elfload.c

qemu虚拟机代码

	}
    }
    return; /* Shouldn't happen... */

 found:
    /* Now know where the strtab and symtab are.  Snarf them. */
    s = malloc(sizeof(*s));
    s->disas_symtab = malloc(symtab.sh_size);
    s->disas_strtab = strings = malloc(strtab.sh_size);
    if (!s->disas_symtab || !s->disas_strtab)
	return;
	
    lseek(fd, symtab.sh_offset, SEEK_SET);
    if (read(fd, s->disas_symtab, symtab.sh_size) != symtab.sh_size)
	return;

#ifdef BSWAP_NEEDED
    for (i = 0; i < symtab.sh_size / sizeof(struct elf_sym); i++)
	bswap_sym(s->disas_symtab + sizeof(struct elf_sym)*i);
#endif

    lseek(fd, strtab.sh_offset, SEEK_SET);
    if (read(fd, strings, strtab.sh_size) != strtab.sh_size)
	return;
    s->disas_num_syms = symtab.sh_size / sizeof(struct elf_sym);
    s->next = syminfos;
    syminfos = s;
}

static int load_elf_binary(struct linux_binprm * bprm, struct target_pt_regs * regs,
                           struct image_info * info)
{
    struct elfhdr elf_ex;
    struct elfhdr interp_elf_ex;
    struct exec interp_ex;
    int interpreter_fd = -1; /* avoid warning */
    unsigned long load_addr, load_bias;
    int load_addr_set = 0;
    unsigned int interpreter_type = INTERPRETER_NONE;
    unsigned char ibcs2_interpreter;
    int i;
    unsigned long mapped_addr;
    struct elf_phdr * elf_ppnt;
    struct elf_phdr *elf_phdata;
    unsigned long elf_bss, k, elf_brk;
    int retval;
    char * elf_interpreter;
    unsigned long elf_entry, interp_load_addr = 0;
    int status;
    unsigned long start_code, end_code, end_data;
    unsigned long elf_stack;
    char passed_fileno[6];

    ibcs2_interpreter = 0;
    status = 0;
    load_addr = 0;
    load_bias = 0;
    elf_ex = *((struct elfhdr *) bprm->buf);          /* exec-header */
#ifdef BSWAP_NEEDED
    bswap_ehdr(&elf_ex);
#endif

    if (elf_ex.e_ident[0] != 0x7f ||
	strncmp(&elf_ex.e_ident[1], "ELF",3) != 0) {
	    return  -ENOEXEC;
    }

    /* First of all, some simple consistency checks */
    if ((elf_ex.e_type != ET_EXEC && elf_ex.e_type != ET_DYN) ||
       				(! elf_check_arch(elf_ex.e_machine))) {
	    return -ENOEXEC;
    }

    /* Now read in all of the header information */
    elf_phdata = (struct elf_phdr *)malloc(elf_ex.e_phentsize*elf_ex.e_phnum);
    if (elf_phdata == NULL) {
	return -ENOMEM;
    }

    retval = lseek(bprm->fd, elf_ex.e_phoff, SEEK_SET);
    if(retval > 0) {
	retval = read(bprm->fd, (char *) elf_phdata, 
				elf_ex.e_phentsize * elf_ex.e_phnum);
    }

    if (retval < 0) {
	perror("load_elf_binary");
	exit(-1);
	free (elf_phdata);
	return -errno;
    }

#ifdef BSWAP_NEEDED
    elf_ppnt = elf_phdata;
    for (i=0; i<elf_ex.e_phnum; i++, elf_ppnt++) {
        bswap_phdr(elf_ppnt);
    }
#endif
    elf_ppnt = elf_phdata;

    elf_bss = 0;
    elf_brk = 0;


    elf_stack = ~0UL;
    elf_interpreter = NULL;
    start_code = ~0UL;
    end_code = 0;
    end_data = 0;

    for(i=0;i < elf_ex.e_phnum; i++) {
	if (elf_ppnt->p_type == PT_INTERP) {
	    if ( elf_interpreter != NULL )
	    {
		free (elf_phdata);
		free(elf_interpreter);
		close(bprm->fd);
		return -EINVAL;
	    }

