On Sat, Oct 19, 2024 at 2:15 AM Xu Kuohai <xukuohai@xxxxxxxxxxxxxxx> wrote: > > From: Xu Kuohai <xukuohai@xxxxxxxxxx> > > The callsite layout for arm64 fentry is: > > mov x9, lr > nop > > When a bpf prog is attached, the nop instruction is patched to a call > to bpf trampoline: > > mov x9, lr > bl <bpf trampoline> > > This passes two return addresses to bpf trampoline: the return address > for the traced function/prog, stored in x9, and the return address for > the bpf trampoline, stored in lr. To ensure stacktrace works properly, > the bpf trampoline constructs two fake function stack frames using x9 > and lr. > > However, struct_ops progs are used as function callbacks and are invoked > directly, without x9 being set as the fentry callsite does. Therefore, > only one stack frame should be constructed using lr for struct_ops. Are you saying that currently stack unwinder on arm64 is completely broken for struct_ops progs ? or it shows an extra frame that doesn't have to be shown ? If former then it's certainly a bpf tree material. If latter then bpf-next will do. Pls clarify.
