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Date: Fri, 24 Sep 2021 18:51:04 +0100
From: Alan Maguire <alan.maguire@...cle.com>
To: Masami Hiramatsu <mhiramat@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>
Cc: Jiri Olsa <jolsa@...hat.com>, Sven Schnelle <svens@...ux.ibm.com>,
bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] tracing/kprobe: Support $$args for function entry
On 23/09/2021 13:39, Masami Hiramatsu wrote:
> Support $$args fetch arg for function entry. This uses
> BTF for finding the function argument. Thus it depends
> on CONFIG_BPF_SYSCALL.
>
> /sys/kernel/tracing # echo 'p vfs_read $$args' >> kprobe_events
> /sys/kernel/tracing # cat kprobe_events
> p:kprobes/p_vfs_read_0 vfs_read file=$arg1:x64 buf=$arg2:x64 count=$arg3:u64 pos=$arg4:x64
>
> Note that $$args must be used without argument name.
This looks great! Can I ask which tree you're building on
top of so I can play around with this a bit?
I also wonder if we could rework btf_show_name() to help
render full type info for the args? in kernel/bpf/btf.c:
/*
* Populate show->state.name with type name information.
* Format of type name is
*
* [.member_name = ] (type_name)
*/
The (type_name) part is what we'd want from here; no reason
we can't refactor that function to make the type name available
as a cast. It would rework the output to be something like
p:kprobes/p_vfs_read_0 vfs_read struct file *file=$arg1 , char *buf=$arg2 , size_t count=$arg3 , loff_t pos=$arg4
...if that's wanted of course (not sure what the constraints on format are here)? Thanks for pushing this along!
Alan
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---
> kernel/trace/trace_kprobe.c | 60 ++++++++++++++++++++++++-
> kernel/trace/trace_probe.c | 105 +++++++++++++++++++++++++++++++++++++++++++
> kernel/trace/trace_probe.h | 5 ++
> 3 files changed, 168 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 3dd4fb719aa3..fe88ee8c8cd8 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -712,6 +712,58 @@ static int trace_kprobe_module_callback(struct notifier_block *nb,
> return NOTIFY_DONE;
> }
>
> +#ifdef CONFIG_BPF_SYSCALL
> +
> +static int trace_kprobe_parse_btf_args(struct trace_kprobe *tk, int i,
> + const char *arg, unsigned int flags)
> +{
> + struct trace_probe *tp = &tk->tp;
> + static struct btf *btf;
> + const struct btf_type *t;
> + const struct btf_param *args;
> + s32 id, nargs;
> + int ret;
> +
> + if (!(flags & TPARG_FL_FENTRY))
> + return -EINVAL;
> + if (!tk->symbol)
> + return -EINVAL;
> +
> + if (!btf)
> + btf = btf_parse_vmlinux();
> +
> + id = btf_find_by_name_kind(btf, tk->symbol, BTF_KIND_FUNC);
> + if (id <= 0)
> + return -ENOENT;
> +
> + /* Get BTF_KIND_FUNC type */
> + t = btf_type_by_id(btf, id);
> + if (!btf_type_is_func(t))
> + return -ENOENT;
> +
> + /* The type of BTF_KIND_FUNC is BTF_KIND_FUNC_PROTO */
> + t = btf_type_by_id(btf, t->type);
> + if (!btf_type_is_func_proto(t))
> + return -ENOENT;
> +
> + args = (const struct btf_param *)(t + 1);
> + nargs = btf_type_vlen(t);
> + for (i = 0; i < nargs; i++) {
> + ret = traceprobe_parse_btf_arg(tp, i, btf, &args[i]);
> + if (ret < 0)
> + break;
> + }
> +
> + return ret;
> +}
> +#else
> +static int trace_kprobe_parse_btf_args(struct trace_kprobe *tk, int i,
> + const char *arg, unsigned int flags)
> +{
> + return -EOPNOTSUPP;
> +}
> +#endif
> +
> static struct notifier_block trace_kprobe_module_nb = {
> .notifier_call = trace_kprobe_module_callback,
> .priority = 1 /* Invoked after kprobe module callback */
> @@ -733,12 +785,13 @@ static int __trace_kprobe_create(int argc, const char *argv[])
> * $stack : fetch stack address
> * $stackN : fetch Nth of stack (N:0-)
> * $comm : fetch current task comm
> + * $$args : fetch parameters using BTF
> * @ADDR : fetch memory at ADDR (ADDR should be in kernel)
> * @SYM[+|-offs] : fetch memory at SYM +|- offs (SYM is a data symbol)
> * %REG : fetch register REG
> * Dereferencing memory fetch:
> * +|-offs(ARG) : fetch memory at ARG +|- offs address.
> - * Alias name of args:
> + * Alias name of args (except for $$args) :
> * NAME=FETCHARG : set NAME as alias of FETCHARG.
> * Type of args:
> * FETCHARG:TYPE : use TYPE instead of unsigned long.
