base/loader/elf_object.cc

/*
 * Copyright (c) 2011-2013 ARM Limited
 * All rights reserved
 *
 * The license below extends only to copyright in the software and shall
 * not be construed as granting a license to any other intellectual
 * property including but not limited to intellectual property relating
 * to a hardware implementation of the functionality of the software
 * licensed hereunder.  You may use the software subject to the license
 * terms below provided that you ensure that this notice is replicated
 * unmodified and in its entirety in all distributions of the software,
 * modified or unmodified, in source code or in binary form.
 *
 * Copyright (c) 2003-2005 The Regents of The University of Michigan
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met: redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer;
 * redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution;
 * neither the name of the copyright holders nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Authors: Steve Reinhardt
 *          Ali Saidi
 */

#include "base/loader/elf_object.hh"

#include <fcntl.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

#include <cassert>
#include <string>

#include "base/bitfield.hh"
#include "base/loader/symtab.hh"
#include "base/misc.hh"
#include "base/trace.hh"
#include "debug/Loader.hh"
#include "gelf.h"
#include "sim/byteswap.hh"

using namespace std;

ObjectFile *
ElfObject::tryFile(const string &fname, size_t len, uint8_t *data,
                   bool skip_interp_check)
{
    Elf *elf;
    GElf_Ehdr ehdr;
    Arch arch = UnknownArch;
    OpSys opSys = UnknownOpSys;

    // check that header matches library version
    if (elf_version(EV_CURRENT) == EV_NONE)
        panic("wrong elf version number!");

    // get a pointer to elf structure
    elf = elf_memory((char*)data,len);
    assert(elf != NULL);

    // Check that we actually have a elf file
    if (gelf_getehdr(elf, &ehdr) == 0) {
        DPRINTFR(Loader, "Not ELF\n");
        elf_end(elf);
        return NULL;
    } else {
        //Detect the architecture
        //Since we don't know how to check for alpha right now, we'll
        //just assume if it wasn't something else and it's 64 bit, that's
        //what it must be.
        if (ehdr.e_machine == EM_SPARC64 ||
                (ehdr.e_machine == EM_SPARC &&
                 ehdr.e_ident[EI_CLASS] == ELFCLASS64)||
                ehdr.e_machine == EM_SPARCV9) {
            arch = ObjectFile::SPARC64;
        } else if (ehdr.e_machine == EM_SPARC32PLUS ||
                        (ehdr.e_machine == EM_SPARC &&
                         ehdr.e_ident[EI_CLASS] == ELFCLASS32)) {
            arch = ObjectFile::SPARC32;
        } else if (ehdr.e_machine == EM_MIPS
                && ehdr.e_ident[EI_CLASS] == ELFCLASS32) {
            if (ehdr.e_ident[EI_DATA] == ELFDATA2LSB) {
                arch = ObjectFile::Mips;
            } else {
                fatal("The binary you're trying to load is compiled for big "
                        "endian MIPS. M5\nonly supports little endian MIPS. "
                        "Please recompile your binary.\n");
            }
        } else if (ehdr.e_machine == EM_X86_64 &&
                ehdr.e_ident[EI_CLASS] == ELFCLASS64) {
            arch = ObjectFile::X86_64;
        } else if (ehdr.e_machine == EM_386 &&
                ehdr.e_ident[EI_CLASS] == ELFCLASS32) {
            arch = ObjectFile::I386;
        } else if (ehdr.e_machine == EM_ARM &&
                ehdr.e_ident[EI_CLASS] == ELFCLASS32) {
            if (bits(ehdr.e_entry, 0)) {
                arch = ObjectFile::Thumb;
            } else {
                arch = ObjectFile::Arm;
            }
        } else if ((ehdr.e_machine == EM_AARCH64) &&
                ehdr.e_ident[EI_CLASS] == ELFCLASS64) {
            arch = ObjectFile::Arm64;
        } else if (ehdr.e_ident[EI_CLASS] == ELFCLASS64) {
            arch = ObjectFile::Alpha;
        } else if (ehdr.e_machine == EM_PPC &&
                ehdr.e_ident[EI_CLASS] == ELFCLASS32) {
            if (ehdr.e_ident[EI_DATA] == ELFDATA2MSB) {
                  arch = ObjectFile::Power;
            } else {
                  fatal("The binary you're trying to load is compiled for "
                        "little endian Power.\nM5 only supports big "
                        "endian Power. Please recompile your binary.\n");
            }
        } else if (ehdr.e_machine == EM_PPC64) {
            fatal("The binary you're trying to load is compiled for 64-bit "
                  "Power. M5\n only supports 32-bit Power. Please "
                  "recompile your binary.\n");
        } else {
            warn("Unknown architecture: %d\n", ehdr.e_machine);
            arch = ObjectFile::UnknownArch;
        }

