ntldr support

PATCH In review Robert Millan 5 participants 17 messages Aug 2, 2009 – Aug 10, 2009

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Robert Millan

author

2009-08-02 23:24 UTC #0 lore raw

PATCH 1/1 ntldr support

Hi,

This patch implements a loader for NTLDR boot semantics (which are the same in BootMGR, hence both are supported).

It still needs some cleanup in chainloader.c before it can be merged [1], but I submit it so that others can test it and report if it works for them.

[1] ideally, we should be able to share most code with the chainloader

Signature · 5 lines

Robert Millan

  The DRM opt-in fallacy: "Your data belongs to us. We will decide when (and
  how) you may access your data; but nobody's threatening your freedom: we
  still allow you to remove your data and not access it at all."

i386/pc/startup.S +30 -1

Index: kern/i386/pc/startup.S
===================================================================
@@ -1,6 +1,6 @@
 /*
  *  GRUB  --  GRand Unified Bootloader
- *  Copyright (C) 1999,2000,2001,2002,2003,2005,2006,2007,2008 Free Software Foundation, Inc.
+ *  Copyright (C) 1999,2000,2001,2002,2003,2005,2006,2007,2008,2009 Free Software Foundation, Inc.
  *
  *  GRUB is free software: you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by

@@ -576,6 +576,35 @@
 	ljmp	$0, $GRUB_MEMORY_MACHINE_BOOT_LOADER_ADDR
 	.code32
 
+/*
+ *  void grub_ntldr_real_boot (grub_uint8_t *boot_file, int drive, grub_uint32_t boot_file_size)
+ *
+ *  This starts NTLDR.
+ *
+ *  Register allocations for parameters:
+ *  %eax		*boot_file
+ *  %edx		drive
+ *  %ecx		boot_file_size
+ */
+
+ntldr_tmp_stack:
+	.long	0
+FUNCTION(grub_ntldr_real_boot)
+	/* Copy NTLDR from heap to its link address.  */
+	movl	%eax, %esi
+	movl	$GRUB_MEMORY_MACHINE_NTLDR_ADDR, %edi
+	cld
+	rep
+	movsb
+
+	/* Relocation may have taken over our stack, so use this one to
+	   hold our return address.  */
+	movl	$(ntldr_tmp_stack + 4), %esp
+	call	prot_to_real
+	.code16
+	ljmp	$(GRUB_MEMORY_MACHINE_NTLDR_ADDR >> 4), $0x0
+	.code32
+
 #include "../loader.S"
 
 /*

grub/i386/pc/console.h +1 -1

Index: include/grub/i386/pc/console.h
===================================================================
@@ -51,7 +51,7 @@
 void grub_console_init (void);
 
 /* Finish the console system.  */
-void grub_console_fini (void);
+void EXPORT_FUNC(grub_console_fini) (void);
 
 #endif

grub/i386/pc/loader.h +4 -1

Index: include/grub/i386/pc/loader.h
===================================================================
@@ -1,6 +1,6 @@
 /*
  *  GRUB  --  GRand Unified Bootloader
- *  Copyright (C) 2002,2003,2004,2007  Free Software Foundation, Inc.
+ *  Copyright (C) 2002,2003,2004,2007,2009  Free Software Foundation, Inc.
  *
  *  GRUB is free software: you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by

@@ -25,4 +25,7 @@
 /* This is an asm part of the chainloader.  */
 void EXPORT_FUNC(grub_chainloader_real_boot) (int drive, void *part_addr) __attribute__ ((noreturn));
 
+void EXPORT_FUNC(grub_ntldr_real_boot) (grub_uint8_t *boot_file, int drive,
+					grub_uint32_t boot_file_size) __attribute__ ((noreturn));
+
 #endif /* ! GRUB_LOADER_MACHINE_HEADER */

grub/i386/pc/memory.h +4 -1

Index: include/grub/i386/pc/memory.h
===================================================================
@@ -1,7 +1,7 @@
 /* memory.h - describe the memory map */
 /*
  *  GRUB  --  GRand Unified Bootloader
- *  Copyright (C) 2002,2007,2008  Free Software Foundation, Inc.
+ *  Copyright (C) 2002,2007,2008,2009  Free Software Foundation, Inc.
  *
  *  GRUB is free software: you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by

