Re: [RFC PATCH 1/3] arm64: entry: Remove unnecessary calculation for S_SP in EL1h

From: James Morse
Date: Mon Sep 07 2015 - 10:49:15 EST

On 04/09/15 15:23, Jungseok Lee wrote:
> Under EL1h, S_SP data is not seen in kernel_exit. Thus, x21 calculation
> is not needed in kernel_entry. Currently, S_SP information is vaild only
> when sp_el0 is used.
> Signed-off-by: Jungseok Lee <jungseoklee85@xxxxxxxxx>
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index e163518..d23ca0d 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -91,8 +91,6 @@
> get_thread_info tsk // Ensure MDSCR_EL1.SS is clear,
> ldr x19, [tsk, #TI_FLAGS] // since we can unmask debug
> disable_step_tsk x19, x20 // exceptions when scheduling.
> - .else
> - add x21, sp, #S_FRAME_SIZE
> .endif
> mrs x22, elr_el1
> mrs x23, spsr_el1

This sp value gets written to the struct pt_regs that is built on the
stack, and passed to the fault handlers, see 'el1_sp_pc' in kernel/entry.S,
which goes on to call do_sp_pc_abort() which prints this value out. (Other
fault handlers may make decisions based on this value).
It should be present and correct.


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