From mboxrd@z Thu Jan 1 00:00:00 1970 From: yang.shi@linaro.org (Shi, Yang) Date: Fri, 13 Nov 2015 09:28:45 -0800 Subject: [PATCH 2/2] arm64: bpf: make BPF prologue and epilogue align with ARM64 AAPCS In-Reply-To: References: <1447365421-1309-1-git-send-email-yang.shi@linaro.org> <1447365421-1309-3-git-send-email-yang.shi@linaro.org> Message-ID: <56461DCD.4020701@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 11/12/2015 7:28 PM, Z Lim wrote: > On Thu, Nov 12, 2015 at 1:57 PM, Yang Shi 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. When BPF prog exits, it could be just tossed. >> >> So, the BPF stack layout looks like: >> >> high >> original A64_SP => 0:+-----+ BPF prologue >> | | FP/LR and callee saved registers >> BPF fp register => -64:+-----+ >> | | >> | ... | BPF prog stack >> | | >> | | >> current A64_SP/FP => +-----+ >> | | >> | ... | Function call stack >> | | >> +-----+ >> low >> > > Yang, for stack unwinding to work, shouldn't it be something like the following? Yes, thanks for catching this. v3 will be post soon. Yang > > | LR | > A64_FP => | FP | > | .. | >