@@ -63,6 +63,9 @@
 /* The address where another boot loader is loaded.  */
 #define GRUB_MEMORY_MACHINE_BOOT_LOADER_ADDR	0x7c00
 
+/* The address where NTLDR is loaded.  */
+#define GRUB_MEMORY_MACHINE_NTLDR_ADDR		0x20000
+
 /* The flag for protected mode.  */
 #define GRUB_MEMORY_MACHINE_CR0_PE_ON		0x1

i386/pc/chainloader.c +30 ~~-22~~

105 lines not on this page · raw message

Christian Franke

2009-08-04 18:37 UTC #1 lore raw

Quoted 8 lines · Robert Millan

This patch implements a loader for NTLDR boot semantics (which are the same in BootMGR, hence both are supported).
It still needs some cleanup in chainloader.c before it can be merged [1], but I submit it so that others can test it and report if it works for them.

Tested with WinXP in a VM:

Before the test, original boot code behind partition boot sector was destroyed. (dd if=/dev/zero of=/dev/hda1 bs=512 seek=1 count=20)

Then this fails:

root=(hd0,1)
chainloader (hd0,1)+1
boot

But with the patch this still works:

root=(hd0,1)
ntldr /ntldr
boot

Thanks.

Signature · 2 lines

Regards,
Christian Franke

Robert Millan

author

2009-08-04 19:27 UTC #2 lore raw

In reply to Robert Millan

After thinking a bit about this, I don't think we want this command in its current form.

The problem is it is misleading. It leads the user to think it can load ntldr as a standalone file, but in fact it is reading the PBR behind the scenes.

If we want this feature at all, I think it should be an option in the chainloader rather than a standalone command. It's almost the same as the chainloader really, the only difference is that ntldr is load after PBR by GRUB instead of by PBR itself.

But I'm not even sure it makes sense to support this at all. Perhaps if people who are interested in it explain the use case and how did they got there, I would change my mind about it.

Quoted 239 lines · Robert Millan

Hi,

This patch implements a loader for NTLDR boot semantics (which are the same in BootMGR, hence both are supported).

It still needs some cleanup in chainloader.c before it can be merged [1], but I submit it so that others can test it and report if it works for them.

[1] ideally, we should be able to share most code with the chainloader

Signature · 8 lines

Robert Millan

  The DRM opt-in fallacy: "Your data belongs to us. We will decide when (and
  how) you may access your data; but nobody's threatening your freedom: we
  still allow you to remove your data and not access it at all."

Index: kern/i386/pc/startup.S
===================================================================

i386/pc/startup.S +30 -1

@@ -1,6 +1,6 @@
 /*
  *  GRUB  --  GRand Unified Bootloader
- *  Copyright (C) 1999,2000,2001,2002,2003,2005,2006,2007,2008 Free Software Foundation, Inc.
+ *  Copyright (C) 1999,2000,2001,2002,2003,2005,2006,2007,2008,2009 Free Software Foundation, Inc.
  *
  *  GRUB is free software: you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by

@@ -576,6 +576,35 @@
 	ljmp	$0, $GRUB_MEMORY_MACHINE_BOOT_LOADER_ADDR
 	.code32
 
+/*
+ *  void grub_ntldr_real_boot (grub_uint8_t *boot_file, int drive, grub_uint32_t boot_file_size)
+ *
+ *  This starts NTLDR.
+ *
+ *  Register allocations for parameters:
+ *  %eax		*boot_file
+ *  %edx		drive
+ *  %ecx		boot_file_size
+ */
+
+ntldr_tmp_stack:
+	.long	0
+FUNCTION(grub_ntldr_real_boot)
+	/* Copy NTLDR from heap to its link address.  */
+	movl	%eax, %esi
+	movl	$GRUB_MEMORY_MACHINE_NTLDR_ADDR, %edi
+	cld
+	rep
+	movsb
+
+	/* Relocation may have taken over our stack, so use this one to
+	   hold our return address.  */
+	movl	$(ntldr_tmp_stack + 4), %esp
+	call	prot_to_real
+	.code16
+	ljmp	$(GRUB_MEMORY_MACHINE_NTLDR_ADDR >> 4), $0x0
+	.code32
+
 #include "../loader.S"
 
