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#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
unsigned char buf[16384];
main(int argc, char **argv)
{
int len,i, stubfd, st2fd, outfd, retval=0;
unsigned char checksum=0;
memset(buf, 0xff, 16384);
if (argc < 4) {
fprintf(stderr, "Usage: makecsum <stubfile> <stage2> <outfile>\n");
exit(1);
}
stubfd = open(argv[1], O_RDONLY);
if (stubfd < 0) {
perror("open stub file");
exit(1);
}
st2fd = open(argv[2], O_RDONLY);
if (st2fd < 0) {
perror("open stage2 file");
close(stubfd);
exit(1);
}
outfd = open(argv[3], O_WRONLY | O_CREAT | O_TRUNC, 0664);
if (outfd < 0) {
perror("open output file");
exit(1);
}
/* Read the stub loader (stage1) */
len = read(stubfd,buf,769);
if (len < 0) {
perror("read from stub file");
close(outfd);
close(st2fd);
close(stubfd);
exit(1);
}
if (len > 768) {
fprintf(stderr, "stub file is too large (>768 bytes)\n");
close(outfd);
close(st2fd);
close(stubfd);
exit(1);
}
close(stubfd);
/* Read enough of the remainder to calculate the csum */
len = read(st2fd, buf+768, 16384-768);
if (len < 0) {
perror("read from stage2 file\n");
close(outfd);
close(st2fd);
exit(1);
}
/* Calculate the csum for 512-byte-page devices */
buf[767] = 0;
i=0;
while (i<16384) {
checksum += buf[i];
i++;
if ((i >> 8)&1)
i += 256;
}
/* Set the slack byte to fix the csum */
buf[767] = 0x55 - checksum;
/* Calculate the csum for 256-byte-page devices */
checksum = 0;
buf[511] = 0;
i=0;
while (i<8192) {
checksum += buf[i++];
}
/* Set the slack byte to fix the csum */
buf[511] = 0x55 - checksum;
/* Write the original buffer */
len = write(outfd, buf, 16384);
if (len < 0) {
perror("write output file");
close(outfd);
close(st2fd);
exit(1);
}
if (len < 16384) {
fprintf(stderr, "short write of output file (%d bytes < 16384)\n",
len);
close(outfd);
close(st2fd);
exit(1);
}
/* Now chuck out the rest of the stage2 */
while (1) {
len = read(st2fd, buf, 16384);
if (len < 0) {
perror("read stage2 file");
retval = 1;
break;
}
if (len == 0)
break;
i = write(outfd, buf, len);
if (i < 0) {
perror("write output file");
retval = 1;
break;
}
if (i<len) {
fprintf(stderr, "short write of output file (%d bytes < %d)\n",
i,len);
retval = 1;
break;
}
}
close(outfd);
close(st2fd);
return retval;
}
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