Re: [Qemu-devel] [PATCH v2 1/2] arm_boot: Assume Linux boot flow when -dtb given

[Peter Crosthwaite <peter.crosthwaite@petalogix.com>]

On Fri, Jun 22, 2012 at 11:36 PM, Peter Maydell
<peter.maydell@linaro.org> wrote:
> On 22 June 2012 14:27, Peter Crosthwaite
> <peter.crosthwaite@petalogix.com> wrote:
>> Ping!
>>
>> Any thoughts Peter?
>
> Still sounds too specific to your odd use case and hardware to me.
>
> I'd accept some reasonable way of saying "this ELF file is a Linux kernel",
> but magically doing it if you also said -dtb isn't it. I also care about
> backcompat with previous command lines and with being consistent about
> how -kernel works across architectures where possible.

Speaking of other archs, microblaze will accept -dtb with an elf and
implement the r2=foo style behviour before loading the elf entry. A
provocative thought, how bout always using a Linux style bootloader no
matter what? Does it really matter if your elf is bootstrapped by half
a dozen instructions?

Further to that, can we get rid of the bootloader blob altogether and
just setup the cpu->env like other architectures do?

  23 /* The worlds second smallest bootloader.  Set r0-r2, then jump
to kernel.  */
  24 static uint32_t bootloader[] = {
  25   0xe3a00000, /* mov     r0, #0 */
  26   0xe59f1004, /* ldr     r1, [pc, #4] */
  27   0xe59f2004, /* ldr     r2, [pc, #4] */
  28   0xe59ff004, /* ldr     pc, [pc, #4] */
  29   0, /* Board ID */
  30   0, /* Address of kernel args.  Set by integratorcp_init.  */
  31   0  /* Kernel entry point.  Set by integratorcp_init.  */
  32 };

All this code does is set registers and an entry point, which several
bootloaders do just though cpu->env manipulation.

> a somewhat contradictory set of requirements.)
>
> -- PMM