        //Detect the operating system
        switch (ehdr.e_ident[EI_OSABI]) {
          case ELFOSABI_LINUX:
            opSys = ObjectFile::Linux;
            break;
          case ELFOSABI_SOLARIS:
            opSys = ObjectFile::Solaris;
            break;
          case ELFOSABI_TRU64:
            opSys = ObjectFile::Tru64;
            break;
          case ELFOSABI_ARM:
            opSys = ObjectFile::LinuxArmOABI;
            break;
          case ELFOSABI_FREEBSD:
            opSys = ObjectFile::FreeBSD;
            break;
          default:
            opSys = ObjectFile::UnknownOpSys;
        }

        //take a look at the .note.ABI section
        //It can let us know what's what.
        if (opSys == ObjectFile::UnknownOpSys) {
            Elf_Scn *section;
            GElf_Shdr shdr;
            Elf_Data *data;
            uint32_t osAbi;
            uint32_t *elem;
            int secIdx = 1;

            // Get the first section
            section = elf_getscn(elf, secIdx);

            // While there are no more sections
            while (section != NULL && opSys == ObjectFile::UnknownOpSys) {
                gelf_getshdr(section, &shdr);
                if (shdr.sh_type == SHT_NOTE && !strcmp(".note.ABI-tag",
                            elf_strptr(elf, ehdr.e_shstrndx, shdr.sh_name))) {
                    // we have found a ABI note section
                    // Check the 5th 32bit word for OS  0 == linux, 1 == hurd,
                    // 2 == solaris, 3 == freebsd
                    data = elf_rawdata(section, NULL);
                    assert(data->d_buf);
                    if (ehdr.e_ident[EI_DATA] == ELFDATA2LSB)
                        osAbi = htole(((uint32_t*)data->d_buf)[4]);
                    else
                        osAbi = htobe(((uint32_t*)data->d_buf)[4]);

                    switch(osAbi) {
                      case 0:
                        opSys = ObjectFile::Linux;
                        break;
                      case 2:
                        opSys = ObjectFile::Solaris;
                        break;
                    }
                } // if section found
                if (!strcmp(".SUNW_version", elf_strptr(elf, ehdr.e_shstrndx, shdr.sh_name)))
                        opSys = ObjectFile::Solaris;
                if (!strcmp(".stab.index", elf_strptr(elf, ehdr.e_shstrndx, shdr.sh_name)))
                        opSys = ObjectFile::Solaris;
                if (shdr.sh_type == SHT_NOTE && !strcmp(".note.tag",
                            elf_strptr(elf, ehdr.e_shstrndx, shdr.sh_name))) {
                    data = elf_rawdata(section, NULL);
                    assert(data->d_buf);
                    elem = (uint32_t *)data->d_buf;
                    if (elem[0] == 0x8) { //size of name
                        if (memcmp((void *)&elem[3], "FreeBSD", 0x8) == 0)
                                opSys = ObjectFile::FreeBSD;
                    }
                }

            section = elf_getscn(elf, ++secIdx);
            } // while sections
        }

        ElfObject * result = new ElfObject(fname, len, data, arch, opSys);

