[PATCH] ppc: move init-program client stack to 1:1 virt to phys mapped memory

[Mark Cave-Ayland]

The default context used by init-program is allocated from the OpenBIOS
heap which uses a different virt to phys mapping to avoid having to
physically relocate the PROM on startup for PPC machines.

It seems that the OpenBSD bootloader isn't happy with this change
introduced by the context rework, most likely because there is an
assumption that the client stack is mapped 1:1 virt to phys.

Fix this by overriding the default context stack during init-program
to a location just under the MMU hash table (SDR1) which was its
previous hard-coded location in 1:1 virt to phys mapped memory, and
allow OpenBSD to boot.

Signed-off-by: Mark Cave-Ayland 
---
 arch/ppc/qemu/context.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/ppc/qemu/context.c b/arch/ppc/qemu/context.c
index 03ca173..06e0122 100644
--- a/arch/ppc/qemu/context.c
+++ b/arch/ppc/qemu/context.c
@@ -16,6 +16,7 @@
 #include "libopenbios/ofmem.h"
 #include "libopenbios/initprogram.h"
 #include "libopenbios/sys_info.h"
+#include "arch/ppc/processor.h"

#define MAIN_STACK_SIZE 16384
 #define IMAGE_STACK_SIZE 4096*2
@@ -232,6 +233,14 @@ arch_init_program(void)
     ctx->regs[REG_R6] = 0;
     ctx->regs[REG_R7] = 0;

+    /* Override the stack in the default context: the OpenBSD bootloader
+       fails soon after setting up virt to phys mappings with the default
+       stack. My best guess is that this is because the malloc() heap
+       doesn't have a 1:1 virt to phys mapping. So for the moment we use
+       the original (pre-context) location just under the MMU hash table
+       (SDR1) which is mapped 1:1 and makes the bootloader happy. */
+    ctx->sp = mfsdr1() - 32768 - 65536;
+
     /* Set param */
     feval("load-state >ls.param @");
     param = POP();

[Mark Cave-Ayland]

On 17/08/18 10:35, Mark Cave-Ayland wrote:
> The default context used by init-program is allocated from the OpenBIOS
> heap which uses a different virt to phys mapping to avoid having to
> physically relocate the PROM on startup for PPC machines.
>
> It seems that the OpenBSD bootloader isn't happy with this change
> introduced by the context rework, most likely because there is an
> assumption that the client stack is mapped 1:1 virt to phys.
>
> Fix this by overriding the default context stack during init-program
> to a location just under the MMU hash table (SDR1) which was its
> previous hard-coded location in 1:1 virt to phys mapped memory, and
> allow OpenBSD to boot.
> Signed-off-by: Mark Cave-Ayland
>
> arch/ppc/qemu/context.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/arch/ppc/qemu/context.c b/arch/ppc/qemu/context.c
> index 03ca173..06e0122 100644
> --- a/arch/ppc/qemu/context.c
> +++ b/arch/ppc/qemu/context.c
> @@ -16,6 +16,7 @@
>  #include "libopenbios/ofmem.h"
>  #include "libopenbios/initprogram.h"
>  #include "libopenbios/sys_info.h"
> +#include "arch/ppc/processor.h"
>
> #define MAIN_STACK_SIZE 16384
>  #define IMAGE_STACK_SIZE 4096*2
> @@ -232,6 +233,14 @@ arch_init_program(void)
>      ctx->regs[REG_R6] = 0;
>      ctx->regs[REG_R7] = 0;
> /* Override the stack in the default context: the OpenBSD bootloader
>   fails soon after setting up virt to phys mappings with the default
>   stack. My best guess is that this is because the malloc() heap
>   doesn't have a 1:1 virt to phys mapping. So for the moment we use
>   the original (pre-context) location just under the MMU hash table
>   (SDR1) which is mapped 1:1 and makes the bootloader happy. */
> ctx->sp = mfsdr1() - 32768 - 65536;
> /* Set param */
>    feval("load-state >ls.param @");
>    param = POP();

Applied to master.

ATB,

Mark.