Re: [PATCH] ftrace: Fix function name for trampoline

[Tatsuya S]

On 10/11/24 12:03 AM, Masami Hiramatsu (Google) wrote:
> On Thu, 10 Oct 2024 22:02:59 +0900
> Tatsuya S <tatsuya.s2862@xxxxxxxxx> wrote:
>
> > The issue that unrelated function name is shown on stack trace like
> > following even though it should be trampoline code address is caused by
> > the creation of trampoline code in the area where .init.text section
> > of module was freed after module is loaded.
> >
> > bash-1344    [002] .....    43.644608: <stack trace>
> >    => (MODULE INIT FUNCTION)
> >    => vfs_write
> >    => ksys_write
> >    => do_syscall_64
> >    => entry_SYSCALL_64_after_hwframe
> >
> > To resolve this, when function address of stack trace entry is in
> > trampoline, output without looking up symbol name.
> >
> > Signed-off-by: Tatsuya S <tatsuya.s2862@xxxxxxxxx>
> > ---
> >   kernel/trace/trace_output.c | 5 +++++
> >   1 file changed, 5 insertions(+)
> >
> > diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> > index 868f2f912f28..32a0858373e2 100644
> > --- a/kernel/trace/trace_output.c
> > +++ b/kernel/trace/trace_output.c
> > @@ -1246,6 +1246,11 @@ static enum print_line_t trace_stack_print(struct trace_iterator *iter,
> >   			break;
> >   
> >   		trace_seq_puts(s, " => ");
> > +		if (is_ftrace_trampoline((*p) + delta)) {
> > +			trace_seq_printf(s, "0x%08lx", (*p) + delta);
>
> If we know that address is the ftrace trampoline, we'd better show something
> like "[FTRACE TRAMPOLINE]"
>
> > +			trace_seq_putc(s, '\n');
>
> And this is not needed. So for example,
>
> 			trace_seq_puts(s, "[FTRACE TRAMPOLINE]\n");
>
> is enough.

Thanks for review. OK.

> > +			continue;
> > +		}
> >   		seq_print_ip_sym(s, (*p) + delta, flags);
> >   		trace_seq_putc(s, '\n');
> >   	}
>
> Thank you,
>
> > --
> > 2.46.2