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

[Igor Kovalenko]

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(a)gmail.com>

-- 
Kind regards,
Igor V. Kovalenko

[Blue Swirl]

On 5/19/09, Igor Kovalenko <igor.v.kovalenko(a)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(a)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

[Igor Kovalenko]

On Wed, May 20, 2009 at 8:57 PM, Blue Swirl <blauwirbel(a)gmail.com> wrote:
  On 5/19/09, Igor Kovalenko
<igor.v.kovalenko(a)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(a)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.

-- 
Kind regards,
Igor V. Kovalenko

[Blue Swirl]

On 5/27/09, Igor Kovalenko <igor.v.kovalenko(a)gmail.com> wrote:
  On Wed, May 20, 2009 at 8:57 PM, Blue Swirl
<blauwirbel(a)gmail.com> wrote:
  On 5/19/09, Igor Kovalenko
<igor.v.kovalenko(a)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(a)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).