[syslinux] [PATCH] utils/isohybrid.c: 004 Write GPT backup to the very end of the image

[Thomas Schmitt]

The GPT backup header block should start 512 bytes before the end of the
image file (resp. end of the disk device). This block and the backup GPT
array were wrongly written 512 bytes too early.

This change brings the backup GPT at its correct position. 

--- isohybrid.c.003_gpt_part_1_last_lba	2014-06-22 20:05:03.000000000 +0200
+++ isohybrid.c.004_gpt_backup_adr	2014-06-22 20:09:06.000000000 +0200
@@ -1084,7 +1084,7 @@ main(int argc, char *argv[])
 	 * Primary GPT starts at sector 1, secondary GPT starts at 1 sector
 	 * before the end of the image
 	 */
-	initialise_gpt(buf, 1, (isostat.st_size + padding - 1024) / 512, 1);
+	initialise_gpt(buf, 1, (isostat.st_size + padding - 512) / 512, 1);
 
 	if (fseek(fp, 512, SEEK_SET))
 	    err(1, "%s: seek error - 6", argv[0]);
@@ -1122,7 +1122,7 @@ main(int argc, char *argv[])
 
 	buf += orig_gpt_size - sizeof(struct gpt_header);
 
-	initialise_gpt(buf, (isostat.st_size + padding - 1024) / 512, 1, 0);
+	initialise_gpt(buf, (isostat.st_size + padding - 512) / 512, 1, 0);
 
 	/* Shift back far enough to write the 128 GPT entries */
 	buf -= 128 * sizeof(struct gpt_part_header);
@@ -1132,7 +1132,7 @@ main(int argc, char *argv[])
 	 * end of the image
 	 */
 
-	if (fseeko(fp, (isostat.st_size + padding) - orig_gpt_size - 512,
+	if (fseeko(fp, (isostat.st_size + padding) - orig_gpt_size,
 		  SEEK_SET))
 	    err(1, "%s: seek error - 8", argv[0]);