 /*

Index: include/grub/i386/pc/console.h
===================================================================

grub/i386/pc/console.h +1 -1

@@ -51,7 +51,7 @@
 void grub_console_init (void);
 
 /* Finish the console system.  */
-void grub_console_fini (void);
+void EXPORT_FUNC(grub_console_fini) (void);
 
 #endif

Index: include/grub/i386/pc/loader.h
===================================================================

grub/i386/pc/loader.h +4 -1

@@ -1,6 +1,6 @@
 /*
  *  GRUB  --  GRand Unified Bootloader
- *  Copyright (C) 2002,2003,2004,2007  Free Software Foundation, Inc.
+ *  Copyright (C) 2002,2003,2004,2007,2009  Free Software Foundation, Inc.
  *
  *  GRUB is free software: you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by

@@ -25,4 +25,7 @@
 /* This is an asm part of the chainloader.  */
 void EXPORT_FUNC(grub_chainloader_real_boot) (int drive, void *part_addr) __attribute__ ((noreturn));
 
+void EXPORT_FUNC(grub_ntldr_real_boot) (grub_uint8_t *boot_file, int drive,
+					grub_uint32_t boot_file_size) __attribute__ ((noreturn));
+
 #endif /* ! GRUB_LOADER_MACHINE_HEADER */

Index: include/grub/i386/pc/memory.h
===================================================================

grub/i386/pc/memory.h +4 -1

@@ -1,7 +1,7 @@
 /* memory.h - describe the memory map */
 /*
  *  GRUB  --  GRand Unified Bootloader
- *  Copyright (C) 2002,2007,2008  Free Software Foundation, Inc.
+ *  Copyright (C) 2002,2007,2008,2009  Free Software Foundation, Inc.
  *
  *  GRUB is free software: you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by

@@ -63,6 +63,9 @@
 /* The address where another boot loader is loaded.  */
 #define GRUB_MEMORY_MACHINE_BOOT_LOADER_ADDR	0x7c00
 
+/* The address where NTLDR is loaded.  */
+#define GRUB_MEMORY_MACHINE_NTLDR_ADDR		0x20000
+
 /* The flag for protected mode.  */
 #define GRUB_MEMORY_MACHINE_CR0_PE_ON		0x1

Index: loader/i386/pc/chainloader.c
===================================================================

i386/pc/chainloader.c +30 ~~-22~~

@@ -1,7 +1,7 @@
 /* chainloader.c - boot another boot loader */
 /*
  *  GRUB  --  GRand Unified Bootloader
- *  Copyright (C) 2002,2004,2007  Free Software Foundation, Inc.
+ *  Copyright (C) 2002,2004,2007,2009  Free Software Foundation, Inc.
  *
  *  GRUB is free software: you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by

@@ -20,6 +20,7 @@
 #include <grub/loader.h>
 #include <grub/machine/loader.h>
 #include <grub/machine/chainloader.h>
+#include <grub/machine/console.h>
 #include <grub/file.h>
 #include <grub/err.h>
 #include <grub/device.h>

@@ -36,12 +37,17 @@
 static grub_dl_t my_mod;
 static int boot_drive;
 static void *boot_part_addr;
+static grub_uint8_t *boot_file;
+static grub_off_t boot_file_size;
 
 static grub_err_t
 grub_chainloader_boot (void)
 {
-  grub_chainloader_real_boot (boot_drive, boot_part_addr);
+  /* NTLDR expects console in text mode.  */
+  grub_console_fini ();
 
+  grub_ntldr_real_boot (boot_file, boot_drive, (grub_uint32_t) boot_file_size);
+
   /* Never reach here.  */
   return GRUB_ERR_NONE;
 }

