elf_object.cc

linux下基于c++的处理器仿真平台。具有处理器流水线

/*
 * Copyright (c) 2003, 2004, 2005
 * The Regents of The University of Michigan
 * All Rights Reserved
 *
 * This code is part of the M5 simulator, developed by Nathan Binkert,
 * Erik Hallnor, Steve Raasch, and Steve Reinhardt, with contributions
 * from Ron Dreslinski, Dave Greene, Lisa Hsu, Kevin Lim, Ali Saidi,
 * and Andrew Schultz.
 *
 * Permission is granted to use, copy, create derivative works and
 * redistribute this software and such derivative works for any
 * purpose, so long as the copyright notice above, this grant of
 * permission, and the disclaimer below appear in all copies made; and
 * so long as the name of The University of Michigan is not used in
 * any advertising or publicity pertaining to the use or distribution
 * of this software without specific, written prior authorization.
 *
 * THIS SOFTWARE IS PROVIDED AS IS, WITHOUT REPRESENTATION FROM THE
 * UNIVERSITY OF MICHIGAN AS TO ITS FITNESS FOR ANY PURPOSE, AND
 * WITHOUT WARRANTY BY THE UNIVERSITY OF MICHIGAN OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE. THE REGENTS OF THE UNIVERSITY OF MICHIGAN SHALL NOT BE
 * LIABLE FOR ANY DAMAGES, INCLUDING DIRECT, SPECIAL, INDIRECT,
 * INCIDENTAL, OR CONSEQUENTIAL DAMAGES, WITH RESPECT TO ANY CLAIM
 * ARISING OUT OF OR IN CONNECTION WITH THE USE OF THE SOFTWARE, EVEN
 * IF IT HAS BEEN OR IS HEREAFTER ADVISED OF THE POSSIBILITY OF SUCH
 * DAMAGES.
 */

#include <string>

// Because of the -Wundef flag we have to do this
#define __LIBELF_INTERNAL__     0
// counterintuitive, but the flag below causes libelf to define
// 64-bit elf types that apparently didn't exist in some older
// versions of Linux.  They seem to be there in 2.4.x, so don't
// set this now (it causes things to break on 64-bit platforms).
#define __LIBELF64_LINUX        0
#define __LIBELF_NEED_LINK_H    0
#define __LIBELF_SYMBOL_VERSIONS 0

#include <libelf/libelf.h>
#include <libelf/gelf.h>

#include "base/loader/elf_object.hh"

#include "mem/functional/functional.hh"
#include "base/loader/symtab.hh"

#include "base/trace.hh"	// for DPRINTF


using namespace std;

ObjectFile *
ElfObject::tryFile(const string &fname, int fd, size_t len, uint8_t *data)
{
    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*)data,len);
    // will only fail if fd is invalid
    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 {
        if (ehdr.e_ident[EI_CLASS] == ELFCLASS32)
            panic("32 bit ELF Binary, Not Supported");
        /* @todo this emachine value isn't offical yet. 
         *       so we probably shouldn't check it. */
//        if (ehdr.e_machine != EM_ALPHA)
//            panic("Non Alpha Binary, Not Supported");

        elf_end(elf);
	
        return new ElfObject(fname, fd, len, data,
			     ObjectFile::Alpha, ObjectFile::Linux);
    }
}


ElfObject::ElfObject(const string &_filename, int _fd,
		     size_t _len, uint8_t *_data,
		     Arch _arch, OpSys _opSys)
    : ObjectFile(_filename, _fd, _len, _data, _arch, _opSys)

{
    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);
    // will only fail if fd is invalid
    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;

    for (int i = 0; i < ehdr.e_phnum; ++i) {
	GElf_Phdr phdr;
	if (gelf_getphdr(elf, i, &phdr) == 0) {
	    panic("gelf_getphdr failed for section %d", i);
	}

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

	// the headers don't explicitly distinguish text from data,
	// but empirically the text segment comes first.
	if (text.size == 0) {  // haven't seen text segment yet
	    text.baseAddr = phdr.p_vaddr;
	    text.size = phdr.p_filesz;
	    // remember where the data is for loadSections()
	    fileTextBits = fileData + phdr.p_offset;
	    // if there's any padding at the end that's not in the
	    // file, call it the bss.  This happens in the "text"
	    // segment if there's only one loadable segment (as for
	    // kernel images).
	    bss.size = phdr.p_memsz - phdr.p_filesz;
	    bss.baseAddr = phdr.p_vaddr + phdr.p_filesz;
	}
	else if (data.size == 0) { // have text, this must be data
	    data.baseAddr = phdr.p_vaddr;
	    data.size = phdr.p_filesz;
	    // remember where the data is for loadSections()
	    fileDataBits = fileData + phdr.p_offset;
	    // if there's any padding at the end that's not in the
	    // file, call it the bss.  Warn if this happens for both
	    // the text & data segments (should only have one bss).
	    if (phdr.p_memsz - phdr.p_filesz > 0 && bss.size != 0) {
		warn("Two implied bss segments in file!\n");
	    }
 	    bss.size = phdr.p_memsz - phdr.p_filesz;
	    bss.baseAddr = phdr.p_vaddr + phdr.p_filesz;
	}
    }

    // 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::loadSections(FunctionalMemory *mem, bool loadPhys)
{
    Addr textAddr = text.baseAddr;
    Addr dataAddr = data.baseAddr;

    if (loadPhys) {
	textAddr &= (ULL(1) << 40) - 1;
	dataAddr &= (ULL(1) << 40) - 1;
    }

    // Since we don't really have an MMU and all memory is
    // zero-filled, there's no need to set up the BSS segment.
    if (text.size != 0)
	mem->prot_write(textAddr, fileTextBits, text.size);
    if (data.size != 0)
	mem->prot_write(dataAddr, fileDataBits, data.size);

    return true;
}


bool
ElfObject::loadSomeSymbols(SymbolTable *symtab, int binding)
{
    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) {
                   symtab->insert(sym.st_value,
				  elf_strptr(elf, shdr.sh_link, sym.st_name));
                }
            }
        }
        ++sec_idx;
        section = elf_getscn(elf, sec_idx);
    }

    elf_end(elf);

    return found;
}

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

bool
ElfObject::loadLocalSymbols(SymbolTable *symtab)
{
    return loadSomeSymbols(symtab, STB_LOCAL);
}