linux-kernel - Re: [PATCH -tip 3/3] perf-probe: Use the actual address as a hint for uprobes

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Date:	Fri, 20 Dec 2013 15:03:51 -0300
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	David Ahern <dsahern@...il.com>,
	lkml <linux-kernel@...r.kernel.org>,
	"Steven Rostedt (Red Hat)" <rostedt@...dmis.org>,
	Oleg Nesterov <oleg@...hat.com>,
	"David A. Long" <dave.long@...aro.org>, systemtap@...rceware.org,
	yrl.pp-manager.tt@...achi.com, Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH -tip 3/3] perf-probe: Use the actual address as a hint
 for uprobes

Em Fri, Dec 20, 2013 at 10:03:02AM +0000, Masami Hiramatsu escreveu:
> Use the actual address of tracepoint as a hint to find
> different local symbols. Since sometimes there are local
> symbols which have same name, it is impossible to determine
> which symbol should be used. This saves the actual address
> from debuginfo and use it as a hint later.
> 
> The reason why we don't use the address directly is that
> the address stored in the debuginfo has some section offset.
> Thus this just uses the last 12 bits of the address as a
> hint when searching the symbol in the map.

Again, can you provide an example of cases where before this patch the
problem happens, with actual command output?

Then output from the same command with the patch applied, showing how it
works after the fix.

This way users can more quickly use your work and, among others, I can
help you by validating it in my test machines.

Thanks,

- Arnaldo
 
> Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> ---
>  tools/perf/util/probe-event.c  |   16 +++++++++++++---
>  tools/perf/util/probe-event.h  |    1 +
>  tools/perf/util/probe-finder.c |    1 +
>  3 files changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index e27cecb..e5fbda3 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -187,11 +187,18 @@ static int init_user_exec(void)
>  }
>  
>  static const char *__target_symbol;
> +static unsigned long __target_hint;
>  static struct symbol *__result_sym;
> +#define HINT_MASK	0xfff
>  
>  static int filter_target_symbol(struct map *map __maybe_unused,
>  				struct symbol *sym)
>  {
> +	/* Check the last bits is same */
> +	if (__target_hint)
> +		if ((sym->start & HINT_MASK) != (__target_hint & HINT_MASK))
> +			return 0;
> +
>  	if (strcmp(__target_symbol, sym->name) == 0) {
>  		__result_sym = sym;
>  		return 0;
> @@ -201,7 +208,7 @@ static int filter_target_symbol(struct map *map __maybe_unused,
>  
>  /* Find the offset of the symbol in the executable binary */
>  static int find_symbol_offset(const char *exec, const char *function,
> -			      unsigned long *offs)
> +			      unsigned long hint, unsigned long *offs)
>  {
>  	struct symbol *sym;
>  	struct map *map = NULL;
> @@ -218,6 +225,7 @@ static int find_symbol_offset(const char *exec, const char *function,
>  	pr_debug("Search %s in %s\n", function, exec);
>  	__target_symbol = function;
>  	__result_sym = NULL;
> +	__target_hint = hint;
>  	if (map__load(map, filter_target_symbol)) {
>  		pr_err("Failed to find %s in %s.\n", function, exec);
>  		goto out;
> @@ -357,8 +365,10 @@ static int add_exec_to_probe_trace_events(struct probe_trace_event *tevs,
>  		return 0;
>  
>  	for (i = 0; i < ntevs && ret >= 0; i++) {
> +		offset = tevs[i].point.address - tevs[i].point.offset;
>  		/* Get proper offset */
> -		ret = find_symbol_offset(exec, tevs[i].point.symbol, &offset);
> +		ret = find_symbol_offset(exec, tevs[i].point.symbol,
> +					 offset, &offset);
>  		if (ret < 0)
>  			break;
>  		offset += tevs[i].point.offset;
> @@ -2418,7 +2428,7 @@ static int convert_name_to_addr(struct perf_probe_event *pev, const char *exec)
>  		goto out;
>  	}
>  
> -	ret = find_symbol_offset(exec, pp->function, &vaddr);
> +	ret = find_symbol_offset(exec, pp->function, 0, &vaddr);
>  	if (ret < 0)
>  		goto out;
>  
> diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
> index f9f3de8..d481c46 100644
> --- a/tools/perf/util/probe-event.h
> +++ b/tools/perf/util/probe-event.h
> @@ -12,6 +12,7 @@ struct probe_trace_point {
>  	char		*symbol;	/* Base symbol */
>  	char		*module;	/* Module name */
>  	unsigned long	offset;		/* Offset from symbol */
> +	unsigned long	address;	/* Actual address of the trace point */
>  	bool		retprobe;	/* Return probe flag */
>  };
>  
> diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> index ffb657f..7db7e05 100644
> --- a/tools/perf/util/probe-finder.c
> +++ b/tools/perf/util/probe-finder.c
> @@ -729,6 +729,7 @@ static int convert_to_trace_point(Dwarf_Die *sp_die, Dwfl_Module *mod,
>  		return -ENOENT;
>  	}
>  	tp->offset = (unsigned long)(paddr - sym.st_value);
> +	tp->address = (unsigned long)paddr;
>  	tp->symbol = strdup(symbol);
>  	if (!tp->symbol)
>  		return -ENOMEM;
> 
--
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