unexelf.c

早期freebsd实现

/* Copyright (C) 1985, 1986, 1987, 1988 Free Software Foundation, Inc.

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 1, or (at your option)
    any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

In other words, you are welcome to use, share and improve this program.
You are forbidden to forbid anyone else to use, share and improve
what you give them.   Help stamp out software-hoarding!  */


/*
 * unexec.c - Convert a running program into an a.out file.
 *
 * Author:	Spencer W. Thomas
 * 		Computer Science Dept.
 * 		University of Utah
 * Date:	Tue Mar  2 1982
 * Modified heavily since then.
 *
 * Synopsis:
 *	unexec (new_name, a_name, data_start, bss_start, entry_address)
 *	char *new_name, *a_name;
 *	unsigned data_start, bss_start, entry_address;
 *
 * Takes a snapshot of the program and makes an a.out format file in the
 * file named by the string argument new_name.
 * If a_name is non-NULL, the symbol table will be taken from the given file.
 * On some machines, an existing a_name file is required.
 *
 * The boundaries within the a.out file may be adjusted with the data_start
 * and bss_start arguments.  Either or both may be given as 0 for defaults.
 *
 * Data_start gives the boundary between the text segment and the data
 * segment of the program.  The text segment can contain shared, read-only
 * program code and literal data, while the data segment is always unshared
 * and unprotected.  Data_start gives the lowest unprotected address.
 * The value you specify may be rounded down to a suitable boundary
 * as required by the machine you are using.
 *
 * Specifying zero for data_start means the boundary between text and data
 * should not be the same as when the program was loaded.
 * If NO_REMAP is defined, the argument data_start is ignored and the
 * segment boundaries are never changed.
 *
 * Bss_start indicates how much of the data segment is to be saved in the
 * a.out file and restored when the program is executed.  It gives the lowest
 * unsaved address, and is rounded up to a page boundary.  The default when 0
 * is given assumes that the entire data segment is to be stored, including
 * the previous data and bss as well as any additional storage allocated with
 * break (2).
 *
 * The new file is set up to start at entry_address.
 *
 * If you make improvements I'd like to get them too.
 * harpo!utah-cs!thomas, thomas@Utah-20
 *
 */

/* Even more heavily modified by [e-mail] of Dell Computer Co.
 * ELF support added.
 *
 * Basic theory: the data space of the running process needs to be
 * dumped to the output file.  Normally we would just enlarge the size
 * of .data, scooting everything down.  But we can't do that in ELF,
 * because there is often something between the .data space and the
 * .bss space.
 *
 * In the temacs dump below, notice that the Global Offset Table
 * (.got) and the Dynamic link data (.dynamic) come between .data1 and
 * .bss.  It does not work to overlap .data with these fields.
 *
 * The solution is to create a new .data segment.  This segment is
 * filled with data from the current process.  Since the contents of
 * various sections refer to sections by index, the new .data segment
 * is made the last in the table to avoid changing any existing index.

 * This is an example of how the section headers are changed.  "Addr"
 * is a process virtual address.  "Offset" is a file offset.

raid:/nfs/raid/src/dist-18.56/src> dump -h temacs

temacs:

           **** SECTION HEADER TABLE ****
[No]    Type    Flags   Addr         Offset       Size          Name
        Link    Info    Adralgn      Entsize

[1]     1       2       0x80480d4    0xd4         0x13          .interp
        0       0       0x1          0            

[2]     5       2       0x80480e8    0xe8         0x388         .hash
        3       0       0x4          0x4          

[3]     11      2       0x8048470    0x470        0x7f0         .dynsym
        4       1       0x4          0x10         

[4]     3       2       0x8048c60    0xc60        0x3ad         .dynstr
        0       0       0x1          0            

[5]     9       2       0x8049010    0x1010       0x338         .rel.plt
        3       7       0x4          0x8          

[6]     1       6       0x8049348    0x1348       0x3           .init
        0       0       0x4          0            

[7]     1       6       0x804934c    0x134c       0x680         .plt
        0       0       0x4          0x4          

[8]     1       6       0x80499cc    0x19cc       0x3c56f       .text
        0       0       0x4          0            

[9]     1       6       0x8085f3c    0x3df3c      0x3           .fini
        0       0       0x4          0            

[10]    1       2       0x8085f40    0x3df40      0x69c         .rodata
        0       0       0x4          0            

[11]    1       2       0x80865dc    0x3e5dc      0xd51         .rodata1
        0       0       0x4          0            

[12]    1       3       0x8088330    0x3f330      0x20afc       .data
        0       0       0x4          0            

[13]    1       3       0x80a8e2c    0x5fe2c      0x89d         .data1
        0       0       0x4          0            

[14]    1       3       0x80a96cc    0x606cc      0x1a8         .got
        0       0       0x4          0x4          

[15]    6       3       0x80a9874    0x60874      0x80          .dynamic
        4       0       0x4          0x8          

[16]    8       3       0x80a98f4    0x608f4      0x449c        .bss
        0       0       0x4          0            

[17]    2       0       0            0x608f4      0x9b90        .symtab
        18      371     0x4          0x10         

[18]    3       0       0            0x6a484      0x8526        .strtab
        0       0       0x1          0            

[19]    3       0       0            0x729aa      0x93          .shstrtab
        0       0       0x1          0            

