powerpc/32: Clear on-stack exception marker upon exception return

[Michael Ellerman]

On Wed, 2019-02-27 at 11:45:30 UTC, Christophe Leroy wrote:
> Clear the on-stack STACK_FRAME_REGS_MARKER on exception exit in order
> to avoid confusing stacktrace like the one below.
> 
> Call Trace:
> [c0e9dca0] [c01c42a0] print_address_description+0x64/0x2bc (unreliable)
> [c0e9dcd0] [c01c4684] kasan_report+0xfc/0x180
> [c0e9dd10] [c0895130] memchr+0x24/0x74
> [c0e9dd30] [c00a9e38] msg_print_text+0x124/0x574
> [c0e9dde0] [c00ab710] console_unlock+0x114/0x4f8
> [c0e9de40] [c00adc60] vprintk_emit+0x188/0x1c4
> --- interrupt: c0e9df00 at 0x400f330
>     LR = init_stack+0x1f00/0x2000
> [c0e9de80] [c00ae3c4] printk+0xa8/0xcc (unreliable)
> [c0e9df20] [c0c27e44] early_irq_init+0x38/0x108
> [c0e9df50] [c0c15434] start_kernel+0x310/0x488
> [c0e9dff0] [00003484] 0x3484
> 
> With this patch the trace becomes:
> 
> Call Trace:
> [c0e9dca0] [c01c42c0] print_address_description+0x64/0x2bc (unreliable)
> [c0e9dcd0] [c01c46a4] kasan_report+0xfc/0x180
> [c0e9dd10] [c0895150] memchr+0x24/0x74
> [c0e9dd30] [c00a9e58] msg_print_text+0x124/0x574
> [c0e9dde0] [c00ab730] console_unlock+0x114/0x4f8
> [c0e9de40] [c00adc80] vprintk_emit+0x188/0x1c4
> [c0e9de80] [c00ae3e4] printk+0xa8/0xcc
> [c0e9df20] [c0c27e44] early_irq_init+0x38/0x108
> [c0e9df50] [c0c15434] start_kernel+0x310/0x488
> [c0e9dff0] [00003484] 0x3484
> 
> Cc: stable at vger.kernel.org
> Cc: Nicolai Stange <nstange at suse.de>
> 
> Signed-off-by: Christophe Leroy <christophe.leroy at c-s.fr>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/9580b71b5a7863c24a9bd18bcd2ad759

cheers