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

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Thu, 10 Oct 2024 22:02:59 +0900
Tatsuya S <tatsuya.s2862@gmail.com> 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@gmail.com>
> ---
>  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.

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

Thank you,

> -- 
> 2.46.2
> 


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