minix/commands/padtext/padtext.c

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/* padtext: pad out the text segment of a separate I&D a.out binary to a
* multiple of CLICK_SIZE, used for mult-boot
*
* author: Erik van der Kouwe, vdkouwe@cs.vu.nl, June 9th 2010
*/
#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <minix/a.out.h>
#include <minix/config.h>
#include <minix/const.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
/* padding: x86 opcode int 3 (breakpoint) to ensure a trap if the padding area
* accidentally gets executed
*/
#define PADDING_CHAR ((unsigned char) 0xcc)
static const char *argv0, *pathin, *pathout;
static int fdin, fdout;
static int readfixed(void *buffer, size_t count)
{
ssize_t r;
while (count > 0) {
/* read as many bytes as possible */
r = read(fdin, buffer, count);
if (r <= 0) {
if (r < 0) {
fprintf(stderr,
"%s: %s: error while reading: %s\n",
argv0, pathin, strerror(errno));
} else {
fprintf(stderr,
"%s: %s: premature end of file, "
"expected %u more bytes\n",
argv0, pathin, count);
}
return -1;
}
/* maybe we need to read another block */
buffer = (char *) buffer + r;
count -= r;
}
return 0;
}
static int writefixed(const void *buffer, size_t count)
{
ssize_t r;
while (count > 0) {
/* read as many bytes as possible */
r = write(fdout, buffer, count);
if (r <= 0) {
if (r < 0) {
fprintf(stderr,
"%s: %s: error while writing: %s\n",
argv0, pathout, strerror(errno));
} else {
fprintf(stderr,
"%s: %s: premature end of file\n",
argv0, pathout);
}
return -1;
}
/* maybe we need to read another block */
buffer = (const char *) buffer + r;
count -= r;
}
return 0;
}
static int writepadding(size_t padsize)
{
char buffer[CLICK_SIZE];
/* we never write more than a single click */
assert(padsize <= sizeof(buffer));
memset(buffer, PADDING_CHAR, padsize);
return writefixed(buffer, padsize);
}
static int copyfixed(size_t count)
{
char buffer[4096];
size_t countnow;
while (count > 0) {
/* copying a fixed number of bytes, we expect everything to
* succeed
*/
countnow = (count < sizeof(buffer)) ? count : sizeof(buffer);
if (readfixed(buffer, countnow) < 0 ||
writefixed(buffer, countnow) < 0) {
return -1;
}
count -= countnow;
}
return 0;
}
static int copyall(void)
{
char buffer[4096];
ssize_t r;
for (; ; ) {
/* copy everything until EOF */
r = read(fdin, buffer, sizeof(buffer));
if (r <= 0) {
if (r < 0) {
fprintf(stderr,
"%s: %s: error while reading: %s\n",
argv0, pathin, strerror(errno));
return -1;
} else {
/* EOF, stop copying */
break;
}
}
if (writefixed(buffer, r) < 0) {
return -1;
}
}
return 0;
}
static int padtext(void)
{
struct exec headerin, headerout;
long padsize;
/* read header */
assert(A_MINHDR <= sizeof(headerin));
if (readfixed(&headerin, A_MINHDR) < 0) {
return -1;
}
/* check header sanity */
if (BADMAG(headerin) ||
headerin.a_hdrlen < A_MINHDR ||
(headerin.a_flags & ~(A_NSYM | A_EXEC | A_SEP)) != 0 ||
headerin.a_text < 0 ||
headerin.a_data < 0 ||
headerin.a_bss < 0 ||
headerin.a_entry != 0 ||
headerin.a_total < 0 ||
headerin.a_syms < 0) {
fprintf(stderr, "%s: %s: invalid a.out header\n",
argv0, pathin);
return -1;
}
if (headerin.a_cpu != A_I80386) {
fprintf(stderr, "%s: %s: not an i386 executable\n",
argv0, pathin);
return -1;
}
if ((headerin.a_flags & A_SEP) != A_SEP) {
fprintf(stderr,
"%s: %s: combined I&D, padding text is impossible\n",
argv0, pathin);
return -1;
}
/* adjust header */
headerout = headerin;
padsize = CLICK_SIZE - headerout.a_text % CLICK_SIZE;
if (padsize == CLICK_SIZE) padsize = 0;
printf("%s: %s: adding %ld bytes of padding\n", pathin, argv0, padsize);
headerout.a_text += padsize;
/* write header and copy text segment */
if (writefixed(&headerout, A_MINHDR) < 0 ||
copyfixed(headerin.a_hdrlen - A_MINHDR + headerin.a_text) < 0 ||
writepadding(padsize) < 0 ||
copyall() < 0) {
return -1;
}
return 0;
}
int main(int argc, char **argv)
{
/* check parameters */
argv0 = argv[0];
if (argc > 3) {
printf("usage:\n");
printf(" %s [infile [outfile]]\n", argv0);
return 1;
}
if (argc >= 2) {
/* open specified input file */
pathin = argv[1];
fdin = open(pathin, O_RDONLY);
if (fdin < 0) {
fprintf(stderr,
"%s: cannot open input file \"%s\" "
"for reading: %s\n",
argv0, pathin, strerror(errno));
return -1;
}
} else {
/* input from stdin */
pathin = "-";
fdin = STDIN_FILENO;
}
if (argc >= 3) {
/* open specified output file */
pathout = argv[2];
fdout = creat(pathout, 0644);
if (fdout < 0) {
fprintf(stderr,
"%s: cannot open output file \"%s\" "
"for writing: %s\n",
argv0, pathout, strerror(errno));
return -1;
}
} else {
/* output to stdout */
pathout = "-";
fdout = STDOUT_FILENO;
}
/* now do the job using the file handles */
if (padtext() < 0) {
return -1;
}
return 0;
}