freebsd-dev/usr.sbin/crunch/crunchide/crunchide.c
Philippe Charnier b17e90a9c9 Use err(3).
1997-09-15 06:41:09 +00:00

315 lines
8.8 KiB
C

/*
* 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 <a.out.h>
#include <err.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/errno.h>
void usage(void);
void add_to_keep_list(char *symbol);
void add_file_to_keep_list(char *filename);
void hide_syms(char *filename);
int main(argc, argv)
int argc;
char **argv;
{
int ch;
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: crunchide [-k <symbol-name>] [-f <keep-list-file>] <files> ...\n");
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 *) malloc(sizeof(struct keep));
if(newp) newp->sym = strdup(symbol);
if(newp == NULL || newp->sym == NULL) {
errx(1, "out of memory for keep list");
}
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) {
warn("%s", 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)
/* is the relocation entry dependent on a symbol? */
#define IS_SYMBOL_RELOC(rp) \
((rp)->r_extern||(rp)->r_baserel||(rp)->r_jmptable)
void check_reloc(char *filename, struct relocation_info *relp);
void hide_syms(char *filename)
{
int inf, rc;
struct stat infstat;
struct relocation_info *relp;
struct nlist *symp;
/*
* Open the file and do some error checking.
*/
if((inf = open(filename, O_RDWR)) == -1) {
warn("%s", filename);
return;
}
if(fstat(inf, &infstat) == -1) {
warn("%s", filename);
close(inf);
return;
}
if(infstat.st_size < sizeof(struct exec)) {
warnx("%s: short file", filename);
close(inf);
return;
}
/*
* Read the entire file into memory. XXX - Really, we only need to
* read the header and from TRELOFF to the end of the file.
*/
if((aoutdata = (char *) malloc(infstat.st_size)) == NULL) {
warnx("%s: too big to read into memory", filename);
close(inf);
return;
}
if((rc = read(inf, aoutdata, infstat.st_size)) < infstat.st_size) {
warnx("%s: read error: %s", filename,
rc == -1? strerror(errno) : "short read");
close(inf);
return;
}
/*
* Check the header and calculate offsets and sizes from it.
*/
hdrp = (struct exec *) aoutdata;
if(N_BADMAG(*hdrp)) {
warnx("%s: bad magic: not an a.out file", filename);
close(inf);
return;
}
#ifdef __FreeBSD__
textrel = (struct relocation_info *) (aoutdata + N_RELOFF(*hdrp));
datarel = (struct relocation_info *) (aoutdata + N_RELOFF(*hdrp) +
hdrp->a_trsize);
#else
textrel = (struct relocation_info *) (aoutdata + N_TRELOFF(*hdrp));
datarel = (struct relocation_info *) (aoutdata + N_DRELOFF(*hdrp));
#endif
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)))
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);
/*
* Write the .o file back out to disk. XXX - Really, we only need to
* write the symbol table entries back out.
*/
lseek(inf, 0, SEEK_SET);
if((rc = write(inf, aoutdata, infstat.st_size)) < infstat.st_size) {
warnx("%s: write error: %s", filename,
rc == -1? strerror(errno) : "short write");
}
close(inf);
}
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) {
errx(1, "%s: oops, have hanging relocation for %s: bailing out!",
filename, SYMSTR(&symbase[relp->r_symbolnum]));
}
}