The Tor Browser: tools/footprint/foldelf.cpp@97036ab72558 (annotated)

tools/footprint/foldelf.cpp@97036ab72558 (annotated)

tools/footprint/foldelf.cpp

Tue, 06 Jan 2015 21:39:09 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Tue, 06 Jan 2015 21:39:09 +0100
branch: TOR_BUG_9701
changeset 8: 97036ab72558
permissions: -rw-r--r--

Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

 /* -*- Mode: C++; indent-tabs-mode: nil; c-basic-offset: 4 -*-
  *
  * This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 /* This program reads an ELF file and computes information about
  * redundancies.
  */
 #include <algorithm>
 #include <fstream>
 #include <string>
 #include <vector>
 #include <map>
 #include <elf.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <unistd.h>
 #include <errno.h>
 #include <getopt.h>
 //----------------------------------------------------------------------
 char* opt_type    = "func";
 char* opt_section = ".text";
 //----------------------------------------------------------------------
 static void
 hexdump(ostream& out, const char* bytes, size_t count)
 {
     hex(out);
     size_t off = 0;
     while (off < count) {
         out.form("%08lx: ", off);
         const char* p = bytes + off;
         int j = 0;
         while (j < 16) {
             out.form("%02x", p[j++] & 0xff);
             if (j + off >= count)
                 break;
             out.form("%02x ", p[j++] & 0xff);
             if (j + off >= count)
                 break;
         }
         // Pad
         for (; j < 16; ++j)
             out << ((j%2) ? "   " : "  ");
         for (j = 0; j < 16; ++j) {
             if (j + off < count)
                 out.put(isprint(p[j]) ? p[j] : '.');
         }
         out << endl;
         off += 16;
     }
 }
 //----------------------------------------------------------------------
 int
 verify_elf_header(const Elf32_Ehdr* hdr)
 {
     if (hdr->e_ident[EI_MAG0] != ELFMAG0
         || hdr->e_ident[EI_MAG1] != ELFMAG1
         || hdr->e_ident[EI_MAG2] != ELFMAG2
         || hdr->e_ident[EI_MAG3] != ELFMAG3) {
         cerr << "not an elf file" << endl;
         return -1;
     }
     if (hdr->e_ident[EI_CLASS] != ELFCLASS32) {
         cerr << "not a 32-bit elf file" << endl;
         return -1;
     }
     if (hdr->e_ident[EI_DATA] != ELFDATA2LSB) {
         cerr << "not a little endian elf file" << endl;
         return -1;
     }
     if (hdr->e_ident[EI_VERSION] != EV_CURRENT) {
         cerr << "incompatible version" << endl;
         return -1;
     }
     return 0;
 }
 //----------------------------------------------------------------------
 class elf_symbol : public Elf32_Sym
 {
 public:
     elf_symbol(const Elf32_Sym& sym)
     { ::memcpy(static_cast<Elf32_Sym*>(this), &sym, sizeof(Elf32_Sym)); }
     friend bool operator==(const elf_symbol& lhs, const elf_symbol& rhs) {
         return 0 == ::memcmp(static_cast<const Elf32_Sym*>(&lhs),
                              static_cast<const Elf32_Sym*>(&rhs),
                              sizeof(Elf32_Sym)); }
 };
 //----------------------------------------------------------------------
 static const char*
 st_bind(unsigned char info)
 {
     switch (ELF32_ST_BIND(info)) {
     case STB_LOCAL:      return "local";
     case STB_GLOBAL:     return "global";
     case STB_WEAK:       return "weak";
     default:             return "unknown";
     }
 }
 static const char*
 st_type(unsigned char info)
 {
     switch (ELF32_ST_TYPE(info)) {
     case STT_NOTYPE:     return "none";
     case STT_OBJECT:     return "object";
     case STT_FUNC:       return "func";
     case STT_SECTION:    return "section";
     case STT_FILE:       return "file";
     default:             return "unknown";
     }
 }
 static unsigned char
 st_type(const char* type)
 {
     if (strcmp(type, "none") == 0) {
         return STT_NOTYPE;
     }
     else if (strcmp(type, "object") == 0) {
         return STT_OBJECT;
     }
     else if (strcmp(type, "func") == 0) {
         return STT_FUNC;
     }
     else {
         return 0;
     }
 }
 //----------------------------------------------------------------------
 typedef vector<elf_symbol> elf_symbol_table;
 typedef map< basic_string<char>, elf_symbol_table > elf_text_map;
 void
 process_mapping(char* mapping, size_t size)
 {
     const Elf32_Ehdr* ehdr = reinterpret_cast<Elf32_Ehdr*>(mapping);
     if (verify_elf_header(ehdr) < 0)
         return;
     // find the section headers
     const Elf32_Shdr* shdrs = reinterpret_cast<Elf32_Shdr*>(mapping + ehdr->e_shoff);