@@ -68,24 +74,11 @@
   if (! file)
     goto fail;
 
-  /* Read the first block.  */
-  if (grub_file_read (file, (void *) 0x7C00, GRUB_DISK_SECTOR_SIZE)
-      != GRUB_DISK_SECTOR_SIZE)
-    {
-      if (grub_errno == GRUB_ERR_NONE)
-	grub_error (GRUB_ERR_BAD_OS, "too small");
+  boot_file_size = file->size;
 
-      goto fail;
-    }
+  boot_file = grub_malloc (boot_file_size);
 
-  /* Check the signature.  */
-  signature = *((grub_uint16_t *) (0x7C00 + GRUB_DISK_SECTOR_SIZE - 2));
-  if (signature != grub_le_to_cpu16 (0xaa55)
-      && ! (flags & GRUB_CHAINLOADER_FORCE))
-    {
-      grub_error (GRUB_ERR_BAD_OS, "invalid signature");
-      goto fail;
-    }
+  grub_file_read (file, boot_file, boot_file_size);
 
   grub_file_close (file);

@@ -95,11 +88,26 @@
   if (dev && dev->disk && dev->disk->partition)
     {
       grub_disk_read (dev->disk, dev->disk->partition->offset, 446, 64,
-		      (void *) GRUB_MEMORY_MACHINE_PART_TABLE_ADDR);
+		      GRUB_MEMORY_MACHINE_PART_TABLE_ADDR);
       part_addr = (void *) (GRUB_MEMORY_MACHINE_PART_TABLE_ADDR
 			    + (dev->disk->partition->index << 4));
     }
 
+  if (! dev)
+    grub_fatal ("boo");
+
+  /* Read the first block.  */
+  grub_disk_read (dev->disk, 0, 0, GRUB_DISK_SECTOR_SIZE, (void *) 0x7C00);
+
+  /* Check the signature.  */
+  signature = *((grub_uint16_t *) (0x7C00 + GRUB_DISK_SECTOR_SIZE - 2));
+  if (signature != grub_le_to_cpu16 (0xaa55)
+      && ! (flags & GRUB_CHAINLOADER_FORCE))
+    {
+      grub_error (GRUB_ERR_BAD_OS, "invalid signature");
+      goto fail;
+    }
+
   if (dev)
     grub_device_close (dev);

@@ -109,7 +117,7 @@
   boot_drive = drive;
   boot_part_addr = part_addr;
 
-  grub_loader_set (grub_chainloader_boot, grub_chainloader_unload, 1);
+  grub_loader_set (grub_chainloader_boot, grub_chainloader_unload, 0);
   return;
 
  fail:

@@ -145,8 +153,8 @@
 
 GRUB_MOD_INIT(chainloader)
 {
-  cmd = grub_register_command ("chainloader", grub_cmd_chainloader,
-			       0, "load another boot loader");
+  cmd = grub_register_command ("ntldr", grub_cmd_chainloader,
+			       0, "load NTLDR");
   my_mod = mod;
 }

Signature · 5 lines

Robert Millan

  The DRM opt-in fallacy: "Your data belongs to us. We will decide when (and
  how) you may access your data; but nobody's threatening your freedom: we
  still allow you to remove your data and not access it at all."

Vladimir 'phcoder' Serbinenko

2009-08-04 20:09 UTC #3 lore raw

Quoted 8 lines · Robert Millan

After thinking a bit about this, I don't think we want this command in its current form.
The problem is it is misleading. It leads the user to think it can load ntldr as a standalone file, but in fact it is reading the PBR behind the scenes.

I don't think it's of any problem since ntldr uses this PBR only as superblock to identify the partition. As such I would rather consider this loading as a special case of passing $root, just the form of it is a bit weird

Signature · 4 lines

Regards
Vladimir 'phcoder' Serbinenko

Personal git repository: http://repo.or.cz/w/grub2/phcoder.git

Christian Franke

2009-08-05 05:35 UTC #4 lore raw

Quoted 10 lines · Vladimir 'phcoder' Serbinenko

Quoted 8 lines · Robert Millan
After thinking a bit about this, I don't think we want this command in its current form.
The problem is it is misleading. It leads the user to think it can load ntldr as a standalone file, but in fact it is reading the PBR behind the scenes.

