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    SubjectRe: [PATCH v5 04/12] fprobe: Use ftrace_regs in fprobe entry handler
    On Mon, Sep 25, 2023 at 09:15:15PM +0900, Masami Hiramatsu wrote:
    > Hi Jiri,
    >
    > On Mon, 25 Sep 2023 12:41:59 +0200
    > Jiri Olsa <olsajiri@gmail.com> wrote:
    >
    > > On Sun, Sep 24, 2023 at 10:36:36PM +0900, Masami Hiramatsu (Google) wrote:
    > > > From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
    > > >
    > > > This allows fprobes to be available with CONFIG_DYNAMIC_FTRACE_WITH_ARGS
    > > > instead of CONFIG_DYNAMIC_FTRACE_WITH_REGS, then we can enable fprobe
    > > > on arm64.
    > > >
    > > > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
    > > > Acked-by: Florent Revest <revest@chromium.org>
    > >
    > > I was getting bpf selftests failures with this patchset and when
    > > bisecting I'm getting crash when running on top of this change
    >
    > Thanks for bisecting!
    >
    > >
    > > looks like it's missing some of the regs NULL checks added later?
    >
    > yeah, if the RIP (arch_rethook_prepare+0x0/0x30) is correct,
    >
    > void arch_rethook_prepare(struct rethook_node *rh, struct ftrace_regs *fregs, bool mcount)
    >
    > RSI (the 2nd argument) is NULL. This means fregs == NULL and caused the crash.
    > I think ftrace_get_regs(fregs) for the entry handler may return NULL.
    >
    > Ah,
    >
    > @@ -182,7 +182,7 @@ static void fprobe_init(struct fprobe *fp)
    > fp->ops.func = fprobe_kprobe_handler;
    > else
    > fp->ops.func = fprobe_handler;
    > - fp->ops.flags |= FTRACE_OPS_FL_SAVE_REGS;
    > + fp->ops.flags |= FTRACE_OPS_FL_SAVE_ARGS;
    > }
    >
    > static int fprobe_init_rethook(struct fprobe *fp, int num)
    >
    > This may cause the issue, it should keep REGS at this point (this must be done in
    > [9/12]). But after applying [9/12], it shouldn't be a problem...
    >
    > Let me check it again.

    that helped with the crash, I'll continue bisecting to find out
    where it breaks the tests

    thanks,
    jirka

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