Initial commit (from git)
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convert-repo
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# Makefile for sstrip
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sstrip: sstrip.c
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gcc -ggdb -Wall -W -o sstrip sstrip.c
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clean:
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rm -f sstrip
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@@ -0,0 +1,40 @@
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sstrip is a small utility that removes the contents at the end of an
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ELF file that are not part of the program's memory image.
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Most ELF executables are built with both a program header table and a
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section header table. However, only the former is required in order
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for the OS to load, link and execute a program. sstrip attempts to
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extract the ELF header, the program header table, and its contents,
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leaving everything else in the bit bucket. It can only remove parts of
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the file that occur at the end, after the parts to be saved. However,
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this almost always includes the section header table, and occasionally
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a few random sections that are not used when running a program.
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It should be noted that the GNU bfd library is (understandably)
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dependent on the section header table as an index to the file's
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contents. Thus, an executable file that has no section header table
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cannot be used with gdb, objdump, or any other program based upon the
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bfd library, at all. In fact, the program will not even recognize the
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file as a valid executable. (This limitation is noted in the source
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code comments for bfd, and is marked "FIXME", so this may change at
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some future date. However, I would imagine that it is a pretty
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low-priority item, as executables without a section header table are
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rare in the extreme.) This probably also explains why strip doesn't
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offer the option to do this.
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Shared library files may also have their section header table removed.
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Such a library will still function; however, it will no longer be
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possible for a compiler to link a new program against it.
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As an added bonus, sstrip also tries to removes trailing zero bytes
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from the end of the file. (This normally cannot be done with an
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executable that has a section header table.)
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sstrip is a very simplistic program. It depends upon the common
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practice of putting the parts of the file that contribute to the
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memory image at the front, and the remaining material at the end. This
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permits it to discard the latter material without affecting file
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offsets and memory addresses in what remains. However, the ELF
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standard permits files to be organized in almost any order. So
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although this procedure usually works in practice, it is not meant to
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be taken too seriously.
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This distribution is a collection of programs that are generally
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unrelated, except in that they all deal with the ELF file format.
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The main purpose of these programs is to be illustrative and
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educational -- to help fellow programmers understand the ELF file
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format and something of how it works under the Linux platform. For the
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most part, these programs have limited real-world utility. (Although I
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myself have found these programs quite useful while writing the
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others.)
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Each program is independent. There is no shared code between them, and
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in fact they all take slightly different approaches to handling ELF
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files.
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The table of contents:
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sstrip/
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sstrip is a small utility that removes everything from an ELF file
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that is not part of the file's memory image.
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elfls/
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elfls is a utility that displays an ELF file's program and/or
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section header tables, which serve as a kind of global roadmap to
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the file's contents.
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elftoc/
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elftoc takes an ELF file and generates C code that defines a
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structure with the same memory image, using the structures and
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preprocessor symbols defined in <linux/elf.h>.
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ebfc/
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ebfc is a compiler for a tiny programming language. The compiler can
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generate ELF executables, object files, and shared libraries.
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tiny/
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This directory contains a collection of very small ELF executables.
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See the README in each directory for more details.
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The ELF standard is necessary reading if you wish to fully understand
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how these programs work. You can download a copy as a Postscript
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document from ftp://tsx.mit.edu/pub/linux/packages/GCC/ELF.doc.tar.gz.
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Alternately, you can obtain a flat-text transcription of this document
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from http://www.muppetlabs.com/~breadbox/software/ELF.txt.
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All these programs are Copyright (C) 1999 by Brian Raiter.
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These programs are all free software; you can redistribute and/or
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modify them under the terms of the GNU General Public License as
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published by the Free Software Foundation; either version 2 of the
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License, or (at your option) any later version.
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These programs are distributed in the hope that they will be
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interesting, but without any warranty; without even the implied
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warranty of merchantability or fitness for a particular purpose.
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See the GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program, in the file COPYING. If not, write to the
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Free Software Foundation, Inc., 59 Temple Place, Suite 330,
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Boston, MA 02111-1307 USA.
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Bug reports and general feedback should be directed to the author at
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breadbox@muppetlabs.com.
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Share and enjoy.
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Brian Raiter
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breadbox@muppetlabs.com
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July, 1999
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@@ -0,0 +1,218 @@
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/* sstrip, version 1.0: Copyright (C) 1999 by Brian Raiter, under the
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* GNU General Public License. No warranty. See COPYING for details.
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <stdarg.h>
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#include <errno.h>
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#include <unistd.h>
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#include <linux/elf.h>
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#ifndef TRUE
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#define TRUE 1
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#define FALSE 0
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#endif
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/* The memory-allocation macro.
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*/
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#define alloc(p, n) (((p) = realloc(p, n)) \
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|| (fputs("Out of memory.\n", stderr), \
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exit(EXIT_FAILURE), 0))
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static char const *thefilename; /* the current file name */
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static FILE *thefile; /* the current file handle */
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static Elf32_Ehdr elfhdr; /* original ELF header */
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static Elf32_Phdr *phdrs = NULL; /* original program header tbl */
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static unsigned long phdrsize; /* size of program header tbl */
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static unsigned long newsize; /* size of the new file */
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/* An error-handling function. The given error message is used only
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* when errno is not set.
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*/
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static int err(char const *errmsg)
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{
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if (errno)
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perror(thefilename);
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else
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fprintf(stderr, "%s: %s\n", thefilename, errmsg);
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return FALSE;
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}
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/* readheaders() reads the ELF header and the program header table,
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* and checks to make sure that this is in fact a file that we should
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* be munging.
