[U-Boot] [PATCH v4 04/16] sandbox: smbios: Update to support sandbox

[Alexander Graf]

On 07.06.18 22:25, Simon Glass wrote:
> Hi Alex,
> 
> On 3 June 2018 at 04:13, Alexander Graf <agraf at suse.de> wrote:
>>
>>
>> On 25.05.18 04:42, Simon Glass wrote:
>>> Hi Alex,
>>>
>>> On 24 May 2018 at 06:24, Alexander Graf <agraf at suse.de> wrote:
>>>>
>>>>
>>>> On 16.05.18 17:42, Simon Glass wrote:
>>>>> At present this code casts addresses to pointers so cannot be used with
>>>>> sandbox. Update it to use mapmem instead.
>>>>>
>>>>> Signed-off-by: Simon Glass <sjg at chromium.org>
>>>>
>>>> I really dislike the whole fact that you have to call map_sysmem() at
>>>> all. I don't quite understand the whole point of it either - it just
>>>> seems to clutter the code and make it harder to follow.
>>>
>>> The purpose is to map U-Boot addresses (e.g. 0x1234) to actual
>>> user-space addresses in sandbox (gd->arch.ram_buf + 0x1234).
>>>
>>> Otherwise we cannot write tests which use particular addresses, and
>>> people have to worry about the host memory layout when using sandbox.
>>
>> Not if we write a smart enough linker script. I can try to see when I
>> get around to give you an example. But basically all we need to do is
>> reserve a section for guest ram at a constant virtual address.
> 
> Yes, but ideally that would be 0, or something small.

You can't do 0 because 0 is protected on a good number of OSs. And if it
can't be 0, better use something that makes pointers easy to read.

> 
>>
>>>> Can't we just simply make sandbox behave like any other target instead?
>>>
>>> Actually that's the goal of the sandbox support. Memory is modelled as
>>> a contiguous chunk starting at 0x0, regardless of what the OS actually
>>> gives U-Boot in terms of addresses.
>>
>> Most platforms don't have RAM start at 0x0 (and making sure nobody
>> assumes it does start at 0 is a good thing). The only bit we need to
>> make sure is that it always starts at *the same* address on every
>> invocation. But if that address is 256MB, things should still be fine.
> 
> Yes but putting a 10000000 base address on everything is a bit of a pain.

Why? It's what we do on arm systems that have ram starting at higher
offsets already.

Alex