[Qemu-devel] Re: [Bochs-developers] [PATCH v2 4/6] Execute rombios32 code from romaddress 0xe0000.

["Sebastian Herbszt" <herbszt@gmx.de>]

Gleb Natapov wrote:

> Signed-off-by: Gleb Natapov <gleb@redhat.com>
> ---
> 
> bios/Makefile.in      |    1 +
> bios/rombios.c        |   17 +----------------
> bios/rombios32.ld     |    8 +++-----
> bios/rombios32start.S |    9 ++++++++-
> 4 files changed, 13 insertions(+), 22 deletions(-)
> 
> diff --git a/bios/Makefile.in b/bios/Makefile.in
> index b055910..af674b4 100644
> --- a/bios/Makefile.in
> +++ b/bios/Makefile.in
> @@ -106,6 +106,7 @@ rombios32.o: rombios32.c acpi-dsdt.hex
> ifeq ("1", "0")
> acpi-dsdt.hex: acpi-dsdt.dsl
>  iasl -tc -p $@ $<
> + sed -i -e's/^unsigned/const unsigned/' $@
> endif
> 
> rombios32start.o: rombios32start.S
> diff --git a/bios/rombios.c b/bios/rombios.c
> index 03540cb..098543c 100644
> --- a/bios/rombios.c
> +++ b/bios/rombios.c
> @@ -10026,13 +10026,6 @@ rombios32_05:
>   mov gs, ax
>   cld
> 
> -  ;; copy rombios32 code to ram (ram offset = 1MB)
> -  mov esi, #0xfffe0000
> -  mov edi, #0x00040000
> -  mov ecx, #0x10000 / 4
> -  rep
> -    movsd
> -
>   ;; init the stack pointer
>   mov esp, #0x00080000
> 
> @@ -10041,17 +10034,9 @@ rombios32_05:
>   push #0x04b2
> 
>   ;; call rombios32 code
> -  mov eax, #0x00040000
> +  mov eax, #0x000e0000
>   call eax
> 
> -  ;; reset the memory (some boot loaders such as syslinux suppose
> -  ;; that the memory is set to zero)
> -  mov edi, #0x00040000
> -  mov ecx, #0x40000 / 4
> -  xor eax, eax
> -  rep
> -    stosd
> -
>   ;; return to 16 bit protected mode first
>   db 0xea
>   dd rombios32_10
> diff --git a/bios/rombios32.ld b/bios/rombios32.ld
> index c7f6066..113a2c0 100644
> --- a/bios/rombios32.ld
> +++ b/bios/rombios32.ld
> @@ -3,14 +3,12 @@ OUTPUT_ARCH(i386)
> ENTRY(_start);
> SECTIONS
> {
> -        . = 0x00040000;
> +        . = 0x000e0000;
>         .text     : { *(.text)    }
>         .rodata    : { *(.rodata) }
> -        . = ALIGN(4096);
> -        .data     : { *(.data)    }
> -        __bss_start = . ;
> -        .bss      : { *(.bss) *(COMMON) }
>         _end = . ;
> +        .data 0x700 : AT (_end) { __data_start = .; *(.data); __data_end = .;}
> +        .bss      : { __bss_start = .; *(.bss) *(COMMON); __bss_end = .;}
>         /DISCARD/ : { *(.stab)
>                      *(.stabstr)
>                      *(.comment)

The .data section is currently empty because all data is read-only and put
into .rodata, .rodata.str1.1 and .rodata.str1.4. As soon as we put something
into .data we get a link error because .data now overlaps .rodata.str1.1.
The error is gone if we put all .rodata input sections into .rodata output
section with ".rodata    : { *(.rodata*)".

> diff --git a/bios/rombios32start.S b/bios/rombios32start.S
> index 601e2b0..1900261 100644
> --- a/bios/rombios32start.S
> +++ b/bios/rombios32start.S
> @@ -32,10 +32,17 @@ _start:
>   /* clear bss section */
>   xor %eax, %eax
>   mov $__bss_start, %edi
> -  mov $_end, %ecx
> +  mov $__bss_end, %ecx
>   sub %edi, %ecx
>   rep stosb

We do overwrite data at 0x700 here. Is this acceptable for S3 resume?

> +  /* copy data section */
> +  mov $_end, %esi
> +  mov $__data_start, %edi
> +  mov $__data_end, %ecx
> +  sub %edi, %ecx
> +  rep movsb
> +

As described above this is currently a no-op, because
__data_start = __data_end = 0x700.

>   jmp rombios32_init
> 
>   .code16
> 

- Sebastian