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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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