[PATCH v2] powerpc/64/signal: balance return predictor stack in signal trampoline

[Michael Ellerman]

On Mon, 11 May 2020 20:19:52 +1000, Nicholas Piggin wrote:
> Returning from an interrupt or syscall to a signal handler currently
> begins execution directly at the handler's entry point, with LR set to
> the address of the sigreturn trampoline. When the signal handler
> function returns, it runs the trampoline. It looks like this:
> 
>     # interrupt at user address xyz
>     # kernel stuff... signal is raised
>     rfid
>     # void handler(int sig)
>     addis 2,12,.TOC.-.LCF0 at ha
>     addi 2,2,.TOC.-.LCF0 at l
>     mflr 0
>     std 0,16(1)
>     stdu 1,-96(1)
>     # handler stuff
>     ld 0,16(1)
>     mtlr 0
>     blr
>     # __kernel_sigtramp_rt64
>     addi    r1,r1,__SIGNAL_FRAMESIZE
>     li      r0,__NR_rt_sigreturn
>     sc
>     # kernel executes rt_sigreturn
>     rfid
>     # back to user address xyz
> 
> [...]

Applied to powerpc/next.

[1/1] powerpc/64/signal: Balance return predictor stack in signal trampoline
      https://git.kernel.org/powerpc/c/0138ba5783ae0dcc799ad401a1e8ac8333790df9

cheers