> @@ -877,7 +930,10 @@ static int __trace_kprobe_create(int argc, const char *argv[])
> /* parse arguments */
> for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
> trace_probe_log_set_index(i + 2);
> - ret = traceprobe_parse_probe_arg(&tk->tp, i, argv[i], flags);
> + if (strcmp(argv[i], "$$args") == 0)
> + ret = trace_kprobe_parse_btf_args(tk, i, argv[i], flags);
> + else
> + ret = traceprobe_parse_probe_arg(&tk->tp, i, argv[i], flags);
> if (ret)
> goto error; /* This can be -ENOMEM */
> }
> diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> index 2fe104109525..bbac261b1688 100644
> --- a/kernel/trace/trace_probe.c
> +++ b/kernel/trace/trace_probe.c
> @@ -765,6 +765,111 @@ static int traceprobe_conflict_field_name(const char *name,
> return 0;
> }
>
> +#ifdef CONFIG_BPF_SYSCALL
> +
> +static u32 btf_type_int(const struct btf_type *t)
> +{
> + return *(u32 *)(t + 1);
> +}
> +
> +static const char *traceprobe_type_from_btf(struct btf *btf, s32 id)
> +{
> + const struct btf_type *t;
> + u32 intdata;
> + s32 tid;
> +
> + /* TODO: const char * could be converted as a string */
> + t = btf_type_skip_modifiers(btf, id, &tid);
> +
> + switch (BTF_INFO_KIND(t->info)) {
> + case BTF_KIND_ENUM:
> + /* enum is "int", so convert to "s32" */
> + return "s32";
> + case BTF_KIND_PTR:
> + /* pointer will be converted to "x??" */
> + if (IS_ENABLED(CONFIG_64BIT))
> + return "x64";
> + else
> + return "x32";
> + case BTF_KIND_INT:
> + intdata = btf_type_int(t);
> + if (BTF_INT_ENCODING(intdata) & BTF_INT_SIGNED) {
> + switch (BTF_INT_BITS(intdata)) {
> + case 8:
> + return "s8";
> + case 16:
> + return "s16";
> + case 32:
> + return "s32";
> + case 64:
> + return "s64";
> + }
> + } else { /* unsigned */
> + switch (BTF_INT_BITS(intdata)) {
> + case 8:
> + return "u8";
> + case 16:
> + return "u16";
> + case 32:
> + return "u32";
> + case 64:
> + return "u64";
> + }
> + }
> + }
> +
> + /* Default type */
> + if (IS_ENABLED(CONFIG_64BIT))
> + return "x64";
> + else
> + return "x32";
> +}
> +
> +int traceprobe_parse_btf_arg(struct trace_probe *tp, int i, struct btf *btf,
> + const struct btf_param *arg)
> +{
> + struct probe_arg *parg = &tp->args[i];
> + const char *name, *tname;
> + char *body;
> + int ret;
> +
> + tp->nr_args++;
> + name = btf_name_by_offset(btf, arg->name_off);
> + parg->name = kstrdup(name, GFP_KERNEL);
> + if (!parg->name)
> + return -ENOMEM;
> +
> + if (!is_good_name(parg->name)) {
> + trace_probe_log_err(0, BAD_ARG_NAME);
> + return -EINVAL;
> + }
> + if (traceprobe_conflict_field_name(parg->name, tp->args, i)) {
> + trace_probe_log_err(0, USED_ARG_NAME);
> + return -EINVAL;
> + }
> +
> + /*
> + * Since probe event needs an appropriate command for dyn_event interface,
> + * convert BTF type to corresponding fetch-type string.
> + */
> + tname = traceprobe_type_from_btf(btf, arg->type);
> + if (tname)
> + body = kasprintf(GFP_KERNEL, "$arg%d:%s", i + 1, tname);
> + else
> + body = kasprintf(GFP_KERNEL, "$arg%d", i + 1);
> +
> + if (!body)
> + return -ENOMEM;
> + /* Parse fetch argument */
> + ret = traceprobe_parse_probe_arg_body(body, &tp->size, parg,
> + TPARG_FL_KERNEL | TPARG_FL_FENTRY, 0);
> +
> + kfree(body);
> +
> + return ret;
> +}
> +#endif
> +
> int traceprobe_parse_probe_arg(struct trace_probe *tp, int i, const char *arg,
> unsigned int flags)
> {
> diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
> index 355c78a930f8..857b946afe29 100644
> --- a/kernel/trace/trace_probe.h
> +++ b/kernel/trace/trace_probe.h
> @@ -23,6 +23,7 @@
> #include <linux/limits.h>
> #include <linux/uaccess.h>
> #include <linux/bitops.h>
> +#include <linux/btf.h>
> #include <asm/bitsperlong.h>
>
> #include "trace.h"
> @@ -359,6 +360,10 @@ int trace_probe_create(const char *raw_command, int (*createfn)(int, const char
>
> extern int traceprobe_parse_probe_arg(struct trace_probe *tp, int i,
> const char *argv, unsigned int flags);
> +#ifdef CONFIG_BPF_SYSCALL
> +int traceprobe_parse_btf_arg(struct trace_probe *tp, int i, struct btf *btf,
> + const struct btf_param *arg);
> +#endif
>
> extern int traceprobe_update_arg(struct probe_arg *arg);
> extern void traceprobe_free_probe_arg(struct probe_arg *arg);
>
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