[U-Boot] [PATCH v8 12/30] sandbox: Try to start the RAM buffer at a particular address

[Alexander Graf]

On 06/21/2018 04:02 AM, Simon Glass wrote:
> Hi Alex,
>
> On 20 June 2018 at 02:51, Alexander Graf <agraf at suse.de> wrote:
>> On 06/20/2018 12:02 AM, Simon Glass wrote:
>>> Hi Alex,
>>>
>>> On 18 June 2018 at 08:45, Alexander Graf <agraf at suse.de> wrote:
>>>> On 06/18/2018 04:08 PM, Simon Glass wrote:
>>>>> Use a starting address of 256MB which should be available. This helps to
>>>>> make sandbox RAM buffers pointers more recognisable.
>>>>>
>>>>> Signed-off-by: Simon Glass <sjg at chromium.org>
>>>>
>>>> Nak, this has a non-0 chance of failing, in case something else is
>>>> already
>>>> mapped at that address. You don't want to have your CI blow up 1% of the
>>>> time due to this.
>>> It's just a hint though. Everything will still work if it doesn't get
>>> this exact address.
>>
>> I don't see what it buys us then.
> These are my thoughts:
>
> 1. We get an address before 4GB which is needed for grub (so far as I can tell)

We only need that in the memory map which you want virtual (U-Boot 
address space) anyway. So there's no need to also have the Linux address 
be <4GB.

> 2. It will normally be a nice, easy-on-the-eyes address

I'd rather say it's going to confuse people, because now it's easy to 
mistake for a U-Boot address.

> 3. If it isn't, it will hopefully still be an address below 4GB
> 4. Even if not (e.g. on some very strange system) it will still allow
> sandbox to start up
>
> But anyway, as I said, this will never fail, it is just a hint. So I
> think your original comment is incorrect.

It will not fail, it will just potentially not map at exactly the spot 
you wanted the map at, which IMHO would cause even more confusion.

Imagine people now start to assume that %p output is stable between 
invocations - because it is 99% of the cases. They start to integrate 
that into their CI suites and suddenly things fail 1% of the time 
because the linker figured today's a great day to map glibc at that address.


Alex