From: Yang Shi yang.shi@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@linaro.org
Applied, thank you.