Quoted 6 lines

I don't think it's of any problem since ntldr uses this PBR only as superblock to identify the partition. As such I would rather consider this loading as a special case of passing $root, just the form of it is a bit weird

Agree.

A 'ntldr' or 'chainloader --ntldr' command is not mandatory. But it is 'nice to have' because it allows to boot even if the boot code (6 sectors) in the area behind the PBR is not present for whatever reason. See my previsions mail with the test case.

Signature · 2 lines

Regards,
Christian Franke

Robert Millan

author

2009-08-07 10:58 UTC #5 lore raw

Quoted 18 lines · Christian Franke

Quoted 10 lines · Vladimir 'phcoder' Serbinenko
Quoted 8 lines · Robert Millan
After thinking a bit about this, I don't think we want this command in its current form.
The problem is it is misleading. It leads the user to think it can load ntldr as a standalone file, but in fact it is reading the PBR behind the scenes.
Quoted 6 lines
I don't think it's of any problem since ntldr uses this PBR only as superblock to identify the partition. As such I would rather consider this loading as a special case of passing $root, just the form of it is a bit weird

Quoted 6 lines

Agree.
A 'ntldr' or 'chainloader --ntldr' command is not mandatory. But it is 'nice to have' because it allows to boot even if the boot code (6 sectors) in the area behind the PBR is not present for whatever reason. See my previsions mail with the test case.

Ok. Should we settle with 'ntldr' or 'chainloader --ntldr'? In either case, we should try making them share the code (with ifdef trick if necessary), but I'm not completely sure. Will users be confused if they put ntldr in an unrelated partition and try to boot their Windows using it? If ntldr may hang or crash because of it, then I would go for 'chainloader --ntldr' and if it fails with a nice error then 'ntldr'.

Thoughts?

Signature · 5 lines

Robert Millan

  The DRM opt-in fallacy: "Your data belongs to us. We will decide when (and
  how) you may access your data; but nobody's threatening your freedom: we
  still allow you to remove your data and not access it at all."

Michal Suchanek

2009-08-07 11:17 UTC #6 lore raw

2009/8/7 Robert Millan <[email protected]>:

Quoted 26 lines · Christian Franke

Quoted 18 lines
Quoted 10 lines · Vladimir 'phcoder' Serbinenko
Quoted 8 lines · Robert Millan
After thinking a bit about this, I don't think we want this command in its current form.
The problem is it is misleading. It leads the user to think it can load ntldr as a standalone file, but in fact it is reading the PBR behind the scenes.
Quoted 6 lines
I don't think it's of any problem since ntldr uses this PBR only as superblock to identify the partition. As such I would rather consider this loading as a special case of passing $root, just the form of it is a bit weird
Quoted 6 lines
Agree.
A 'ntldr' or 'chainloader --ntldr' command is not mandatory. But it is 'nice to have' because it allows to boot even if the boot code (6 sectors) in the area behind the PBR is not present for whatever reason. See my previsions mail with the test case.

Quoted 9 lines

Ok. Should we settle with 'ntldr' or 'chainloader --ntldr'? In either case, we should try making them share the code (with ifdef trick if necessary), but I'm not completely sure. Will users be confused if they put ntldr in an unrelated partition and try to boot their Windows using it? If ntldr may hang or crash because of it, then I would go for 'chainloader --ntldr' and if it fails with a nice error then 'ntldr'.
Thoughts?

ntldr is a boot loader like any other and it needs its configuration and support files to work. Without them it fails (not sure how) but that is not unexpected.

The Microsoft code for loading ntldr is broken wrt disk geometry so replacing the MS loader with a grub chainloader option might allow booting a disk taken from a system where the BIOS interprets the disk geometry differently. This needs some testing, though.

Thanks

Michal

Robert Millan

author

2009-08-07 11:44 UTC #7 lore raw

Quoted 4 lines · Michal Suchanek

ntldr is a boot loader like any other and it needs its configuration and support files to work. Without them it fails (not sure how) but that is not unexpected.

