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SubjectRe: [PATCH v2 12/39] x86/ibt,ftrace: Search for __fentry__ location
Hi Peter,

On Thu, 24 Feb 2022 15:51:50 +0100
Peter Zijlstra <peterz@infradead.org> wrote:

> Have ftrace_location() search the symbol for the __fentry__ location
> when it isn't at func+0 and use this for {,un}register_ftrace_direct().
>
> This avoids a whole bunch of assumptions about __fentry__ being at
> func+0.
>
> Suggested-by: Steven Rostedt <rostedt@goodmis.org>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
> kernel/trace/ftrace.c | 30 ++++++++++++++++++++++++++++--
> 1 file changed, 28 insertions(+), 2 deletions(-)
>
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -1578,7 +1578,24 @@ unsigned long ftrace_location_range(unsi
> */
> unsigned long ftrace_location(unsigned long ip)
> {
> - return ftrace_location_range(ip, ip);
> + struct dyn_ftrace *rec;
> + unsigned long offset;
> + unsigned long size;
> +
> + rec = lookup_rec(ip, ip);
> + if (!rec) {
> + if (!kallsyms_lookup_size_offset(ip, &size, &offset))
> + goto out;
> +
> + if (!offset)

Isn't this 'if (offset)' ?

> + rec = lookup_rec(ip - offset, (ip - offset) + size);
> + }
> +
> + if (rec)
> + return rec->ip;
> +
> +out:
> + return 0;
> }

Thank you,

>
> /**
> @@ -5110,11 +5127,16 @@ int register_ftrace_direct(unsigned long
> struct ftrace_func_entry *entry;
> struct ftrace_hash *free_hash = NULL;
> struct dyn_ftrace *rec;
> - int ret = -EBUSY;
> + int ret = -ENODEV;
>
> mutex_lock(&direct_mutex);
>
> + ip = ftrace_location(ip);
> + if (!ip)
> + goto out_unlock;
> +
> /* See if there's a direct function at @ip already */
> + ret = -EBUSY;
> if (ftrace_find_rec_direct(ip))
> goto out_unlock;
>
> @@ -5222,6 +5244,10 @@ int unregister_ftrace_direct(unsigned lo
>
> mutex_lock(&direct_mutex);
>
> + ip = ftrace_location(ip);
> + if (!ip)
> + goto out_unlock;
> +
> entry = find_direct_entry(&ip, NULL);
> if (!entry)
> goto out_unlock;
>
>


--
Masami Hiramatsu <mhiramat@kernel.org>

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