On Fri, 10 Nov 2023 11:11:31 +0000 Mark Rutland <mark.rutland@xxxxxxx> wrote: > On Thu, Nov 09, 2023 at 08:14:52AM +0900, Masami Hiramatsu wrote: > > On Wed, 8 Nov 2023 23:24:32 +0900 > > "Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx> wrote: > > > > > From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx> > > > > > > To clarify what will be expected on ftrace_regs, add a comment to the > > > architecture independent definition of the ftrace_regs. > > > > > > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx> > > > --- > > > Changes in v2: > > > - newly added. > > > --- > > > include/linux/ftrace.h | 25 +++++++++++++++++++++++++ > > > 1 file changed, 25 insertions(+) > > > > > > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h > > > index e8921871ef9a..b174af91d8be 100644 > > > --- a/include/linux/ftrace.h > > > +++ b/include/linux/ftrace.h > > > @@ -118,6 +118,31 @@ extern int ftrace_enabled; > > > > > > #ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS > > > > > > +/** > > > + * ftrace_regs - ftrace partial/optimal register set > > > + * > > > + * ftrace_regs represents a group of registers which is used at the > > > + * function entry and exit. There are three types of registers. > > > + * > > > + * - Registers for passing the parameters to callee, including the stack > > > + * pointer. (e.g. rcx, rdx, rdi, rsi, r8, r9 and rsp on x86_64) > > > + * - Registers for passing the return values to caller. > > > + * (e.g. rax and rdx on x86_64) > > > + * - Registers for hooking the function return including the frame pointer > > > + * (the frame pointer is architecture/config dependent) > > > + * (e.g. rbp and rsp for x86_64) > > > > Oops, I found the program counter/instruction pointer must be saved too. > > This is used for live patching. One question is that if the IP is modified > > at the return handler, what should we do? Return to the specified address? > > I'm a bit confused here; currently we use fgraph_ret_regs for function returns, > are we going to replace that with ftrace_regs? Yes. It is limited and does not have APIs compatibility. > > I think it makes sense for the PC/IP to be the address the return handler will > eventually return to (and hence allowing it to be overridden), but that does > mean we'll need to go recover the return address *before* we invoke any return > handlers. The actual return address has been recovered from shadow stack at first, and callback the handlers. See __ftrace_return_to_handler() and ftrace_pop_return_trace(). So it is easy to set it to the ftrace_regs :) Thank you! > > Thanks, > Mark. -- Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
