[OpenBIOS] [PATCH] sparc64: clear unused registers when calling client image

[Blue Swirl]

On 5/27/09, Igor Kovalenko <igor.v.kovalenko at gmail.com> wrote:
> On Wed, May 20, 2009 at 8:57 PM, Blue Swirl <blauwirbel at gmail.com> wrote:
>  > On 5/19/09, Igor Kovalenko <igor.v.kovalenko at gmail.com> wrote:
>  >> This change seems to fix the problem here with silo not being able
>  >>  to deal with bss data. The problem is that silo does access to an address
>  >>  which is calculated from %i3 + bss offset, so %i3 must be somehow initialized.
>  >>
>  >>  To do this I created start_client_image() helper which initializes
>  >>  clear context,
>  >>  fills it with stack pointer and client interface handler pointer then
>  >>  switches to it.
>  >>  According to docs all registers not used to convey data to client code must be
>  >>  cleared.
>  >>
>  >>  Since my sparc64-elf-gcc cross compiler managed to discard stores
>  >>  to __context in switch_to() I had to make __context a volatile pointer.
>  >>
>  >>  Signed-off-by: Igor Kovalenko <igor.v.kovalenko at gmail.com>
>  >
>  > There is something strange with the patch, for example SILO on Gentoo
>  > 2008.0 install CD does not load completely:
>  > [sparc64] Booting file 'cdrom' with parameters ''
>  > Not a bootable ELF image
>  > Not a Linux kernel image
>  > Loading a.out image...
>  > Loaded 7680 bytes
>  > entry point is 0x4000
>  > Jumping to entry point...
>  > switching to new context: entry point 0x4000 stack 0xffe50a51
>  > SIUnhandled Exception 0x0000000000000068
>  > PC = 0x00000000ffd0fd44 NPC = 0x00000000ffd0fd48
>  > Stopping execution
>  >
>
>
> I now see there are other issues with that patch, for example stack
>  pointer is assigned at bottom of client image stack.
>
>  Let's do a workaround instead. This patch just clears %i3 before
>  calling client image, allowing silo to initialize and boot image.

Thanks, applied (r500).