On Mon, Nov 16, 2015 at 2:35 PM, Yang Shi <[email protected]> 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. > 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: > > high > original A64_SP => 0:+-----+ BPF prologue > |FP/LR| > current A64_FP => -16:+-----+ > | ... | callee saved registers > +-----+ > | | x25/x26 > BPF fp register => -80:+-----+ > | | > | ... | BPF prog stack > | | > | | > current A64_SP => +-----+ > | | > | ... | Function call stack > | | > +-----+ > low > > CC: Zi Shen Lim <[email protected]> > CC: Xi Wang <[email protected]> > Signed-off-by: Yang Shi <[email protected]>
Acked-by: Zi Shen Lim <[email protected]> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
