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unexsunos4.c
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C/C++ Source or Header
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1993-07-23
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8KB
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280 lines
/* Contributed by Viktor Dukhovni. */
/*
* Unexec for Berkeley a.out format + SUNOS shared libraries
* The unexeced executable contains the __DYNAMIC area from the
* original text file, and then the rest of data + bss + malloced area of
* the current process. (The __DYNAMIC area is at the top of the process
* data segment, we use "data_start" defined externally to mark the start
* of the "real" data segment.)
*
* For programs that want to remap some of the data segment read only
* a run_time_remap is provided. This attempts to remap largest area starting
* and ending on page boundaries between "data_start" and "bndry"
* For this it to figure out where the text file is located. A path search
* is attempted after trying argv[0] and if all fails we simply do not remap
*
* One feature of run_time_remap () is mandatory: reseting the break.
*
* Note that we can no longer map data into the text segment, as this causes
* the __DYNAMIC struct to become read only, breaking the runtime loader.
* Thus we no longer need to mess with a private crt0.c, the standard one
* will do just fine, since environ can live in the writable area between
* __DYNAMIC and data_start, just make sure that pre-crt0.o (the name
* is somewhat abused here) is loaded first!
*
*/
#ifdef emacs
#include "config.h"
#endif
#include <sys/param.h>
#include <sys/mman.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <string.h>
#include <stdio.h>
#include <a.out.h>
/*
* for programs other than emacs
* define data_start + initialized here, and make sure
* this object is loaded first!
* emacs will define these elsewhere, and load the object containing
* data_start (pre-crt0.o or firstfile.o?) first!
* The custom crt0.o *must not* be loaded!
*/
#ifndef emacs
static int data_start = 0;
static int initialized = 0;
#else
extern int initialized;
extern unsigned data_start;
extern int pureptr;
#endif
extern char *getenv ();
static unsigned Brk;
static struct exec nhdr;
static int rd_only_len;
static long cookie;
unexec (new_name, a_name, bndry, bss_start, entry)
char *new_name, *a_name;
unsigned bndry, bss_start, entry;
{
char buf[PAGSIZ];
int fd, new;
char *old;
struct exec ohdr; /* Allocate on the stack, not needed in the next life */
struct stat stat;
#ifdef emacs
fprintf (stderr, "Used %d bytes of Pure Storage\n", pureptr);
#endif
if ((fd = open (a_name, O_RDONLY)) < 0)
{
fprintf (stderr, "%s: open: ", a_name);
perror (a_name);
exit (1);
}
if ((new = open (new_name, O_WRONLY | O_CREAT, 0666)) == -1)
{
fprintf (stderr, "%s: open: ", a_name);
perror (new_name);
exit (1);
}
if ((fstat (fd, &stat) == -1))
{
fprintf (stderr, "%s: ", a_name);
perror ("fstat");
exit (1);
}
old = (char *)mmap (0, stat.st_size, PROT_READ, MAP_SHARED, fd, 0);
if (old == (char *)-1)
{
fprintf (stderr, "%s: ", a_name);
perror ("mmap");
exit (1);
}
close (fd);
nhdr = ohdr = (*(struct exec *)old);
/*
* Remember a magic cookie so we know we've got the right binary
* when remapping.
*/
cookie = time (0);
Brk = sbrk (0); /* Save the break, it is reset to &_end (by ld.so?) */
/*
* Round up data start to a page boundary (Lose if not a 2 power!)
*/
data_start = ((((int)&data_start) - 1) & ~(N_PAGSIZ (nhdr) - 1)) + N_PAGSIZ (nhdr);
/*
* Round down read only pages to a multiple of the page size
*/
if (bndry)
rd_only_len = ((int)bndry & ~(N_PAGSIZ (nhdr) - 1)) - data_start;
#ifndef emacs
/* Have to do this some time before dumping the data */
initialized = 1;
#endif
/*
* Handle new data and bss sizes and optional new entry point.