        //The number of headers in the file
        result->_programHeaderCount = ehdr.e_phnum;
        //Record the size of each entry
        result->_programHeaderSize = ehdr.e_phentsize;
        if (result->_programHeaderCount) //If there is a program header table
        {
            //Figure out the virtual address of the header table in the
            //final memory image. We use the program headers themselves
            //to translate from a file offset to the address in the image.
            GElf_Phdr phdr;
            uint64_t e_phoff = ehdr.e_phoff;
            result->_programHeaderTable = 0;
            for (int hdrnum = 0; hdrnum < result->_programHeaderCount; hdrnum++)
            {
                gelf_getphdr(elf, hdrnum, &phdr);
                //Check if we've found the segment with the headers in it
                if (phdr.p_offset <= e_phoff &&
                        phdr.p_offset + phdr.p_filesz > e_phoff)
                {
                    result->_programHeaderTable =
                        phdr.p_paddr + (e_phoff - phdr.p_offset);
                    break;
                }
            }
        }
        else
            result->_programHeaderTable = 0;


        if (!skip_interp_check) {
            for (int i = 0; i < ehdr.e_phnum; i++) {
                GElf_Phdr phdr;
                M5_VAR_USED void *check_p = gelf_getphdr(elf, i, &phdr);
                assert(check_p != nullptr);

                if (phdr.p_type != PT_INTERP)
                    continue;

                char *interp_path = (char*)data + phdr.p_offset;
                int fd = open(interp_path, O_RDONLY);
                if (fd == -1) {
                    fatal("Unable to open dynamic executable's "
                          "interpreter.\n");
                }

                struct stat sb;
                M5_VAR_USED int check_i = fstat(fd, &sb);
                assert(check_i == 0);

                void *mm = mmap(nullptr, sb.st_size, PROT_READ,
                                MAP_PRIVATE, fd, 0);
                assert(mm != MAP_FAILED);
                ::close(fd);

                uint8_t *interp_image = (uint8_t*)mm;
                ObjectFile *obj = tryFile(interp_path, sb.st_size,
                                          interp_image, true);
                assert(obj != nullptr);
                result->interpreter = dynamic_cast<ElfObject*>(obj);
                assert(result->interpreter != nullptr);
                break;
            }
        }

        elf_end(elf);
        return result;
    }
}


ElfObject::ElfObject(const string &_filename, size_t _len, uint8_t *_data,
                     Arch _arch, OpSys _opSys)
    : ObjectFile(_filename, _len, _data, _arch, _opSys),
      _programHeaderTable(0), _programHeaderSize(0), _programHeaderCount(0),
      interpreter(nullptr), ldBias(0), relocate(true),
      ldMin(std::numeric_limits<Addr>::max()),
      ldMax(std::numeric_limits<Addr>::min())
{
    Elf *elf;
    GElf_Ehdr ehdr;

    // check that header matches library version
    if (elf_version(EV_CURRENT) == EV_NONE)
        panic("wrong elf version number!");

    // get a pointer to elf structure
    elf = elf_memory((char*)fileData,len);
    assert(elf != NULL);

    // Check that we actually have a elf file
    if (gelf_getehdr(elf, &ehdr) ==0) {
        panic("Not ELF, shouldn't be here");
    }

    entry = ehdr.e_entry;

    // initialize segment sizes to 0 in case they're not present
    text.size = data.size = bss.size = 0;
    text.baseAddr = data.baseAddr = bss.baseAddr = 0;

    int secIdx = 1;
    Elf_Scn *section;
    GElf_Shdr shdr;

    // The first address of some important sections.
    Addr textSecStart = 0;
    Addr dataSecStart = 0;
    Addr bssSecStart = 0;

    // Get the first section
    section = elf_getscn(elf, secIdx);