I tend to agree, but in this particular case, it's conceivable that Microsoft didn't expect anyone to do this, and therefore neglected to provide a graceful response.

Could anyone test it and report how this behaves?

Signature · 5 lines

Robert Millan

  The DRM opt-in fallacy: "Your data belongs to us. We will decide when (and
  how) you may access your data; but nobody's threatening your freedom: we
  still allow you to remove your data and not access it at all."

Michal Suchanek

2009-08-07 22:55 UTC #8 lore raw

2009/8/7 Robert Millan <[email protected]>:

Quoted 10 lines · Michal Suchanek

Quoted 4 lines
ntldr is a boot loader like any other and it needs its configuration and support files to work. Without them it fails (not sure how) but that is not unexpected.
I tend to agree, but in this particular case, it's conceivable that Microsoft didn't expect anyone to do this, and therefore neglected to provide a graceful response.

Quoted 9 lines

Could anyone test it and report how this behaves?
--
Robert Millan
The DRM opt-in fallacy: "Your data belongs to us. We will decide when (and how) you may access your data; but nobody's threatening your freedom: we still allow you to remove your data and not access it at all."

I tried putting the ntldr binary on an empty fat32 disk and loading with the grub ntldr command.

The system just reboots.

Thanks

Michal

Christian Franke

2009-08-08 21:45 UTC #9 lore raw

Quoted 7 lines · Michal Suchanek

I tried putting the ntldr binary on an empty fat32 disk and loading with the grub ntldr command.
The system just reboots.

This also happens when ntldr is loaded by the regular boot code in PBR+boot area. It is apparently the normal(?-) behavior when ntdetect.com is missing.

Signature · 2 lines

Regards,
Christian Franke

Yves Blusseau

2009-08-08 11:45 UTC #10 lore raw

In reply to Robert Millan

Quoted 6 lines · Robert Millan

Quoted 4 lines · Michal Suchanek
ntldr is a boot loader like any other and it needs its configuration and support files to work. Without them it fails (not sure how) but that is not unexpected.

Quoted 6 lines

I tend to agree, but in this particular case, it's conceivable that Microsoft didn't expect anyone to do this, and therefore neglected to provide a graceful response.
Could anyone test it and report how this behaves?

Hi i try to boot my vista with ntldr command directly and it works like a charm.

I have try to put the file on another partition and made:
root= partition where BCD are
ntldr /bootmgr

but without success. But i think it's because of a bad BCD file.

About the command, i think that it will be simpler for the user if we have only one command: chainloader (like in grub4dos) that will try to detect the type of the bootloader. This is only my personal opinion.

Yves Blusseau

Vladimir 'phcoder' Serbinenko

2009-08-08 11:55 UTC #11 lore raw

Quoted 3 lines

About the command, i think that it will be simpler for the user if we have only one command: chainloader (like in grub4dos) that will try to detect the type of the bootloader. This is only my personal opinion.

I don't agree with this. chainloader and ntldr don't share the same
syntax: chainloader expects a bootsector whereas ntldr expects an ntldr ot bootmgr file. GRUB2 is done to break with bad design decisions of GRUB1 one of them being "kernel" command. GRUB4DOS follows GRUB1 on this subject.
Additionally people may want to embed chainloader or ntldr into core.img to be able to have an emergency boot method. For this reason I consider we should split functionality into 2 modules which requires 2 different commands

Quoted 11 lines

Yves Blusseau
_______________________________________________
Grub-devel mailing list
[email protected]
http://lists.gnu.org/mailman/listinfo/grub-devel

Signature · 4 lines

Regards
Vladimir 'phcoder' Serbinenko

Personal git repository: http://repo.or.cz/w/grub2/phcoder.git

Christian Franke

2009-08-08 21:58 UTC #12 lore raw

Quoted 10 lines · Vladimir 'phcoder' Serbinenko

Quoted 4 lines
About the command, i think that it will be simpler for the user if we have only one command: chainloader (like in grub4dos) that will try to detect the type of the bootloader. This is only my personal opinion.
I don't agree with this. chainloader and ntldr don't share the same
syntax: chainloader expects a bootsector whereas ntldr expects an ntldr ot bootmgr file. GRUB2 is done to break with bad design decisions of GRUB1 one of them being "kernel" command. GRUB4DOS follows GRUB1 on this subject.