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*/
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static int readheaders(void)
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{
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int bigend;
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errno = 0;
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if (fread(&elfhdr, sizeof elfhdr, 1, thefile) != 1)
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return err("not an ELF file.");
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if (elfhdr.e_ident[EI_MAG0] != ELFMAG0
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|| elfhdr.e_ident[EI_MAG1] != ELFMAG1
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|| elfhdr.e_ident[EI_MAG2] != ELFMAG2
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|| elfhdr.e_ident[EI_MAG3] != ELFMAG3)
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return err("not an ELF file.");
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bigend = TRUE;
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*(char*)&bigend = 0;
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if (elfhdr.e_ident[EI_DATA] != (bigend ? ELFDATA2MSB : ELFDATA2LSB)) {
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fprintf(stderr, "%s: not %s-endian.\n",
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thefilename, bigend ? "big" : "little");
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return FALSE;
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}
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if (elfhdr.e_ehsize != sizeof(Elf32_Ehdr)) {
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fprintf(stderr, "%s: unrecognized ELF header size "
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"(size = %u instead of %u).\n",
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thefilename, elfhdr.e_ehsize, sizeof(Elf32_Ehdr));
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return FALSE;
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}
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if (!elfhdr.e_phoff)
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return err("no program header table.");
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if (elfhdr.e_phentsize != sizeof(Elf32_Phdr)) {
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fprintf(stderr, "%s: unrecognized program header size "
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"(size = %u instead of %u).\n",
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thefilename, elfhdr.e_phentsize, sizeof(Elf32_Ehdr));
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return FALSE;
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}
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phdrsize = elfhdr.e_phnum * elfhdr.e_phentsize;
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alloc(phdrs, phdrsize);
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errno = 0;
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if (fread(phdrs, phdrsize, 1, thefile) != 1)
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return err("invalid program header table.");
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return TRUE;
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}
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/* getloadsize() determines the offset of the last byte of the file
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* that is actually loaded into memory. Anything after this point can
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* be safely discarded.
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*/
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static int getloadsize(void)
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{
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Elf32_Phdr *phdr;
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unsigned long n;
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int i;
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newsize = elfhdr.e_phoff + phdrsize;
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phdr = phdrs;
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for (i = 0 ; i < elfhdr.e_phnum ; ++i) {
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if (phdr->p_type == PT_NULL || phdr->p_type == PT_NOTE)
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continue;
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n = phdr->p_offset + phdr->p_filesz;
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if (n > newsize)
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newsize = n;
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phdr = (Elf32_Phdr*)((char*)phdr + elfhdr.e_phentsize);
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}
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for (i = 0 ; i < elfhdr.e_phnum ; ++i)
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if (phdr->p_filesz > 0 && phdr->p_offset >= newsize)
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memset(phdr, 0, elfhdr.e_phentsize);
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return TRUE;
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}
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/* truncatezeros() examines the bytes at the end of the file's
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* size-to-be, and reduces the size to exclude trailing zero bytes.
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*/
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static int truncatezeros(void)
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{
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char contents[1024];
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unsigned long n;
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do {
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n = sizeof contents;
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if (n > newsize)
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n = newsize;
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if (fseek(thefile, newsize - n, SEEK_SET)
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|| fread(contents, n, 1, thefile) != 1)
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return err("cannot read file contents");
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while (n && !contents[--n])
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--newsize;
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} while (newsize && !n);
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return TRUE;
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}
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/* modifyheaders() removes references to the section header table if
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* it was removed, and reduces program header table entries that
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* included truncated bytes at the end of the file.
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*/
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static int modifyheaders(void)
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{
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Elf32_Phdr *phdr;
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int i;
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if (elfhdr.e_shoff >= newsize) {
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elfhdr.e_shoff = 0;
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elfhdr.e_shnum = 0;
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elfhdr.e_shentsize = 0;
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elfhdr.e_shstrndx = 0;
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}
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phdr = phdrs;
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for (i = 0 ; i < elfhdr.e_phnum ; ++i) {
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if (phdr->p_offset + phdr->p_filesz > newsize) {
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if (phdr->p_offset >= newsize)
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phdr->p_filesz = 0;
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else
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phdr->p_filesz = newsize - phdr->p_offset;
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}
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phdr = (Elf32_Phdr*)((char*)phdr + elfhdr.e_phentsize);
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}
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return TRUE;
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}
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/* savestripped() writes the new headers back to the original file
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* and sets the new file size.
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*/
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static int savestripped(void)
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{
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rewind(thefile);
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errno = 0;
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if (fwrite(&elfhdr, sizeof elfhdr, 1, thefile) != 1
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|| fwrite(phdrs, phdrsize, 1, thefile) != 1
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|| ftruncate(fileno(thefile), newsize)) {
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err("could not write contents");
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fprintf(stderr, "WARNING: %s may be corrupted!\n", thefilename);
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return FALSE;
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}
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return TRUE;
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}
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/* main() loops over the cmdline arguments, leaving all the real work
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* to the other functions.
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*/
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int main(int argc, char *argv[])
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{
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char **arg;
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int ret = 0;
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if (argc < 2 || !strcmp(argv[1], "-h")) {
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printf("sstrip, version 2.0: Copyright (C) 1999 Brian Raiter\n"
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"Usage: sstrip FILE...\n");
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return 0;
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}
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for (arg = argv + 1 ; (thefilename = *arg) != NULL ; ++arg) {
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if (!(thefile = fopen(thefilename, "rb+"))) {
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err("unable to open.");
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++ret;
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continue;
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}
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if (!readheaders() || !getloadsize() || !truncatezeros()
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|| !modifyheaders() || !savestripped())
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++ret;
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fclose(thefile);
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}
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return ret;
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}
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