(elf);
163
164    // We will actually read the sections when we need to load them
165}
166
167
168bool
169ElfObject::loadSections(FunctionalMemory *mem, bool loadPhys)
170{
171    Addr textAddr = text.baseAddr;
172    Addr dataAddr = data.baseAddr;
173
174    if (loadPhys) {
175        textAddr &= (ULL(1) << 40) - 1;
176        dataAddr &= (ULL(1) << 40) - 1;
177    }
178
179    // Since we don't really have an MMU and all memory is
180    // zero-filled, there's no need to set up the BSS segment.
181    if (text.size != 0)
182        mem->prot_write(textAddr, fileTextBits, text.size);
183    if (data.size != 0)
184        mem->prot_write(dataAddr, fileDataBits, data.size);
185
186    return true;
187}
188
189
190bool
191ElfObject::loadSomeSymbols(SymbolTable *symtab, int binding)
192{
193    Elf *elf;
194    int secidx = 1; // there is a 0 but it is nothing, go figure
195    Elf_Scn *section;
196    GElf_Shdr shdr;
197    Elf_Data *data;
198    int count, ii;
199    bool found = false;
200    GElf_Sym sym;
201
202    if (!symtab)
203        return false;
204
205    // check that header matches library version
206    assert(elf_version(EV_CURRENT) != EV_NONE);
207
208    // get a pointer to elf structure
209    elf = elf_memory((char*)fileData,len);
210
211    assert(elf != NULL);
212
213    // Get the first section
214    section = elf_getscn(elf, secidx);
215
216    // While there are no more sections
217    while (section != NULL) {
218        gelf_getshdr(section, &shdr);
219
220        if (shdr.sh_type == SHT_SYMTAB) {
221            found = true;
222            data = elf_getdata(section, NULL);
223            count = shdr.sh_size / shdr.sh_entsize;
224            DPRINTF(Loader, "Found Symbol Table, %d symbols present\n", count);
225
226            // loop through all the symbols, only loading global ones
227            for (ii = 0; ii < count; ++ii) {
228                gelf_getsym(data, ii, &sym);
229                if (GELF_ST_BIND(sym.st_info) & binding) {
230                   symtab->insert(sym.st_value,
231                                  elf_strptr(elf, shdr.sh_link, sym.st_name));
232                }
233            }
234        }
235        ++secidx;
236        section = elf_getscn(elf, secidx);
237    }
238
239    elf_end(elf);
240
241    return found;
242}
243
244bool
245ElfObject::loadGlobalSymbols(SymbolTable *symtab)
246{
247    return loadSomeSymbols(symtab, STB_GLOBAL);
248}
249
250bool
251ElfObject::loadLocalSymbols(SymbolTable *symtab)
252{
253    return loadSomeSymbols(symtab, STB_LOCAL);
254}
255