[coreboot] NULL pointer dereference in search_bus_device()

[Myles Watson]

>> > That doesn't happen, because the if (subbus... is in the for loop, which
>> > checks for NULL. the search_bus_resources() is always called outside the
>> > for loop.
>> You're right.  I should have looked at the code first, instead of just
>> the patch.  There wasn't enough context.
>>
>> If there is no bus there, maybe the resource shouldn't be subtractive.
>>  Maybe we should print a message when that happens so that we can fix
>> the problem.
>
> What would cause it to be subtractive? We should print an error message
> if this occurs, but be should also react sanely. How do we proceed?

This has always been confusing to me.  I don't know if we use it
"correctly" anywhere in coreboot.

My understanding is that subtractive resources should be used when
there is nothing explicitly directing an address range to a specific
bus or device.  So, if an address arrives that doesn't match anything
you have and there is a subtractive resource, pass it that way.

I'd guess that it's left over from another era, but I'm not sure.  Is
there another use for subtractive resources?

Thanks,
Myles