	    /* This is the program interpreter used for
	     * shared libraries - for now assume that this
	     * is an a.out format binary
	     */

	    elf_interpreter = (char *)malloc(elf_ppnt->p_filesz);

	    if (elf_interpreter == NULL) {
		free (elf_phdata);
		close(bprm->fd);
		return -ENOMEM;
	    }

	    retval = lseek(bprm->fd, elf_ppnt->p_offset, SEEK_SET);
	    if(retval >= 0) {
		retval = read(bprm->fd, elf_interpreter, elf_ppnt->p_filesz);
	    }
	    if(retval < 0) {
	 	perror("load_elf_binary2");
		exit(-1);
	    }	

	    /* If the program interpreter is one of these two,
	       then assume an iBCS2 image. Otherwise assume
	       a native linux image. */

	    /* JRP - Need to add X86 lib dir stuff here... */

	    if (strcmp(elf_interpreter,"/usr/lib/libc.so.1") == 0 ||
		strcmp(elf_interpreter,"/usr/lib/ld.so.1") == 0) {
	      ibcs2_interpreter = 1;
	    }

#if 0
	    printf("Using ELF interpreter %s\n", elf_interpreter);
#endif
	    if (retval >= 0) {
		retval = open(path(elf_interpreter), O_RDONLY);
		if(retval >= 0) {
		    interpreter_fd = retval;
		}
		else {
		    perror(elf_interpreter);
		    exit(-1);
		    /* retval = -errno; */
		}
	    }

	    if (retval >= 0) {
		retval = lseek(interpreter_fd, 0, SEEK_SET);
		if(retval >= 0) {
		    retval = read(interpreter_fd,bprm->buf,128);
		}
	    }
	    if (retval >= 0) {
		interp_ex = *((struct exec *) bprm->buf); /* aout exec-header */
		interp_elf_ex=*((struct elfhdr *) bprm->buf); /* elf exec-header */
	    }
	    if (retval < 0) {
		perror("load_elf_binary3");
		exit(-1);
		free (elf_phdata);
		free(elf_interpreter);
		close(bprm->fd);
		return retval;
	    }
	}
	elf_ppnt++;
    }

    /* Some simple consistency checks for the interpreter */
    if (elf_interpreter){
	interpreter_type = INTERPRETER_ELF | INTERPRETER_AOUT;

	/* Now figure out which format our binary is */
	if ((N_MAGIC(interp_ex) != OMAGIC) && (N_MAGIC(interp_ex) != ZMAGIC) &&
	    	(N_MAGIC(interp_ex) != QMAGIC)) {
	  interpreter_type = INTERPRETER_ELF;
	}

	if (interp_elf_ex.e_ident[0] != 0x7f ||
	    	strncmp(&interp_elf_ex.e_ident[1], "ELF",3) != 0) {
	    interpreter_type &= ~INTERPRETER_ELF;
	}

	if (!interpreter_type) {
	    free(elf_interpreter);
	    free(elf_phdata);
	    close(bprm->fd);
	    return -ELIBBAD;
	}
    }

    /* OK, we are done with that, now set up the arg stuff,
       and then start this sucker up */

    if (!bprm->sh_bang) {
	char * passed_p;

	if (interpreter_type == INTERPRETER_AOUT) {
	    snprintf(passed_fileno, sizeof(passed_fileno), "%d", bprm->fd);
	    passed_p = passed_fileno;

	    if (elf_interpreter) {
		bprm->p = copy_strings(1,&passed_p,bprm->page,bprm->p);
		bprm->argc++;
	    }
	}
	if (!bprm->p) {
	    if (elf_interpreter) {
	        free(elf_interpreter);
	    }
	    free (elf_phdata);
	    close(bprm->fd);
	    return -E2BIG;
	}
    }

    /* OK, This is the point of no return */
    info->end_data = 0;
    info->end_code = 0;
    info->start_mmap = (unsigned long)ELF_START_MMAP;
    info->mmap = 0;
    elf_entry = (unsigned long) elf_ex.e_entry;

    /* Do this so that we can load the interpreter, if need be.  We will
       change some of these later */
    info->rss = 0;
    bprm->p = setup_arg_pages(bprm->p, bprm, info);
    info->start_stack = bprm->p;

