On 2025/10/14 22:51, Masami Hiramatsu wrote: > Hi Menglong, > > I remember why I haven't implement this. > > On Fri, 10 Oct 2025 11:38:46 +0800 > Menglong Dong <[email protected]> wrote: > > > + > > +static struct ftrace_ops fprobe_ftrace_ops = { > > + .func = fprobe_ftrace_entry, > > + .flags = FTRACE_OPS_FL_SAVE_REGS, > > Actually, this flag is the problem. This can fail fprobe on architecture > which does not support CONFIG_DYNAMIC_FTRACE_WITH_REGS (e.g. arm64, riscv) > > * SAVE_REGS - The ftrace_ops wants regs saved at each function called > * and passed to the callback. If this flag is set, but the > * architecture does not support passing regs > * (CONFIG_DYNAMIC_FTRACE_WITH_REGS is not defined), then the > * ftrace_ops will fail to register, unless the next flag > * is set. > > fgraph has a special entry code for saving ftrace_regs. > So at least we need to fail back to fgraph if arch does not > support CONFIG_DYNAMIC_FTRACE_WITH_REGS.
Ah, I have be working on x86_64 and didn't notice it. You are right, we do need fallback if CONFIG_DYNAMIC_FTRACE_WITH_REGS not supported. I'll send a V4 later. BTW, is the FTRACE_OPS_FL_SAVE_REGS necessary here? I guess not all architectures save the function argument regs in fentry_caller() like x86_64, that's why we need it here :/ Thanks! Menglong Dong > > Thank you, > >
