Re: [Qemu-devel] [PATCH 3/3] PPC PReP: can run without bios image

[Fabien Chouteau <chouteau@adacore.com>]

On 04/04/2013 02:43 PM, Peter Maydell wrote:
> On 4 April 2013 12:53, Andreas Färber <afaerber@suse.de> wrote:
>> Alex, isn't ARM running without -bios? Instead of a firmware blob it has
>> some hardcoded firmware'ish instructions in the loader code.
>
> Varies from board to board, but yes, generally we have a trivial
> bootloader (which on uniprocessor machines doesn't actually run
> guest code, it just sets registers and memory up to jump to the
> kernel).
>
>> For PReP, Fabien has not stated what his use case actually is (in
>> particular which hardware?), so it's hard for me to comment on what the
>> hardware actually does and I thus won't accept random changes just
>> because they happen to be in Leon3 code. There's nothing conceptually
>> wrong with loading ELF code so I'm positive we will find a solution to
>> accommodate all use cases in some way. :)
>
> ARM also lets you pass an ELF file to -kernel which it treats
> as "just pull this blob into RAM and jump to its entrypoint".

That's what we do for almost all the targets we are using at AdaCore
(leon, leon3, PReP(602), wrSbc8349(e300), wrSbc8548(e500v2),
lm3s(arm-M3), TMS570(arm-R4F)).

> This is useful for 'bare metal' type test cases (equivalent
> of dumping a file in over JTAG).

Exactly, maybe I have to explain how we use QEMU here:

The Ada language provides run-time features (tasking, timing services,
protected objects, etc...). These can be implemented on top of an OS
(Windows, Linux, Solaris, vxWorks, etc...). There's also the Ravenscar
profile, which restrict the language to a subset of run-time features
suitable for embedded and safety-critical tasks.

In that case there's no need for and OS, but the program itself can be a
simple kernel (scheduling, interrupts, timing services...) running on
bare metal. The program will also do the initialization of the board, so
there's no need for bootloader/firmware.

We run hundreds of thousands of tests on QEMU each days, on all the
guest platforms above and on Windows and Linux hosts. These tests are
very short programs that usually run for less than 2 secs.

In that context having a boot loader that initialize the board and load
the program from network or disk is not very interesting, it's time
consuming and it's complicated. Our compiler builds and ELF file, it's
easier to run it right away.

> The UI is all wrong, though:
> -kernel should always mean "load a Linux kernel" and we should
> have some other way (ideally a cross-architecture way) of saying
> "just load this binary blob and start it". (-bios isn't that
> because -bios tends to (a) mean different things on different
> boards and (b) mean 'put this in flash or whatever' rather than
> 'dump stuff in RAM and go'.)
>

I think -kernel works fine for all architecture. Linux is not the only
kernel available ;)

-- 
Fabien Chouteau