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

[Simon Glass]

Hi Alex,

On 7 June 2018 at 12:36, Alexander Graf <agraf at suse.de> wrote:
>
>
> 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.

Yes this is one reason for map_sysmem().

>
>>
>>>
>>>>> 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.

It's a pain because you have to type 1 and 5-6 zeroes before you can
get to the address you want. Otherwise sandbox just segfaults, which
is annoying.

Regards,
Simon