2023-06-12 12:19:42

by Masami Hiramatsu

Subject: [PATCH] tracing/probes: Fix tracepoint event with $arg* to fetch correct argument

From: Masami Hiramatsu (Google) <[email protected]>

To hide the first dummy 'data' argument on the tracepoint probe events,
the BTF argument array was modified (skip the first argument for tracepoint),
but the '$arg*' meta argument parser missed that.

Fix to increment the argument index if it is tracepoint probe. And decrement
the index when searching the type of the argument.

Signed-off-by: Masami Hiramatsu (Google) <[email protected]>
---
kernel/trace/trace_probe.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 473e1c43bc57..643aa3a51d5a 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -456,7 +456,10 @@ static int parse_btf_arg(const char *varname, struct fetch_insn *code,

if (name && !strcmp(name, varname)) {
code->op = FETCH_OP_ARG;
- code->param = i;
+ if (ctx->flags & TPARG_FL_TPOINT)
+ code->param = i + 1;
+ else
+ code->param = i;
return 0;
}
}
@@ -470,8 +473,11 @@ static const struct fetch_type *parse_btf_arg_type(int arg_idx,
struct btf *btf = traceprobe_get_btf();
const char *typestr = NULL;

- if (btf && ctx->params)
+ if (btf && ctx->params) {
+ if (ctx->flags & TPARG_FL_TPOINT)
+ arg_idx--;
typestr = type_from_btf_id(btf, ctx->params[arg_idx].type);
+ }

return find_fetch_type(typestr, ctx->flags);
}

2023-06-14 20:39:01

by Kui-Feng Lee

Subject: Re: [PATCH] tracing/probes: Fix tracepoint event with $arg* to fetch correct argument

On 6/12/23 04:58, Masami Hiramatsu (Google) wrote:
> From: Masami Hiramatsu (Google) <[email protected]>
>
> To hide the first dummy 'data' argument on the tracepoint probe events,
> the BTF argument array was modified (skip the first argument for tracepoint),
> but the '$arg*' meta argument parser missed that.
>
> Fix to increment the argument index if it is tracepoint probe. And decrement
> the index when searching the type of the argument.
>
> Signed-off-by: Masami Hiramatsu (Google) <[email protected]>
> ---
> kernel/trace/trace_probe.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> index 473e1c43bc57..643aa3a51d5a 100644
> --- a/kernel/trace/trace_probe.c
> +++ b/kernel/trace/trace_probe.c
> @@ -456,7 +456,10 @@ static int parse_btf_arg(const char *varname, struct fetch_insn *code,
>
> if (name && !strcmp(name, varname)) {
> code->op = FETCH_OP_ARG;
> - code->param = i;
> + if (ctx->flags & TPARG_FL_TPOINT)
> + code->param = i + 1;
> + else
> + code->param = i;
> return 0;
> }
> }
> @@ -470,8 +473,11 @@ static const struct fetch_type *parse_btf_arg_type(int arg_idx,
> struct btf *btf = traceprobe_get_btf();
> const char *typestr = NULL;
>
> - if (btf && ctx->params)
> + if (btf && ctx->params) {
> + if (ctx->flags & TPARG_FL_TPOINT)
> + arg_idx--;
> typestr = type_from_btf_id(btf, ctx->params[arg_idx].type);
> + }
>
> return find_fetch_type(typestr, ctx->flags);
> }
>
>

I failed to apply this patch.
Would you mind to rebase this patch?

2023-06-21 23:39:06

by Steven Rostedt

Subject: Re: [PATCH] tracing/probes: Fix tracepoint event with $arg* to fetch correct argument

On Mon, 12 Jun 2023 20:58:57 +0900
"Masami Hiramatsu (Google)" <[email protected]> wrote:

> From: Masami Hiramatsu (Google) <[email protected]>
>
> To hide the first dummy 'data' argument on the tracepoint probe events,
> the BTF argument array was modified (skip the first argument for tracepoint),
> but the '$arg*' meta argument parser missed that.
>
> Fix to increment the argument index if it is tracepoint probe. And decrement
> the index when searching the type of the argument.

I'm curious. What if we want a variable that points to that data argument? ;-)

Probably just add a new type I guess.

Anyway,

Reviewed-by: Steven Rostedt (Google) <[email protected]>

-- Steve

>
> Signed-off-by: Masami Hiramatsu (Google) <[email protected]>
> ---
> kernel/trace/trace_probe.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> index 473e1c43bc57..643aa3a51d5a 100644
> --- a/kernel/trace/trace_probe.c
> +++ b/kernel/trace/trace_probe.c
> @@ -456,7 +456,10 @@ static int parse_btf_arg(const char *varname, struct fetch_insn *code,
>
> if (name && !strcmp(name, varname)) {
> code->op = FETCH_OP_ARG;
> - code->param = i;
> + if (ctx->flags & TPARG_FL_TPOINT)
> + code->param = i + 1;
> + else
> + code->param = i;
> return 0;
> }
> }
> @@ -470,8 +473,11 @@ static const struct fetch_type *parse_btf_arg_type(int arg_idx,
> struct btf *btf = traceprobe_get_btf();
> const char *typestr = NULL;
>
> - if (btf && ctx->params)
> + if (btf && ctx->params) {
> + if (ctx->flags & TPARG_FL_TPOINT)
> + arg_idx--;
> typestr = type_from_btf_id(btf, ctx->params[arg_idx].type);
> + }
>
> return find_fetch_type(typestr, ctx->flags);
> }

