330 lines
9.2 KiB
C
330 lines
9.2 KiB
C
/*
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* Copyright (c) 1994 University of Maryland
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* All Rights Reserved.
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*
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* Permission to use, copy, modify, distribute, and sell this software and its
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* documentation for any purpose is hereby granted without fee, provided that
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* the above copyright notice appear in all copies and that both that
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* copyright notice and this permission notice appear in supporting
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* documentation, and that the name of U.M. not be used in advertising or
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* publicity pertaining to distribution of the software without specific,
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* written prior permission. U.M. makes no representations about the
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* suitability of this software for any purpose. It is provided "as is"
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* without express or implied warranty.
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*
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* U.M. DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL U.M.
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* BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
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* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
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* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*
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* Author: James da Silva, Systems Design and Analysis Group
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* Computer Science Department
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* University of Maryland at College Park
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*/
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/*
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* crunchide.c - tiptoes through an a.out symbol table, hiding all defined
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* global symbols. Allows the user to supply a "keep list" of symbols
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* that are not to be hidden. This program relies on the use of the
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* linker's -dc flag to actually put global bss data into the file's
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* bss segment (rather than leaving it as undefined "common" data).
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*
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* The point of all this is to allow multiple programs to be linked
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* together without getting multiple-defined errors.
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*
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* For example, consider a program "foo.c". It can be linked with a
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* small stub routine, called "foostub.c", eg:
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* int foo_main(int argc, char **argv){ return main(argc, argv); }
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* like so:
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* cc -c foo.c foostub.c
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* ld -dc -r foo.o foostub.o -o foo.combined.o
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* crunchide -k _foo_main foo.combined.o
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* at this point, foo.combined.o can be linked with another program
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* and invoked with "foo_main(argc, argv)". foo's main() and any
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* other globals are hidden and will not conflict with other symbols.
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*
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* TODO:
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* - resolve the theoretical hanging reloc problem (see check_reloc()
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* below). I have yet to see this problem actually occur in any real
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* program. In what cases will gcc/gas generate code that needs a
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* relative reloc from a global symbol, other than PIC? The
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* solution is to not hide the symbol from the linker in this case,
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* but to generate some random name for it so that it doesn't link
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* with anything but holds the place for the reloc.
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* - arrange that all the BSS segments start at the same address, so
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* that the final crunched binary BSS size is the max of all the
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* component programs' BSS sizes, rather than their sum.
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*/
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#include <unistd.h>
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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 <fcntl.h>
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#include <a.out.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <sys/errno.h>
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char *pname = "crunchide";
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void usage(void);
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void add_to_keep_list(char *symbol);
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void add_file_to_keep_list(char *filename);
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void hide_syms(char *filename);
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int main(argc, argv)
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int argc;
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char **argv;
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{
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int ch;
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if(argc > 0) pname = argv[0];
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while ((ch = getopt(argc, argv, "k:f:")) != EOF)
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switch(ch) {
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case 'k':
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add_to_keep_list(optarg);
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break;
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case 'f':
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add_file_to_keep_list(optarg);
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break;
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default:
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usage();
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}
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argc -= optind;
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argv += optind;
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if(argc == 0) usage();
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while(argc) {
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hide_syms(*argv);
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argc--, argv++;
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}
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return 0;
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}
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void usage(void)
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{
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fprintf(stderr,
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"Usage: %s [-k <symbol-name>] [-f <keep-list-file>] <files> ...\n",
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pname);
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exit(1);
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}
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/* ---------------------------- */
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struct keep {
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struct keep *next;
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char *sym;
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} *keep_list;
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void add_to_keep_list(char *symbol)
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{
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struct keep *newp, *prevp, *curp;
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int cmp;
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for(curp = keep_list, prevp = NULL; curp; prevp = curp, curp = curp->next)
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if((cmp = strcmp(symbol, curp->sym)) <= 0) break;
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if(curp && cmp == 0)
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return; /* already in table */
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newp = (struct keep *) malloc(sizeof(struct keep));
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if(newp) newp->sym = strdup(symbol);
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if(newp == NULL || newp->sym == NULL) {
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fprintf(stderr, "%s: out of memory for keep list\n", pname);
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exit(1);
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}
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newp->next = curp;
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if(prevp) prevp->next = newp;
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else keep_list = newp;
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}
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int in_keep_list(char *symbol)
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{
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struct keep *curp;
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int cmp;
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for(curp = keep_list; curp; curp = curp->next)
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if((cmp = strcmp(symbol, curp->sym)) <= 0) break;
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return curp && cmp == 0;
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}
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void add_file_to_keep_list(char *filename)
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{
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FILE *keepf;
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char symbol[1024];
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int len;
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if((keepf = fopen(filename, "r")) == NULL) {
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perror(filename);
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usage();
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}
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while(fgets(symbol, 1024, keepf)) {
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len = strlen(symbol);
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if(len && symbol[len-1] == '\n')
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symbol[len-1] = '\0';
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add_to_keep_list(symbol);
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}
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fclose(keepf);
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}
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/* ---------------------- */
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int nsyms, ntextrel, ndatarel;
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struct exec *hdrp;
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char *aoutdata, *strbase;
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struct relocation_info *textrel, *datarel;
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struct nlist *symbase;
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#define SYMSTR(sp) &strbase[(sp)->n_un.n_strx]
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/* is the symbol a global symbol defined in the current file? */
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#define IS_GLOBAL_DEFINED(sp) \
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(((sp)->n_type & N_EXT) && ((sp)->n_type & N_TYPE) != N_UNDF)
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#ifdef __sparc
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/* is the relocation entry dependent on a symbol? */
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#define IS_SYMBOL_RELOC(rp) \
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((rp)->r_extern || \
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((rp)->r_type >= RELOC_BASE10 && (rp)->r_type <= RELOC_BASE22) || \
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(rp)->r_type == RELOC_JMP_TBL)
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#else
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/* is the relocation entry dependent on a symbol? */
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#define IS_SYMBOL_RELOC(rp) \
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((rp)->r_extern||(rp)->r_baserel||(rp)->r_jmptable)
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#endif
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void check_reloc(char *filename, struct relocation_info *relp);
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void hide_syms(char *filename)
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{
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int inf, outf, rc;
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struct stat infstat;
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struct relocation_info *relp;
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struct nlist *symp;
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/*
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* Open the file and do some error checking.