    /* Now we do a little grungy work by mmaping the ELF image into
     * the correct location in memory.  At this point, we assume that
     * the image should be loaded at fixed address, not at a variable
     * address.
     */

    for(i = 0, elf_ppnt = elf_phdata; i < elf_ex.e_phnum; i++, elf_ppnt++) {
        int elf_prot = 0;
        int elf_flags = 0;
        unsigned long error;
        
	if (elf_ppnt->p_type != PT_LOAD)
            continue;
        
        if (elf_ppnt->p_flags & PF_R) elf_prot |= PROT_READ;
        if (elf_ppnt->p_flags & PF_W) elf_prot |= PROT_WRITE;
        if (elf_ppnt->p_flags & PF_X) elf_prot |= PROT_EXEC;
        elf_flags = MAP_PRIVATE | MAP_DENYWRITE;
        if (elf_ex.e_type == ET_EXEC || load_addr_set) {
            elf_flags |= MAP_FIXED;
        } else if (elf_ex.e_type == ET_DYN) {
            /* Try and get dynamic programs out of the way of the default mmap
               base, as well as whatever program they might try to exec.  This
               is because the brk will follow the loader, and is not movable.  */
            /* NOTE: for qemu, we do a big mmap to get enough space
               without harcoding any address */
            error = target_mmap(0, ET_DYN_MAP_SIZE,
                                PROT_NONE, MAP_PRIVATE | MAP_ANON, 
                                -1, 0);
            if (error == -1) {
                perror("mmap");
                exit(-1);
            }
            load_bias = TARGET_ELF_PAGESTART(error - elf_ppnt->p_vaddr);
        }
        
        error = target_mmap(TARGET_ELF_PAGESTART(load_bias + elf_ppnt->p_vaddr),
                            (elf_ppnt->p_filesz +
                             TARGET_ELF_PAGEOFFSET(elf_ppnt->p_vaddr)),
                            elf_prot,
                            (MAP_FIXED | MAP_PRIVATE | MAP_DENYWRITE),
                            bprm->fd,
                            (elf_ppnt->p_offset - 
                             TARGET_ELF_PAGEOFFSET(elf_ppnt->p_vaddr)));
        if (error == -1) {
            perror("mmap");
            exit(-1);
        }

#ifdef LOW_ELF_STACK
        if (TARGET_ELF_PAGESTART(elf_ppnt->p_vaddr) < elf_stack)
            elf_stack = TARGET_ELF_PAGESTART(elf_ppnt->p_vaddr);
#endif
        
        if (!load_addr_set) {
            load_addr_set = 1;
            load_addr = elf_ppnt->p_vaddr - elf_ppnt->p_offset;
            if (elf_ex.e_type == ET_DYN) {
                load_bias += error -
                    TARGET_ELF_PAGESTART(load_bias + elf_ppnt->p_vaddr);
                load_addr += load_bias;
            }
        }
        k = elf_ppnt->p_vaddr;
        if (k < start_code) 
            start_code = k;
        k = elf_ppnt->p_vaddr + elf_ppnt->p_filesz;
        if (k > elf_bss) 
            elf_bss = k;
        if ((elf_ppnt->p_flags & PF_X) && end_code <  k)
            end_code = k;
        if (end_data < k) 
            end_data = k;
        k = elf_ppnt->p_vaddr + elf_ppnt->p_memsz;
        if (k > elf_brk) elf_brk = k;
    }

    elf_entry += load_bias;
    elf_bss += load_bias;
    elf_brk += load_bias;
    start_code += load_bias;
    end_code += load_bias;
    //    start_data += load_bias;
    end_data += load_bias;

    if (elf_interpreter) {
	if (interpreter_type & 1) {
	    elf_entry = load_aout_interp(&interp_ex, interpreter_fd);
	}
	else if (interpreter_type & 2) {
	    elf_entry = load_elf_interp(&interp_elf_ex, interpreter_fd,
					    &interp_load_addr);
	}

	close(interpreter_fd);
	free(elf_interpreter);

	if (elf_entry == ~0UL) {
	    printf("Unable to load interpreter\n");
	    free(elf_phdata);
	    exit(-1);
	    return 0;
	}
    }

    free(elf_phdata);

    if (loglevel)
	load_symbols(&elf_ex, bprm->fd);

    if (interpreter_type != INTERPRETER_AOUT) close(bprm->fd);
    info->personality = (ibcs2_interpreter ? PER_SVR4 : PER_LINUX);