* No one actually uses bss_start and entry, but tradition compels
* one to support them.
* Could complain if bss_start > Brk, but the caller is *supposed* to know
* what she is doing.
*/
nhdr.a_data = (bss_start ? bss_start : Brk) - N_DATADDR (nhdr);
nhdr.a_bss = bss_start ? Brk - bss_start : 0;
if (entry)
nhdr.a_entry = entry;
/*
* Write out the text segment with new header
* Dynamic executables are ZMAGIC with N_TXTOFF==0 and the header
* part of the text segment, but no need to rely on this.
* So write the TEXT first, then go back replace the header.
* Doing it in the other order is less general!
*/
lseek (new, N_TXTOFF (nhdr), L_SET);
write (new, old + N_TXTOFF (ohdr), N_TXTOFF (ohdr) + ohdr.a_text);
lseek (new, 0L, L_SET);
write (new, &nhdr, sizeof (nhdr));
/*
* Write out the head of the old data segment from the file not
* from core, this has the unresolved __DYNAMIC relocation data
* we need to reload
*/
lseek (new, N_DATOFF (nhdr), L_SET);
write (new, old + N_DATOFF (ohdr), (int)&data_start - N_DATADDR (ohdr));
/*
* Copy the rest of the data from core
*/
write (new, &data_start, N_BSSADDR (nhdr) - (int)&data_start);
/*
* Copy the symbol table and line numbers
*/
lseek (new, N_TRELOFF (nhdr), L_SET);
write (new, old + N_TRELOFF (ohdr), stat.st_size - N_TRELOFF (ohdr));
fchmod (new, 0755);
}
void
run_time_remap (progname)
char *progname;
{
char aout[MAXPATHLEN];
register char *path, *p;
/* Just in case */
if (!initialized)
return;
/* Restore the break */
brk (Brk);
/* If nothing to remap: we are done! */
if (rd_only_len == 0)
return;
/*
* Attempt to find the executable
* First try argv[0], will almost always succeed as shells tend to give
* the full path from the hash list rather than using execvp ()
*/
if (is_it (progname))
return;
/*
* If argv[0] is a full path and does not exist, not much sense in
* searching further
*/
if (strchr (progname, '/'))
return;
/*
* Try to search for argv[0] on the PATH
*/
path = getenv ("PATH");
if (path == NULL)
return;
while (*path)
{
/* copy through ':' or end */
for (p = aout; *p = *path; ++p, ++path)
if (*p == ':')
{
++path; /* move past ':' */
break;
}
*p++ = '/';
strcpy (p, progname);
/*
* aout is a candidate full path name
*/
if (is_it (aout))
return;
}
}
is_it (path)
char *path;
{
int fd;
long paths_cookie;
struct exec hdr;
/*
* Open an executable and check for a valid header!
* Can't bcmp() the header with what we had, it may have been stripped!
* so we may save looking at non executables with the same name, mostly
* directories.
*/
fd = open (path, O_RDONLY);
if (fd != -1)
{
if (read (fd, &hdr, sizeof (hdr)) == sizeof (hdr)
&& !N_BADMAG (hdr) && N_DATOFF (hdr) == N_DATOFF (nhdr)
&& N_TRELOFF (hdr) == N_TRELOFF (nhdr))
{
/* compare cookies */
lseek (fd, N_DATOFF (hdr) + (int)&cookie - N_DATADDR (hdr), L_SET);
read (fd, &paths_cookie, sizeof (paths_cookie));
if (paths_cookie == cookie)
{ /* Eureka */
/*
* Do the mapping
* The PROT_EXEC may not be needed, but it is safer this way.
* should the shared library decide to indirect through
* addresses in the data segment not part of __DYNAMIC
*/
mmap (data_start, rd_only_len, PROT_READ | PROT_EXEC,
MAP_SHARED | MAP_FIXED, fd,
N_DATOFF (hdr) + data_start - N_DATADDR (hdr));
close (fd);
return 1;
}
}
close (fd);
}
return 0;
}