Commit 768171d7 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Ingo Molnar
Browse files

x86/boot: Remove the 'bugger off' message 



Ancient (pre-2003) x86 kernels could boot from a floppy disk straight from
the BIOS, using a small real mode boot stub at the start of the image
where the BIOS would expect the boot record (or boot block) to appear.

Due to its limitations (kernel size < 1 MiB, no support for IDE, USB or
El Torito floppy emulation), this support was dropped, and a Linux aware
bootloader is now always required to boot the kernel from a legacy BIOS.

To smoothen this transition, the boot stub was not removed entirely, but
replaced with one that just prints an error message telling the user to
install a bootloader.

As it is unlikely that anyone doing direct floppy boot with such an
ancient kernel is going to upgrade to v6.5+ and expect that this boot
method still works, printing this message is kind of pointless, and so
it should be possible to remove the logic that emits it.

Let's free up this space so it can be used to expand the PE header in a
subsequent patch.

Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Acked-by: default avatarH. Peter Anvin (Intel) <hpa@zytor.com>
Link: https://lore.kernel.org/r/20230912090051.4014114-21-ardb@google.com
parent bfab35f5

arch/x86/boot/header.S

+0 −49
Original line number Diff line number Diff line
@@ -38,64 +38,15 @@ SYSSEG = 0x1000 /* historical load address >> 4 */ 


	.code16

	.section ".bstext", "ax"



	.global bootsect_start

bootsect_start:

#ifdef CONFIG_EFI_STUB

	# "MZ", MS-DOS header

	.word	MZ_MAGIC

#endif



	# Normalize the start address

	ljmp	$BOOTSEG, $start2



start2:

	movw	%cs, %ax

	movw	%ax, %ds

	movw	%ax, %es

	movw	%ax, %ss

	xorw	%sp, %sp

	sti

	cld



	movw	$bugger_off_msg, %si



msg_loop:

	lodsb

	andb	%al, %al

	jz	bs_die

	movb	$0xe, %ah

	movw	$7, %bx

	int	$0x10

	jmp	msg_loop



bs_die:

	# Allow the user to press a key, then reboot

	xorw	%ax, %ax

	int	$0x16

	int	$0x19



	# int 0x19 should never return.  In case it does anyway,

	# invoke the BIOS reset code...

	ljmp	$0xf000,$0xfff0



#ifdef CONFIG_EFI_STUB

	.org	0x38

	#

	# Offset to the PE header.

	#

	.long	LINUX_PE_MAGIC

	.long	pe_header

#endif /* CONFIG_EFI_STUB */



	.section ".bsdata", "a"

bugger_off_msg:

	.ascii	"Use a boot loader.\r\n"

	.ascii	"\n"

	.ascii	"Remove disk and press any key to reboot...\r\n"

	.byte	0



#ifdef CONFIG_EFI_STUB

pe_header:

	.long	PE_MAGIC

arch/x86/boot/setup.ld

+4 −3
Original line number Diff line number Diff line
@@ -10,10 +10,11 @@ ENTRY(_start) 
SECTIONS

{

	. = 0;

	.bstext		: { *(.bstext) }

	.bsdata		: { *(.bsdata) }



	.bstext	: {

		*(.bstext)

		. = 495;

	} =0xffffffff



	.header		: { *(.header) }

	.entrytext	: { *(.entrytext) }

	.inittext	: { *(.inittext) }