     // find the section header string table, .shstrtab
     const Elf32_Shdr* shstrtabsh = shdrs + ehdr->e_shstrndx;
     const char* shstrtab = mapping + shstrtabsh->sh_offset;
     // find the sections we care about
     const Elf32_Shdr *symtabsh, *strtabsh, *textsh;
     int textndx;
     for (int i = 0; i < ehdr->e_shnum; ++i) {
         basic_string<char> name(shstrtab + shdrs[i].sh_name);
         if (name == opt_section) {
             textsh = shdrs + i;
             textndx = i;
         }
         else if (name == ".symtab") {
             symtabsh = shdrs + i;
         }
         else if (name == ".strtab") {
             strtabsh = shdrs + i;
         }
     }
     // find the .strtab
     char* strtab = mapping + strtabsh->sh_offset;
     // find the .text
     char* text = mapping + textsh->sh_offset;
     int textaddr = textsh->sh_addr;
     // find the symbol table
     int nentries = symtabsh->sh_size / sizeof(Elf32_Sym);
     Elf32_Sym* symtab = reinterpret_cast<Elf32_Sym*>(mapping + symtabsh->sh_offset);
     // look for symbols in the .text section
     elf_text_map textmap;
     for (int i = 0; i < nentries; ++i) {
         const Elf32_Sym* sym = symtab + i;
         if (sym->st_shndx == textndx &&
             ELF32_ST_TYPE(sym->st_info) == st_type(opt_type) &&
             sym->st_size) {
             basic_string<char> functext(text + sym->st_value - textaddr, sym->st_size);
             elf_symbol_table& syms = textmap[functext];
             if (syms.end() == find(syms.begin(), syms.end(), elf_symbol(*sym)))
                 syms.insert(syms.end(), *sym);
         }
     }
     int uniquebytes = 0, totalbytes = 0;
     int uniquecount = 0, totalcount = 0;
     for (elf_text_map::const_iterator entry = textmap.begin();
          entry != textmap.end();
          ++entry) {
         const elf_symbol_table& syms = entry->second;
         if (syms.size() <= 1)
             continue;
         int sz = syms.begin()->st_size;
         uniquebytes += sz;
         totalbytes += sz * syms.size();
         uniquecount += 1;
         totalcount += syms.size();
         for (elf_symbol_table::const_iterator sym = syms.begin(); sym != syms.end(); ++sym)
             cout << strtab + sym->st_name << endl;
         dec(cout);
         cout << syms.size() << " copies of " << sz << " bytes";
         cout << " (" << ((syms.size() - 1) * sz) << " redundant bytes)" << endl;
         hexdump(cout, entry->first.data(), entry->first.size());
         cout << endl;
     }
     dec(cout);
     cout << "bytes unique=" << uniquebytes << ", total=" << totalbytes << endl;
     cout << "entries unique=" << uniquecount << ", total=" << totalcount << endl;
 }
 void
 process_file(const char* name)
 {
     int fd = open(name, O_RDWR);
     if (fd >= 0) {
         struct stat statbuf;
         if (fstat(fd, &statbuf) >= 0) {
             size_t size = statbuf.st_size;
             void* mapping = mmap(0, size, PROT_READ, MAP_SHARED, fd, 0);
             if (mapping != MAP_FAILED) {
                 process_mapping(static_cast<char*>(mapping), size);
                 munmap(mapping, size);
             }
         }
         close(fd);
     }
 }
 static void
 usage()
 {
     cerr << "foldelf [--section=<section>] [--type=<type>] [file ...]\n\
    --section, -s  the section of the ELF file to scan; defaults\n\
                   to ``.text''. Valid values include any section\n\
                   of the ELF file.\n\
    --type, -t     the type of object to examine in the section;\n\
                   defaults to ``func''. Valid values include\n\
                   ``none'', ``func'', or ``object''.\n";
 }
 static struct option opts[] = {
     { "type",    required_argument, 0, 't' },
     { "section", required_argument, 0, 's' },
     { "help",    no_argument,       0, '?' },
     { 0,         0, 0, 0 }
 };
 int
 main(int argc, char* argv[])
 {
     while (1) {
         int option_index = 0;
         int c = getopt_long(argc, argv, "t:s:", opts, &option_index);
         if (c < 0) break;
         switch (c) {
         case 't':
             opt_type = optarg;
             break;
         case 's':
             opt_section = optarg;
             break;
         case '?':
             usage();
             break;
         }
     }
     for (int i = optind; i < argc; ++i)
         process_file(argv[i]);
     return 0;
 }

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tools/footprint/foldelf.cpp@97036ab72558 (annotated)

tools/footprint/foldelf.cpp