[syslinux] [PATCH] chain.c32: add support for booting the Recovery Console of Windows NT/2K/XP

[Kim Mik]

The following patch for chain.c32 adds support to boot the Recovery Console of Windows NT/2K/XP.
Normally when you want to boot the recovery console, you need to patch "cmdcons\0" into the
bootsectorof the partition (8 bytes starting at 0x3 (4th byte)).

We can do this patching in memory:
  strcpy((char *) 0x7c03, "cmdcons");

To boot the recovery console with chain.c32:
  chain.c32 cmldr=/cmldr

- Gert Hulselmans


$ diff -u chain.c.textmode chain.c.cmldr
--- chain.c.textmode    2009-12-28 21:32:17.658783777 +0100
+++ chain.c.cmldr    2009-12-28 22:23:15.118787984 +0100
@@ -48,6 +48,10 @@
  * ntldr=<loader>:
  *    equivalent to -seg 0x2000 -file <loader>, used with WinNT's loaders
  *
+ * cmldr=<loader>:
+ *    used with Recovery Console of Windows NT/2K/XP.
+ *      same as ntldr=<loader> & "cmdcons\0" written to memory address 0000:7C03
+ *
  * freedos=<loader>:
  *    equivalent to -seg 0x60 -file <loader>, used with FreeDOS kernel.sys.
  *
@@ -85,6 +89,7 @@
     uint16_t keeppxe;
     uint16_t seg;
     bool isolinux;
+    bool cmldr;
     bool swap;
     bool hide;
 } opt;
@@ -679,6 +684,10 @@
     } else if (!strncmp(argv[i], "ntldr=", 6)) {
         opt.seg = 0x2000;    /* NTLDR wants this address */
         opt.loadfile = argv[i] + 6;
+    } else if (!strncmp(argv[i], "cmldr=", 6)) {
+        opt.seg = 0x2000;    /* CMLDR wants this address */
+        opt.loadfile = argv[i] + 6;
+        opt.cmldr = true;
     } else if (!strncmp(argv[i], "freedos=", 8)) {
         opt.seg = 0x60;    /* FREEDOS wants this address */
         opt.loadfile = argv[i] + 8;
@@ -714,7 +723,8 @@
          "         chain.c32 boot [<partition>] [options]\n"
          "Options: file=<loader>      load file, instead of boot sector\n"
          "         isolinux=<loader>  load another version of ISOLINUX\n"
-         "         ntldr=<loader>     load Windows bootloaders: NTLDR, SETUPLDR, BOOTMGR\n"
+         "         ntldr=<loader>     load Windows loaders NTLDR, SETUPLDR.BIN or BOOTMGR\n"
+         "         cmldr=<loader>     load Recovery Console of Windows NT/2K/XP (cmldr)\n"
          "         freedos=<loader>   load FreeDOS kernel.sys\n"
          "         msdos=<loader>     load MS-DOS io.sys\n"
          "         pcdos=<loader>     load PC-DOS ibmbio.com\n"
@@ -876,6 +886,13 @@
         }
     }
 
+    /* To boot the Recovery Console of Windows NT/2K/XP we need to write
+       the string "cmdcons\0" to memory location 0000:7C03.
+       Memory location 0000:7C00 contains the bootsector of the partition.
+     */
+    if (opt.cmldr)
+        strcpy((char *) 0x7c03, "cmdcons");
+
     } else if (partinfo) {
     /* Actually read the boot sector */
     /* Pick the first buffer that isn't already in use */