Chaining to ReactOS

I have added an option to chain-load ReactOS' FreeLdr from Syslinux using the chain.c32 COMBOOT32 module. Until it has been committed to the main Syslinux branch, I have attached the modified chain.c32 to this post.

You can use it by including the following in your syslinux.cfg or pxelinux.cfg/default config-file:

LABEL freeldr

  COM32 chain.c32

  APPEND freeldr=freeldr.sys keeppxe

With very special thanks to Hervé Poussineau for recently adding PXE as a FreeLdr filesystem type, you can use net(0) in the ARC path in your FreeLdr.ini file:

...

[ReactOS]

BootType=Windows2003

SystemPath=ramdisk(0)\reactos

Options=/DEBUGPORT=COM1 /SOS /MININT /RDPATH=net(0)\ReactOS-LiveCD.iso

Unfortunately, there is currently a RAM disk regression in ReactOS, but it is good to be able to chain FreeLdr anyway.

no source code available?

no source code available?

It's been added to Syslinux proper now, courtesy of H. Peter Anvin. Source code here.

Now as a matter of fact, he has added the ability to choose segment, offset, and entry point for arbitrary binaries (see the seg= option). Please use with extreme caution.

why I can't chaining to ReactOS from grub4dos

title ReactOS (freeldr.sys)\n Uruchamia FreeLoader from ReactOS (freeldr.sys)...

	find --set-root /freeldr.sys

	uuid ()

	kernel /freeldr.sys

I have only black screen

why I can't chaining to ReactOS from grub4dos

Oops. Wrong forum for that.

@ireneuszp:
You may try the following:

chainloader --force --load-offset=0x8000 --boot-ip=0x9000 /freeldr.sys

but the --boot-ip value may change in the future.

@Sha0:
You may look for ROS's boot sector for better loading freeldr:

FoundFreeLoader:

		; We found freeldr.sys on the disk

		; so we need to load the first 512

		; bytes of it to 0000:8000

        ; ES:DI has dir entry (ES:DI == 07E0:XXXX)

        mov  ax,WORD [es:di+1ah]				; Get start cluster

		push ax									; Save start cluster

		push WORD 800h							; Put 800h on the stack and load it

		pop  es									; Into ES so that we load the cluster at 0000:8000

		call ReadCluster						; Read the cluster

		pop  ax									; Restore start cluster of FreeLoader



		; Save the addresses of needed functions so

		; the helper code will know where to call them.

		mov  WORD [BYTE bp-ReadSectorsOffset],ReadSectors		; Save the address of ReadSectors

		mov  WORD [BYTE bp-ReadClusterOffset],ReadCluster		; Save the address of ReadCluster

		mov  WORD [BYTE bp-PutCharsOffset],PutChars				; Save the address of PutChars



		; Now AX has start cluster of FreeLoader and we

		; have loaded the helper code in the first 512 bytes

		; of FreeLoader to 0000:8000. Now transfer control

		; to the helper code. Skip the first three bytes

		; because they contain a jump instruction to skip

		; over the helper code in the FreeLoader image.

		;jmp  0000:9003h

		push 0						; push segment (0x0000)

		mov bx, [0x8000 + 0xA8]		; load the RVA of the EntryPoint into eax

		add bx, 0x8003				; RVA -> VA and skip 3 bytes (jump to fathelper code)

		push bx						; push offset

		retf						; Transfer control to FreeLoader

The above code is for FAT16.
for others:

LoadFileDone:

        mov  dl,[BYTE bp+BootDrive]		; Load boot drive into DL

		mov  dh,[BootPartition]			; Load boot partition into DH



		push 0						; push segment (0x0000)

		mov eax, [0x8000 + 0xA8]	; load the RVA of the EntryPoint into eax

		add eax, 0x8000				; RVA -> VA

		push ax						; push offset

		retf						; Transfer control to FreeLoader

@ireneuszp: a new grub4dos patch is uploaded to google code. http://code.google.c...es/detail?id=24

@ireneuszp: a new grub4dos patch is uploaded to google code. http://code.google.c...es/detail?id=24

And was applied.
http://code.google.c...-06.7z&can=2&q=

And was applied.
http://code.google.c...-06.7z&can=2&q=

Hi roytam1

Thank you very much for your excellent work and tips. Best regards

@ireneuszp:
You may try the following:

chainloader --force --load-offset=0x8000 --boot-ip=0x9000 /freeldr.sys

but the --boot-ip value may change in the future.

That's nice, but... It's off-topic. The topic is Syslinux.

@Sha0:
You may look for ROS's boot sector for better loading freeldr:

What do you mean by "better"? That's nice of you to share the ReactOS source code, but... The chain.c32 code was inspired by ReactOS source code, so I don't understand your suggestion.

That's nice, but... It's off-topic. The topic is Syslinux.


What do you mean by "better"? That's nice of you to share the ReactOS source code, but... The chain.c32 code was inspired by ReactOS source code, so I don't understand your suggestion.

to fix a TODO in the code:
+ /* TODO: Properly parse the PE. Right now, this is hard-coded */

freeldr.sys and setupldr.sys of ReactOS are now multiboot compliant (in the last test versions).

Syslinux:

LABEL reactos

MENU LABEL Boot ReactOS

COM32 mboot.c32

APPEND /freeldr.sys



LABEL reactos_install

MENU LABEL Install ReactOS

COM32 mboot.c32

APPEND /loader/setupldr.sys

Grub4dos:

title Boot ReactOS

kernel /freeldr.sys



title Install ReactOS

kernel /loader/setupldr.sys

So the need for ugly hacks is gone.