    // Find the beginning of the most interesting sections.
    while (section != NULL) {
        gelf_getshdr(section, &shdr);
        char * secName = elf_strptr(elf, ehdr.e_shstrndx, shdr.sh_name);

        if (secName) {
            if (!strcmp(".text", secName)) {
                textSecStart = shdr.sh_addr;
            } else if (!strcmp(".data", secName)) {
                dataSecStart = shdr.sh_addr;
            } else if (!strcmp(".bss", secName)) {
                bssSecStart = shdr.sh_addr;
            }
        } else {
            Elf_Error errorNum = (Elf_Error)elf_errno();
            if (errorNum != ELF_E_NONE) {
                const char *errorMessage = elf_errmsg(errorNum);
                fatal("Error from libelf: %s.\n", errorMessage);
            }
        }

        section = elf_getscn(elf, ++secIdx);
    }

    // Go through all the segments in the program, record them, and scrape
    // out information about the text, data, and bss areas needed by other
    // code.
    for (int i = 0; i < ehdr.e_phnum; ++i) {
        GElf_Phdr phdr;
        if (gelf_getphdr(elf, i, &phdr) == 0) {
            panic("gelf_getphdr failed for segment %d.", i);
        }

        // for now we don't care about non-loadable segments
        if (!(phdr.p_type & PT_LOAD))
            continue;

        ldMin = std::min(ldMin, phdr.p_vaddr);
        ldMax = std::max(ldMax, phdr.p_vaddr + phdr.p_memsz);

        // Check to see if this segment contains the bss section.
        if (phdr.p_paddr <= bssSecStart &&
                phdr.p_paddr + phdr.p_memsz > bssSecStart &&
                phdr.p_memsz - phdr.p_filesz > 0) {
            bss.baseAddr = phdr.p_paddr + phdr.p_filesz;
            bss.size = phdr.p_memsz - phdr.p_filesz;
            bss.fileImage = NULL;
        }

        // Check to see if this is the text or data segment
        if (phdr.p_vaddr <= textSecStart &&
                phdr.p_vaddr + phdr.p_filesz > textSecStart) {

            // If this value is nonzero, we need to flip the relocate flag.
            if (phdr.p_vaddr != 0)
                relocate = false;

            text.baseAddr = phdr.p_paddr;
            text.size = phdr.p_filesz;
            text.fileImage = fileData + phdr.p_offset;
        } else if (phdr.p_vaddr <= dataSecStart &&
                phdr.p_vaddr + phdr.p_filesz > dataSecStart) {
            data.baseAddr = phdr.p_paddr;
            data.size = phdr.p_filesz;
            data.fileImage = fileData + phdr.p_offset;
        } else {
            // If it's none of the above but is loadable,
            // load the filesize worth of data
            Segment extra;
            extra.baseAddr = phdr.p_paddr;
            extra.size = phdr.p_filesz;
            extra.fileImage = fileData + phdr.p_offset;
            extraSegments.push_back(extra);
        }
    }

    // should have found at least one loadable segment
    assert(text.size != 0);

    DPRINTFR(Loader, "text: 0x%x %d\ndata: 0x%x %d\nbss: 0x%x %d\n",
             text.baseAddr, text.size, data.baseAddr, data.size,
             bss.baseAddr, bss.size);

    elf_end(elf);

    // We will actually read the sections when we need to load them
}


bool
ElfObject::loadSomeSymbols(SymbolTable *symtab, int binding, Addr mask)
{
    Elf *elf;
    int sec_idx = 1; // there is a 0 but it is nothing, go figure
    Elf_Scn *section;
    GElf_Shdr shdr;
    Elf_Data *data;
    int count, ii;
    bool found = false;
    GElf_Sym sym;

    if (!symtab)
        return false;

    // check that header matches library version
    if (elf_version(EV_CURRENT) == EV_NONE)
        panic("wrong elf version number!");

    // get a pointer to elf structure
    elf = elf_memory((char*)fileData,len);

    assert(elf != NULL);

    // Get the first section
    section = elf_getscn(elf, sec_idx);

