On Wed, 9 Aug 2023 12:31:00 +0200
Florent Revest [off-list ref] wrote:

On Mon, Aug 7, 2023 at 8:49 AM Masami Hiramatsu (Google)
[off-list ref] wrote:

quoted

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Allow fprobe events to be enabled with CONFIG_DYNAMIC_FTRACE_WITH_ARGS.
With this change, fprobe events mostly use ftrace_regs instead of pt_regs.
Note that if the arch doesn't enable HAVE_PT_REGS_COMPAT_FTRACE_REGS,
fprobe events will not be able to use from perf.

nit: "to be used from perf" ?

OK.

quoted

--- a/kernel/trace/trace_fprobe.c
+++ b/kernel/trace/trace_fprobe.c

@@ -132,25 +132,30 @@ static int
 process_fetch_insn(struct fetch_insn *code, void *rec, void *dest,
                   void *base)
 {
-       struct pt_regs *regs = rec;
-       unsigned long val;
+       struct ftrace_regs *fregs = rec;
+       unsigned long val, *stackp;
        int ret;

 retry:
        /* 1st stage: get value from context */
        switch (code->op) {
        case FETCH_OP_STACK:
-               val = regs_get_kernel_stack_nth(regs, code->param);
+               stackp = (unsigned long *)ftrace_regs_get_stack_pointer(fregs);
+               if (((unsigned long)(stackp + code->param) & ~(THREAD_SIZE - 1)) ==
+                   ((unsigned long)stackp & ~(THREAD_SIZE - 1)))

Maybe it'd be worth extracting a local
"ftrace_regs_get_kernel_stack_nth_addr" helper function and/or
"ftrace_regs_within_kernel_stack" ?

Yeah, maybe we can make it a generic inline function in linux/ftrace.h.

Thank you!


-- 
Masami Hiramatsu (Google) [off-list ref]