path: root/distrib/crunch/crunchide/crunchide.c

/* $OpenBSD: crunchide.c,v 1.20 2005/12/21 01:40:22 millert Exp $	 */

/*
 * Copyright (c) 1994 University of Maryland
 * All Rights Reserved.
 *
 * Permission to use, copy, modify, distribute, and sell this software and its
 * documentation for any purpose is hereby granted without fee, provided that
 * the above copyright notice appear in all copies and that both that
 * copyright notice and this permission notice appear in supporting
 * documentation, and that the name of U.M. not be used in advertising or
 * publicity pertaining to distribution of the software without specific,
 * written prior permission.  U.M. makes no representations about the
 * suitability of this software for any purpose.  It is provided "as is"
 * without express or implied warranty.
 *
 * U.M. DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL U.M.
 * BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 * Author: James da Silva, Systems Design and Analysis Group
 *			   Computer Science Department
 *			   University of Maryland at College Park
 */
/*
 * crunchide.c - tiptoes through an a.out symbol table, hiding all defined
 *	global symbols.  Allows the user to supply a "keep list" of symbols
 *	that are not to be hidden.  This program relies on the use of the
 * 	linker's -dc flag to actually put global bss data into the file's
 * 	bss segment (rather than leaving it as undefined "common" data).
 *
 * 	The point of all this is to allow multiple programs to be linked
 *	together without getting multiple-defined errors.
 *
 *	For example, consider a program "foo.c".  It can be linked with a
 *	small stub routine, called "foostub.c", eg:
 *	    int foo_main(int argc, char **argv){ return main(argc, argv); }
 *      like so:
 *	    cc -c foo.c foostub.c
 *	    ld -dc -r foo.o foostub.o -o foo.combined.o
 *	    crunchide -k _foo_main foo.combined.o
 *	at this point, foo.combined.o can be linked with another program
 * 	and invoked with "foo_main(argc, argv)".  foo's main() and any
 * 	other globals are hidden and will not conflict with other symbols.
 *
 * TODO:
 *	- resolve the theoretical hanging reloc problem (see check_reloc()
 *	  below). I have yet to see this problem actually occur in any real
 *	  program. In what cases will gcc/gas generate code that needs a
 *	  relative reloc from a global symbol, other than PIC?  The
 *	  solution is to not hide the symbol from the linker in this case,
 *	  but to generate some random name for it so that it doesn't link
 *	  with anything but holds the place for the reloc.
 *      - arrange that all the BSS segments start at the same address, so
 *	  that the final crunched binary BSS size is the max of all the
 *	  component programs' BSS sizes, rather than their sum.
 */
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <a.out.h>
#include <sys/types.h>
#ifdef _NLIST_DO_ECOFF
#include <sys/exec_ecoff.h>
#endif
#include <sys/mman.h>
#include <sys/stat.h>

/*
 * if __ELF__ is defined, do not bother supporting AOUT.
 */
#if defined(_NLIST_DO_AOUT) && !(defined(__ELF__))
#define DO_AOUT
#endif

char           *pname = "crunchide";

void            usage(void);

void            add_to_keep_list(char *);
void            add_file_to_keep_list(char *);

void            hide_syms(char *);
#ifdef _NLIST_DO_ECOFF
void            ecoff_hide(int, char *);
#endif
#ifdef _NLIST_DO_ELF
void            elf_hide(int, char *);
#endif

int 
main(int argc, char *argv[])
{
	int             ch;

	if (argc > 0)
		pname = argv[0];

	while ((ch = getopt(argc, argv, "k:f:")) != -1)
		switch (ch) {
		case 'k':
			add_to_keep_list(optarg);
			break;
		case 'f':
			add_file_to_keep_list(optarg);
			break;
		default:
			usage();
		}

	argc -= optind;
	argv += optind;

	if (argc == 0)
		usage();

	while (argc) {
		hide_syms(*argv);
		argc--;
		argv++;
	}

	return 0;
}

void 
usage(void)
{
	fprintf(stderr,
	    "Usage: %s [-f keep-list-file] [-k keep-symbol] object-file ...\n",
	    pname);
	exit(1);
}

struct keep {
	struct keep    *next;
	char           *sym;
} *keep_list;

void 
add_to_keep_list(char *symbol)
{
	struct keep    *newp, *prevp, *curp;
	int             cmp;

	for (curp = keep_list, prevp = NULL; curp; prevp = curp, curp = curp->next)
		if ((cmp = strcmp(symbol, curp->sym)) <= 0)
			break;

	if (curp && cmp == 0)
		return;		/* already in table */

	newp = (struct keep *) calloc(1, sizeof(struct keep));
	if (newp)
		newp->sym = strdup(symbol);
	if (newp == NULL || newp->sym == NULL) {
		fprintf(stderr, "%s: out of memory for keep list\n", pname);
		exit(1);
	}
	newp->next = curp;
	if (prevp)
		prevp->next = newp;
	else
		keep_list = newp;
}

int 
in_keep_list(char *symbol)
{
	struct keep    *curp;
	int             cmp;

	for (curp = keep_list; curp; curp = curp->next)
		if ((cmp = strcmp(symbol, curp->sym)) <= 0)
			break;

	return curp && cmp == 0;
}

void 
add_file_to_keep_list(char *filename)
{
	FILE           *keepf;
	char            symbol[1024];
	int             len;

	if ((keepf = fopen(filename, "r")) == NULL) {
		perror(filename);
		usage();
	}
	while (fgets(symbol, 1024, keepf)) {
		len = strlen(symbol);
		if (len && symbol[len - 1] == '\n')
			symbol[len - 1] = '\0';

		add_to_keep_list(symbol);
	}
	fclose(keepf);
}

int             nsyms, ntextrel, ndatarel;
struct exec    *hdrp;
char           *aoutdata, *strbase;
struct relocation_info *textrel, *datarel;
struct nlist   *symbase;