I agree.

It probably would make sense that the 'ntldr' command does simple signature checks and fail on unknown files unless '--force' is specified.

Signature · 2 lines

Regards,
Christian Franke

Robert Millan

author

2009-08-10 11:52 UTC #13 lore raw

Quoted 5 lines · Christian Franke

Quoted 4 lines · Vladimir 'phcoder' Serbinenko
Quoted 4 lines
About the command, i think that it will be simpler for the user if we have only one command: chainloader (like in grub4dos) that will try to detect the type of the bootloader. This is only my personal opinion.

Quoted 8 lines

Quoted 6 lines
I don't agree with this. chainloader and ntldr don't share the same
syntax: chainloader expects a bootsector whereas ntldr expects an ntldr ot bootmgr file. GRUB2 is done to break with bad design decisions of GRUB1 one of them being "kernel" command. GRUB4DOS follows GRUB1 on this subject.
I agree.

Alright. Let's make it a separate command. I think it should still share code with chainloader.c though (with some ifdefs).

I'll sort this out and make a newer patch when I find a free minute.

Quoted 2 lines

It probably would make sense that the 'ntldr' command does simple signature checks and fail on unknown files unless '--force' is specified.

You mean checking for the PE signature? Yes, this would be nice too.

Signature · 5 lines

Robert Millan

  The DRM opt-in fallacy: "Your data belongs to us. We will decide when (and
  how) you may access your data; but nobody's threatening your freedom: we
  still allow you to remove your data and not access it at all."

Christian Franke

2009-08-10 18:57 UTC #14 lore raw

Quoted 6 lines · Robert Millan

Quoted 2 lines
It probably would make sense that the 'ntldr' command does simple signature checks and fail on unknown files unless '--force' is specified.
You mean checking for the PE signature? Yes, this would be nice too.

A check of the first byte (jmp, 0xe9) and some file size range check (e.g. 0x30000...0x40000) may be enough for a first ntldr command. May also work for bootmgr.exe.

EXE ("MZ") and PE headers appear at larger offsets:

ntldr from XP SP2: size 251184, EXE header at 0x4d30, PE at 0x4e00 ntldr from XP SP3: size 251712, EXE header at 0x4d40, PE at 0x4e10 bootmgr.exe from Vista: ???

grub4dos checks for ntldr as follows:
- file starts with 0xe9, 0x??, 0x01,
- first sector does not end with bootsector signature 0x55,0xaa,
- file size exceeds 0x30000.

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Vladimir 'phcoder' Serbinenko

2009-08-10 19:56 UTC #15 lore raw

Quoted 4 lines

grub4dos checks for ntldr as follows:
- file starts with 0xe9, 0x??, 0x01,
- first sector does not end with bootsector signature 0x55,0xaa,
- file size exceeds 0x30000.

For me it sounds like a heuristic. I would prefer to trust user rather than introducing heuristics to check file type.

Quoted 12 lines

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Christian Franke

2009-08-10 21:00 UTC #16 lore raw

Quoted 8 lines · Vladimir 'phcoder' Serbinenko

Quoted 5 lines
grub4dos checks for ntldr as follows:
- file starts with 0xe9, 0x??, 0x01,
- first sector does not end with bootsector signature 0x55,0xaa,
- file size exceeds 0x30000.
For me it sounds like a heuristic. I would prefer to trust user rather than introducing heuristics to check file type.

I agree that such a heuristic is not needed. Grub2 uses different commands for different loaders (which is good) and therefore there is no need to auto-detect the loader type.

But a simple health check (like in 'chainloader') would IMO make sense for any load command. For 'ntldr': check that the file size is reasonable and that code starts with a jmp instruction. Allow to override the check with '--force'.

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Christian Franke