On 11/13/2015 6:39 PM, Z Lim wrote:
Yang, I noticed another thing...
On Fri, Nov 13, 2015 at 10:09 AM, Yang Shi yang.shi@linaro.org wrote:
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.
Can you please add save/restore for x25 also? :)
Sure. BTW, since PUSH invokes stp instruction and SP need 16-bytes alignment, so we have to save x26 with x25 together. Anyway, it won't introduce any harm overhead since one instruction saves two registers.
Yang
It is initialized in BPF prog prologue when BPF prog is started to run everytime. When BPF prog exits, it could be just tossed.