From 4febb814e430f002fad750810ad6cc12b7d84a5a Mon Sep 17 00:00:00 2001
From: Greg Haerr <greg@censoft.com>
Date: Mon, 21 Oct 2024 12:04:44 -0700
Subject: [PATCH] [boot] Fix bad MBR partition generated by setboot

---
 elks/tools/setboot/setboot.c | 6 ++++--
 elkscmd/disk_utils/fdisk.c   | 8 ++++----
 image/Makefile               | 4 ++--
 3 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/elks/tools/setboot/setboot.c b/elks/tools/setboot/setboot.c
index f9f1f4ec3..dcbe9687c 100644
--- a/elks/tools/setboot/setboot.c
+++ b/elks/tools/setboot/setboot.c
@@ -78,17 +78,19 @@ static void writePartition(unsigned char *buf)
 	p->sector = 1;				/* next cylinder after MBR, standard*/
 	p->cyl = 0;
 	p->start_sect = NumTracks;	/* zero-relative start sector here*/
+	nr_sects -= SecPerTrk;
 #else
 	p->head = 0;
 	p->sector = 2;				/* next sector after MBR, non-standard*/
 	p->cyl = 0;
 	p->start_sect = 1;			/* zero-relative start sector here*/
+	nr_sects -= 1;
 #endif
 	StartSector = p->start_sect;
 	p->sys_ind = 0x80;			/* ELKS, Old Minix*/
 	p->end_head = NumHeads;
-	p->end_sector = SecPerTrk | ((NumTracks >> 2) & 0xc0);
-	p->end_cyl = NumTracks & 0xff;
+	p->end_sector = SecPerTrk | (((NumTracks-1) >> 2) & 0xc0);
+	p->end_cyl = (NumTracks-1) & 0xff;
 	p->start_sect_hi = 0;
 	p->nr_sects = nr_sects & 0xffff;
 	p->nr_sects_hi = nr_sects >> 16;
diff --git a/elkscmd/disk_utils/fdisk.c b/elkscmd/disk_utils/fdisk.c
index d9ce27d9e..1b5dce8ea 100644
--- a/elkscmd/disk_utils/fdisk.c
+++ b/elkscmd/disk_utils/fdisk.c
@@ -164,8 +164,8 @@ void add_part(void)
     oset = MBR + PARTITION_START + ((part - 1) * 16);
 
     printf("Total cylinders: %d\n", geometry.cylinders);
-    for (scyl = geometry.cylinders + 1; scyl < 0 || scyl > geometry.cylinders;) {
-        printf("First cylinder (%d-%d): ", 0, geometry.cylinders);
+    for (scyl = geometry.cylinders; scyl < 0 || scyl > geometry.cylinders-1;) {
+        printf("First cylinder (%d-%d): ", 0, geometry.cylinders-1);
         fflush(stdout);
         fgets(buf, 31, stdin);
         scyl = atoi(buf);
@@ -185,8 +185,8 @@ void add_part(void)
     p.cyl       = (scyl & 0xff);
     p.sys_ind   = PARTITION_TYPE;
 
-    for (ecyl = geometry.cylinders + 1; ecyl < scyl || ecyl > geometry.cylinders;) {
-        printf("Ending cylinder (%d-%d): ", 0, geometry.cylinders);
+    for (ecyl = geometry.cylinders; ecyl < scyl || ecyl > geometry.cylinders-1;) {
+        printf("Ending cylinder (%d-%d): ", 0, geometry.cylinders-1);
         fflush(stdout);
         fgets(buf, 31, stdin);
         ecyl = atoi(buf);
diff --git a/image/Makefile b/image/Makefile
index 97773b8b9..42aae1bac 100644
--- a/image/Makefile
+++ b/image/Makefile
@@ -202,11 +202,11 @@ hd32-fat:
 	rm Config
 
 # MBR images
-hd32mbr-minix:
+hd32mbr-minix: hd32-minix
 	dd if=/dev/zero bs=512 count=63 | cat - hd32-minix.img > hd32mbr-minix.img
 	setboot hd32mbr-minix.img -P63,16,63 -Sm $(HD_MBR_BOOT)
 
-hd32mbr-fat:
+hd32mbr-fat: hd32-fat
 	dd if=/dev/zero bs=512 count=63 | cat - hd32-fat.img > hd32mbr-fat.img
 	setboot hd32mbr-fat.img -P63,16,63 -Sf $(HD_MBR_BOOT)