[20]    1       0       0            0x72a3d      0x68b7        .comment
        0       0       0x1          0            

raid:/nfs/raid/src/dist-18.56/src> dump -h xemacs

xemacs:

           **** SECTION HEADER TABLE ****
[No]    Type    Flags   Addr         Offset       Size          Name
        Link    Info    Adralgn      Entsize

[1]     1       2       0x80480d4    0xd4         0x13          .interp
        0       0       0x1          0            

[2]     5       2       0x80480e8    0xe8         0x388         .hash
        3       0       0x4          0x4          

[3]     11      2       0x8048470    0x470        0x7f0         .dynsym
        4       1       0x4          0x10         

[4]     3       2       0x8048c60    0xc60        0x3ad         .dynstr
        0       0       0x1          0            

[5]     9       2       0x8049010    0x1010       0x338         .rel.plt
        3       7       0x4          0x8          

[6]     1       6       0x8049348    0x1348       0x3           .init
        0       0       0x4          0            

[7]     1       6       0x804934c    0x134c       0x680         .plt
        0       0       0x4          0x4          

[8]     1       6       0x80499cc    0x19cc       0x3c56f       .text
        0       0       0x4          0            

[9]     1       6       0x8085f3c    0x3df3c      0x3           .fini
        0       0       0x4          0            

[10]    1       2       0x8085f40    0x3df40      0x69c         .rodata
        0       0       0x4          0            

[11]    1       2       0x80865dc    0x3e5dc      0xd51         .rodata1
        0       0       0x4          0            

[12]    1       3       0x8088330    0x3f330      0x20afc       .data
        0       0       0x4          0            

[13]    1       3       0x80a8e2c    0x5fe2c      0x89d         .data1
        0       0       0x4          0            

[14]    1       3       0x80a96cc    0x606cc      0x1a8         .got
        0       0       0x4          0x4          

[15]    6       3       0x80a9874    0x60874      0x80          .dynamic
        4       0       0x4          0x8          

[16]    8       3       0x80c6800    0x7d800      0             .bss
        0       0       0x4          0            

[17]    2       0       0            0x7d800      0x9b90        .symtab
        18      371     0x4          0x10         

[18]    3       0       0            0x87390      0x8526        .strtab
        0       0       0x1          0            

[19]    3       0       0            0x8f8b6      0x93          .shstrtab
        0       0       0x1          0            

[20]    1       0       0            0x8f949      0x68b7        .comment
        0       0       0x1          0            

[21]    1       3       0x80a98f4    0x608f4      0x1cf0c       .data
        0       0       0x4          0            

 * This is an example of how the file header is changed.  "Shoff" is
 * the section header offset within the file.  Since that table is
 * after the new .data section, it is moved.  "Shnum" is the number of
 * sections, which we increment.
 *
 * "Phoff" is the file offset to the program header.  "Phentsize" and
 * "Shentsz" are the program and section header entries sizes respectively.
 * These can be larger than the apparent struct sizes.

raid:/nfs/raid/src/dist-18.56/src> dump -f temacs

temacs:

                    **** ELF HEADER ****
Class        Data       Type         Machine     Version
Entry        Phoff      Shoff        Flags       Ehsize
Phentsize    Phnum      Shentsz      Shnum       Shstrndx

1            1          2            3           1
0x80499cc    0x34       0x792f4      0           0x34
0x20         5          0x28         21          19

raid:/nfs/raid/src/dist-18.56/src> dump -f xemacs

xemacs:

                    **** ELF HEADER ****
Class        Data       Type         Machine     Version
Entry        Phoff      Shoff        Flags       Ehsize
Phentsize    Phnum      Shentsz      Shnum       Shstrndx

1            1          2            3           1
0x80499cc    0x34       0x96200      0           0x34
0x20         5          0x28         22          19

 * These are the program headers.  "Offset" is the file offset to the
 * segment.  "Vaddr" is the memory load address.  "Filesz" is the
 * segment size as it appears in the file, and "Memsz" is the size in
 * memory.  Below, the third segment is the code and the fourth is the
 * data: the difference between Filesz and Memsz is .bss

raid:/nfs/raid/src/dist-18.56/src> dump -o temacs

temacs:
 ***** PROGRAM EXECUTION HEADER *****
Type        Offset      Vaddr       Paddr
Filesz      Memsz       Flags       Align

6           0x34        0x8048034   0           
0xa0        0xa0        5           0           

3           0xd4        0           0           
0x13        0           4           0           

1           0x34        0x8048034   0           
0x3f2f9     0x3f2f9     5           0x1000      

1           0x3f330     0x8088330   0           
0x215c4     0x25a60     7           0x1000      

2           0x60874     0x80a9874   0           
0x80        0           7           0           

raid:/nfs/raid/src/dist-18.56/src> dump -o xemacs

xemacs:
 ***** PROGRAM EXECUTION HEADER *****
Type        Offset      Vaddr       Paddr
Filesz      Memsz       Flags       Align

6           0x34        0x8048034   0           
0xa0        0xa0        5           0           

3           0xd4        0           0           
0x13        0           4           0           

1           0x34        0x8048034   0           
0x3f2f9     0x3f2f9     5           0x1000      

1           0x3f330     0x8088330   0           
0x3e4d0     0x3e4d0     7           0x1000