[v4,17/26] x86/boot: Reduce size of the DOS stub

  This is required to fit more sections in PE section tables,
since its size is restricted by zero page located at specific offset
after the PE header.

Tested-by: Mario Limonciello <mario.limonciello@amd.com>
Tested-by: Peter Jones <pjones@redhat.com>
Signed-off-by: Evgeniy Baskov <baskov@ispras.ru>
---
 arch/x86/boot/header.S | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)
  

On Thu, 15 Dec 2022 at 13:40, Evgeniy Baskov <baskov@ispras.ru> wrote:
>
> This is required to fit more sections in PE section tables,
> since its size is restricted by zero page located at specific offset
> after the PE header.
>
> Tested-by: Mario Limonciello <mario.limonciello@amd.com>
> Tested-by: Peter Jones <pjones@redhat.com>
> Signed-off-by: Evgeniy Baskov <baskov@ispras.ru>

I'd prefer to rip this out altogether.

https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/commit/?id=9510f6f04f579b9a3f54ad762c75ab2d905e37d8

(and refer to the other thread in linux-efi@)

> ---
>  arch/x86/boot/header.S | 14 ++++++--------
>  1 file changed, 6 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
> index 9338c68e7413..9fec80bc504b 100644
> --- a/arch/x86/boot/header.S
> +++ b/arch/x86/boot/header.S
> @@ -59,17 +59,16 @@ start2:
>         cld
>
>         movw    $bugger_off_msg, %si
> +       movw    $bugger_off_msg_size, %cx
>
>  msg_loop:
>         lodsb
> -       andb    %al, %al
> -       jz      bs_die
>         movb    $0xe, %ah
>         movw    $7, %bx
>         int     $0x10
> -       jmp     msg_loop
> +       decw    %cx
> +       jnz     msg_loop
>
> -bs_die:
>         # Allow the user to press a key, then reboot
>         xorw    %ax, %ax
>         int     $0x16
> @@ -90,10 +89,9 @@ bs_die:
>
>         .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
> +       .ascii  "Use a boot loader. "
> +       .ascii  "Press a key to reboot"
> +       .set    bugger_off_msg_size, . - bugger_off_msg
>
>  #ifdef CONFIG_EFI_STUB
>  pe_header:
> --
> 2.37.4
>
  

On 2023-03-10 17:59, Ard Biesheuvel wrote:
> On Thu, 15 Dec 2022 at 13:40, Evgeniy Baskov <baskov@ispras.ru> wrote:
>> 
>> This is required to fit more sections in PE section tables,
>> since its size is restricted by zero page located at specific offset
>> after the PE header.
>> 
>> Tested-by: Mario Limonciello <mario.limonciello@amd.com>
>> Tested-by: Peter Jones <pjones@redhat.com>
>> Signed-off-by: Evgeniy Baskov <baskov@ispras.ru>
> 
> I'd prefer to rip this out altogether.
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/commit/?id=9510f6f04f579b9a3f54ad762c75ab2d905e37d8

Sounds great! Can I replace this patch with yours in v5?

> 
> (and refer to the other thread in linux-efi@)

Which thread exactly? The one about the removal of
real-mode code?

> 
>> ---
>>  arch/x86/boot/header.S | 14 ++++++--------
>>  1 file changed, 6 insertions(+), 8 deletions(-)
>> 
>> diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
>> index 9338c68e7413..9fec80bc504b 100644
>> --- a/arch/x86/boot/header.S
>> +++ b/arch/x86/boot/header.S
>> @@ -59,17 +59,16 @@ start2:
>>         cld
>> 
>>         movw    $bugger_off_msg, %si
>> +       movw    $bugger_off_msg_size, %cx
>> 
>>  msg_loop:
>>         lodsb
>> -       andb    %al, %al
>> -       jz      bs_die
>>         movb    $0xe, %ah
>>         movw    $7, %bx
>>         int     $0x10
>> -       jmp     msg_loop
>> +       decw    %cx
>> +       jnz     msg_loop
>> 
>> -bs_die:
>>         # Allow the user to press a key, then reboot
>>         xorw    %ax, %ax
>>         int     $0x16
>> @@ -90,10 +89,9 @@ bs_die:
>> 
>>         .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
>> +       .ascii  "Use a boot loader. "
>> +       .ascii  "Press a key to reboot"
>> +       .set    bugger_off_msg_size, . - bugger_off_msg
>> 
>>  #ifdef CONFIG_EFI_STUB
>>  pe_header:
>> --
>> 2.37.4
>>
  

On Sat, 11 Mar 2023 at 15:49, Evgeniy Baskov <baskov@ispras.ru> wrote:
>
> On 2023-03-10 17:59, Ard Biesheuvel wrote:
> > On Thu, 15 Dec 2022 at 13:40, Evgeniy Baskov <baskov@ispras.ru> wrote:
> >>
> >> This is required to fit more sections in PE section tables,
> >> since its size is restricted by zero page located at specific offset
> >> after the PE header.
> >>
> >> Tested-by: Mario Limonciello <mario.limonciello@amd.com>
> >> Tested-by: Peter Jones <pjones@redhat.com>
> >> Signed-off-by: Evgeniy Baskov <baskov@ispras.ru>
> >
> > I'd prefer to rip this out altogether.
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/commit/?id=9510f6f04f579b9a3f54ad762c75ab2d905e37d8
>
> Sounds great! Can I replace this patch with yours in v5?
>

Of course.

> >
> > (and refer to the other thread in linux-efi@)
>
> Which thread exactly? The one about the removal of
> real-mode code?
>

Yes, this one

https://lore.kernel.org/linux-efi/20230308202209.2980947-1-ardb@kernel.org/
  

On 2023-03-11 20:27, Ard Biesheuvel wrote:
> On Sat, 11 Mar 2023 at 15:49, Evgeniy Baskov <baskov@ispras.ru> wrote:
>> 
>> On 2023-03-10 17:59, Ard Biesheuvel wrote:
>> > On Thu, 15 Dec 2022 at 13:40, Evgeniy Baskov <baskov@ispras.ru> wrote:
>> >>
>> >> This is required to fit more sections in PE section tables,
>> >> since its size is restricted by zero page located at specific offset
>> >> after the PE header.
>> >>
>> >> Tested-by: Mario Limonciello <mario.limonciello@amd.com>
>> >> Tested-by: Peter Jones <pjones@redhat.com>
>> >> Signed-off-by: Evgeniy Baskov <baskov@ispras.ru>
>> >
>> > I'd prefer to rip this out altogether.
>> >
>> > https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/commit/?id=9510f6f04f579b9a3f54ad762c75ab2d905e37d8
>> 
>> Sounds great! Can I replace this patch with yours in v5?
>> 
> 
> Of course.
> 
>> >
>> > (and refer to the other thread in linux-efi@)
>> 
>> Which thread exactly? The one about the removal of
>> real-mode code?
>> 
> 
> Yes, this one
> 
> https://lore.kernel.org/linux-efi/20230308202209.2980947-1-ardb@kernel.org/

Thanks!