Re: [Xen-devel] [PATCH] x86/boot: Annotate the multiboot headers with size and type information

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.03.18 at 19:58, <andrew.cooper3@xxxxxxxxxx> wrote:
> This causes objdump not to try and disassemble the data.
> 
> While altering this area, switch to using .balign, and fill with 0xc2 to help
> highlight the embedded padding (rather than having it filled with 0f 1f 40 00
> which is a long nop).  Also, shorten the labels by stripping off the _start
> suffix.
> 
> The end result is now:
>   ffff82d080200000 <_start>:
>   ffff82d080200000:       e9 af c1 1c 00          jmpq   ffff82d0803cc1b4 
> <__start>
>   ffff82d080200005:       0f 1f 00                nopl   (%rax)
> 
>   ffff82d080200008 <multiboot1_header>:
>   ffff82d080200008:       02 b0 ad 1b 03 00 00 00 fb 4f 52 e4 c2 c2 c2 c2     
> .........OR.....
> 
>   ffff82d080200018 <multiboot2_header>:
>   ffff82d080200018:       d6 50 52 e8 00 00 00 00 88 00 00 00 a2 ae ad 17     
> .PR.............
>   ffff82d080200028:       01 00 00 00 10 00 00 00 04 00 00 00 06 00 00 00     
> ................
>   ffff82d080200038:       06 00 00 00 08 00 00 00 0a 00 01 00 18 00 00 00     
> ................
>   ffff82d080200048:       00 00 20 00 ff ff ff ff 00 00 20 00 02 00 00 00     
> .. ....... .....
>   ffff82d080200058:       04 00 01 00 0c 00 00 00 02 00 00 00 c2 c2 c2 c2     
> ................
>   ffff82d080200068:       05 00 01 00 14 00 00 00 00 00 00 00 00 00 00 00     
> ................
>   ffff82d080200078:       00 00 00 00 c2 c2 c2 c2 07 00 01 00 08 00 00 00     
> ................
>   ffff82d080200088:       09 00 01 00 0c 00 00 00 5e c0 3c 00 c2 c2 c2 c2     
> ........^.<.....
>   ffff82d080200098:       00 00 00 00 08 00 00 00                            
>  ........
> 
>   ffff82d0802000a0 <__high_start>:
>   ffff82d0802000a0:       0f 01 15 5f 8f 25 00    lgdt   0x258f5f(%rip)       
>  # ffff82d080459006 <gdt_descr>
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

> I was considering whether it was worth splitting the multiboot headers out
> into a separate file, to declutter the top of head.S

That would probably help overall readability, I agree.

Jan


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