    // While there are no more sections
    while (section != NULL) {
        gelf_getshdr(section, &shdr);

        if (shdr.sh_type == SHT_SYMTAB) {
            found = true;
            data = elf_getdata(section, NULL);
            count = shdr.sh_size / shdr.sh_entsize;
            DPRINTF(Loader, "Found Symbol Table, %d symbols present\n", count);

            // loop through all the symbols, only loading global ones
            for (ii = 0; ii < count; ++ii) {
                gelf_getsym(data, ii, &sym);
                if (GELF_ST_BIND(sym.st_info) == binding) {
                    char *sym_name = elf_strptr(elf, shdr.sh_link, sym.st_name);
                    if (sym_name && sym_name[0] != '$') {
                        DPRINTF(Loader, "Symbol: %-40s value %#x\n",
                                sym_name, sym.st_value);
                        symtab->insert(sym.st_value & mask, sym_name);
                    }
                }
            }
        }
        ++sec_idx;
        section = elf_getscn(elf, sec_idx);
    }

    elf_end(elf);

    return found;
}

bool
ElfObject::loadGlobalSymbols(SymbolTable *symtab, Addr addrMask)
{
    return loadSomeSymbols(symtab, STB_GLOBAL, addrMask);
}

bool
ElfObject::loadLocalSymbols(SymbolTable *symtab, Addr addrMask)
{
    bool found_local = loadSomeSymbols(symtab, STB_LOCAL, addrMask);
    bool found_weak = loadSomeSymbols(symtab, STB_WEAK, addrMask);
    return found_local || found_weak;
}

bool
ElfObject::loadWeakSymbols(SymbolTable *symtab, Addr addrMask)
{
    return loadSomeSymbols(symtab, STB_WEAK, addrMask);
}

bool
ElfObject::loadSections(PortProxy& memProxy, Addr addrMask, Addr offset)
{
    if (!ObjectFile::loadSections(memProxy, addrMask, offset))
        return false;

    vector<Segment>::iterator extraIt;
    for (extraIt = extraSegments.begin();
            extraIt != extraSegments.end(); extraIt++) {
        if (!loadSection(&(*extraIt), memProxy, addrMask, offset)) {
            return false;
        }
    }

    if (interpreter)
        interpreter->loadSections(memProxy, addrMask, offset);

    return true;
}

void
ElfObject::getSections()
{
    Elf *elf;
    int sec_idx = 1; // there is a 0 but it is nothing, go figure
    Elf_Scn *section;
    GElf_Shdr shdr;

    GElf_Ehdr ehdr;

    assert(!sectionNames.size());

    // check that header matches library version
    if (elf_version(EV_CURRENT) == EV_NONE)
        panic("wrong elf version number!");

    // get a pointer to elf structure
    elf = elf_memory((char*)fileData,len);
    assert(elf != NULL);

    // Check that we actually have a elf file
    if (gelf_getehdr(elf, &ehdr) ==0) {
        panic("Not ELF, shouldn't be here");
    }

    // Get the first section
    section = elf_getscn(elf, sec_idx);

    // While there are no more sections
    while (section != NULL) {
        gelf_getshdr(section, &shdr);
        sectionNames.insert(elf_strptr(elf, ehdr.e_shstrndx, shdr.sh_name));
        section = elf_getscn(elf, ++sec_idx);
    } // while sections
}

bool
ElfObject::sectionExists(string sec)
{
    if (!sectionNames.size())
        getSections();
    return sectionNames.find(sec) != sectionNames.end();
}


void
ElfObject::updateBias(Addr bias_addr)
{
    // Record the bias.
    ldBias = bias_addr;

    // Patch the entry point with bias_addr.
    entry += bias_addr;

    // Patch segments with the bias_addr.
    text.baseAddr += bias_addr;
    data.baseAddr += bias_addr;
    bss.baseAddr  += bias_addr;
    for (auto &segment : extraSegments)
        segment.baseAddr += bias_addr;
}