Re: [PATCH 4/5] perf probe: Support DW_AT_const_value constant value

From: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	linux-kernel@vger.kernel.org,
	Tom Zanussi <tom.zanussi@linux.intel.com>,
	Ravi Bangoria <ravi.bangoria@linux.ibm.com>,
	Namhyung Kim <namhyung@kernel.org>
Subject: Re: [PATCH 4/5] perf probe: Support DW_AT_const_value constant value
Date: Wed, 6 Nov 2019 16:56:59 -0300	[thread overview]
Message-ID: <20191106195659.GD11935@kernel.org> (raw)
In-Reply-To: <157291303888.19771.11876536314853955934.stgit@devnote2>

Em Tue, Nov 05, 2019 at 09:17:19AM +0900, Masami Hiramatsu escreveu:
> Support DW_AT_const_value for variable assignment instead of location.
> Note that this requires ftrace supporting immediate value.

This one could have come before the other two, depends on the previous
two being applied.

- Arnaldo

> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> ---
>  tools/perf/util/probe-file.c   |    7 +++++++
>  tools/perf/util/probe-file.h   |    1 +
>  tools/perf/util/probe-finder.c |   11 +++++++++++
>  3 files changed, 19 insertions(+)
> 
> diff --git a/tools/perf/util/probe-file.c b/tools/perf/util/probe-file.c
> index a63f1a19b0e8..5003ba403345 100644
> --- a/tools/perf/util/probe-file.c
> +++ b/tools/perf/util/probe-file.c
> @@ -1008,6 +1008,7 @@ enum ftrace_readme {
>  	FTRACE_README_UPROBE_REF_CTR,
>  	FTRACE_README_USER_ACCESS,
>  	FTRACE_README_MULTIPROBE_EVENT,
> +	FTRACE_README_IMMEDIATE_VALUE,
>  	FTRACE_README_END,
>  };
>  
> @@ -1022,6 +1023,7 @@ static struct {
>  	DEFINE_TYPE(FTRACE_README_UPROBE_REF_CTR, "*ref_ctr_offset*"),
>  	DEFINE_TYPE(FTRACE_README_USER_ACCESS, "*[u]<offset>*"),
>  	DEFINE_TYPE(FTRACE_README_MULTIPROBE_EVENT, "*Create/append/*"),
> +	DEFINE_TYPE(FTRACE_README_IMMEDIATE_VALUE, "*\\imm-value,*"),
>  };
>  
>  static bool scan_ftrace_readme(enum ftrace_readme type)
> @@ -1092,3 +1094,8 @@ bool multiprobe_event_is_supported(void)
>  {
>  	return scan_ftrace_readme(FTRACE_README_MULTIPROBE_EVENT);
>  }
> +
> +bool immediate_value_is_supported(void)
> +{
> +	return scan_ftrace_readme(FTRACE_README_IMMEDIATE_VALUE);
> +}
> diff --git a/tools/perf/util/probe-file.h b/tools/perf/util/probe-file.h
> index 850d1b52d60a..0dba88c0f5f0 100644
> --- a/tools/perf/util/probe-file.h
> +++ b/tools/perf/util/probe-file.h
> @@ -72,6 +72,7 @@ bool kretprobe_offset_is_supported(void);
>  bool uprobe_ref_ctr_is_supported(void);
>  bool user_access_is_supported(void);
>  bool multiprobe_event_is_supported(void);
> +bool immediate_value_is_supported(void);
>  #else	/* ! HAVE_LIBELF_SUPPORT */
>  static inline struct probe_cache *probe_cache__new(const char *tgt __maybe_unused, struct nsinfo *nsi __maybe_unused)
>  {
> diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> index 9ecea45da4ca..2e3a468c8350 100644
> --- a/tools/perf/util/probe-finder.c
> +++ b/tools/perf/util/probe-finder.c
> @@ -177,6 +177,17 @@ static int convert_variable_location(Dwarf_Die *vr_die, Dwarf_Addr addr,
>  	if (dwarf_attr(vr_die, DW_AT_external, &attr) != NULL)
>  		goto static_var;
>  
> +	/* Constant value */
> +	if (dwarf_attr(vr_die, DW_AT_const_value, &attr) &&
> +	    immediate_value_is_supported()) {
> +		Dwarf_Sword snum;
> +
> +		dwarf_formsdata(&attr, &snum);
> +		ret = asprintf(&tvar->value, "\\%ld", (long)snum);
> +
> +		return ret < 0 ? -ENOMEM : 0;
> +	}
> +
>  	/* TODO: handle more than 1 exprs */
>  	if (dwarf_attr(vr_die, DW_AT_location, &attr) == NULL)
>  		return -EINVAL;	/* Broken DIE ? */

-- 

- Arnaldo