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*/
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if((inf = open(filename, O_RDWR)) == -1) {
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perror(filename);
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return;
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}
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if(fstat(inf, &infstat) == -1) {
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perror(filename);
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close(inf);
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return;
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}
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if(infstat.st_size < sizeof(struct exec)) {
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fprintf(stderr, "%s: short file\n", filename);
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close(inf);
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return;
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}
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/*
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* Read the entire file into memory. XXX - Really, we only need to
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* read the header and from TRELOFF to the end of the file.
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*/
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if((aoutdata = (char *) malloc(infstat.st_size)) == NULL) {
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fprintf(stderr, "%s: too big to read into memory\n", filename);
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close(inf);
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return;
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}
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if((rc = read(inf, aoutdata, infstat.st_size)) < infstat.st_size) {
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fprintf(stderr, "%s: read error: %s\n", filename,
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rc == -1? strerror(errno) : "short read");
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close(inf);
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return;
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}
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/*
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* Check the header and calculate offsets and sizes from it.
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*/
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hdrp = (struct exec *) aoutdata;
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if(N_BADMAG(*hdrp)) {
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fprintf(stderr, "%s: bad magic: not an a.out file\n", filename);
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close(inf);
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return;
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}
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#ifdef __FreeBSD__
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textrel = (struct relocation_info *) (aoutdata + N_RELOFF(*hdrp));
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datarel = (struct relocation_info *) (aoutdata + N_RELOFF(*hdrp) +
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hdrp->a_trsize);
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#else
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textrel = (struct relocation_info *) (aoutdata + N_TRELOFF(*hdrp));
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datarel = (struct relocation_info *) (aoutdata + N_DRELOFF(*hdrp));
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#endif
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symbase = (struct nlist *) (aoutdata + N_SYMOFF(*hdrp));
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strbase = (char *) (aoutdata + N_STROFF(*hdrp));
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ntextrel = hdrp->a_trsize / sizeof(struct relocation_info);
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ndatarel = hdrp->a_drsize / sizeof(struct relocation_info);
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nsyms = hdrp->a_syms / sizeof(struct nlist);
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/*
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* Zap the type field of all globally-defined symbols. The linker will
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* subsequently ignore these entries. Don't zap any symbols in the
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* keep list.
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*/
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for(symp = symbase; symp < symbase + nsyms; symp++)
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if(IS_GLOBAL_DEFINED(symp) && !in_keep_list(SYMSTR(symp)))
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symp->n_type = 0;
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/*
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* Check whether the relocation entries reference any symbols that we
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* just zapped. I don't know whether ld can handle this case, but I
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* haven't encountered it yet. These checks are here so that the program
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* doesn't fail silently should such symbols be encountered.
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*/
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for(relp = textrel; relp < textrel + ntextrel; relp++)
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check_reloc(filename, relp);
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for(relp = datarel; relp < datarel + ndatarel; relp++)
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check_reloc(filename, relp);
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/*
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* Write the .o file back out to disk. XXX - Really, we only need to
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* write the symbol table entries back out.
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*/
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lseek(inf, 0, SEEK_SET);
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if((rc = write(inf, aoutdata, infstat.st_size)) < infstat.st_size) {
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fprintf(stderr, "%s: write error: %s\n", filename,
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rc == -1? strerror(errno) : "short write");
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}
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close(inf);
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}
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void check_reloc(char *filename, struct relocation_info *relp)
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{
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/* bail out if we zapped a symbol that is needed */
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if(IS_SYMBOL_RELOC(relp) && symbase[relp->r_symbolnum].n_type == 0) {
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fprintf(stderr,
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"%s: oops, have hanging relocation for %s: bailing out!\n",
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filename, SYMSTR(&symbase[relp->r_symbolnum]));
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exit(1);
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}
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}
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