From: Ard Biesheuvel <ardb@xxxxxxxxxx> [ Commit 768171d7ebbce005210e1cf8456f043304805c15 upstream ] 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: Ard Biesheuvel <ardb@xxxxxxxxxx> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Acked-by: H. Peter Anvin (Intel) <hpa@xxxxxxxxx> Link: https://lore.kernel.org/r/20230912090051.4014114-21-ardb@xxxxxxxxxx Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx> --- arch/x86/boot/header.S | 49 -------------------- arch/x86/boot/setup.ld | 7 +-- 2 files changed, 4 insertions(+), 52 deletions(-) diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S index 38b611eb1a3c..b8d241e57b49 100644 --- a/arch/x86/boot/header.S +++ b/arch/x86/boot/header.S @@ -38,63 +38,14 @@ 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 0x3c # # Offset to the PE header. # .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 diff --git a/arch/x86/boot/setup.ld b/arch/x86/boot/setup.ld index 49546c247ae2..b11c45b9e51e 100644 --- a/arch/x86/boot/setup.ld +++ b/arch/x86/boot/setup.ld @@ -10,10 +10,11 @@ ENTRY(_start) SECTIONS { . = 0; - .bstext : { *(.bstext) } - .bsdata : { *(.bsdata) } + .bstext : { + *(.bstext) + . = 495; + } =0xffffffff - . = 495; .header : { *(.header) } .entrytext : { *(.entrytext) } .inittext : { *(.inittext) } -- 2.44.0.769.g3c40516874-goog
