Programming

#!/usr/bin/env bash

# @(#) s1	Demonstrate execute-only file.

# Utility functions: print-as-echo, print-line-with-visual-space, debug.
# export PATH="/usr/local/bin:/usr/bin:/bin"
LC_ALL=C ; LANG=C ; export LC_ALL LANG
pe() { for _i;do printf "%s" "$_i";done; printf "\n"; }
pl() { pe;pe "-----" ;pe "$*"; }
db() { ( printf " db, ";for _i;do printf "%s" "$_i";done;printf "\n" ) >&2 ; }
db() { : ; }
C=$HOME/bin/context && [ -f $C ] && $C file objdump gdb strace

FILE=${1-t.c}

pl " Input c source file $FILE:"
cat $FILE

pl " Results:"
gcc $FILE
ls -lgG a.out

pl " Execute only results:"
chmod 111 a.out
ls -lgG a.out
./a.out

pl " Results, attempt to read a.out with file, objdump:"
file a.out
objdump -s a.out

pl " Results, debug execution of execute only file:"
gdb ./a.out </dev/null

pl " Results, trace execution of execute only file, I/O calls:"
strace ./a.out 2>&1 |
egrep 'open|close|read|write'

exit 0

$ ./s1

Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: Linux, 2.6.26-2-amd64, x86_64
Distribution        : Debian 5.0.8 (lenny, workstation) 
bash GNU bash 3.2.39
file - ( /usr/bin/file, 2008-09-08 )
objdump GNU objdump (GNU Binutils for Debian) 2.18.0.20080103
gdb GNU gdb 6.8-debian
strace -- version 4.5.17

-----
 Input c source file t.c:
#include <stdio.h>
#include <string.h>
#define VERSION  "1.0"
#define PROGRAM  "main"

int
main (int argc, char *argv[])
{
  {				/* separate scope for version processing */
    char *ver = "--version";
    if (argc == 2 && (strstr (ver, argv[1]) != NULL))
      {
	printf ("%s %s\n", PROGRAM, VERSION);
	return 0;
      }
  }
  int j = 1;
  printf (" Hello, world from c: %s, %s.\n", PROGRAM, VERSION);
  while (--argc > 0)
    printf ("(%d) %s%s", j++, *++argv, (argc > 1) ? " " : "");
  printf ("\n");
  return (0);
}

-----
 Results:
-rwxr-xr-x 1 9290 Oct 23 10:33 a.out

-----
 Execute only results:
---x--x--x 1 9290 Oct 23 10:33 a.out
 Hello, world from c: main, 1.0.


-----
 Results, attempt to read a.out with file, objdump:
a.out: executable, regular file, no read permission
objdump: a.out: Permission denied

-----
 Results, debug execution of execute only file:
GNU gdb 6.8-debian
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu"...
./a.out: Permission denied.
(gdb) quit

-----
 Results, trace execution of execute only file, I/O calls:
open("/etc/ld.so.cache", O_RDONLY)      = 3
close(3)                                = 0
open("/lib/libc.so.6", O_RDONLY)        = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\300\342\1\0\0\0\0\0@"..., 832) = 832
close(3)                                = 0
write(1, " Hello, world from c: main, 1.0.\n"..., 34 Hello, world from c: main, 1.0.