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Message-ID: <20230816144213.0f24cc62@gandalf.local.home>
Date: Wed, 16 Aug 2023 14:42:13 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Francis Laniel <flaniel@...ux.microsoft.com>
Cc: linux-kernel@...r.kernel.org,
Masami Hiramatsu <mhiramat@...nel.org>,
linux-trace-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 1/1] tracing/kprobe: Add multi-probe support for
'perf_kprobe' PMU
On Wed, 16 Aug 2023 18:35:17 +0200
Francis Laniel <flaniel@...ux.microsoft.com> wrote:
> When using sysfs, it is possible to create kprobe for several kernel functions
> sharing the same name, but of course with different addresses, by writing their
> addresses in kprobe_events file.
So this only happens if you write in the address?
>
> When using PMU, if only the symbol name is given, the event will be created for
> the first address which matches the symbol, as returned by
> kallsyms_lookup_name().
> The idea here is to search all kernel functions which match this symbol and
> create a trace_kprobe for each of them.
> All these trace_kprobes are linked together by sharing the same trace_probe.
>
So this makes the PMU version enable all by name, so there's still a
disconnect between how sysfs works and how PMU does.
Why can't you just pass in the address like sysfs does?
-- Steve
> Signed-off-by: Francis Laniel <flaniel@...ux.microsoft.com>
> ---
> kernel/trace/trace_kprobe.c | 86 +++++++++++++++++++++++++++++++++++++
> 1 file changed, 86 insertions(+)
>
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 1b3fa7b854aa..08580f1466c7 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -1682,13 +1682,42 @@ static int unregister_kprobe_event(struct trace_kprobe *tk)
> }
>
> #ifdef CONFIG_PERF_EVENTS
> +
> +struct address_array {
> + unsigned long *addrs;
> + size_t size;
> +};
> +
> +static int add_addr(void *data, unsigned long addr)
> +{
> + struct address_array *array = data;
> + unsigned long *p;
> +
> + array->size++;
> + p = krealloc(array->addrs,
> + sizeof(*array->addrs) * array->size,
> + GFP_KERNEL);
> + if (!p) {
> + kfree(array->addrs);
> + return -ENOMEM;
> + }
> +
> + array->addrs = p;
> + array->addrs[array->size - 1] = addr;
> +
> + return 0;
> +}
> +
> /* create a trace_kprobe, but don't add it to global lists */
> struct trace_event_call *
> create_local_trace_kprobe(char *func, void *addr, unsigned long offs,
> bool is_return)
> {
> enum probe_print_type ptype;
> + struct address_array array;
> struct trace_kprobe *tk;
> + unsigned long func_addr;
> + unsigned int i;
> int ret;
> char *event;
>
> @@ -1722,7 +1751,64 @@ create_local_trace_kprobe(char *func, void *addr, unsigned long offs,
> if (ret < 0)
> goto error;
>
> + array.addrs = NULL;
> + array.size = 0;
> + ret = kallsyms_on_each_match_symbol(add_addr, func, &array);
> + if (ret)
> + goto error_free;
> +
> + if (array.size == 1)
> + goto end;
> +
> + /*
> + * Below loop allocates a trace_kprobe for each function with the same
> + * name in kernel source code.
> + * All this differente trace_kprobes will be linked together through
> + * append_trace_kprobe().
> + * NOTE append_trace_kprobe() is called in register_trace_kprobe() which
> + * is called when a kprobe is added through sysfs.
> + */
> + func_addr = kallsyms_lookup_name(func);
> + for (i = 0; i < array.size; i++) {
> + struct trace_kprobe *tk_same_name;
> + unsigned long address;
> +
> + address = array.addrs[i];
> + /* Skip the function address as we already registered it. */
> + if (address == func_addr)
> + continue;
> +
> + /*
> + * alloc_trace_kprobe() first considers symbol name, so we set
> + * this to NULL to allocate this kprobe on the given address.
> + */
> + tk_same_name = alloc_trace_kprobe(KPROBE_EVENT_SYSTEM, event,
> + (void *)address, NULL, offs,
> + 0 /* maxactive */,
> + 0 /* nargs */, is_return);
> +
> + if (IS_ERR(tk_same_name)) {
> + ret = -ENOMEM;
> + goto error_free;
> + }
> +
> + init_trace_event_call(tk_same_name);
> +
> + if (traceprobe_set_print_fmt(&tk_same_name->tp, ptype) < 0) {
> + ret = -ENOMEM;
> + goto error_free;
> + }
> +
> + ret = append_trace_kprobe(tk_same_name, tk);
> + if (ret)
> + goto error_free;
> + }
> +
> +end:
> + kfree(array.addrs);
> return trace_probe_event_call(&tk->tp);
> +error_free:
> + kfree(array.addrs);
> error:
> free_trace_kprobe(tk);
> return ERR_PTR(ret);
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