#ifdef LOW_ELF_STACK
    info->start_stack = bprm->p = elf_stack - 4;
#endif
    bprm->p = create_elf_tables(bprm->p,
		    bprm->argc,
		    bprm->envc,
                    &elf_ex,
                    load_addr, load_bias,
		    interp_load_addr,
		    (interpreter_type == INTERPRETER_AOUT ? 0 : 1),
		    info);
    if (interpreter_type == INTERPRETER_AOUT)
      info->arg_start += strlen(passed_fileno) + 1;
    info->start_brk = info->brk = elf_brk;
    info->end_code = end_code;
    info->start_code = start_code;
    info->end_data = end_data;
    info->start_stack = bprm->p;

    /* Calling set_brk effectively mmaps the pages that we need for the bss and break
       sections */
    set_brk(elf_bss, elf_brk);

    padzero(elf_bss);

#if 0
    printf("(start_brk) %x\n" , info->start_brk);
    printf("(end_code) %x\n" , info->end_code);
    printf("(start_code) %x\n" , info->start_code);
    printf("(end_data) %x\n" , info->end_data);
    printf("(start_stack) %x\n" , info->start_stack);
    printf("(brk) %x\n" , info->brk);
#endif

    if ( info->personality == PER_SVR4 )
    {
	    /* Why this, you ask???  Well SVr4 maps page 0 as read-only,
	       and some applications "depend" upon this behavior.
	       Since we do not have the power to recompile these, we
	       emulate the SVr4 behavior.  Sigh.  */
	    mapped_addr = target_mmap(0, qemu_host_page_size, PROT_READ | PROT_EXEC,
                                      MAP_FIXED | MAP_PRIVATE, -1, 0);
    }

#ifdef ELF_PLAT_INIT
    /*
     * The ABI may specify that certain registers be set up in special
     * ways (on i386 %edx is the address of a DT_FINI function, for
     * example.  This macro performs whatever initialization to
     * the regs structure is required.
     */
    ELF_PLAT_INIT(regs);
#endif


    info->entry = elf_entry;

    return 0;
}



int elf_exec(const char * filename, char ** argv, char ** envp, 
             struct target_pt_regs * regs, struct image_info *infop)
{
        struct linux_binprm bprm;
        int retval;
        int i;

        bprm.p = TARGET_PAGE_SIZE*MAX_ARG_PAGES-sizeof(unsigned int);
        for (i=0 ; i<MAX_ARG_PAGES ; i++)       /* clear page-table */
                bprm.page[i] = 0;
        retval = open(filename, O_RDONLY);
        if (retval < 0)
            return retval;
        bprm.fd = retval;
        bprm.filename = (char *)filename;
        bprm.sh_bang = 0;
        bprm.loader = 0;
        bprm.exec = 0;
        bprm.dont_iput = 0;
	bprm.argc = count(argv);
	bprm.envc = count(envp);

        retval = prepare_binprm(&bprm);

        if(retval>=0) {
	    bprm.p = copy_strings(1, &bprm.filename, bprm.page, bprm.p);
	    bprm.exec = bprm.p;
	    bprm.p = copy_strings(bprm.envc,envp,bprm.page,bprm.p);
	    bprm.p = copy_strings(bprm.argc,argv,bprm.page,bprm.p);
	    if (!bprm.p) {
		retval = -E2BIG;
	    }
        }

        if(retval>=0) {
	    retval = load_elf_binary(&bprm,regs,infop);
	}
        
        if(retval>=0) {
	    /* success.  Initialize important registers */
            init_thread(regs, infop);
	    return retval;
	}

        /* Something went wrong, return the inode and free the argument pages*/
        for (i=0 ; i<MAX_ARG_PAGES ; i++) {
	    free(bprm.page[i]);
	}
        return(retval);
}


static int load_aout_interp(void * exptr, int interp_fd)
{
    printf("a.out interpreter not yet supported\n");
    return(0);
}