#define SYMSTR(sp)	&strbase[(sp)->n_un.n_strx]

/* is the symbol a global symbol defined in the current file? */
#define IS_GLOBAL_DEFINED(sp) \
	(((sp)->n_type & N_EXT) && ((sp)->n_type & N_TYPE) != N_UNDF)

#ifdef DO_AOUT
#if defined(__sparc__)
/* is the relocation entry dependent on a symbol? */
#define IS_SYMBOL_RELOC(rp)   \
	((rp)->r_extern || \
	((rp)->r_type >= RELOC_BASE10 && (rp)->r_type <= RELOC_BASE22) || \
	(rp)->r_type == RELOC_JMP_TBL)
#else
/* is the relocation entry dependent on a symbol? */
#define IS_SYMBOL_RELOC(rp)   \
		  ((rp)->r_extern||(rp)->r_baserel||(rp)->r_jmptable)
#endif
#endif

void            check_reloc(char *filename, struct relocation_info * relp);

void 
hide_syms(char *filename)
{
	int             inf, outf, rc;
	struct stat     infstat;
	struct relocation_info *relp;
	struct nlist   *symp;
	char           *buf;
	u_char          zero = 0;

	/*
         * Open the file and do some error checking.
         */

	if ((inf = open(filename, O_RDWR)) == -1) {
		perror(filename);
		return;
	}
	if (fstat(inf, &infstat) == -1) {
		perror(filename);
		close(inf);
		return;
	}
	if (infstat.st_size < sizeof(struct exec)) {
		fprintf(stderr, "%s: short file\n", filename);
		close(inf);
		return;
	}
	if ((buf = mmap(NULL, infstat.st_size, PROT_READ | PROT_WRITE,
	    MAP_FILE | MAP_SHARED, inf, 0)) == MAP_FAILED) {
		fprintf(stderr, "%s: cannot map\n", filename);
		close(inf);
		return;
	}

#ifdef _NLIST_DO_ELF
	if (buf[0] == 0x7f && (buf[1] == 'E' || buf[1] == 'O') &&
	    buf[2] == 'L' && buf[3] == 'F') {
		elf_hide(inf, buf);
		return;
	}
#endif				/* _NLIST_DO_ELF */

#ifdef _NLIST_DO_ECOFF
	if (!ECOFF_BADMAG((struct ecoff_exechdr *) buf)) {
		ecoff_hide(inf, buf);
		return;
	}
#endif				/* _NLIST_DO_ECOFF */

#ifdef DO_AOUT
	aoutdata = buf;

	/*
         * Check the header and calculate offsets and sizes from it.
         */
	hdrp = (struct exec *) aoutdata;

	if (N_BADMAG(*hdrp)) {
		fprintf(stderr, "%s: bad magic: not an a.out, ecoff or elf  file\n",
		    filename);
		close(inf);
		return;
	}
	textrel = (struct relocation_info *) (aoutdata + N_TRELOFF(*hdrp));
	datarel = (struct relocation_info *) (aoutdata + N_DRELOFF(*hdrp));
	symbase = (struct nlist *) (aoutdata + N_SYMOFF(*hdrp));
	strbase = (char *) (aoutdata + N_STROFF(*hdrp));

	ntextrel = hdrp->a_trsize / sizeof(struct relocation_info);
	ndatarel = hdrp->a_drsize / sizeof(struct relocation_info);
	nsyms = hdrp->a_syms / sizeof(struct nlist);

	/*
         * Zap the type field of all globally-defined symbols.  The linker will
         * subsequently ignore these entries.  Don't zap any symbols in the
         * keep list.
         */
	for (symp = symbase; symp < symbase + nsyms; symp++)
		if (IS_GLOBAL_DEFINED(symp) && !in_keep_list(SYMSTR(symp))) {
			/*
		         * XXX Our VM system has some problems, so
		         * avoid the VM system....
		         */
			lseek(inf, (off_t) ((void *) &symp->n_type -
			    (void *) buf), SEEK_SET);
			write(inf, &zero, sizeof zero);
			symp->n_type = 0;
		}
	/*
         * Check whether the relocation entries reference any symbols that we
         * just zapped.  I don't know whether ld can handle this case, but I
         * haven't encountered it yet.  These checks are here so that the program
         * doesn't fail silently should such symbols be encountered.
         */
	for (relp = textrel; relp < textrel + ntextrel; relp++)
		check_reloc(filename, relp);
	for (relp = datarel; relp < datarel + ndatarel; relp++)
		check_reloc(filename, relp);

	msync(buf, infstat.st_size, MS_SYNC);
	munmap(buf, infstat.st_size);
	close(inf);
#endif				/* DO_AOUT */
}

#ifdef DO_AOUT
void 
check_reloc(char *filename, struct relocation_info * relp)
{
	/* bail out if we zapped a symbol that is needed */
	if (IS_SYMBOL_RELOC(relp) && symbase[relp->r_symbolnum].n_type == 0) {
		fprintf(stderr,
		    "%s: oops, have hanging relocation for %s: bailing out!\n",
		    filename, SYMSTR(&symbase[relp->r_symbolnum]));
		exit(1);
	}
}
#endif				/* DO_AOUT */