amd64/186515: Doesn't boot with GPT when # of entries over than 128.

[Warren Block]

On Fri, 7 Feb 2014, Andrey V. Elsukov wrote:

> On 06.02.2014 23:30, John Baldwin wrote:
>>  Using more entries to pad out the table isn't the normal way to handle 4k
>>  alignment.  You can just leave a gap before the start of freebsd-boot.  Having
>>  the sectors "free" vs having them contain zero'd GPT entries doesn't really
>>  make a difference.  One question is when does the boot break?  Does it make it
>>  into the loader and break trying to boot the kernel?  Does it make it into
>>  gptboot and break trying to load the loader?
>
> Hi John,
>
> this is gptboot's restriction. Look at the sys/boot/common/gpt.c.

It is mentioned at the start of gptboot(8) under Implementation Notes, 
too.

Alignment of freebsd-boot is usually not very important.  It is only 
rarely written, and the bootcode is so small that it will probably not 
take appreciably longer to read or write even when misaligned. 
Filesystem partitions are where alignment really matters.