[PATCH V4 2/2] arm64: bpf: make BPF prologue and epilogue align with ARM64 AAPCS

[David Miller]

From: Yang Shi <yang.shi at linaro.org>
Date: Mon, 16 Nov 2015 14:35:35 -0800

> Save and restore FP/LR in BPF prog prologue and epilogue, save SP to FP
> in prologue in order to get the correct stack backtrace.
> 
> However, ARM64 JIT used FP (x29) as eBPF fp register, FP is subjected to
> change during function call so it may cause the BPF prog stack base address
> change too.
> 
> Use x25 to replace FP as BPF stack base register (fp). Since x25 is callee
> saved register, so it will keep intact during function call.
> It is initialized in BPF prog prologue when BPF prog is started to run
> everytime. Save and restore x25/x26 in BPF prologue and epilogue to keep
> them intact for the outside of BPF. Actually, x26 is unnecessary, but SP
> requires 16 bytes alignment.
> 
> So, the BPF stack layout looks like:
 ...
> Signed-off-by: Yang Shi <yang.shi at linaro.org>

Applied, thank you.