2023-06-22 01:12:55

by Masami Hiramatsu

Subject: Re: [PATCH] tracing/probes: Fix tracepoint event with $arg* to fetch correct argument

On Wed, 14 Jun 2023 12:50:34 -0700
Kui-Feng Lee <[email protected]> wrote:

>
>
> On 6/12/23 04:58, Masami Hiramatsu (Google) wrote:
> > From: Masami Hiramatsu (Google) <[email protected]>
> >
> > To hide the first dummy 'data' argument on the tracepoint probe events,
> > the BTF argument array was modified (skip the first argument for tracepoint),
> > but the '$arg*' meta argument parser missed that.
> >
> > Fix to increment the argument index if it is tracepoint probe. And decrement
> > the index when searching the type of the argument.
> >
> > Signed-off-by: Masami Hiramatsu (Google) <[email protected]>
> > ---
> > kernel/trace/trace_probe.c | 10 ++++++++--
> > 1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> > index 473e1c43bc57..643aa3a51d5a 100644
> > --- a/kernel/trace/trace_probe.c
> > +++ b/kernel/trace/trace_probe.c
> > @@ -456,7 +456,10 @@ static int parse_btf_arg(const char *varname, struct fetch_insn *code,
> >
> > if (name && !strcmp(name, varname)) {
> > code->op = FETCH_OP_ARG;
> > - code->param = i;
> > + if (ctx->flags & TPARG_FL_TPOINT)
> > + code->param = i + 1;
> > + else
> > + code->param = i;
> > return 0;
> > }
> > }
> > @@ -470,8 +473,11 @@ static const struct fetch_type *parse_btf_arg_type(int arg_idx,
> > struct btf *btf = traceprobe_get_btf();
> > const char *typestr = NULL;
> >
> > - if (btf && ctx->params)
> > + if (btf && ctx->params) {
> > + if (ctx->flags & TPARG_FL_TPOINT)
> > + arg_idx--;
> > typestr = type_from_btf_id(btf, ctx->params[arg_idx].type);
> > + }
> >
> > return find_fetch_type(typestr, ctx->flags);
> > }
> >
> >
>
> I failed to apply this patch.
> Would you mind to rebase this patch?

Ah, this is against for the probes/for-next branch on
git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git

Thanks,

>


--
Masami Hiramatsu (Google) <[email protected]>

2023-06-22 01:27:18

by Masami Hiramatsu

Subject: Re: [PATCH] tracing/probes: Fix tracepoint event with $arg* to fetch correct argument

On Wed, 21 Jun 2023 19:03:37 -0400
Steven Rostedt <[email protected]> wrote:

> On Mon, 12 Jun 2023 20:58:57 +0900
> "Masami Hiramatsu (Google)" <[email protected]> wrote:
>
> > From: Masami Hiramatsu (Google) <[email protected]>
> >
> > To hide the first dummy 'data' argument on the tracepoint probe events,
> > the BTF argument array was modified (skip the first argument for tracepoint),
> > but the '$arg*' meta argument parser missed that.
> >
> > Fix to increment the argument index if it is tracepoint probe. And decrement
> > the index when searching the type of the argument.
>
> I'm curious. What if we want a variable that points to that data argument? ;-)

That is a dummy parameter which is passed when registering the callback, so
it is passed from trace_fprobe.c. Currently trace_fprobe.c passed NULL to
the data argument.

>
> Probably just add a new type I guess.

Yeah, if we get any idea to use it, it will be accessed by a new $-variable.

>
> Anyway,
>
> Reviewed-by: Steven Rostedt (Google) <[email protected]>

Thank you!

>
> -- Steve
>
> >
> > Signed-off-by: Masami Hiramatsu (Google) <[email protected]>
> > ---
> > kernel/trace/trace_probe.c | 10 ++++++++--
> > 1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> > index 473e1c43bc57..643aa3a51d5a 100644
> > --- a/kernel/trace/trace_probe.c
> > +++ b/kernel/trace/trace_probe.c
> > @@ -456,7 +456,10 @@ static int parse_btf_arg(const char *varname, struct fetch_insn *code,
> >
> > if (name && !strcmp(name, varname)) {
> > code->op = FETCH_OP_ARG;
> > - code->param = i;
> > + if (ctx->flags & TPARG_FL_TPOINT)
> > + code->param = i + 1;
> > + else
> > + code->param = i;
> > return 0;
> > }
> > }
> > @@ -470,8 +473,11 @@ static const struct fetch_type *parse_btf_arg_type(int arg_idx,
> > struct btf *btf = traceprobe_get_btf();
> > const char *typestr = NULL;
> >
> > - if (btf && ctx->params)
> > + if (btf && ctx->params) {
> > + if (ctx->flags & TPARG_FL_TPOINT)
> > + arg_idx--;
> > typestr = type_from_btf_id(btf, ctx->params[arg_idx].type);
> > + }
> >
> > return find_fetch_type(typestr, ctx->flags);
> > }
>


--
Masami Hiramatsu (Google) <[email protected]>